Vintage BMW Motorcycle Owners

My '75 R 90/6 has started slipping in low gear. It's the transmission and not the clutch because if I get too heavy on the throttle it jumps and clunks. I think the dogs have worn out. I don't know why. The bike only has 153K miles on it. My question is: is it possible to pull the transmission without pulling the engine. I haven't worked on a bike transmission since 1968 and it was an Italian bike.

The starter relay burned out on my R75/5 and I ordered a new one from Max. $183!!! While I wait for it to get here I boogered a wire from the solenoid to under the seat. To crank the starter I just touch the wire to the battery. Starts fine.

Craig

You might want to drain the oil in the transmission and look for bits of metal if you think something is going on with the gears. I'm not sure what you mean by "slipping" in low gear...is it jumping out of gear...that would certainly point to the dogs that mesh between gears. Slipping usually means you apply throttle, the engine revs as seen on the tach, but the bike doesn't accelerate.

Yes it's possible to remove the transmission without removing the engine. You would need to remove the battery and tray. Also remove the exhaust headers and muffler...be careful of the exhaust nuts potentially galling if the anti seize is not working. Remove the airbox. Remove the clutch cable. Then you can loosen the motor mounts and use a jack to raise the rear of the engine/trans. Once at an angle, you can loosen the transmission mounting bolts and slide the transmission out along that angled axis and then out of the bike.

It is like the dogs catch in one hole - then slip to the next. The bike would be in neutral briefly until the next dog catches.
I found a manual in the club library with comprehensive instructions. Unfortunately it appears to require several special tools.
Thanks for your thoughts.

Craig

I can’t help about the transmission, other than recommending sending it to Bob Clement at Bob's Motorwerks in Montana if you are in the US (yes, he's my brother, but he's one of the best in the country anyway). But, you can get that relay MUCH cheaper from EME. Good luck with the tranny.

Does your brother possibly have a used or rebuilt 5 speed R series transmission laying around that he would swap out?

I already have the relay in, but thanks for the reference.

cbclemmens wrote: ↑

Sun May 01, 2022 3:28 pm

Does your brother possibly have a used or rebuilt 5 speed R series transmission laying around that he would swap out?

I already have the relay in, but thanks for the reference.

I have no idea, but you could ask. It's Bob's Motorwerks in Robert’s, MT. 406-445-2044. I just read that Mat Parkhouse in Colorado Springs was rebuilding some transmissions to sell, but I don’t know what he would have, nor do I have contact information for him. Maybe there is some on the airhead site. Good luck. Also, Tom Cutter might have an idea for you.

Does the slipping occur in all gears or certain gears? In the 5 speed transmission first and second gears share dogs, third and fourth gear share dogs, and fifth has its own set. Try to narrow it down. Dogs have broken off gears before.

If it occurs in all gears, then I’d suspect something has broken in input shaft gear and “spring“ assembly. Those have also been known to fail and would cause a slipping problem in all gears.

Either way, the transmission needs to come apart. Have you drained the oil to see if any parts come out with the oil?

Have you checked Snowbum’s site? It’s long and you can skip the parts about the circlip issue on the later five speeds.

There are a few independent mechanics on the east coast who do Airhead transmission work.

https://bmwmotorcycletech.info/transmission.htm

Thanks Chris. It only slips in 1st gear. But I haven't started to get into it yet.

A more correct and accurate description would be CHATTERING and/or skipping.
This condition MAY also be attributable to a BEARING begining to self destruct.
Ask me HOW I KNOW....