After I got the engine installed in the frame, it’s time to get the transmission installed. I had refinished the transmission earlier, but did not rebuild it. You can read about these parts of the project here.
Refinished Transmission Ready to Install in the Frame
I used the following references to plan my work.
- Bob Fleischer: BMW Airhead Clutch Information
- Bob Fleischer: Serving Transmission Input (clutch) Splines, Throwout Bearing, Clutch Arm
- Duane Auscherman: BMW Motorcycle Clutch Removal, Inspection and Repair
Parts List
I installed the following new parts that I purchased from Hucky’s.
| Part # | Description | Qty |
| 23 41 1 232 116 | Shift Lever Boot, 4 Speed | 1 |
| 21 51 1 230 109 | Clutch throw out lever rubber cup/seal | 1 |
| 21 52 1 020 109 | Clutch throw out Seal | 1 |
| 23 21 1 230 440 | Clutch throw our rod felt ring | 1 |
| 23 21 1 230 106 | Clutch thrust rod /5, 4 speed | 1 |
Install Clutch Throw Out Rod Assembly
The clutch throw out rod assembly has to be installed into the transmission in the housing to the right of the kick start lever.
Rear of Transmission with Tunnel for Clutch Throw Out Assembly
Below are the throw out lever, pivot pin with cotter pin and return spring on the left. The throw out lever pushes on a piston with rubber gasket in the middle of the piston. The other side of the piston contacts the flat face of the throw out rod. The throw out rod passes through a a circular ball bearing race and it’s outer race. The throw out rod has a felt oil seal that fits in a groove to keep water and dirt from getting into the clutch housing. The throw out rod goes through the center line of the clutch and the tapered end of the rod pushes on the clutch pressure plate to disengage it from the clutch plate.
Clutch Throw Out Assembly Parts
This is the front face (towards the transmission) of the outer bearing race with the hole for the throw out rod.
Inner Bearing Disk, Front Face, Goes Against the Transmission Inside the Housing
This shows the back side of the outer race with the groove that rides on the ball bearings which are shown behind it. The grooved back side of the outer race fits on top of the ball bearings, not the flat front side.
Inner Bearing Disk, Rear Face, with Bearing Groove Goes Against the Ball Bearings
The ball bearing race presses against the piston assembly that has a large gasket ring in the middle and a pin on the other that goes through a rubber boot into the cup on the lever arm. The clutch lever adjuster pushes on the pin of the piston assembly to adjust the clutch free play.
Clutch Throw Out Assembly and Clutch Lever
The cup in the clutch lever holds grease to lubricate the piston pin. There is also a zerks grease fitting that is used to lubricate the pin holding the clutch lever on the ears on the back of the transmission.
Grease in Throwout Rod Cup
Install the Felt on the Throw Out RodThe felt for the throw out rod is slit on a diagonal so it fits in the groove on the throw out rod. It is often a bit too large to insert into the transmission and needs to be trimmed. I trimmed a small amount and test fit the throw out rod and continued trimming until it was snug but I could still push and pull it in and out of the transmission Here is how much I removed from the edge of the slit.
Throwout Rod Felt Trimings
Then I oiled the felt with engine oil.
Oiling Throwout Rod Felt
Greasing the Transmission Input Shaft SplinesThe Transmission input splines need to be greased. I use Honda Moly-60 Paste and use a toothbrush to put it on the transmission splines but I don’t overdo it.
Honda Moly-60 Paste
CAUTION: Do not put any grease on the internal splines of the clutch plate as it will get throw off and will lubricate the clutch plate. ONLY put grease on the transmission spline.Install Clutch Throw Out Rod In the TransmissionIt is easier to put the rod in from the front of the transmission (the end that mounts to the engine).
Sliding Throwout Rod with Felt into Front of Transmission
I also put a VERY SMALL dab of grease on the point of the throw out rod which presses on the clutch pressure plate.
A VERY Small Dab of Moly-60 Paste Dab on the End of Throwout Rod
Install the Transmission Into the FrameI added padded the frame with some sponge matting that was used to warp my powder coated parts so I won’t scratch the frame as I install the transmission.
Frame Protection Before Inserting Transmission In the Frame
I pushed the clutch throw rod all the way into the hole in the center of the transmission input shaft spline. I also removed the kick starter for more clearance but didn’t remove the shift lever. I used it to help hold onto the transmission as I carefully guided it into the frame from the left side. I found that tipping it about 45 degrees from the horizontal made it easier to clear the frame members. I put it down inside the frame tipped on the side so I could then get behind the frame and easily pick it up and hang it on the upper left stud.
Transmission Tipped Up 45 Degrees Inside Frame
Transmission Mounting HardwareThe left side of the transmission mounts with two Allen head cap screws that go into tapped holes in the engine. One bolt has a polished head and goes on the bottom. The other with the knurling on the head goes on top and holds the left side air box cover on. It goes through a metal tab and a thick spacer to offset the tab from the engine case.The right side mounts to a stud on the top left of the engine with a nut and on the bottom it mounts with a long Allen head cap screw that goes through a hole in the engine casing and the transmission.
