23 BMW 1983 R100RS Disassemble Transmission

TRANSMISSION REBUILD 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. 

I previously rebuilt the transmission of my 1977 R100RS. This is the second time I have done this work. Therefore, I am not an expert, I am an amateur. I estimate I have invested around $700 in acquiring the necessary tools. This work requires a clean environment, precision measuring tools, multiple special tools, patience, skill and a close attention to detail. And, for both these rebuilds, I have access to long time, skilled airhead mechanics who are willing to support me with advice, part inspection and analysis, and answers to procedural questions.

If you don’t have all the above and you haven’t rebuilt multiple airhead motorcycles, I strongly advise you NOT TO DO THIS WORK. You should have it done by an expert mechanic.

The odometer shows 84,000+ miles. I have found evidence of some abuse to the bike including rust in parts of the engine and evidence that the transmission seals are leaking. Since I have no maintenance history for the bike, I open up the transmission, disassemble it and inspect it. I plan to replace all the bearings, seals and the rear cover gasket. I have access to two long time BMW airhead mechanics so I can seek advice about the serviceability of any parts that show a lot of wear or evidence of abuse.

In separate write-ups, I show how I rebuild the transmission which involves removing bearings on the three shafts and installing new ones, installing new seals and replacing the high wear parts in the shift cam mechanism.

NOTE:
Some of the pictures shown later are ones I took when I rebuilt the 1977 R100RS transmission showing the same parts and/or procedure.

Resources

I used the following resources to guide me when I did my first transmission rebuild on my 1977 R100RS. The 1983 transmission has numerous changes to internal parts, but operates the same way and the procedures and tools to disassemble and reassemble it are the same.

I published documentation of how I did this work on the 1977 R100RS.

When I rebuilt the 1977 RS transmission, I shot a number of short videos about how the gears and shift cam mechanism work and some showing parts of the work I did. You can see these on my YouTube site:

I was fortunate to have access to a respected, long time BMW airhead mechanic who provided invaluable support and advice.

You can read about how I rebuild the shift cam assembly, input & intermediate shafts, output shaft and assemble the transmission here.

Tools

I use the Cycle Works transmission flange tool to remove the flange.

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

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

I use a hook seal puller to remove the gear change shaft seal.

Hook Seal Puller

Hook Seal Puller

I use two MAP gas torches (available at Home Depot) to heat the rear cover so I can remove it and also to heat the bearing bores that the gear shaft front bearings fit into inside the transmission.

MAP Gas Torch

MAP Gas Torch

I made a transmission holder from a scrap piece of 1″ stair tread I had 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 plate 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

Brief Tour of The Transmission Gears and How They Work

The BMW transmission has three shafts; input, intermediate and output. Each end of the shafts has a bearing. With the exception of the input shaft front bearing what is a roller bearing, all the bearings are ball bearings. The input and intermediate shafts are turning all the time the engine is running. The output shaft only turns when you have selected a gear with the gear shift.

Transmission internal components and how they work when changing gears are a mystery to many. The following video demonstrates how the three shafts, input, intermediate and output, and the gears on each of them work together to change the speed the output shaft rotates in relation to the input shaft speed when you select a gear.

VIDEO: How the Transmission Gears Work

Video

I put together a video that summarizes how I disassemble the transmission.

VIDEO: 1983 BMW R100RS Disassemble The Transmission

First Things First

For some reason, many people believe that working on engines and transmissions is dirty work. Well, nothing is farther from the truth. These are precision instruments and I never work on them unless they are clean and the shop and work bench have been cleaned and fresh newspaper is on the bench. I do not want to contaminate any internal parts with dirt, grit or debris of any kind.  If you don’t have a clean workspace, DO NOT do this kind of work as you are asking for trouble.

So, what did I start with? It looked like this transmission had more than one leaking seal and had not been cleaned in a long time.

Transmission Before A Bath

Transmission Before A Bath

Transmission Before A Bath

Transmission Before A Bath

Transmission Before A Bath

Transmission Before A Bath

Transmission Before A Bath

Transmission Before A Bath

So, time for a bath with engine cleaner followed by kerosene applied with a paint brush, scrubbing with stiff bristle brushes and then a hot water rinse in the sink.

Time For A Bath

Time For A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Transmission After A Bath

Although not yet spotless, the case is clean enough to start work opening the transmission. I plan to refinish the case and rear cover to match the patina of the engine block. I show how I do that and the result later.

Remove Neutral Switch And Gear Change Shaft

The neutral switch mounts on the bottom and the shift shaft is on the left side of the transmission housing. I remove them.

