23 BMW 1977 R100RS Transmission Refresh and Assembly

I removed, and disassembled the transmission and you can read about how I did that work here.

Summary of Transmission Refresh Work

The refresh includes repair to damage I found when inspecting the transmission parts and replacing parts subject to wear and tear after 40 years.

Component Inspection Results

The inspection revealed the following:

  • Input Shaft
    • Helical gear has erosion and pits on several helical gear teeth.
    • Front roller bearing inner race has a groove from shaft seal.
  • Intermediate Shaft
    • 2nd gear has chips on two of the dogs.
  • Output Shaft
    • 5th gear wobbles (a common problem) so the gear and the output shaft are badly worn.

The available solutions to these problems, in order of cost, include:

  • Do nothing as the damage is not excessive
  • Repair or refurbish the part
  • Replace the part with a used one
  • Replace the part with a new one

Here is what I decided to do

  • Input Shaft – Do nothing about gear wear on some teeth. Replace the roller bearing to eliminate the groove worn by the seal in the inner race.
  • Intermediate Shaft – Do nothing about the minor chips to two gear dogs per recommendation of a local airhead mechanic. Monitor drain plug for any signs of further dog teeth degradation.
  • Output ShaftCycle Works offers a service to repair the output shaft and 5th gear. They hard chrome plate the gear and shaft to build them up and then hone them to fit eliminating the wear.

Wear and Tear Parts Replacement

Due to the 40 year age of the transmission, I replace the following parts:

  • Input Shaft
    • Replace front roller bearing, rear ball bearing and snap ring.
  • Intermediate Shaft
    • Replace front and rear ball bearings
  • Output Shaft
    • Replace front and rear ball bearings
    • Replace all circlips and snap rings.
    • Add small snap ring to the new front ball bearing hole so the circlip has a more surface to hold the bearing in place.
  • Shift Cam Mechanism
    • Replace “pawl return spring” (part #:  23 31 1 242 910)
    • Replace “gear change lever return spring” (part # 23 31 1 234 791)
    • Replace shift cam plastic roller (part # 23 31 1 231 572)
    • Replace all circlips removed with new ones
  • Shim Shafts and Replace Seals and Gaskets
    • Shim end play on all three shafts with shim kit from Cycle works and reuse of existing shims
    • Install new input shaft seal
    • Install new output shaft seal
    • Install new shift lever seal
    • Install new rear cover gasket

Resources

In preparation for, and while doing this work, I used the following resources.

I shot a number of short videos about how the gears and shift cam mechanism work and part of the work I did. You can find these on my YouTube site:

I was fortunate to have access to two respected, long time BMW airhead mechanics who provided invaluable support, advice and tools along the way.

WARNING:
Due to the complexity and numerous changes made by BMW in the airhead transmissions, I would recommend having access to an experienced mechanic who has worked on these transmission for guidance before attempting to work on yours. Increasingly, new parts are made from “unobtanium” and many are expensive so mistakes will be costly. It is also a critical drive-line component and sudden failure can be injurious. 

Tools

I needed a variety of special tools to do this work.

Transmission Tools

I borrowed a number of special tools from a retired airhead mechanic.

Special Tool For Removing Rear Input Shaft Ball Bearing

Special Tool For Removing Rear Input Shaft Ball Bearing

Special Tool to Remove Input Shaft Torsion Spring Collar Snap Ring

Special Tool to Remove Input Shaft Torsion Spring Collar Snap Ring

Input Shaft Seal Install Tool Parts-(Right) Outer Tube, (Left) Cup

Input Shaft Seal Install Tool Parts-(Right) Outer Tube, (Left) Cup

Shop Press

I use a 20 ton shop press to assemble the input shaft, to remove some of the bearings and to press the new bearings onto all the shafts.

20 Ton Hydraulic Press

20 Ton Hydraulic Press – Harbor Freight

Bearing Puller

I use a Harbor Freight bearing puller. It comes with a bearing separator (the top shiny part with two halves) to pull bearings off shafts with the press. I also used it to pull bearings off shafts without the press.

Harbor Freight Bearing Puller Parts

Harbor Freight Bearing Puller Parts

Propane or MAP Gas

I picked up a MAP gas torch at Home Depot to heat the rear cover so I can remove it and also to heat the bearing bores the gear shaft front bearings fit into inside the transmission.

MAP Gas Torch

MAP Gas Torch

Transmission Holder

I made a transmission holder from a scrap piece of 1″ stair tread to hold the transmission so the input shaft is off the bench as I work. I drilled two holes where the top mounting bolts go and put two short bolts into them to keep the transmission from turning on the wood tread when I work on it.

Stair Tread Wood Jib with Hole for Input Shaft

Wood Jig with Hole for Input Shaft and Holes for Small Bolts To Hold Transmission in Place

Cycle Works Flat Plate For Shimming

I bought the Cycle Works plate for shimming 5 speed transmissions. It fits over the shafts so I can measure the height of the of the outer bearing race above the edge of the case.

Cycle Works Flat Plate

Cycle Works Flat Plate

Cycle Works Output Shaft Flange Puller

I use Cycle Works transmission flange tool to install the output flange nut.

Transmission Output Flange Holder/Puller-1955 To 1995 Twins [SOURCE: Cycle Works]

Transmission Output Flange Holder/Puller-1955 To 1995 Twins [SOURCE: Cycle Works]

Depth Gauge

I use a depth gauge to measure the depth of the bearing holes in the rear cover and the depth of the outer bearing races from the top of the Cycle Works shim measuring plate.

Depth Gauge (0.001 " Resolution)

Depth Gauge (0.001 ” Resolution)

Parts

I bought new parts for the transmission and for the clutch throw-out mechanism.

Transmission Parts

Here is a list of the transmission parts I used.