Transmission Mounting Hardware, Left Side and Right Side
I aligned the splines by spinning the transmission input shaft a small amount until the transmission slide into the clutch carrier splines.
Transmission Input Splines, Male (Right) Sliding Into Clutch Plate Splines, Female (Left)
Then, I slide the transmission firmly into the back of the engine case and put a nut and wave washer, finger tight, on the upper right stud to hold it in place.
Top Right Nut on Engine Stud
I added the lower left bolt and wave washer, then the bottom right bolt leaving the top left bolt with the thick spacer and metal tab for last, again finger tight.
Bottom Left Short Transmission Bolt
Lower Right Long Transmission Bolt and Nut
Finally, I assembled the upper left bolt, bracket and spacer finger tight and test fit the left air box cover to ensure it would fit correctly. The edge of the cover slides between the transmission housing and the metal tab and under the bottom of the transmission bolt.
Top Left Transmission Bolt with Air Box Strap and Spacer
Install Throw Out Rod Bearing AssemblyThe throw out rod is visible from the rear of the transmission. The throw out rod bearing assembly goes over the throw out rod inside the throw out bearing housing.
Clutch Throw Out Rod and Felt Installed Inside Throw Out Bearing Housing
The bearing stack is inserted, as shown below, with the outer bearing plate with the hole in it going in first, followed by the circular bearing race and then the piston with rubber gasket last. I lubricated the bearings before installing the assembly.
Clutch Throw Out Bearing Assembly Showing Direction and Order of Insertion into Bearing Housing
When the bearing assembly is installed the pin on the end of the piston extends between the ears that hold the clutch lever.
Clutch Throw Out Piston Rod Between Clutch Lever Mounting Ears
Attach the Clutch Lever AssemblyThe clutch lever has a rubber cup installed as shown below. Note, the rod at an angle extending from the cup is really a screw driver on the floor and not a part of the throw out lever 🙂
Clutch Lever with Rubber Cup
The pin on the end of the piston assembly goes through the hole in the rubber cub when the clutch lever is inserted between the mounting ears.
Rubber Cup Installed on Clutch Throw Out Lever and Throw Out Piston Rod
The clutch lever is secured with a pin that is pressed through the holes in the mounting ears on the transmission and secured with a cotter pin. There are two grooves in the pin. It is inserted until the outside groove is flush with the outside of the mounting ear.
Clutch Throw Out Lever Pivot Pin
The cotter pin slides into the holes in one of the mounting ears and passes through the first groove in the pin securing it in the mounting ears.
Clutch Throw Out Lever Pivot Pin with Cotter Pin in First Groove
Finally, the return spring is installed on the pin on the clutch lever and the pin on the outside of the transmission housing.
Clutch Throw Out Lever Return Spring
Torque the Transmission Bolts & Install Kick Start LeverWith everything assembled, I torqued the transmission bolts to 17 FOOT/pounds.
Torquing Transmission Bolts
I checked again to be sure the left side air box cover slides behind the top left metal tab.
Left Air Box Cover Mounts Behind Strap on Top Left Transmission Bolt
Install Kick Start LeverI installed the kick start lever with the beveled pin and torqued the nut to 15 FOOT/Pounds.
Installing Kick Start Lever and Wedge Bolt
Here is the transmission installed in the frame.
Transmission Install Job Done
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Hi:
Thanks for the great write-up and quality pictures. I purchased a r75/6 that already had the transmission and clutch removed, and having not taken them apart myself, your guide became invaluable when I went to put everything back together.
Followed your clutch and transmission fitting method and worked like a charm. Got about 400 miles on her since, and so far so good! heh.
Hi Joshua,
Well, I’m pleased the content here helped you out. It’s nice to have another airhead on the road again.
Best.
Brook.
In regards to the Top Right Nut on Engine Stud did you release the nut to install the Right Air Box and then retention the nut?
Thank you,
Mark
Mark,
Yes, I did loosen that to install the right side air box cover.
Best.
Brook.
This website is invaluable to me and hundreds if not thousands of other Airheads. Thank you for your write-ups.
I’m experiencing squeak when letting my clutch out into first gear with throttle. No other shifting causes it, I have 2mm of free play at the handle. A fellow airhead told me to grease the actuator bearing but in your pictures it looks as though there’s regular oil (not even gear oil) on yours?
Any suggestions on this procedure? Should I grease the entire assembly including the entire bearing stack before insertion?
Thanks!
Hi Benjamin,
Thanks for the kind words and I’m glad this material has been helpful.
I would grease the bearing throwout rod bearing assembly and see if that eliminates the squeak. In theory, the rod gets some lubrication from the transmission lube.
I hope this helps.
Best.
Brook.
Hi Thanks so much for all of your time working on this blog. It’s incredible!
I just finished a ride and the Kickstarter would no longer engage with the transmission. Any thoughts?