NOTE:
The neutral switch comes with a flat washer just the correct thickness to ensure the switch operates properly. Don’t loose it.

Neutral Switch On The Bottom Of The Transmission Housing

Neutral Switch On The Bottom Of The Transmission Housing

Removing Neutral Switch with 19 mm Crescent Wrench

Removing Neutral Switch with 19 mm Crescent Wrench

Neutral Switch Removed

Neutral Switch Removed

NOTE:
In the above picture, there is a milky sealant around the brown phenolic and aluminum case of the the neutral switch. The switch is prone to leaking and over tightening it can damage the seal between the phenolic and the aluminum case. I installed a new switch a few years ago and applied some Plast-Aid as a test to see how well it works. I will continue to use this switch to see how well it holds up.

Gear Change Shaft

Gear Change Shaft

Removing Gear Change Shaft Allen Bolt

Removing Gear Change Shaft Allen Bolt

Gear Change Shaft Removed

Gear Change Shaft Removed

Remove Output Shaft Flange

The transmission output shaft bolts to the drive shaft via a flange that is bolted onto a the tapered output shaft. I use the Cycle Works tool to remove the flange. I start by assembling the tool on top of the transmission output flange. I use a 27 mm socket to remove the nut and washer that are supposed to be torqued to 160 FT-Lbs.

Cycle Works Output Flange Puller Tool

Cycle Works Output Flange Puller Tool

Transmission Output Flange Has Four Legs with Tapped Holes

Transmission Output Flange Has Four Legs with Tapped Holes

27 mm Socket Used To Remove Output Flange Nut

27 mm Socket Used To Remove Output Flange Nut

Cycle Works Puller Plate Goes On Top Of Output Flange

Cycle Works Puller Plate Goes On Top Of Output Flange

Cycle Works Puller Ring with Handle Goes On Top Of Puller Plate

Cycle Works Puller Ring with Handle Goes On Top Of Puller Plate

Four Bolts Attach Puller Plate and Handle To Output Flange

Four Bolts Attach Puller Plate and Handle To Output Flange

I use a couple damaged fork tubes as cheaters to get enough leverage to break the nut loose. I find sitting on the shop floor and bracing one of the tubes with my feet while I pull the other toward me makes this an easy task.

Remove Transmission Output Shaft Flange Nut With Cheaters On Flange Puller Handle and Breaker Bar

Remove Transmission Output Shaft Flange Nut With Cheaters On Flange Puller Handle and Breaker Bar

Output Flange Wave Washer and Nut

Output Flange Wave Washer and Nut

I remove the socket. Before I install the puller bolt and sleeve, I put grease on the puller bolt threads. Then I install the puller bolt and threaded sleeve into the threads of the puller block. I screw the sleeve down until it’s flush with the puller handle and then tighten the puller bolt. I put a 30 mm socket over the puller bolt and use the same technique with my legs and arms to back the output flange off the taper of the output flange. The flange can be very tight and it may come loose with a loud pop.

Output Shaft Tapered End

Output Shaft Tapered End

Cycle Works Output Flange Puller Bolt Screws Into Puller Sleeve

Cycle Works Output Flange Puller Bolt Screws Into Puller Sleeve

Greasing Threads of Cycle Works Output Flange Puller Bolt

Greasing Threads of Cycle Works Output Flange Puller Bolt

Cycle Works Output Flange Puller Bolt with Sleeve Installed

Cycle Works Output Flange Puller Bolt with Sleeve Installed

Use 30 mm Socket On Puller Bolt with Breaker Bar and Fork Tube Cheater

Use 30 mm Socket On Puller Bolt with Breaker Bar and Fork Tube Cheater

Remove Transmission Output Flange

Remove Transmission Output Flange

This flange came off without too much trouble. I remove the flange from the tool. With the flange removed its easy to see the large diameter output shaft seal.

Output Flange Attached To Puller

Output Flange Attached To Puller

Output Flange Removed

Output Flange Removed

Output Flange-Helical Thread Drives Speedometer Gear

Output Flange-Helical Thread Drives Speedometer Gear

Transmission Output Flange

Transmission Output Flange

Transmission Output Flange Taper

Transmission Output Flange Taper

Output Shaft and Seal Are Exposed

Output Shaft and Seal Are Exposed

Remove Speedometer Gear

With the output flange removed, I can remove the speedometer gear. I remove the special bolt with the longitudinal hole down it’s length that lets the drive shaft breath, then the plastic bushing that holds the speedometer cable. I can push the gear out with my fingers.