Part #                  Description                                                   Qty
23 12 1 338 726  SHAFT SEAL – 40X26,5X9 1
23 12 1 232 681  SHAFT SEAL – 70X40X7 INN66,3 1
23 12 1 338 740  SHAFT SEAL – 26X16X7 1
23 11 1 338 596  GASKET ASBESTOS FREE 1
 Cycle Works /6 & LATER TRANSMISSION SHIM KIT 1
23 12 1 233 808 /6 & LATER COUNTER SHAFT BEARING, FRONT-20X52X15 1
23 12 1 231 495 /6 & LATER COUNTER SHAFT BEARING, REAR-52X20X15 1
23 12 1 231 495 /6 & LATER OUTPUT SHAFT BEARING, REAR-52X20X15 1
23 12 1 338 795 /6 & LATER OUTPUT SHAFT BEARING, FRONT-62X17X17 1
23 12 1 231 495 /6 & LATER INPUT SHAFT BEARING, REAR-52X20X15 1
23 21 1 235 449 CYLINDRICAL ROLLER BEARING,RADIAL-47X38X26 1
23 31 1 234 791  SPRING 1
23 31 1 242 910  SPRING 1
07 11 9 934 100  LOCK RING – 17X1 1
23 21 1 235 006  SNAP RING 1
07 11 9 934 186  LOCK RING – 28X1,5 2
07 11 9 934 060  LOCK RING – 12X1,0 3
07 11 9 932 841  CIRCLIP – D=6MM 1
23 31 1 231 572  ROLL PIN 1
07 11 9 934 034  LOCK RING – 8X0,8 1
07 11 9 933 516  SNAP RING – A20 1

Clutch Throw Out Mechanism Parts

Here are the parts for the clutch throw out mechanism. I replaced most of the parts.

Part #                 Description                                  Qty
23 13 1 232 089  ROD 1
23 21 1 230 440  FELT RING 1
23 13 1 232 088  WASHER-RACE 1
23 13 1 232 079  NEEDLE CAGE – 23X6X2 1
21 52 1 020 109  GASKET RING 1
21 51 1 230 109  CUP 1

Overhaul Shift Cam Mechanism.

The shift cam mechanism has springs for the shift pawl arm and the shift cam roller arm, and a cam plate roller roller which can wear. I replace these two springs, the roller and  all the circlips that secure these parts.

When the shift pawl return spring breaks, you can’t shift the gear box and are stuck in whatever gear you were in when the spring snaps. The cam roller spring keeps the shift cam located on the proper detent. If it breaks, the two cam plates can move causing gears to disengage.

How the Shift Cam Mechanism Works

Here is a short video of how the shift cam mechanism works.

VIDEO: How The Shift Cam Mechanism Operates

Disassemble the Shift Cam Mechanism

I shot a short video showing detail about how to access the shift cam mechanism parts I replace followed by pictures showing the steps in the procedure.

Shift Cam Mechanism Parts Removal Video

VIDEO: Shift Cam Mechanism Parts Removal

Remove Shift Cam Plates

I start by putting the shift cam mechanism in first gear with the plastic roller in the right most detent. I use a paint pen to marke the pins on the two cams so I can ensure they go together correctly.

Shift Cam Assemble in First Gear

Shift Cam Assemble in First Gear

Orientation of Teeth in Two Shift Cam Plates in 1st Gear

Orientation of Teeth in Two Shift Cam Plates in 1st Gear

Paint Marks on Shift Cam Gear Teeth When in 1st Gear

Paint Marks on Shift Cam Gear Teeth When in 1st Gear

I use circlip pliers to remove the circlips holding the cams on the pins.

Small Shift Cam Plate Circlip

Small Shift Cam Plate Circlip

Using Circlip Pliers to Remove Small Shift Cam Plate Circlip

Using Circlip Pliers to Remove Small Shift Cam Plate Circlip

Small Shift Cam Plate Removed

Small Shift Cam Plate Removed

Large Shift Cam Plate Circlip

Large Shift Cam Plate Circlip

Large Shift Cam Plate Comes Off Shaft

Large Shift Cam Plate Comes Off Shaft

NOTE:
The discoloration on the second, larger shift cam plate comes from spot welds during manufacture and are not signs of a problem with the plate.

Remove Shift Pawl, Replace Spring and Circlip

The shift pawl lever is under the two cam plates. The finger on the end engages pins in the larger shift cam plate to ratchet it clockwise or counterclockwise depending when you up or down shift.

Shift Pawl Arm

Shift Pawl Arm

Large Shift Cam Plate Has Pins Shift Pawl Engages to Rotate Shift Cams

Large Shift Cam Plate Has Pins Shift Pawl Engages to Rotate Shift Cams

The pawl has a spring that I replace as it rubs against the cam plate which can weaken it and cause it to break. When that happens, the transmission remains in whatever gear it was in when the spring breaks.

Location of One Spring Finger of Shift Pawl Spring

Location of One Spring Finger of Shift Pawl Spring

Location of Other Finger of Shift Pawl Spring

Location of Other Finger of Shift Pawl Spring

The pawl arm is secured with a circlip on the inside of the pawl. I use a small screw driver to remove the circlip and pull the pawl arm and spring off the pin.

Shift Pawl Circlip Location

Shift Pawl Circlip Location

Shift Pawl Shaft Circlip

Shift Pawl Shaft Circlip

Shift Pawl Mechanism Showing Spring Orientation

Shift Pawl Mechanism Showing Spring Orientation

Disassemble Shift Cam Roller Arm

The shiftcam roller and arm are spring loaded.

Shift Roller Arm Spring Orientation

Shift Roller Arm Spring Orientation

Roller Arm Spring Finger Removed From Cam Plate

Roller Arm Spring Finger Removed From Shift Cam Plate

The arm is secured with a circlip on the back of the shift cam mechanism plate.

Circlip Securing Shift Roller Arm Shaft to Shift Cam Assembly Plate

Circlip Securing Shift Roller Arm Shaft to Shift Cam Mechanism Plate

I remove the circlip and remove the arm and spring.

Shift Cam Roller Arm, Spring and Rear Circlip

Shift Cam Roller Arm, Spring and Rear Circlip

The plastic roller is secured with a circlip that I remove.

Circlip Holds Shift Roller on Pin

Circlip Holds Shift Roller on Pin

Shift Cam Roller Arm Parts

Shift Cam Roller Arm Parts

Assemble Shift Cam Mechanism

I shot a short video showing how I install the replacement parts and assemble the shift cam mechanism followed by pictures showing the procedure.

Video of Shift Cam Mechanism Assembly Procedure

VIDEO: Assembling Shift Cam Mechanism

Assembly Shift Pawl Mechanism

I replace the shift pawl spring and the circlip.

