23 BMW 1973 R75/5 Refinish Transmission

The transmission on the bike was rebuilt at the 50,000 mile mark and the bike has 97,500 on it now. It was very grimy so perhaps I have a seal leak somewhere, but I’m betting on the grime coming from the drive shaft boot and rear main seal on the engine that I will replace.  Here’s what I started with.

Transmission Rear Grunge

Transmission Rear Grunge

Transmission Top Grunge

Transmission Top Grunge

Transmission Top Grunge

Transmission Top Grunge

Transmission Front Gunge

Transmission Front Gunge

Transmission Right Side Grunge

Transmission Right Side Grunge

The kick start and gear shift levers are secured with a threaded bolt that is tapered and has a notch cut into the side to slide into a notch in the shaft. The nut draws the bolt down securing it into the notch in the shaft.

Bottom of Shift Lever with Nut on Bottom of the Tapered Bolt

Bottom of Shift Lever with Nut on Bottom of the Tapered Bolt

Kick Stater in Vertical Position with Tapered Bolt and Nut

Kick Stater in Vertical Position with Tapered Bolt and Nut

The bolts are notorious for being hard to withdraw. The Haynes manual mentions using a soft mallet to knock the bolt out of the hole. After removing the nuts from the kick starter and shifter and rapping on the bottom of the bolts, the expected happened–nothing. I used my trusty can of Kroil and let it seep into the holes overnight to take care of any rust that maybe binding the bolts in the holes.

Kroil to Ease Removal of Kick Starter and Shift Lever Bolts

Kroil to Ease Removal of Kick Starter and Shift Lever Bolts

I had no luck getting either bolt to budge with a soft mallet. So, I took a piece of steel bar stock and placed it carefully on the bottom of the shifter bolt and hit it with a steel hammer. I didn’t what to damage the threads and the flat stock should keep an off center blow from doing that. This worked and I was able to get the shifter bolt to move. I used a drift to tap the bolt out of the hole.

The problem with the kick start lever is it is not easy to get to the bottom of the bolt and the lever rotates. I found putting the transmission on the floor let me put my left foot on the kick start lever rotating it to the floor. This put the bottom of the bolt where I could get the bar on it and I could hit it hard with the steel hammer. Nothing. Next I heated the kick start lever in hopes the aluminum would expand a bit more than the steel shaft. Nothing.

Time for bigger weapons and potentially more risk of destruction. I found a drift that matched the bolt diameter closely and my hand sledge. I carefully placed the drift on the end of the bolt and took a hard whack with the sledge. I was very careful to keep the drift squarely on the bottom of the bolt and to strike it squarely with the sledge. I started with light hits, increasing them a bit as I went. In the end, it took a hit from about 9 inches from the end of the drift to get the bolt to move. I hate using that much force to get the bolt to move, but that bolt was jammed in there tight.

Hand Sledge, Drift and Kick Starter Bolt

Hand Sledge, Drift and Kick Starter Bolt

Here are the levers removed. The two large washers or behind the shift lever next to the transmission. The washers on the end of the tapered bolts aren’t shown in this picture.

Kick Starter and Shifter Removed

Kick Starter and Shifter Removed

Polishing and Refinishing

Now I cleaned up the levers and hardware. I cleaned the parts in the carburetor parts soaking can and then used AutoSol Aluminum Cleaner and “00” steel wool on the kick starter, shift and air cleaner retaining strap. I followed that with “000” steel wool and then AutoSol Aluminum polish to put a nice luster on them. Their are two flat washers shown on the transmission breather bolt and a wave washer is shown on the kick starter bolt, which is incorrect.  A flat washer goes on the kick starter and shift bolts under the nuts. A flat washer and wave washer go on the transmission breather bolt and the larger wave washer goes on the bolt holding the air box strap. Sorry about the confusion in the picture.

Polished Parts

Polished Parts

To clean the rough casting of the transmission, I plugged the speedometer shaft opening with a spare silicone seal nozzel and the hole for the clutch push rod with shop towels. I used a fair amount of Gunk engine degreaser, stiff bristle nylon brush and a tooth brush to get the baked on grime off. Next, I used the parts washer to finish up removing the top layer of grunge.

Removing Burs on Tapered Bolts and Holes

I cleaned up the tapered bolts. The kick starter bolt had a bur on the tapered edge that I filed smooth.

Burr on Kick Starter Bolt Taper

Bur on Kick Starter Bolt Taper

I also used 320 and then 1500 grit to polish the tapered part of the bolts so they were smooth to the touch. I used a drill bit and wrapped the wet/dry sand paper on it and burnished the holes and then test fit the bolts until I could easily slide them in and out of the holes. This took awhile to get everything smooth again, but the scratches and burs were why it was so hard to remove the kick starter bolt.

Removing Scratchs & Burrs in Kick Starter Lever Bolt Hole

Removing Scratchs & Burs in Kick Starter Lever Bolt Hole

Then I worked on polishing the transmission. I used some brake cleaner to soften up the hard material in the webbing area on the front side. I used AutoSol Aluminum Cleaner and Scotch Brite pads on the rough castings, then more Aluminum Cleaner with “00” steel wool and lots of blue paper shop towels to remove the cleaner. Under the speedometer housing, there was corrosion and some copper from the battery ground cable that a leak from the battery caused. I used some 600 grit sand paper and also a wire disk in the Dremel tool to get the copper and corrosion out and then worked that area with “00 steel wool to get a similar luster to the rest of the casting. I finished up the transmission with AutoSol Aluminum polish.