Speedometer Drive Pulls Out When Output Flange Is Removed

Speedometer Drive Pulls Out When Output Flange Is Removed

Speedometer Drive Gear-Helical Thread Mates with Output Flange Helical Thread

Speedometer Drive Gear-Helical Thread Mates with Output Flange Helical Thread

Speedometer Gear, Speedometer Cable Bushing and Swing Arm Breather Bolt

Speedometer Gear, Speedometer Cable Bushing and Swing Arm Breather Bolt

Remove Transmission Rear Cover

The rear cover is attached to the transmission housing with nine Allen bolts with wave washers. I remove the bolts.

Rear Transmission Cover Secured with Nine Allen Bolts

Rear Transmission Cover Secured with Nine Allen Bolts

Removing Rear Cover Allen Bolts

Removing Rear Cover Allen Bolts

Transmission Cover Bolt and Wave Washer

Transmission Cover Bolt and Wave Washer

Nine Rear Cover Bolts Removed

Nine Rear Cover Bolts Removed

Rear Cover Bolts with Wave Washers

Rear Cover Bolts with Wave Washers

I heat the aluminum rear cover to expand the three pockets in the cover that capture the rear bearings of the three transmission shafts. I use two MAPP gas torches and direct the heat towards the bearing pockets on the rear cover.

Three Shaft Bearing Locations For Heating

Three Shaft Bearing Locations For Heating

Heating Rear Cover Around The Three Shaft Bearings

Heating Rear Cover Around The Three Shaft Bearings

When the cover is “sizzle hot”, I use a plastic mallet and tap on the edge of the cover to loosen it from the outer races of the three bearings.

Gently Tapping on Side Lug of Rear Cover To Loosen It

Gently Tapping on Side Lug of Rear Cover To Loosen It

When the cover is loose, I pull it straight up off the two locating pins in the edge of the transmission housing. There are shims on the tops of the three bearings and I want them stay there.

Transmission Shafts (Left Side) & Shift Cam Assembly (Right Side)

Transmission Shafts (Left Side) & Shift Cam Mechanism (Right Side; One Of The Rear Cover Locating Pins Is At The Bottom Of The Case

The rear cover has a casting number cast inside.

Rear Cover Casting Number

I remove the shims on the top of the output, intermediate and input shafts and put them in a labeled baggies. There is also an oil baffle plate on the top of the intermediate shaft that I put with the intermediate shims.

Output Shaft Shims Sit On Top Of Outer Bearing Race

Output Shaft Shims Sit On Top Of Outer Bearing Race

Intermediate Shaft Baffle Plate and Shim (One Was Still Inside The Rear Cover)

Intermediate Shaft Baffle Plate and Shim (One Was Still Inside The Rear Cover); Other Rear Cover Locating Pin Is At The Top Of The Case

NOTE:
One of the intermediate shaft shims stayed in the bearing pocket of the rear cover. Be sure to check the bearing pockets in the rear cover for shims.

Remove Shift Cam Mechanism

The shift cam mechanism engages the shift forks and connects them with the foot shift lever. It is secured to the front of the case with two bolts with machined shoulders that tightly engage with the holes in the front of the case.

Shift Forks and Shift Cam Assembly To The Right

Shift Forks and Shift Cam Mechanism To The Right

I heat the front of the gas with a MAPP gas torch around the two bolts (shown in the red circles in the picture below) so they will be easier to remove. I unscrew them so I can remove the shift cam mechanism.

Heating Around The Shift Cam Assembly Bolts On The Front Of The Transmission Case

Heating Around The Shift Cam Mechanism Bolts On The Front Of The Transmission Case

Removing Two Shift Cam Mechanism Bolts

Removing Two Shift Cam Mechanism Bolts

Shift Cam Mechanism Bolt Has A Shoulder That Is A Tight Fit In The Hole

Shift Cam Mechanism Bolt Has A Shoulder That Is A Tight Fit In The Hole

I pull the shift cam mechanism up and to the side (to the right in the picture below) to slide it off the pins on the three shift forks to remove it.

Pull Shift Cam Mechanism Out Of The Transmission Case

Pull Shift Cam Mechanism Out Of The Transmission Case

Shift Cam Mechanism

Shift Cam Mechanism

The three shift forks are exposed. Two of them are on a removable shaft at the bottom of the picture below and the the third engages the intermediate shaft and is on a fixed shaft toward the top of the picture below. I pull up on the removable shaft and then pull out the two shift forks the engage on the output shaft.