Installing New Shift Pawl Spring

Installing New Shift Pawl Spring on Shift Pawl

New Shift Pawl Spring Fits Over Shift Plate Bushing

Shift Pawl Spring Installed on Outside of Shift Pawl Bushing with One Finger Against Notch

Location of 2nd Shift Pawl Spring Finger Inside Slot of Shift Pawl Arm

Location of 2nd Shift Pawl Spring Finger Inside Slot of Shift Pawl Arm

New Circlip Inserted on Shift Pawl Shaft

New Circlip Inserted on Shift Pawl Shaft

Verifying Shift Pawl Works

Verifying Shift Pawl Works

Verifying Shift Pawl Works

Verifying Shift Pawl Works

Assemble Cam Roller Arm

I install the new roller and circlip and then attach the roller arm to the shift cam plate with a new circlip.

New Shift Cam Roller and Circlip Installed

New Shift Cam Roller and Circlip Installed

NOTE:
It turned out the cam roller circlip I bought from my BMW dealer was not the correct size; it’s bigger than the original so I got an incorrect part. I didn’t compare it to the one I removed, so I didn’t catch this mistake. Humans make mistakes and BMW has humans pull parts to fill orders. My mistake was not verifying I got the correct size circlip.

It came off and the shift cam roller came off the pin about 2,000 miles later as I was riding in Indiana to the 40th R100RS anniversary rally in Pennsylvania. That created a bit of an adventure, and you can read about that it and the rally here:

Small details like this really matter when working on the transmission. Check your parts carefully. 🙂

Shift Cam Roller Arm Spring Orientation

Shift Cam Roller Arm Spring Orientation

Circlip Holding Shift Cam Roller Arm Shaft

Circlip Holding Shift Cam Roller Arm Shaft

New Shift Cam Roller, Circlip and Spring Installed

New Shift Cam Roller, Circlip and Spring Installed

Replace Input Shaft Bearings

I disassemble the input shaft using a 20 ton shop press I have access to and special tools I borrowed from a long time airhead mechanic. The front bearing is a roller bearing and the rear bearing is a ball bearing.

The ball bearing has a shield. I use a special sleeve to pull the bearing so I won’t damage the shield when I press the bearing off the shaft.

Input Shaft Rear Ball Bearing with Shield

Input Shaft Rear Ball Bearing with Shield

Special Tool Orientation For Removing Rear Input Shaft Ball Bearing

Special Tool Orientation For Removing Rear Input Shaft Ball Bearing

Special Tool Orientation on Input Shaft Rear Bearing

Special Tool Orientation on Input Shaft Rear Bearing

I hold the bearing in the special sleeve, mount it in the plates of the press and use a rod to press the shaft down to remove it from the bearing.

Shop Press Ready For Removing Input Shaft Rear Bearing

Shop Press Ready For Removing Input Shaft Rear Bearing

Rod Pressing On Shaft To Remove Input Shaft Rear Bearing

Rod Pressing On Shaft To Remove Input Shaft Rear Bearing

Pressing Input Shaft Through Rear Ball Bearing

Pressing Input Shaft Through Rear Ball Bearing

Input Shaft Rear Ball Bearing Removed

Input Shaft Rear Ball Bearing Removed

The shield sits on a “top hat” sleeve and comes right off. I will remove the top hat sleeve that later.

Input Shaft Rear Ball Bearing Shield

Input Shaft Rear Ball Bearing Shield Sits on a “Top Hat” Pressed on the Shaft

Input Shaft with Top Hat and Torsion Spring Collar

Input Shaft with Top Hat and Torsion Spring Collar

To remove the other bearing, I have to remove the torsion spring. I use another special sleeve to press down on the spring so I can remove a snap ring that holds a retaining collar on top of the spring, and then take the pressure off the spring to remove the collar and spring.

Input Shaft Torsion Spring Collar Snap Ring Location

Input Shaft Torsion Spring Collar Snap Ring Location

Special Tool to Remove Input Shaft Torsion Spring Collar Snap Ring

Special Tool to Remove Input Shaft Torsion Spring Collar Snap Ring

Tool Orientation to Remove Input Shaft Torsion Spring Collar Snap Ring

Tool Orientation to Remove Input Shaft Torsion Spring Collar Snap Ring

Shop Press Ready To Compress Torsion Spring and Remove Snap Ring

Shop Press Ready To Compress Torsion Spring and Remove Snap Ring

As I push the spring down, the snap ring is exposed. I use a couple of small blade screw drivers to pry the spring out of its groove and move it up the shaft.

Torsion Spring Compress Exposing Collar Snap Ring

Torsion Spring Compress Exposing Collar Snap Ring

Snap Ring Out of Groove - Still Needs To Be Moved Higher on Shaft

Snap Ring Out of Groove – Still Needs To Be Moved Higher on Shaft

I decided to use a bearing puller to remove the top hat on the end of the shaft, but I could have used the press. I insert a bolt into the hole in the shaft so the bearing puller bolt to push against so I don’t damage the end of the input shaft.

Bolt Used to Protect Input Shaft Prior To Pulling Rear Ball Bearing Bushing

Bolt Used to Protect Input Shaft Prior To Pulling Rear Ball Bearing Bushing

Pulling Input Shaft Rear Ball Bearing Bushing

Pulling Input Shaft Rear Ball Bearing Bushing

 

Input Shaft Rear Top Hat Bush Removed

Input Shaft Rear Top Hat Bush Removed

I remove the snap ring, torsion spring collar, the spring, the yoke and the helical 5th gear

Input Shaft Torsion Spring Collar Snap Ring Removed

Input Shaft Torsion Spring Collar Snap Ring Removed

Input Shaft Torsion Spring Collar Orientation

Input Shaft Torsion Spring Collar Orientation

Input Shaft Torsion Spring

Input Shaft Torsion Spring

Input Shaft Torsion Spring Yoke Orientation

Input Shaft Torsion Spring Yoke Orientation

Input Shaft Helical 5th Gear Orientation

Input Shaft Helical 5th Gear Orientation

Here is the order of the input shaft torsion damper parts.

Input Shaft Torsion Spring Assembly Parts Order

Input Shaft Torsion Spring Assembly Parts Order

I use the bearing puller to press the inner roller bearing race off the shaft. It’s a tight fit and requires a good deal of force to move it off the shaft.

