Transmission Cover replacement - 78 R100/7

Kidasters · Post by **Kidasters** » Fri Mar 22, 2019 10:47 pm

Hey guys -

Bad day today. One of the tabs that holds the pin on the clutch arm broke today. In order to fix it, I'm going to replace the transmission cover. it looks like to do that, I'm going to have to remove the swing arm and drive shaft. Any hints or tips for this job? Not looking forward to this one.

schrader7032 · Post by **schrader7032** » Sat Mar 23, 2019 6:32 am

Have you diagnosed why it failed? I suspect that the small c-clip holding the pin in place came loose, allowing the pin to work out of the boss which ended up breaking it out. There are fixes for that...replacing the bolt with one that is threaded on the end and using a nylock nut.

You should be able to undo the 4 bolts at the back of the transmission output shaft and move the whole rear end backwards to give enough clearance to get the transmission out. A few other things will need to be removed such as the brake rod wing nut, probably the muffler mounts. You'll also need to remove the battery and battery box. The swingarm pins need to be pulled as well. In the end, they'll need to be tightened in a special sequence. Plus you'll need a special tool to get to the thin nuts on the inside of the swingarm holding the pins in place. It's a modified 27mm nut with the outside edge ground down as well as the inside chamfer removed. Snowbum has some info on this here:

http://bmwmotorcycletech.info/inputsplinesthrowout.htm

You'll need to reshim the transmission since the rear cover is going to be different in dimensions that the original. Here's a page on general gearbox overhaul and it talks about the shimming as well:

https://www.schweizerschrauber.ch/mot/gearbox.html

Kidasters · Post by **Kidasters** » Sat Mar 23, 2019 7:41 am

My guess as to why it failed is (per Snowbum's write-up) is that it started to work it's way out, and that's what caused it to fail.

Damn - I was hoping that I could replace the cover without pulling the entire transmission, but that does not seem to be the case.

It's probably for the best, so that I can get everything apart and cleaned properly.

So disappointed.

schrader7032 · Post by **schrader7032** » Sat Mar 23, 2019 7:58 am

Yeah, the cover will need to be heated at various spots in order to get it off. I've seen Matt Parkhouse do it at one of the MOA Nationals.

Kidasters · Post by **Kidasters** » Wed Mar 27, 2019 10:12 pm

I'll also have to pull the drive flange off to get the cover off.

The BMW factory tool (23 1 700) is impossible to find.

Any thoughts on this too? Just use a gear puller?

schrader7032 · Post by **schrader7032** » Thu Mar 28, 2019 6:24 am

This is a pretty critical joint...I think you need the proper tool or something that will do the same job...a simple puller probably won't cut it. The flange is on with some serious torque, like 150-170 ft-lbs.

Cycleworks has the puller...plus there's a DVD on transmission work:

https://www.cycleworks.net/

Kidasters · Post by **Kidasters** » Thu Mar 28, 2019 6:30 am

Kurt - you rule. This is the one:

https://www.cycleworks.net/index.php?ma ... cts_id=321

I'm purchasing it. Thanks!!

Kidasters · Post by **Kidasters** » Sat Apr 20, 2019 6:02 pm

Hey Guys -

A couple more questions.

To remove the transmission, it says shift into 4th or 5th, as it is imperative that the transmission doesn't move. Since the clutch is basically broken, I shifted up to what I thought was 5th last time I messed with the bike. I had to move it today, so I wanted to go back down to Neutral.

And, one click down, I was in Neutral. So - turns out I had it in 2nd. So - my question to the group, is there a better way to find 5th? Or, is there another way to immobilize the transmission for this work?

Also - I was worried about my 75 R90/6 having the same problem. I was looking at it, and the linkage is slightly different on the 75 than the 78. On the 78, the cable hooks directly to the fork at the end of the lever that pushed the throwout bearing. On the 75, it is much more complicated. The clutch cable hooks to a small chain that wraps around a gear on the end of the throwout bearing lever. The pin looks different too.

It made me nervous, so on my 75 I put a cotter pin on the slot at the bottom of the pin. But, it still doesn't look like there is anything holding the pin in on my 75. I'm thinking about not riding the 75 until I can replace the pin on it as well - as I don't want to replace 2 transmissions.

Replacing the pin seems like it should be pretty straightforward, but I'm sure there will be scope creep.

Looking for advice.

schrader7032 · Post by **schrader7032** » Sat Apr 20, 2019 6:38 pm

You say "remove the transmission"...what does that mean? Are you trying to get it out of the bike? If so, it doesn't matter what gear it's in.

As for the different mechanism on the '75, sounds like that's what called an Easy-Clutch...maybe something like this:

http://www.benchmarkworks.com/articles/ ... lutch.html

The '75 and '78 would have had similar stock clutch engagement setups...some differences, but not that much.

Kidasters · Post by **Kidasters** » Sat Apr 20, 2019 9:55 pm

Yes - it is an Easy-Clutch! Perfect.

For removing the transmission, I'm just trying to do what it said in this guide:

http://bmwmotorcycletech.info/inputsplinesthrowout.htm

Plus - he seems to say that there should be service on the input shaft every so often, and I figured while I was there I would do that.

I've decided before I ride it more, I'm going to remove the pin and replace it with a bolt. That's the safe thing to do.

Vintage BMW Motorcycle Owners

Transmission Cover replacement - 78 R100/7

Transmission Cover replacement - 78 R100/7

Have you diagnosed why it

I'm not completely sure

Yeah, the cover will need to

There's more than that

This is a pretty critical

Brilliant!

Still making small progress

You say "remove the

You have all the answers