Shift Cam Mechanism Removed

Shift Cam Mechanism Removed

The two shift forks that engage the output shaft are different. The top one has a slight bend in the arm that attaches to the fork. Each shift fork is a different part number. I marked the top and bottom ones that engage the output shaft gears before I pulled them out.

Marking Output Shaft Shift Forks "T"-Top, "B"-Bottom

Marking Output Shaft Shift Forks “T”-Top, “B”-Bottom

Remove Output, Intermediate Shaft and Input Bearing Race From Case

The outer bearing races of the output, intermediate and input shafts are captive in the aluminum transmission housing. I remove them by heating the front of the housing around the pockets the bearing races fit into with two MAPP torches. I direct the heat to the bearing pockets.

I invert the housing on two 2×4’s over my parts washer so gravity will assist in removing the two shafts and the input shaft outer bearing race. I had to tap/jiggle the housing a little for everything to fall out of the case. What I fell out was the output shaft, the intermediate shaft and it’s front baffle plate, the input shaft outer bearing race and the intermediate shaft shift fork.

Getting Ready To Heat Front Of Transmission Housing

Getting Ready To Heat Front Of Transmission Housing

Output Shaft Bearing Pocket

Output Shaft Bearing Pocket

Transmission Shafts, Intermediate Shaft Shift Fork and Input Shaft Outer Bearing Race Removed From Transmission Case

Transmission Shafts, Intermediate Shaft Shift Fork and Input Shaft Outer Bearing Race Removed From Transmission Case

Inside Transmission Case

Inside Of The Transmission Case

Here is the output shaft and the oil baffle plate that fits inside the front bearing pocket of the transmission case.

Output Shaft with Front Bearing Oil Baffle

Output Shaft with Front Bearing Oil Baffle

The intermediate shaft has two oil baffles the same size. One fits into the front bearing pocket of the transmission case and the other fits into the pocket of the rear cover.

Intermediate Shaft with Identical Front and Rear Bearing Oil Baffles

Intermediate Shaft with Identical Front and Rear Bearing Oil Baffles

The input shaft is the only shaft that has a roller bearing on one end. The inner race is a shrink fit on the input shaft and the outer race with the rollers is held captive in the transmission case. The output shaft slides into the outer race which is the output shaft can be removed without heating the case.

Input Shaft with Roller Bearing Outer Race

Input Shaft with Roller Bearing Outer Race

Input Shaft Roller Bearing Slides Onto Shaft

Input Shaft Roller Bearing Slides Onto Shaft

How To Identify Shift Forks

Each shift fork is marked with a casting number on one side and a mark consisting of a letter “S” in a circle and three digit number on the other side. The casting number has a prefix, “1234” and a three digit suffix, The prefix matches digits 5-8 of the part number and the three digit suffix is one less than the last three digits of the part number. The table below shows how to identify which shift fork goes where.

NOTE:
I labeled the output shaft shift forks (T) and (B) for top and bottom as I looked at them from the rear of the transmission case. But, they also are next to the front or the rear of transmission. The way I have the transmission housing on my work bench, the front of the transmission is down (bottom) and the rear of the transmission is up (top).

Part No.              Description           Casting # Mark Location
23 31 1 234 219 5th Gear 1234-218 (S)274 Output Shaft,
Front (Bottom)
23 31 1 234 215 1st & 2nd Gear 1234-214 (S)287 Output Shaft,
Rear (Top)
23 31 1 234 217 3rd & 4th Gear 1234-216 (S)281 Intermediate Shaft
Output Shaft Shift Forks-Note "Bottom" Shift Fork Arm Has A Slight Bend

Output Shaft Shift Forks-Note “Bottom” Shift Fork Arm Has A Slight Bend

Output Shaft "Top" Casting # (1234 214)

Output Shaft “Top” Casting # (1234 214)

Output Shaft "Top" Marking (S)274

Output Shaft “Top” Marking (S)274

Output Shaft "Bottom" Casting # (1234 218)

Output Shaft “Bottom” Casting # (1234 218)

Output Shaft "Bottom" Marking (S) 287

Output Shaft “Bottom” Marking (S) 287

Intermediate Shaft Shift Fork

Intermediate Shaft Shift Fork

Intermediate Shaft Casting # (1234 216)

Intermediate Shaft Casting # (1234 216)

Intermediate Shaft Marking (S)281

Intermediate Shaft Marking (S)281

Remove Transmission Seals & Rear Cover Gasket

The transmission has three seals that I remove as I am replacing them: the output shaft, input shaft and gear change shaft. There is a gasket between the rear cover and the case.