Input Shaft Front Roller Bearing Inner Race

Input Shaft Front Roller Bearing Inner Race

Removing Input Shaft Front Roller Bearing Inner Race

Removing Input Shaft Front Roller Bearing Inner Race

Input Shaft and Old Roller Bearing Inner Race Removed

Input Shaft and Old Roller Bearing Inner Race Removed

I take the new inner race and install it on the input shaft using the shop press and a bearing separator. I push the other end of the shaft through the inner race until it stops at the machined area of the shaft the bearing fits on. I press the shaft through the bearing race until it seats against the splines.

Input Shaft with New Front Roller Bearing

Input Shaft with New Front Roller Bearing

Pressing New Front Roller Bearing Inner Race on Input Shaft

Pressing New Front Roller Bearing Inner Race on Input Shaft

Pressing Input Shaft Roller Bearing Inner Race Up To End of Splines

Pressing Input Shaft Roller Bearing Inner Race Up To End of Splines

Input Shaft New Roller Bearing Inner Race Installed

Input Shaft New Roller Bearing Inner Race Installed

I inspected the surface of the saddle end of the bearing and the yoke. I saw no cracks or signs of damage.

Minor Wear on Input Shaft Helical 5th Gear Saddle

Minor Wear on Input Shaft Helical 5th Gear Saddle

Minor Wear on Input Shaft Torsion Spring Assembly Yoke

Minor Wear on Input Shaft Torsion Spring Assembly Yoke

I slide 5th gear on the shaft then the yoke, the spring (it has no required orientation) and finally the retaining collar.

Sliding Input Shaft Helical 5th Gear Onto Shaft

Sliding Input Shaft Helical 5th Gear Onto Shaft

Sliding Input Shaft Torsion Spring Assembly Yoke Onto Shaft

Sliding Input Shaft Torsion Spring Assembly Yoke Onto Shaft

Sliding Input Shaft Torsion Spring Onto Shaft

Sliding Input Shaft Torsion Spring Onto Shaft

Input Shaft Torsion Spring Coupling Ready to Press Onto Shaft

Input Shaft Torsion Spring Coupling Ready to Press Onto Shaft

I use the special tool and the shop press to compress the torsion spring so I can install a new snap ring. I have to use screw drivers to wiggle the new snap ring down the shaft so it is next to the groove. Note how expanded the old ring became when I removed it.

(Left) New Input Shaft Snap Ring; (Right) Old One Has Expanded

(Left) New Input Shaft Snap Ring; (Right) Old One Has Expanded

Tool for Compressing Input Shaft Torsion Spring Coupling to Install New Snap Ring

Tool for Compressing Input Shaft Torsion Spring Coupling to Install New Snap Ring

Input Shaft New Snap Ring Position Prior to Using Hydraulic Press

Input Shaft New Snap Ring Position Prior to Using Hydraulic Press

Ready to Push New Input Shaft Snap Ring Down Into Groove

Ready to Push New Input Shaft Snap Ring Down Into Groove

I had to use two screw drivers to push the snap ring into the groove and to ensure it didn’t walk out of the groove as I released the pressure on the torsion spring. It didn’t seat in the groove correctly the first time so I compressed the spring again and used the screw drivers to keep it in place until it was captured by the collar.

Input Shaft Torsion Spring Collar Snap Ring Fully Seated In Collar

Input Shaft Torsion Spring Collar Snap Ring Fully Seated In Collar

I press the collar that the bearing shield sits on onto the shaft using a deep socket and a hammer.

Input Shaft Rear Bearing Top Hat Orientation

Input Shaft Rear Bearing Top Hat Orientation

Input Shaft Rear Bearing Top Hat Installed

Input Shaft Rear Bearing Top Hat Installed

I install the bearing shield against the collar and then press the ball bearing on the shaft using the shop press and a suitable socket to press on the inner race.

Input Shaft Rear Ball Bearing Shield

Input Shaft Rear Ball Bearing Shield

Input Shaft Rear Ball Bearing Shield Sits On Top of Top Hat Sleeve

Input Shaft Rear Ball Bearing Shield Sits On Top of Top Hat Sleeve

Ready to Press Input Shaft Rear Ball Bearing Onto Shaft

Ready to Press Input Shaft Rear Ball Bearing Onto Shaft

Ready to Press Input Shaft Rear Ball Bearing Onto Shaft

Ready to Press Input Shaft Rear Ball Bearing Onto Shaft

Input Shaft Rear Ball Bearing Installed

Input Shaft Rear Ball Bearing Installed

Replace Intermediate Shaft Bearings

I replace the two ball bearings on the intermediate shaft using the shop press I have access to.

The rear bearing next to first gear has a single rubber baffle on the side of the bearing the fits into the hole in the rear cover.

Intermediate Shaft Rear Ball Bearing With Rubber Cover

Intermediate Shaft Rear Ball Bearing With Rubber Cover

The front bearing next to the helical 5th gear fits into the case and does not have a baffle.

Intermediate Shaft Front Ball Bearing Without Rubber Cover

Intermediate Shaft Front Ball Bearing Without Rubber Cover

I tighten the bearing separator halves under the bearing. The press pushes the shaft down through the bearing. I put a bolt in the hole of the shaft and place a rod between it and the press arbor. The bolt protects the shaft from being damaged by the rod.

Intermediate Shaft Front Ball Bearing Removed

Intermediate Shaft Front Ball Bearing Removed

After I remove both bearings, I press the new ones on each end of the shaft being careful to have the bearing WITHOUT the black rubber cover nest to the helical 5th gear. I use a socket that fits over the inner race so the inner race takes the force of the press NOT THE OUTER RACE.

Pressing Intermediate Shaft Front Ball Bearing On The Shaft

Pressing Intermediate Shaft Front Ball Bearing On The Shaft

New Intermediate Shaft Front Ball Bearing Installed

New Intermediate Shaft Front Ball Bearing Installed

Overhaul Output Shaft

I disassemble the output shaft using a bearing puller. This can also be done with a press. I found it very convenient to hold the shaft in the wood jig I made so I didn’t have to wrestle with it. The 5th gear was wobbling on the shaft so it and the shaft were worn. Cycle Works refurbished the shaft and gear with hard chrome plating and honing to eliminate the wear on the shaft and hole in the gear.

Remove Output Shaft Front Bearing, 5th  and 3rd Gears

I start by removing the front circlip and front bearing so I can remove 5th and 3rd gears. Once the circlip is removed, 5th gear, a washer and 4th gear slide off the input shaft.

