I’m not going to disassemble the rear drive as there were no problems with it. Since the rear brakes are mounted on the rear drive, I advise a face mask and gloves to avoid getting brake dust where it doesn’t belong, your lungs.
Here are the pictures of the rear drive when I took it off the bike.
Rear Drive Before Cleaning
Brake Shoe Orientation and Components
I pulled the rear brake arm off the shaft so I can push the shaft out to remove the rear brakes. There is a felt ring under the arm.
Felt Washer Under Brake Lever
Using a soft mallet, I knocked the brake lever shaft out the back to release the brake shoe assembly.
Removing Braker Lever Pivot Shaft
Then, using a screw driver I lifted the other side of the brake shoes over the fixed pivot to remove them. Here is the disassembled brake components.
Brake Assembly Parts
Inspecting the brake lining, I could see the lining had cracked, so some more parts to order.
Rear Shoe and Cracked Linning
And here is the washer that goes between the boss and shoulder of the brake shaft. It stuck to the boss.
Washer Between Boss and Brake Shaft
I put the rear drive in a plastic pan and liberally applied Gunk engine degreaser and worked on the hardened grunge with a stiff nylon brush and tooth brush. After rinsing the Gunk off, I used the parts washer and a tooth brush to get another layer of grime off the cast aluminum. Then, using AutoSol aluminum cleaner and a Scotch Brite pad, I got the stains and corrosion off the housing. Then I used “00” steel wool with more aluminum cleaner get a luster on the rough casting finishing up with aluminum polish. On the left is the cleaned and polished casting and on the right is after parts washing with gear lube stains still showing.
On the inside of the drive where there was a crusty mix of brake dust, some brake cleaner did the trick. Using a stiff nylon bush and toothbrush, I got all the grunge off the nuts and casting.
I used Permatex gasket remover and a putty knife to clean the old gasket off the end that connects to the swing arm. I finished up with “000” steel wool to polish the surface making it ready for a new gasket.
I used aluminum cleaner on the brake lever with “000” steel wool to bring the shine back finishing up with aluminum polish. The wire wheel cleaned the pivot lever, springs, brake lever Allan head bolt and the brake rod bushing. These I finished up with metal polish.
Refinished Inside Side of Rear Drive and Polished Parts
Refinished Outside of Rear Drive
When the brake shoes come in, I’ll assemble the brake shoes and the rear drive will be ready for attaching to the swing arm.
Good morning from Canada!
I have a question and was hoping to see if I can get some sagely advice. I am 25 and in the midst of my first rebuild – a 1970 Bmw 75/5. It’s been extremely fun and challenging and requires a lot of research. Now on to my issue:
I am reassembling the rear end and when trying to put the rear wheel back into the final drive i am left with a 2-3mm gap all the way around. It should sit more flush to the final drive but no amount of maneuvering can get it to sit flush. Additionally, the gear ring on the wheel has some play (very minimal), do I need to re-rivet this piece and have it stay perfectly solid? An old bike mechanic in my area said it isn’t a huge concern, but now that I am here and having this other issue I wonder if I should just fix that as well. Any thoughts and insights would be greatly appreciated.
Hi Ivan,
It sounds like you are having fun 🙂
I think you would be well served to post a note to the Airheads forum with your question on the rear drive.
http://micapeak.com/mailman/listinfo/airheads
There are several very knowledgeable mechanics and owners on this forum and I’m sure they can advise you of what to do.
I hope this helps.
Best.
Brook
Hello Brook,
Oil overflow through the breather located on top of my final drive (R75/6) appears to indicate a driveshaft-to-final drive oil leak caused–probably–by a faulty oil seal (the one located between the crown spline and the pinion).
Do you have advice on where to obtain illustrated instructions on how to replace the old seal? I believe I will need a special tool by Cycle Works which allows for the removal of a four-slot “ring nut” which holds the seal, but other than that, I’ll have to adventure into unchartered waters.
I believe common sense might help (plain reverse-engineering…), but I want to play it safe. Thank you as always!
Best,
Luis Etchenique
South Ponte Vedra Beach, Fla.
Hi Luis,
Ah, well I haven’t done this work yet, but it’s on my list of project candidates.
Duane Auscherman has information about this on his web site:
http://www.w6rec.com/duane/bmw/finaldrive/index.htm
The seal he refers to I think is (#5) in this exploded view from MAX BMW:
http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000737.png?v=07012015
Duane indicates that gasket sealer is your friend when fixing the leaking around the splines on the inside of the pinion gear and along the threads of the seal holder (I think that is #6 in MAX diagram).
Bob Fleischer also has information about this type of leak on his web site:
http://bmwmotorcycletech.info/rearwhlsplines.htm
He describes the work, identifies a type of gasket sealer and says that some of the Cycle Works tools are needed for getting to the seal and replacing it.
I hope this helpful to you.
Best.
Brook.
Thank you Brook; will follow your advice. In fact, I think I’ll be taking photos as I go–and I’ll forward them to you.
Best,
–Luis
very nice
Hey Brook,
I noticed you didn’t remove the screws for oil or the plug at the top before refinishing the outer casing. It would make cleaning it a lot easier.
Is the plug at the top just pulled out or is it screwed in? Is there any risk of damaging it when removing? Is there a gasket?
Thanks!
Jonathan
Hi Jonathan,
I didn’t want any of the steel wool or cleaning agents to get inside the rear drive unit. I believe the plug at the top is pressed in. I’ve never had need to remove it.
Best.
Brook.
Brooks,
Thanks for the awesome explanation. I’m local to Denver, CO and own a 1974 R90/6.
I’m refurbishing my final drive and need to replace the spline as well. Do you know anyone in the Denver area who might be able to help out with this portion of the refurb?
Cheers,
Leo
Hi Leo,
I’d contact Matt Parkhouse who lives in Colorado Springs to see if he can help you out: [email protected]. He is a long time airhead mechanic.
I hope that helps.
Best.
Brook.
Thanks for the reference. Matt was a pleasure to meet and an incredible resource!
Thanks for showing this, I’m trying to do the same, clean rear drive without disassembly. For the inside side, how do you handle the middle spline area — did you spray cleaner in there, or could that harm the seal?
Hi Mike,
It depends on the kind of “cleaner”. I used some engine degreaser followed by a water flush and then blew dry with compressed air.
Best.
Brook.