I carefully use a single edge razor blade to separate the gasket from the rear cover so I do not nick or gouge the mating surface. Then I use a flat block of wood and 600 wet/dry paper to clean up the mating surface on the rear cover removing small bits of gasket and any adhesive stuck on the surface. I do the same on the mating surface of the transmission case.

Carefully Use Single Edge Razor Blade To Separate Old Gasket From Mating Surface

Carefully Use Single Edge Razor Blade To Separate Old Gasket From Mating Surface

Use Flat Block & 600 Wet/Dry Paper To Clean Up Rear Cover Mating Surface

Use Flat Block & 600 Wet/Dry Paper To Clean Up Rear Cover Mating Surface

I remove the large diameter output shaft seal with a flat blade screwdriver using a couple sharp raps with a plastic mallet on the screwdriver handle. It was pretty solid and hard. I did the same thing to remove the smaller diameter input shaft seal.

Remove Output Shaft Seal with Flat Blade Screwdriver

Remove Output Shaft Seal with Flat Blade Screwdriver

Output Shaft Seal Removed

Output Shaft Seal Removed-Front Face Shown Points Toward Inside Of Transmission

When facing the rear of the transmission, you are looking at the rear of the output shaft seal. The front of the seal faces to the inside of the transmission.

The Rear Face Of Output Shaft Seal Points Outward

The Rear Face Of Output Shaft Seal Points Outward

I use a hook seal puller to remove the gear change shaft seal. I’m careful not to scratch the bore with the sharp hook by placing the hook about mid-way across the seal before levering it out.

Hook Seal Puller

Hook Seal Puller

Pulling Gear Shift Shaft Seal

Pulling Gear Change Shaft Seal

Gear Shift Shaft Seal Removed

Gear Change Shaft Seal Removed

Output, Input and Gear Shift Shaft Transmission Seals Removed

Output, Input and Gear Change Shaft Transmission Seals Removed

Case and Cover Inspection

I inspect the case and the cover for signs of damage. There is a casting void in the mating surface of the rear cover. I show how to repair that in the document about how I assemble the transmission.

{link}

Rear Cover Has A Casting Void In Mating Surface

Rear Cover Has A Casting Void In Mating Surface

Bearing Bore Inspection

I inspect the cover and the bearing bores in the cover. All three show discoloration including some that looks like rust.

Rear Transmission Cover Inside

Rear Transmission Cover Inside

Rear Transmission Cover Casting Number

Rear Transmission Cover Casting Number

Discoloration In Rear Cover Input Shaft Bearing Bore

Discoloration In Rear Cover Input Shaft Bearing Bore

Discoloration In Rear Cover Input Shaft Bearing Bore

Discoloration In Rear Cover Input Shaft Bearing Bore

Discoloration In Rear Cover Intermediate Shaft Bearing Bore

Discoloration In Rear Cover Intermediate Shaft Bearing Bore

Discoloration In Cover Intermediate Shaft Bearing Bore

Discoloration In Cover Intermediate Shaft Bearing Bore

Discoloration In Rear Cover Output Shaft Bearing Bore

Discoloration In Rear Cover Output Shaft Bearing Bore

Discoloration In Cover Output Shaft Bearing Bore

Discoloration In Cover Output Shaft Bearing Bore

I see similar discoloration in the bearing bores in the transmission case.

Discoloration In Case Intermediate Shaft Bearing Bore

Discoloration In Case Intermediate Shaft Bearing Bore

Discoloration In Case Intermediate Shaft Bearing Bore

Discoloration In Case Intermediate Shaft Bearing Bore

Discoloration In Case Input Shaft Bearing Bore

Discoloration In Case Input Shaft Bearing Bore

A common area of the case that can be damaged is the boss the clutch cable mounts in. There are no signs of abuse on mine.

Transmission Case Clutch Cable Bushing Is Not Damaged

Transmission Case Clutch Cable Bushing Is Not Damaged

I send pictures of the case and cover to a long time BMW mechanic for his inspection and opinion about the condition. His opinion is the discoloration in the bearing bores is sign of a condition called fretting. This is caused by small oscillatory movement of a bearing in the bore.

A cause for this can be shafts that were incorrectly shimmed with too much end play allowing the bearings to vibrate in the bore after the transmission is up to temperature. All three shafts have a helical gear and helical gears create oscillating axial loads on a shaft. But, the cover and case are serviceable.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.