Output Shaft with 5th Gear Removed

Output Shaft with 5th Gear Removed

Output Shaft 5th Gear-Uneven Wear on Face

Output Shaft 5th Gear-Uneven Wear on Face

The output shaft front bearing has a special detail. The circlip fits against the front face of the bearing and to increase the contact surface between the bearing face and the circlip, the hole in the bearing has a more abrupt or “square” profile than the rear bearing face. You can see the difference in the pictures below.

Output Shaft Front Bearing Squared Front Face

Output Shaft Front Bearing Squared Front Face

Output Shaft Circlip on Front Bearing on Square Front Face-More Contact

Output Shaft Circlip on Front Bearing on Square Front Face-More Contact

Output Shaft Front Bearing Rounded Rear Face

Output Shaft Front Bearing Rounded Rear Face

Output Shaft Circlip on Front Bearing Rounded Rear Face-Little Contact

Output Shaft Circlip on Front Bearing Rounded Rear Face-Little Contact

Here is the output shaft showing the parts removed so far.

Output Shaft After Removing Front Circlip, Bearing, 5th Gear, Washer and 3rd Gear

Output Shaft After Removing Front Circlip, Bearing, 5th Gear, Washer and 3rd Gear

Using Bearing Puller to Remove Rear Bearing

I put the rear of the output shaft in the wood jig so I can remove the rear bearing and the other gears on the shaft.

Output Shaft Front End Inserted in Jig

Output Shaft Front End Inserted in Jig

I assemble the parts I need from a Harbor Freight bearing puller kit. In the picture below; Top Center-Separator Plate; Top Sides-Separator Plate Pillar Bolts; Bottom-Yoke and Pusher Bolt.

Harbor Freight Bearing Puller Parts

Harbor Freight Bearing Puller Parts

First I insert the separator plate in the gap between the bearing face and 1st gear and then tighten the two bolts in an alternating pattern to evenly insert the knife edge of the plate between the bearing and the gear. I keep tightening until I can see the bearing move upward a bit and a good portion of the knife edge is under the outer race of the bearing.

Tightening Puller Plate Bolts

Tightening Puller Plate Bolts

I assemble the pillar bolts, top yoke and pusher bolt. I grease the threads of the pusher bolt. I put a bolt with its head on top of the output shaft to protect it from damage by the pusher bolt.

Bearing Puller Plate and Rods Assembled

Bearing Puller Plate and Rods Assembled

Bearing Puller Threads Greased

Bearing Puller Threads Greased

10 mm Bolt Protects Face of Output Shaft

10 mm Bolt Protects Face of Output Shaft

Bearing Puller Assembled

Bearing Puller Assembled

I tighten the pusher bolt until I pull the bearing off the shaft.

Tightening Bearing Puller Bolt

Tightening Bearing Pusher Bolt

Bearing Puller Removing Output Shaft Rear Bearing

Bearing Puller Removing Output Shaft Rear Bearing

Output Shaft Rear Ball Bearing

Output Shaft Rear Ball Bearing

When I use the shop press, I assemble the bearing separator under a bearing as I did above, but I use the press to push the shaft down out of the bearing.

Remove Output Shaft 1st Gear

I remove the washer and then 1st gear from the output shaft. The side of the washer against 1st gear has a flat edge around the hole while the other side that goes next to the splines on the shaft has a beveled edge around the hole. The splines have a chamfer so the beveled hole of the washer lets it fit snugly against the face of the splines.

Output Shaft 1st Gear Washer Removed

Output Shaft 1st Gear Washer Removed

Output Shaft 1st Gear Washer-Flat Side

Output Shaft 1st Gear Washer-Flat Side

Output Shaft 1st Gear Washer-Beveled Side

Output Shaft 1st Gear Washer-Beveled Side

The rear face of 1st gear is flat with a colored inspection mark and the front side has slots that engage with the dogs on 4th gear. There is a bronze bush that fits in the hole of the gear.

Output Shaft 1st Gear

Output Shaft 1st Gear

Output Shaft 1st Gear

Output Shaft 1st Gear

Ouput Shaft 1st Gear Bushing

Ouput Shaft 1st Gear Bushing

Remove Output Shaft 4th Gear

The 4th gear has dogs on both faces and has a washer on the rear face.

Output Shaft 4th Gear

Output Shaft 4th Gear-Note 4 Dots of White Paint on Dogs

Output Shaft 4th Gear Washer

Output Shaft 4th Gear Washer

Output Shaft 4th Gear

Output Shaft 4th Gear

Output Shaft 4th Gear

Output Shaft 4th Gear

Remove Output Shaft 2nd Gear

Second gear is secured to the output shaft with two circlips. I remove the rear circlip and the washer, 2nd gear and the washer and front circlip. Second gear also has a bushing in the hole of the gear.

Output Shaft 2nd Gear Rear Circlip

Output Shaft 2nd Gear Rear Circlip

Removing Output Shaft 2nd Gear Circlip

Removing Output Shaft 2nd Gear Circlip

Output Shaft 2nd Gear Rear Circlip

Output Shaft 2nd Gear Rear Circlip

Output Shaft 2nd Gear Rear Serrated Washer

Output Shaft 2nd Gear Rear Serrated Washer

Output Shaft 2nd Gear Rear Serrated Washer

Output Shaft 2nd Gear Rear Serrated Washer

Output Shaft 2nd Gear Slots for Gear Dog Engagement

Output Shaft 2nd Gear Slots for Gear Dog Engagement

Output Shaft 2nd Gear Bushing That Fits Over Splines on the Shaft

Output Shaft 2nd Gear Bushing That Fits Over Splines on the Shaft

Output Shaft 2nd Gear Front Serated Washer

Output Shaft 2nd Gear Front Serated Washer

Output Shaft 2nd Gear Front Circlip

Output Shaft 2nd Gear Front Circlip

Here is the output shaft after all the bearings, circlips, washers and gears.

Output Shaft Ready for Repair

Output Shaft Ready for Repair

Here is a short video showing the order of the parts on the output shaft.

VIDEO: Output Shaft Parts Sequence

Assemble Output Shaft

I bought new bearings and new circlips. I use the hydraulic press to assemble the parts on the output shaft. Cycle Works built up the output shaft and 5th gear bore and then honed them so I now have “like new” parts.

