I rebuilt the transmission and refinished the case and rear cover so now it’s time to install it. Beside connecting the transmission to the engine block and mounting it in the frame, installation includes attaching the neutral switch & oil pressure wiring sub-harness, attaching the transmission output shaft flange to the drive shaft, centering the swing arm in the frame, installing the clutch throw-out mechanism, installing the foot shift lever mechanism, and adjusting the clutch cable.

Tools

There is not enough room for a standard Allen key to fit on the left lower transmission bolt. The boss around the foot shift lever is too close to the bolt head. I cut off a 6 mm Allen key so it will fit on the bolt.

Parts

The clutch throw-out mechanism is installed after the transmission is mounted on the engine block. I replace parts that fit inside the rear transmission cover and upgraded the separate bearing and piston with an integrated unit (part# 23 13 1 464 167).

I also replace the sub-harness that connects the neutral switch and oil pressure sender to the main wiring harness. I replaced the neutral switch when I got the bike and it has less than 2000 miles on it so I did not replace it.

The transmission attaches to the drive shaft with four 12-sided bolts which I always replace when I do a rebuild: They are inexpensive and subject to a lot of stress so this is cheap insurance against a bolt failure. I replace the bellows and the two straps that secure it to the swing arm and transmission.

Part #	Description	Qty
23 13 1 464 167	PISTON (from 09/80), Replaces ball bear & races	1
23 13 1 241 849	SPRING (from 09/80), Clutch throw-out rod return	1
23 13 1 241 844	ROD (from 09/80), Clutch Throw-out	1
23 13 1 338 731	CUP (from 09/80), Bellows	1
23 13 1 241 872	CLAMP – D=40 (from 09/80), Bellows	1
23 31 1 232 097	BUSHING-Shift Lever Rubber	1
26 11 1 242 297	SCREW, Drive Shaft To Output Flange	4
33 17 1 230 304	RUBBER COVER, Swing Arm To Transmission	1
33 17 1 230 297	TENSION STRAP – D=82 (to 09/78)	2
61 12 1 243 523	WIRING TRANSMISSION-SWITCH (from 09/77)	1

Video

This video summarizes the transmission installation procedure.

VIDEO: 1983 BMW R100RS Install Transmission

Prepare Transmission

Before I install the transmission there are some things I need to do to prepare it.

Lube Input Shaft Splines

I apply Moly-60 paste to the transmission input shaft splines. I use a toothbrush to apply a light, even coat. I don’t over do the amount of paste applied to the splines as I don’t want it to get thrown off and contaminate the clutch plates. Moly-60 is sticky and stays put when it’s applied as a light coating.

NOTE:
Honda’s Moly-60 paste seems to be no longer available. A suitable replacement is MolyKote M77 paste.

Install Clutch Throw-Out Rod

I like to install the throw-out rod before I attach the transmission to the engine block. It’s easier to push it gently past the seal in the rear of the input shaft. After I install the push rod, I put a small dab of Moly-60 paste on both ends to lubricate them as the clutch rod spins and one end fits in a hole in the clutch plate and the other end fits into a seal in the front of the combination piston-bearing.

Fill Transmission With Gear Lube

I fill the transmission with Spectro 80w/90 petroleum gear lube before I attach the transmission to the engine block. This lets me spin the input and output shafts with the transmission sitting on the work bench. I spin the input and output shafts with the front and rear of the transmission facing up to lubricate the gears and bearings to ensure they are coated with gear lube before the transmission first runs.

Attach Neutral Switch & Oil Pressure Sub-harness

I attach the BROWN and BROWN-Black wires of the sub-harness to the terminals of the neutral switch. Since the switch is on the bottom of the transmission, it’s easier to connect the wires to the switch terminals before I install the transmission in the frame and attach it to the engine block.

After I attach the transmission to the engine block I will attach the BROWN–Green wire to the oil pressure sending unit on the left side of the engine block.

Attach Transmission To Engine Block

The swing arm and drive shaft have to be pulled back so there is enough clearance to install the transmission on the engine block. I use a bungee cord through the rear wheel and over the rear sub-frame to pull the swing arm out of the way.

I pad the frame tubes with plastic shipping wrap to protect them from being gouged as I move the transmission into the frame. Once I get it between the frame tubes, I hang it on the top right stud in the engine block and align the input shaft with the hole in the center of the clutch plate. To get the splines to mate, I rotate the transmission input shaft in very small increments until the input shaft splines slide into the clutch plate splines.

The transmission mounts to the engine block with three bolts and one nut. The top and bottom bolts on the left side are the same. The top left bolt has a thick flat washer while the bottom left bolt has a thinner flat washer and a wave washer. The top right is where the nut and thick washer go on the stud in the engine block. The bottom right is where the long Allen bolt with two flat washers, wave washer and nut go.

