23 BMW 1973 R75/5 Install the Transmission

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 Left Side

Refinished Transmission Ready to Install in the Frame

I used the following references to plan my work.

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
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 Throwout Parts
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.

Clutch Throw Out Bearing Inner Race, Front Face
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 Disk With Groove and Circular Bearing Race
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 Throwout Assembly
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
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 Shavings
Throwout Rod Felt Trimings

Then I oiled the felt with engine oil.

Oiling Throwout Rod Felt
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
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
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.

Moly-60 Paste Dab on End of Throwout Rod
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
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 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
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 Sliding Into Clutch Plate 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
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 Transmission Bolt
Bottom Left Short Transmission Bolt
Lower Left Transmission Bolt and Nut
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
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 Throwout Rod and Felt Installed
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 Throwout Rod Bearing 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
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 🙂

Rubber Cup on Clutch 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 Between Clutch Throwout Lever and Throwout Rod
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
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 & Cotter Pin
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
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
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
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
Installing Kick Start Lever and Wedge Bolt

Here is the transmission installed in the frame.

Job Done
Transmission Install Job Done

12 thoughts on “23 BMW 1973 R75/5 Install the Transmission

  1. Pingback: 1973 BMW R75/5 Rebuild: Installing the Engine and Transmission | Motorcycles & Other Musings

  2. Pingback: 1973 BMW R75/5 Rebuild: Install Swing Arm and Rear Drive | Motorcycles & Other Musings

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

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