5th Gear Section of Output Shaft After Hard Chrome Plating and Honing

5th Gear Section of Output Shaft After Hard Chrome Plating and Honing

5th Gear Thrust Washer-Flat Face

5th Gear Thrust Washer-Flat Face

5th Gear Thrust Washer-Flat Face (Facing the Camera) Goes Against Gear and Bevel Face Against Spline

5th Gear Thrust Washer-Flat Face (Facing the Camera) Goes Against Gear, Bevel Face Against Spline

I slide 5th gear onto the shaft against the thrust washer with the face with holes facing the thrust washer. It is secured with a new circlip in a groove. However, the new bearing does not have the special square face on one side of the inner race. This reduces the the contact area between the clip and the bearing.

 

Front Output Shaft Bearing Inner Race Beveled on Both Ends

Front Output Shaft Bearing Inner Race Beveled on Both Ends

New Front Output Shaft Bearing Inner Race Beveled on Both Ends

New Front Output Shaft Bearing Inner Race Beveled on Both Ends

Output Shaft Circlip on Front Bearing Rounded Rear Face-Little Contact

Output Shaft Circlip on Front Bearing Rounded Rear Face-Little Contact

A fix for this is inserting a snap ring (part# 23 21 1 235 006) into the hole on the side the circlip goes on to increase the contact area.

 

5th Gear Bearing Snap Ring (Left) and Lock Ring (Right)

Output Shaft Front Bearing Snap Ring (Left) and Lock Ring (Right)

Output Shaft Front Bearing Snap Ring Fills In Void Between Inner Race and Shaft

Output Shaft Front Bearing Snap Ring Fills In Void Between Inner Race and Shaft

 

Output Shaft Front Bearing Lock Ring Installed Over Snap Ring

Output Shaft Front Bearing Lock Ring Installed Over Snap Ring

I slide 3rd gear down the splines on the shaft so the face with the dogs is next to the holes in the face of 5th gear. Then I put the lock ring in the groove next to 3rd gear being careful to expand the ring just enough to slide it into the groove. I don’t want to expand it too much as it will bend it and it wont stay locked into the groove.

3rd Gear Slides Over Splines with Shift Fork Groove On Side Opposite 5th Gear

3rd Gear Slides Over Splines with Shift Fork Groove On Side Opposite 5th Gear

A lock ring secures 3rd gear in place. One side has a sharp edge and the other is rounded. The side with the sharp edge faces away from the gear. I expand it with snap ring pliers just enough to slide it into the groove. I don’t want to bend it so it is loose in the groove.

New 3rd Gear Lock Ring

New 3rd Gear Lock Ring

3rd Gear Lock Ring Installed-Sharp Edge Faces Camera

3rd Gear Lock Ring Installed-Sharp Edge Faces Camera

A thrust washer goes on next followed by the bushing that fits inside the 2nd gear hole.

2nd Gear Thrust Washer

2nd Gear Thrust Washer

2nd Gear Bushing

2nd Gear Bushing

I slide 2nd gear over the bushing and install the other thrust washer.

Thrust Washer Between 3rd and 2nd Gear

Thrust Washer Between 2nd and 3rd Gear

The new lock ring goes on next. One side has a sharp edge and the other is rounded. The side with the sharp edge faces away from the gear. I expand it with snap ring pliers just enough to slide it into the groove. I don’t want to bend it so it is loose in the groove.

New Lock Ring for 2nd Gear

New Lock Ring for 2nd Gear

Second Lock Ring Securing 2nd Gear-Sharp Edge Faces Camera

Lock Ring Securing 2nd Gear-Sharp Edge Faces Camera

I slide 4th gear on the splines. This gear has dogs on both faces of the gear. The face with the groove for the shift fork faces 2nd gear.

4th Gear Orientation

4th Gear Orientation

First gear has a bronze bushing in the hole.

First Gear Bronze Bushing and Face with Slots for Gear Dog Engagement

First Gear Bronze Bushing and Face with Slots for Gear Dog Engagement

I install the thrust washer with the bevel face against the spline and then slide the bronze bushing onto the shaft against the thrust washer.

Output Shaft 1st Gear Thrust Washer and Bushing Installed

Output Shaft 1st Gear Thrust Washer and Bushing Installed

Output Shaft 1st Gear Installed with Slots Facing 4th Gear Dogs

Output Shaft 1st Gear Installed with Slots Facing 4th Gear Dogs

Last, I use the shop press to push the rear ball bearing on the shaft against the face of 1st gear.

Assemble Transmission

I install the oil baffle into the transmission case securing it with the screw and washer.

Oil Tunnel to Output Shaft Front Bearing Cavity

Oil Tunnel to Output Shaft Front Bearing Cavity Orientation

Location of Screw That Secures Oil Tunnel to Output Shaft Front Bearing Cavity

I remove the input and output shaft seals using a drift to push them out of the case.

Input Shaft Seal Removed

Output Shaft Seal Removed Showing Correct Orientation

The input shaft will fit into a tapered roller bearing that is installed into the case.

Input Shaft with Outer Roller Bearing Race

Input Shaft Assembled

The output and intermediate shafts will go into the case together with the 5th gear shift fork. There is a metal baffle that fits on the front bearing of each shaft as shown on the bottom of the following picture.

Output Shaft (Left) and Intermediate Shaft (Right) with Shift Fork

The first-second and third-fourth shift forks and shaft go into the case. The fork fingers fit onto the grooves of the dog gears and the pins slip into the slots of the shift cam along with the shift dog for 5th gear.

Output Shaft Shift Forks and Shaft Orientation

I heat the case in the oven at 280 F for 45 minutes. I install the roller bearing first.

Input Shaft Roller Race Installed

Then the metal baffels for the intermediate and output shafts.

Input Shaft Outer Race Installed in Transmission Case

Then I insert the output and intermediate shaft front bearings into the case while I slip the 5th gear shift fork down the short shaft in the case. I use a rubber mallet on the end of the shafts to ensure they are fully bottomed into the holes in the case.

Output Shaft, Intermediate Shaft and Shift Fork Installed

Gentle Tap To Ensure Bearings Are Bottomed Out

I insert the input shaft into the roller bearing which requires a bit of jiggling and twisting to allow the helical gears to mesh.

Input Shaft Inserted in Roller Bearing with 5th Gear Engaged with Intermediate Shaft 5th Gear

Now I insert the two shift fork fingers into the grooves of the dog gears on the output shaft and slide the shift fork shaft through the hole in the forks and into the hole in the case.