NOTE:
The picture below shows the correct bolts but all the washers are not shown and some are shown with the incorrect bolt. The thick washer shown with the second bolt from the top goes with the nut and wave washer below it. I added a wave washer to the second bolt from the top  which is the lower left bolt that secures the ground wire and I added a second flat washer to the long bolt at the bottom that goes on the lower right of the transmission so there is a flat washer under the bolt head and the nut with wave washer under the nut.

I attach the three bolts; two on the left and the long one with two flat washers , wave washer and nut on the lower right. I make sure the transmission fits into the bell housing of the engine block and the ears on the front of the transmission slide past the edge of the bell housing so the front of the transmission fits flush with bell housing. Sometimes this takes some wiggling of the transmission to get the ears to slide into the bell housing. I don’t force the ears or hammer on the transmission because I don’t want to damage them.

NOTE:
If you can’t get the transmission to line up correctly to slide into the bell housing it’s likely the clutch plate is off center and you will need to center it. I used a clutch centering tool when I assembled the transmission. If you have to recenter the clutch plate, you can loosen the clutch bolts until you can slide the clutch plate. Then align the clutch plate splines so they mate with the splines on the transmission input shaft. Then move the transmission until you can slide it into the bell housing and it fits flush with housing. Carefully remove the transmission so you don’t disturb the clutch plate and tighten the clutch bolts. Install the output shaft in the clutch splines and the transmission should fit flush with the bell housing.

There is a torque for the bolts and top right nut of 15 FT-Lbs, but it’s impossible to get a torque wrench on them, so I use “good  and tight” force on my Allen key to tighten the bolts.

NOTE:
The top bolt and stud with nut are used to mount the airbox to the transmission along with a bolt in the top, middle of the transmission. I tight the top left bolt to be sure the transmission mates correctly to the engine block bell housing. I’ll remove it when I’m ready to install the air box and then tighten it and right top nut to secure the air box to the transmission and the transmission to the engine block.

When I get the transmission mounting bolts tightened I verify that the transmission matted with the bell housing and there is no gap between them.

Then I attach the BROWN–Green wire to the low oil pressure sending switch on the engine block.

Connect Output Flange To Drive Shaft

The swing arm can not be mounted on the pivot bolts when installing the transmission. So after installing the transmission, I move the swing back in place and thread the pivot bolts part way into the frame so the drive shaft will be in the proper location to attach it to the transmission output flange.

The bellows has markings on one face, “OBEN” and “GETRIEBESEITE”. Oben is German for top and Getriesbeseite means transmission. The bellows should be mounted with these words facing the transmission with the “Oben” marking at the top.

The torque for the drive shaft bolts is 29 FT-Lbs, but it’s not easy to use a torque wrench on these bolts. You can buy an extension that fits on the bolt head and accepts a 3/8 inch torque wrench, but it’s cumbersome and you may have to compute an adjusted torque based on the length of the extension. Or you can do it by feel, which is how I torque these bolts.

NOTE:
My bolts came pre-coated with Loctite but If your bolts are not pre-coated, use blue Loctite on the threads to ensure the drive shaft bolts do not come loose.

Now comes the fun part. With the bellows installed on the swing arm side only, I peel it back and align a drive shaft flange hole with a transmission output shaft flange hole and thread the bolt onto the output flange. The boot is pretty stiff and wants to fold over to get in the way so this takes patience and strong fingers.

NOTE:
You may end up dropping a bolt and having it slide down the swing arm tube. I have successfully retrieved a bolt with a magnet on a long collapsible shaft to fish them out. That said, try to be careful and avoid dropping the bolts as you thread them into the output flange as this only adds to your frustration.

Once the first bolt is threaded part way, I rotate the rear wheel and thread the next bolt on until all four are threaded part way onto the output flange. I use a 12-sided, 10 mm box wrench to snug them up.

To torque the bolts, I wrap a long screwdriver in shop rags and stick it under the two legs of the swing arm and through the wheel to immobilize the drive shaft. But first, I rotate the wheel so one of the bolts is exposed at the 1:00-2:00 position when facing the front of the bike so I can easily fit the box wrench on it. Then I insert the wrapped screw driver through the wheel and adjust which slot in the cast wheel I stick it through if needed to get the bolt in the proper position.

I lean on the wrench with the palm of my hand until it hurts and there is decent dent in my palm. That’s precisely 29 FT-Lbs 🙂

I put a paint mark on the head of the bolt to indicate I torqued it. This helps me make sure I don’t miss a bolt.

After I torque all four bolts, I slide the bellows over the boss around the transmission output shaft and secure it with the two straps, one on the transmission side and the other on the swing arm side of the bellows. On this year/model swing arm there are two tabs, one on top and one on the bottom, to catch the edge of boot and keep it from slipping off the swing arm when the strap is tightened. I pull the bellows under the tabs before I attach and tighten the strap.