Putting it Back Together

The parts fiche shows a “0.5 mm” washer between the transmission and the shift lever, but I had two washers, not one. When I put them together and used my micrometer, they added up to 0.5 mm.

0.5 mm Shim Stack on Shift Shaft

0.5 mm Shim Stack on Shift Shaft

The tapered bolts when into the holes easily with just a bit of jiggling of the kick start and shift levers to help them slide down into the cutouts on the shafts. I put the washers and nuts on and then tightened the nuts to draw the tapered bolts down until they were seated. Then I put a new shift rubber on the shift lever to replace the cracked one.

Here is the refinished transmission.

Refinished Transmission Top

Refinished Transmission Top

Refinished Transmission Front

Refinished Transmission Front

Refinished Transmission Left Side

Refinished Transmission Left Side

Refinished Right Side

Refinished Bottom

Refinished Rear

6 thoughts on “23 BMW 1973 R75/5 Refinish Transmission

  1. I have been learning a lot. You have done a nice job showing the process of the R75/5 job. My bike is in pieces and I have been cleaning as I wait for ordered parts. I am shooting for mid April to complete the job. May 1 is my deadline. Thank you for being there when I have a question.
    Z

    • Rick,

      Cool beans on getting the project close to the finish line with a target date to complete. I’m glad the write-ups have been helpful. I’m looking forward to a note about the happy day of the 1st ride around the block. 🙂

      Best.
      Brook.

  2. Hey,

    Looks like you did a great job with the rebuild. I’m looking to do something similar in installing my rearsets but can’t seem to remove the shifter shaft in order to install a new shaft. Do you have any suggestions on removing the shift lever while the engine and transmission is still intact?

    • Hi Brant,

      Thanks for stopping by and looking at this material.

      You don’t mention it, but I assume you are working on an R75/5 or similar that uses the wedge shaped threaded bolt to secure the shift lever on the shift shaft. This is an interference fit and the edges of the slot can get deformed making it hard to get the bolt to budge.

      I was able to get the shift lever bolt to move by using Kroil (or any other penetrating oil, but I really like Kroil) and letting it penetrate over night. I used a 2 Lb maul (shown in the photos) and a flat piece of 1 inch bar stock placed on the protruding threaded end of the bolt. The bar stock prevents hitting the shift lever or the shaft which can damage them. A piece of steel bar stock is readily available at ACE, Home Depot and/or Lowes. I used a hack saw to cut off a length about 5 inches long. I hit the bar stock very hard. It budged the bolt enough to then use a steel drift to drive it the rest of the way out of the hole. And, you may have to use a drift, as I had to for the kick start lever, to get enough force to move the bolt. This is more risky as it’s easy for the drift to move off the end of the bolt and damage the shift shaft and or peen over the end of the bolt. However, holding my hand very steady and ensuring the drift was perpendicular to the end of the bolt, I was able to strike it several times with increasing force until it moved. Visualize how the hammer will strike the end of the drift helped me keep the hammer blow straight on to the end of the drift while keeping it straight on the end of the bolt.

      You may want to try heating the end of the shift lever near the bolt to help expand it around the bolt. If you then add some Kroil after you get it hot, it will help draw the Kroil into the crevices around the bolt which can help lubricate the surfaces so the bolt will move when struck.

      Repeated use of heat and Kroil maybe necessary in order to finally get the bolt to budge, so patience can be a virtue 🙂

      I hope this helps.

      Best.
      Brook.

      • Hey Breams,

        Thanks for the timely response. Im working with a r60/5 but the same principles should apply. I managed to get the shift lever off using a technique similar to what you did, but with a bit more brute force and some other tools (including a file and hacksaw… Fortunately I don’t need the lever again).

        What i am trying to do now is actually remove the shift shaft from the transmission so I can install a new shaft, lever and rearset peg. The new shaft seems to have a threaded bolt running through a machined bit with an end resembling a more squared U. Once I remove the old shaft I will be able to thread in the new one, assuming i don’t damage the threads.

        Is there any specific technique you have for removing the shaft without disassembling the transmission?

        Thanks
        Brant

        • Brant,

          Well, yes, you did say “shift shaft” but I jumped to “shift lever” in my mind. Duhooo ….

          Based on what I see in the MAX BMW parts fiche for this part of the transmission, it appears that removing the shaft requires opening up the transmission:

          http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51882&rnd=07012015

          scroll on the left to the picture with “Diagram 23-0264” at the bottom and “Gearshift” title at the top. Then look at part (19) which I believe is the “shift shaft” the shift lever attaches to. That said, note that (19) is not just a shaft. It’s an integral part of the shift mechanism inside the transmission. If you replace it, the part must match the design of the original shaft.

          I’m not familiar with the rear set you are using. However, I was under the impression rear sets used the original shift shaft with a linkage that mounted to it. At the other end of the linkage, toward the rear, a shift lever attached. So, in that design, there would be no need to replace the shift shaft.

          I hope this helps.

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