NOTE:
I temporarily removed the input shaft to better show the shift forks engaging the dog gears the output shaft. Then I Installed the input shaft and the shift forks.

Output Shaft Shift Forks and Shift Fork Shaft Installed

I put the shift cam plate into neutral. Then I install the shift cam assembly so the pins on the end of the sift forks fit into the slots in the two cam plates. When the pins are in the slots, I install both of the special bolts to secure the shift cam mechanism to the case.

Cam Plate in Neutral

Intermediate Shaft Shift Fork Pin Inserted in Cam Profile of Cam Plate

Output Shaft Shift Fork Pins Inserted in Cam Profile of Cam Plate

Cam Plate Bolts

Can Plate Bolts Inserted

Torque Cam Plate Bolts

Here is the case with the shafts and shift cam mechanism installed.

Shafts and Cam Plate Mechanism Installed

I let the case cool down before proceeding. Then I install the Cycle Works shim measuring plate and the shift lever and verify I can shift up and down through all five gears. I rotate the input shaft by hand to help the gears engage.

Cycle Works Measuring Plate

Cycle Works Measuring Plate

Shim Shafts

The axial play, or end float, for the three transmission shafts is between 0.05 mm (0.002 inch) to 0.1 mm (0.004 in). I purchased a shim kit from Cycle Works and I have the existing shims I found when I opened the transmission so I should have enough of the right thickness to shim all three shafts.

I start by zeroing the depth gauge using the top of the Cycle Works shim measuring plate. I rest the gauge on the plate and turn the thimble until it clicks. I adjust the barrel so that corresponds to zero on the gauge.

Depth Gauge (0.001 " Resolution)

Depth Gauge (0.001 ” Resolution)

Zero Depth Gauge Using Plate

Zero Depth Gauge Using Plate

I measure the depth of the holes in the rear cover for each shaft at four locations: 12, 3, 6 and 9 o’clock. I average the measurements to get the depth of the hole. I take the measurements at the middle of the shelf the bearing rests on to avoid the curved surface between the horizontal shelf and the vertical side of the hole.

Measuring Depth of Cover Bearing Hole

Measuring Depth of Cover Bearing Hole

NOTE:
I marked each hole to be sure I didn’t confuse what measurements went with each shaft. I found it easy to get confused when just looking at the cover. 

I measure the thickness of the Cycle Works plate with a micrometer. Then I put the gasket on the case and attach the Cycle Works plate and measure the depth of the outer bearing race from the top of the plate at four positions as I did for the rear cover and average them.

Cycle Works Measuring Plate

Cycle Works Measuring Plate

Measuring Depth of Outer Race of Bearing

Measuring Depth of Outer Race of Bearing

I use a spreadsheet I made to compute the range of shim thickness required for a clearance of 0.002 – 0.004 inches of end play. I measured all the shims with a micrometer and mark each shim with its thickness; for exmaple, 0.195 was marked as “195”.

I use combinations of shims to get within the end play range for each shaft. Then I measured the shims in a stack to be sure the final measurement matches is within the range of end play just to be sure I didn’t make a mistake.

NOTE:
For the intermediate shaft, I include the thickness of the rear baffle plate when computing how much additional shimming is needed to fall within the 0.002 – 0.004 inch end play range. 

Intermediate Shaft Front Bearing Cap

Intermediate Shaft Front Bearing Cap

I put some grease on the shims to help keep them together and put the stack of shims on top of each bearing.

NOTE:
It is easy to get confused which shim stack goes on which bearing. So I placed each stack in the correct hole of the rear cover and put a bit of masking tape around the stack labeled “In”, “Inter”, “Out” for insurance. It’s easy to bump things or confuse yourself when you are playing with three shafts and multiple shims.

Grease Keeps Shims Together

Grease Keeps Shims Together

Placing Shims on Output Shaft

Placing Shims on Output Shaft

Shims In Place on Each Shaft-Note Shims Marked with Thickness

Shims In Place on Each Shaft-Note Shims Marked with Thickness

I heat the cover with the MAP gas torch concentrating the heat around the areas where the bearing holes are until it is “sizzle hot” and then place the cover on the transmission aligning it with the locating pins. As I position the cover, I’m careful to not disturb the shims on top of the bearings so they will go into the holes in the cover and not get bent or misplaced. Then I tap the cover with a plastic mallet so it seats against the case.

Rear Cover Seated Fully Against Case

Rear Cover Seated Fully Against Case

I put washers on the nine new stainless steel bolts that secure the rear cover to the case and insert the bolts and tighten them hand tight.

New Rear Stainless Cover Bolts and Washers with Anti-seize On Threads

New Rear Stainless Cover Bolts and Washers with Anti-seize On Threads

I visually inspect the input shaft and output shaft to verify the shims are not bent of damaged.

Checking Output Shaft Shims Are Not Bent or Folded

Checking Output Shaft Shims Are Not Bent or Folded

I torque the cover bolts to 72 INCH/Lbs NOT FOOT/lbs with an inch/pound torque wrench.

Torque Rear Cover Bolts to 72 INCH-Lbs NOT FOOT-Lbs

Torque Rear Cover Bolts to 72 INCH-Lbs NOT FOOT-Lbs

When the cover cools, I twist the output shaft to feel how hard it is to turn. I also had a long time airhead mechanic check it as well. The best way to describe it is the splines will put a good indent in my fingers when I turn the shaft. As the transmission heats up, the shaft will turn more easily as the end clearance increases as the aluminum case and cover expand faster than the steel shafts.

Install Shaft Seals

I install a new shift shaft seal using a socket to drive it home.

Driving Shift Shaft Seal with Deep Socket

Driving Shift Shaft Seal with Deep Socket

New Shift Shaft Seal Installed

New Shift Shaft Seal Installed

The output shaft seal flat face goes inside the transmission, not outside.

New Output Shaft Seal-Flat Face Goes Inside

New Output Shaft Seal-Flat Face Goes Inside

New Output Shaft Seal-Grooved Face Goes Outside

New Output Shaft Seal-Grooved Face Goes Outside

There is a small slot in the output shaft seal that allows air equalization between the transmission and the drive shaft. This should be clear so the drive shaft boot does not balloon.

Note Groove at 12:00, It Should Be Clean

Note Groove at 12:00, It Should Be Clean

Before I install the new seal, I use brake cleaner to clean the taper on output shaft. I keep cleaning them until there is no residue on a clean blue shop towel.

