1978 R100RS clutch issues

[Tarmapper]

Well that didn't go as well as I'd hoped. I've just had the gearbox on my R100 RS rebuilt and changed the clutch plate while the box was out. This afternoon I reassembled it all, centred the plate, torqued the bolts etc but when I reattached the clutch cable, there's no resistance at all - it's as if I forgot to put the rod back in (I didn't, before you ask). I installed a new felt ring on the rod while I was at it which took a bit of fiddling to seat but, other than that, the whole thing seemed quite straightforward. Before I strip it all out again, am I missing something? Or is there something obvious I could try.

I'd be grateful for any advice before I order up replacement bolts and start the whole exercise again.

John

 

[Stirlingmoz]

Did you lubricate the clutch thrust piston or the bore it runs in on the rear gearbox cover ?

If the piston sticks in the bore, and the clutch can’t release, you can get a floppy lever with no ‘feel’ at all.

Doesn’t need a big strip down to get at either.

 

[Tarmapper]

I gave a little grease to the needle bearing not the piston. I have taken the piston and bearing back out though (just to make sure I'd put them in in the first place) and they're very free in the bore. Could the felt be affecting things? The rod needed a bit of effort to move to and fro after the new felt was inserted - nothing too demanding but a definite "push and pull".

 

[Gelandestrasse]

All these bits go back, including the big spring?

 

[mikeyboy]

Was there no resistance on the first pull of the lever?
Do you think something has jammed or stuck?
Try turning the adjuster screw in until you get contact.

 

[theoneandonly]

what bits are still on the bench ???

 

[Stirlingmoz]

I think you may be on the right track with the felt bush.

New ones can be tricky to fit.

I lightly oil the felt and then wrap fishing line round it to compress it.

Once inserted, gently pull out the fishing line.

The push rod (like the thrust piston - my first guess) must be able to move freely back and forth.

 

[Tarmapper]

I found getting the felt into place was more than just tricky. I managed it eventually (I thought) by using a short length of petrol pipe which was a tight fit on the rod to compress the felt. As I pushed the rod in, the pipe was pushed back and released. I'm going to have to take the box out again and this time I'll try fishing line next. Thanks for the tip.

Mikeyboy - there was no resistance the first time, or when I tightened the adjuster as far as it would go. I'll strip the box back out and try again!

 

[DrFarkoff]

To be honest Don;t just pull the box out !

There has to be an issue The felt washer won't be screwing things up that bad it may be making things Sluggish

Check all the components are in place

 

[Tarmapper]

It's progress of sorts: I have a working clutch but not the way BMW designed it and I don't think I'll take it on the road as it is.

I took the box out to check that everything on the fiche was in there. Without any fishing line to hand, I put the old felt back in and the rod moved much more smoothly. Everything seems as per the book so the box went back in and ... no clutch.

So I took the box out again, and then stripped out the clutch as well ... checked it all and refitted it (just a trial fitting until new stretch bolts arrive from Motorworks). No clutch. It's as if the rod isn't there at all, regardless of where the adjuster is screwed to.

This afternoon I cut 5mm off a suitably sized drill bit, greased it up and stuck it into the bore of the piston. Now I have a working clutch - but not one I'm very happy with. I don't know what the Donald Trump is going on. It's the same rod, same everything (apart from the friction plate and single-use bolts) but it won't work without 5mm extra length.

Any ideas?

 

[DrFarkoff]

This afternoon I cut 5mm off a suitably sized drill bit, greased it up and stuck it into the bore of the piston. Now I have a working clutch - but not one I'm very happy with. I don't know what the Donald Trump is going on. It's the same rod, same everything (apart from the friction plate and single-use bolts) but it won't work without 5mm extra length.

Any ideas?

Is it a heavy flywheel version?

What clutch piston set up ??

Diaphragm spring with or without steel ring ??

 

[Gelandestrasse]

Check Part 10 looks like this:


Also, Part 4 is about 5mm in thickness...

And Part No 1 should look like this:


Hope this helps.

 

[Tarmapper]

Thanks for the replies. I feel less alone ....

Dr Farkoff: Yes, it's a heavy flywheel version. No steel ring on the diaphragm (I didn't know they ever had them). And the "piston set up" is just the one that came off it when I stripped it down. It came out of the gearbox, into a bowl and sat on the workbench while the box was away for six weeks, then went back on the bike.

Gelandstrasse: Thanks for posting the pics. I'll check the dimensions of both when I get back on it this afternoon (hopefully). I'd be very surprised if either were wrong - they came out off the bike, into a bowl and then sat on the workbench while the box was away for six weeks, then went back on the bike.

The good news is that the new stretch bolts have arrived - I only ordered them at midday yesterday and they're here (by 8.30) this morning. Well done, Motorworks!

​

 

[Gelandestrasse]

I must say Motorworks have pulled up their socks of late regarding delivery times. They now compete with Motobins and Sherlocks on that front. Something has changed there.....

 

[Bubb]

Could one part be installed back-to-front, thereby causing the lack of the 5mm or so.?

 

[Steptoe]

Could one part be installed back-to-front, thereby causing the lack of the 5mm or so.?

I was thinking the same thing .., is the clutch diaphragm spring fitted the correct way round .,

 

[Bubb]

I’m no expert like steptoe, but glad my suggestion wasn’t totally daft.

 

[Gelandestrasse]

I was thinking the same thing .., is the clutch diaphragm spring fitted the correct way round .,

Crikey, have you ever known that to happen? Or have I just fallen onto a trap?

 

[Steptoe]

Crikey, have you ever known that to happen? Or have I just fallen onto a trap?

I had someone put a clutch plate in the wrong way around in an 1100GS - the splined unit pushed/compressed the diaphragm spring so the clutch couldn’t compress

 

[Tarmapper]

Thanks again for your suggestions and interest. I've come to the conclusion that I'm incompetent - although not quite so incompetent that I'd put the diaphragm spring in back to front. If I did, I probably wouldn't admit to it. But I didn't. Honest!

It was suggested to me that I should put the old friction plate back in to see if that restored any clutch resistance. It did. So I compared the old with the new, checked the new one for warping, ran callipers across all parts as if I knew what i was doing and could find no difference (apart from the wear on the old plate). So I bolted the whole thing back together and - lo and behold - I have the clutch back again.

I don't know what I did but I must have done something wrong. I've had the gearbox/clutch out of an airhead before and it was effortless. This was a headache. But by tomorrow afternoon I'll have her back on the road and enjoying the sunshine. And I'm now very good at getting the gearbox in and out of the bike!

I feel I've wasted your time but I'm grateful for your help and support. It's good to know there are people out there willing to help. Thank you.