Ryan
Hi Ryan,
I’m pleased this information is helpful to you. And, I’m sorry to hear the kickstarter is not working on your bike. I assume the bike is one of the “/5” models (500, 600 or 750) with a 4-speed transmission, but you don’t say.
I’ve not opened these transmissions, so I haven’t written about them. However, in looking at a parts fiche, there is a toothed “sector shaft” shown that engages teeth on mainshaft so the kickstarter can rotate the engine to start it. An hypothesis about the cause if that a tooth on the sector shaft has broken or a tooth on the mating gear on the mainshaft has broken. This would prevent engagement when you stand on the kickstart lever.
If your electric start is working, you can start the bike at least 🙂 That said, a bit of broken tooth loose inside the transmission would make me worry about later collateral damage to very expensive parts inside. It sounds like its time to have the transmission removed, opened and rebuilt while you are at it. This is not inexpensive, but required at a certain age and mileage on these transmissions. Tom Cutter (www.rubberchickenracinggarage.com/), Ted Porter (www.beemershop.com/) are reported to do excellent transmission work. Note the these transmissions had numerous updates and changes to their parts during the years they were manufactured, so having someone with that knowledge to the work makes sense to me.
I hope this helps.
Best.
Brook.
Fantastic blog, your clear pictures and detailed notes have helped me a bunch. I started restoring my ’71 R75/5 about 5 years ago and have forgotten some things on disassembly, I should have taken more detailed notes.
One question I have is, what type of grease are you using on the throw out rod cup?
Thanks, Rob
Hi Rob,
I’m pleased the information helped you on your project.
I used NLGP2 EP red grease that is readily available at auto parts stores. I suspect any tacky water resistant grease will do a good job.
I hope this helps.
Best.
Brook Reams.
Brook, what a coolio blog you have here! Just wanted to let you know it helped me determine what needs to be done to repair the leaky clutch throw arm seal on the R60/2. https://candybuttorg.ipage.com/cba/node/648
Take care and Thanks Again!
Don
Hi Don,
Thanks for the kind words.
Best.
Brook.
Thanks very much for posting your work on the R75, it’s been very helpful to me in assembling my R75. I wonder if you have thoughts on one issue I am having. On a bench test, my transmission turns and shifts fine and the kickstart also engages and rotated well. My engine also turns freely at the flywheel. When I install the transmission, everything locks up. During install, there was no resistance at the spline and the gearbox installed easily. I don’t know why all is locked once the transmission is installed. Any thoughts? Gord
Hi Gord,
Well, that’s interesting. If the transmission spins on the bench and the engine spins when you turn the flywheel, (and the clutch?), but not when the transmission is installed, is it possible the transmission is in gear after you installed it?
The only other component in the drive line is the clutch. Is there some obstruction that blocks it from turning after the transmission is installed? For instance, has a clutch bolt backed out?
The above are WAGs (wild-assed guesses) on my part.
Best.
Brook.
Hi Brook,
First off…thanks for the very detailed blog of your /5 project. It has been an indispensable reference as I work on my ’72.
I am experiencing the same issue as Gord with regards to my kickstarter being locked up once I installed the transmission.
Like Gord, both the transmission and the engine turned freely on their own but as soon as it was installed, the kickstarter won’t budge past half way down.
Any thoughts would be appreciated.
Cheers,
Shane
Hi Shane,
Since I never heard back from Gord, I don’t know any more than I did when I made the SWAG suggestions. That is to say, I don’t know what causes this problem.
Best.
Brook.
Hi Shane and Brooks, I did get around that issue. By engaging the clutch and moving the kickstart down about half way I was able to work things loose. At lease that seemed to work unless it was all my imagination. I’ve since had the bike running smoothly but not ridden it yet as I need to work through some leaks etc.
Gord
I should be more clear. After moving the kickstart down half way and letting the clutch out, the kickstart started to work the rest of the way. In short time, I could kickstart from the top.
Hi Gord,
I didn’t see your response until recently but I did what you had suggested this weekend and I am happy to report that your method worked perfectly!
Thank you for taking the time to respond, very much appreciated.
Cheers,
Shane
Hi Brook, thanks again for all the info. I’ve got a special problem and i don’t know what I’m doing wrong: my clutch lever is scraping the frame when i fukushima pull the clutch lever on the steering wheel. Does that ring a bell? I’ve made the cable as long as possible but still at the end is scratches the frame. I hope my description is understandable.
Thanks and keep up the good work
Hi Luc,
I’m not sure I understand. Is it the throw-out lever on the transmission that is rubbing?
Best.
Brook.
Hi Brook, indeed, the throw out lever on the transmission: the end where the clutch cable is attached is rubbing the frame
Luc,
You might want to follow these instructions about proper clutch adjustment.
–> http://www.rubberchickenracinggarage.com/Downloads/Airhead%20Clutch%20Cable%20Replacement%20and%20Adjustment.pdf
Best.
Brook.
Hi Brook, thanks for your reply. Funny enough i had this text already. I’m not a reader but this time i did read and especially noticed the 201mm: problem solved. Thanks again!