I used an old front crankshaft bearing carrier to drive the seal, but any suitable sized sleeve can be used.

Output Shaft Seal Installed with Front Engine Bearing Carrier as Drift

Output Shaft Seal Installed with Front Engine Bearing Carrier as Drift

Orientation of New Output Seal-Groove Faces You

Orientation of New Output Seal-Groove Faces You

The input shaft has splines that will damage seal if it is pushed over them.

Input Shaft with Splines

Input Shaft with Splines

I use a special two piece tool I borrowed from an airhead mechanic to drive the seal. The smaller diameter cup fits over the splines, the seal is pushed over the cup and the larger diameter drift slides over the cup so I can hammer the seal home.

Input Shaft Seal Install Tool Parts-(Right) Outer Tube, (Left) Cup

Input Shaft Seal Install Tool Parts-(Right) Outer Tube, (Left) Cup

Input Shaft Seal Install Tool Parts

Input Shaft Seal Install Tool Parts

Inner Tools Fits Over Input Shaft Splines to Protect the Seal

Inner Tools Fits Over Input Shaft Splines to Protect the Seal

Seal Slides Over Inner Tool

Seal Slides Over Inner Tool

Outer Tool Goes Over Inner Tool

Outer Tool Goes Over Inner Tool And Is Hammered Home To Seat the Seal

Transmission Input Shaft Seal Installed

Transmission Input Shaft Seal Installed

Install New Neutral Switch

I install a new neutral switch with the spacer. Before I installed it, I put some green wicking loctite around the seam between the metal cover the plastic inset to help prevent it from leaking.

New Neutral Switch with Washer

New Neutral Switch with Washer

New Neutral Switch with Green Wicking Loctite Around the Seam

New Neutral Switch with Green Wicking Loctite Around the Seam

New Neutral Switch Installed

New Neutral Switch Installed

Install Output Flange

I use the Cycle Works Flange Puller to install the output flange. I use brake cleaner to clean the taper inside the flange and once again on the tapered output shaft. I keep cleaning them until there is no residue on a clean blue shop towel.

Output Flange with Spline

Output Flange with Spline (Picture Taken During Disassembly)

Output Flange Taper Need To Be Clean - NOT EVEN FINGER PRINTS

Output Flange Taper Need To Be Clean – NOT EVEN FINGER PRINTS (Picture Taken During Disassembly)

I install the flange on the taper and tap it with a rubber mallet. Then I twist the flange to spin the transmission. If the flange and taper are clean, they will not slip. It they do slip, I need to go back and clean them again.

Next, I install the speedometer drive helical gear into the hole in the transmission case.

Speedometer Drive Gear Fits In Hole in Transmission Case and Engages Output Flange Helical Gear

Speedometer Drive Gear Fits In Hole in Transmission Case and Engages Splines on Output Flange (Picture Taken During Disassembly)

Then I install the flange holder on the flange with the four bolts.

Cycle Works Transmission Output Shaft Flange Tool Assembly

Cycle Works Transmission Output Shaft Flange Tool Assembly

Cycle Works Transmission Output Shaft Flange Tool Assembly

Cycle Works Transmission Output Shaft Flange Tool Assembly

I torque the center nut to 160 FT-Lbs. I put the transmission in the wood holder. I put an old fork tube over the flange handle. Then I put my feet on the fork tube while I pull the torque wrench.

Tightening Transmission Output Shaft Flange Nut to 160 FT-Lbs

Tightening Transmission Output Shaft Flange Nut to 160 FT-Lbs

At this point, I want to test the transmission to be sure I can shift up and down through all five gears. It is hard to shift by hand with the short lever used for the adjustable linkage, so I remove the the shift lever from my /6 which is the stock lever used on the 1977 RS transmission. I spin the input shaft by hand to help ease the gear engagement and can get all five gears and neutral.

Install Speedometer Cable Bolt

The speedometer cable bolt has a hole drilled through it to allow breathing. It needs to be clear.

Ensuring Transmission Speedometer Bolt Hole is Open

It has two washers on it and fits into the threaded hole on the right rear of the transmission. The ground cable fits on the bolt, but due to the ease of stripping the bolt hole in the transmission, I attach the ground to the frame under a coil bracket mounting bolt.

.

Install Clutch Throw Out Rod

I replace a number of worn parts as shown in the Clutch Throw Out Mechanism parts list above. The assembly is the same as used on the 1973 R75/5 which I document here:

For now, I want to insert the throw out rod with the new oiled felt before I install the transmission.

Clutch Push Rod with New Oiled Felt Seal

Clutch Push Rod with New Oiled Felt Seal

I insert the flat end of the rod through the output shaft from the front of the transmission.

Inserting Clutch Push Rod Inside Input Shaft From Front of Transmission

Inserting Clutch Push Rod Inside Input Shaft From Front of Transmission

The beveled end points to the front.

Clutch Push Rod Inserted Inside Input Shaft

Clutch Push Rod Inserted Inside Input Shaft

Here is the transmission installed in the frame.

Transmission Installed

Transmission Installed

Revisions

2017-10-31 Added link to YouTube transmission videos.

 

4 thoughts on “23 BMW 1977 R100RS Transmission Refresh and Assembly

  1. Very good write up Brooks. Good Pictures and you covered the bases pretty well. I see that you did not replace the helical gear on the input shaft and the gear on the intermediate shaft with the broken dogs. That should work ok for a while as the broken dogs were on opposite sides of the gear. Smooth shifting practices will help longevity too. I had an input shaft helical gear that had spalling on the teeth and spalling on the the cam ramps. BMW does not supply this gear anymore, but i was able to find on at Motoren-Israel. Keep up the good work.

    • Hi Jim,

      Thank you for the kind words.

      I would have liked to repair all the wear I found, but based on “unobtainium” parts and judgement of more experienced folks, I decided to let some of the sleeping dogs lie (pun intended):-)

      Best.
      Brook.

  2. Brook,
    Thanks for the thorough transmission write-up.
    I will need to look into my 74 R90/6 gearbox this winter. It seems to have decided 5th gear was unnecessary.
    You have made this job far less intimidating.
    Ride safe,

    Brett

    • Hi Brett,

      Rumor says the 1974 5-speed had need for a number of “improvements”. Changes were made for 1975 to try and improve reliability. That said, I’m not knowledgeable about what the changes are.

      Best.
      Brook.

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