I open up the straps and wrap them around the bellows rather than install them over the ends of the bellows when I put it on the swing arm because they get in the way while I install the drive shaft bolts.

Center Swing Arm In The Frame

I show how I do that here:

• 33 BMW 1983 R100RS Install Swing Arm and Rear Drive
  • Center The Swing Arm

Install Clutch Throw-out Mechanism

I installed the clutch throw-out rod in the hole of the input shaft before I installed the transmission. Now I install the combination piston-bearing, throw-out lever return spring, rubber cap and strap on the rear of the transmission and then attach the throw-out lever.

NOTE:
Some of these pictures were taken with the transmission on the workbench prior to installing it so they would be easier to take. But you can’t install the transmission with the throw-out mechanism installed as the clutch push rod extends too far from the front of the transmission.

I use Moly-60 paste to lubricate the end of the throw-out rod that fits into the combination piston-bearing. I lubricate the outside of the piston-bearing and the face of the piston bearing the spring presses with transmission gear lube. When the transmission is running, these parts eventually get lubricated with transmission gear lube.

I insert the end of the push rod into the seal on the end of the combination piston-bearing and slide the piston-bearing into the hole in the rear of the transmission.

Then I insert the return spring and then push the rubber boot over the boss on the rear transmission cover securing it with the metal strap.

I apply some Moly-60 paste to the throw-out lever arm roller bearing and the shank of the pivot bolt. I insert the throw-out arm between the legs of the boss in the rear transmission cover. I insert the bolt from the top so if the nut comes off the bolt won’t drop out. I also put some Moly-60 on the shank of the bolt and some blue loctite on the threads to ensure the nut stays on the bolt.

All done.

Attach Speedometer Drive Cable

The speedometer drive cable fits into a black plastic bushing in the hole the speedometer drive gear is installed in on the rear transmission cover. The drive gear has a square hole that fits the square end on the speedometer cable. The drive cable and black plastic bushing are secured with a special “breather” bolt that has a hole drilled through its length. This equalizes pressure inside the swing arm as the swing arm moves up and down. I always run a piece of wire through the hole in the breather bolt before installing to ensure it is not plugged.

The slot in the black plastic bushing should line up with the hole for the breather bolt so the bolt will pass through the slot.

The rubber boot that slides down the speedometer cable and over the casting on the transmission prevents water from getting into the transmission via the speedometer gear opening. It is critical to long transmission life that this boot be tight fitting and not leak. I put a smear of silicon seal on the lip of the boot before I push it over the lip of the transmission housing to improve the seal.

Install Foot Shift Mechanism

The foot shift lever is attached to the left front foot peg bracket with a special pivot bolt. The bolt attaches from the back of the foot peg bracket.

Repair Foot Shift Lever Bushing

The foot shift lever pivot bolt is loose in the bushing. This is not uncommon. A solution is to buy a new foot shift lever that uses a needle bearing rather than the bushing. But I’ve repaired the worn busing before using beer can aluminum as a shim around the pivot bolt. I find that as the shim covers more of the pivot bolt circumference, the bolt gets tighter in the bushing. So I cut several lengths of shim and experiment to find the length that wraps around enough of the pivot bolt circumference to eliminate the wobble of the pivot bolt in the bushing but allows the lever to pivot without binding.

I use Ruglyde, which is used for mounting tires, as a lubricant in the hole of the shift lever rubber and slide it on the shank.

I install the foot rubber on the foot peg using Ruglyde. I put wheel bearing grease on the inside of the bushing and the outside of the pivot bolt before I attach the foot shift lever to the back of the foot peg bracket with the pivot bolt. The pivot bolt hole is tapped so there is no nut to secure the foot shift lever pivot bolt.

I install the foot peg bracket on the frame with the special bolt that fits in a recess on the front of the bracket. The back of the bracket is serrated and to match the serrations on the foot peg boss so you can adjust the height of the peg and it will stay in that position.

I lubricate the ball on the end of the gear change lever and the foot shift linkage with Moly-60 paste.

The shift linkage attaches to the ball ends with cups that have a retaining ring inside the cup. They are locked onto the ball with a pin that fits through two holes in the cup and goes under the ball and then rotates to lock onto the backside of the cup in a groove.

Install Right Foot Peg

While I’m at it, I install the right side foot peg. It mounts the same way the left foot peg bracket does, but uses a shorter version of the special bolt that fits in a recess on the front of the bracket. I use Ruglyde to install the foot rubber on the peg.

Adjust Clutch Cable

I show how I adjust the clutch in the document showing how I install the handlebar perches, switches and cables.

• 32 BMW R100RT Install Handlebar Perch Assemblies
  • Adjust Clutch Cable

Revisions

2020-07-23  Add links to adjust clutch cable and minor edits.