Grabby /7 Clutch

[Flash]

My 1978 BMW R100S had developed a "grabby" vlutch.

When cold, the clutch operates fine, When hot (15-20 miles) it's very difficult to engage it smoothly from a stop. It begins to engage and then BAM and the bike lurches forward. Even at higher speeds when changing gears, you can feel the clutch engaging hard. There was also a "screeching" noise from time to time while moving.

My local dealer pulled the trans and replaced the clutch components. The screech is gone, but it stills grabs when hot.

Thoughts or suggestions?

Thanks

[dbrick]

The symptoms suggest that there's too much play in the gearbox's input shaft. Correction requires removal and disassembly of the gearbox, and re-shimming.

[flash412]

If I were you, I would START by lubing the handlebar lever pivot, disassembling, cleaning, lubing and reinstalling the throwout lever and pivot and then installing a new clutch cable.

If THAT didn't fix it, I'd pull the transmission and take a look at the clutch splines on the input shaft. I bet they're VERY dry and possibly worn. Lube the splines, CAREFULLY.

While you have the gearbox where you can get to the end of the input shaft to lube it, feel it for endplay. If and only if there is a lot of slop, break open the gearbox for a reshim. Those shims don't go bad. If the gearbox suddenly (or gradually) started doing this, I put my money on insufficient lubrication somewhere. If it needs new shims all of a sudden... then it NEEDS new bearings, too.

[dbrick]

Flash is quite correct. I assumed (from "...My local dealer pulled the trans and replaced the clutch components....") that the lube-and-cable issues had already been addressed. You should look at them first.

[Flash]

Originally posted by flash412
If I were you, I would START by lubing the handlebar lever pivot, disassembling, cleaning, lubing and reinstalling the throwout lever and pivot and then installing a new clutch cable.

If THAT didn't fix it, I'd pull the transmission and take a look at the clutch splines on the input shaft. I bet they're VERY dry and possibly worn. Lube the splines, CAREFULLY.

While you have the gearbox where you can get to the end of the input shaft to lube it, feel it for endplay. If and only if there is a lot of slop, break open the gearbox for a reshim. Those shims don't go bad. If the gearbox suddenly (or gradually) started doing this, I put my money on insufficient lubrication somewhere. If it needs new shims all of a sudden... then it NEEDS new bearings, too.

Thanks dbrick and flash412, Sunday, I went thru and cleaned and lubed from the hand lever to trans actuating lever. About 20 minutes and 2 cups of coffee. Then i put 100 miles on the new clutch. The grabbing seems to be gone.

:bliss

[Cosmoline52]

Maybe you need a new dealer, Flash...

I've owned my '78 S since new and when grabbiness first appeared between services I found that greasing the pivoting points of the levers at both ends of the cable would solve the problem. As you discovered, this is a minor fix with virtually zero $ required.

Any dealer that would replace a clutch assembly without trying the minor stuff first would be on my questionable list. Could be worse, I guess, they could have done the greasing and the clutch pack and you would have come away thinking that the replaced clutch fixed your problem...

I've found that the actuating arm on the trans can be subjected to a lot of environmental abuse because of its location. My MO has been to clean and lube it at the valve adj/oil change. The clearance to the pushrod and cable play adjustment also make a big difference when adjusted correctly.

And yes those splines need their required attention! When I first found out about this requirement it seemed to me a bungle on the part of the engineers. At the time I bought my S there were some very NICE Euro chaindrives out there but the Bimmer drivetrain influenced my decision since I was sick of chains. So then I find that I must regularly disassemble half of my bike to apply some grease to a part. I actually looked forward to the procedure after the first time, since it set aside an afternoon to really get into the motorcycle and afterward that simple swipe of anti-seize on the teeth would make a very noticeable difference in clutch action.

So far as the clutch cable, mine is the second for this bike and has over 100k mile on it and still works great. Big change from my Honda I rode prior where I found out I should carry a spare.

Beemers need a little more attention occasionally but that time spent results in extreme satisfaction in operation, at least IMHO!

Dean

[Flash]

Thanks Dean

I bought the bike last summer. The odometer showed about 8,000 miles, but upon examining the bike, I seriously doubt the miles are correct. It was a "bitsa" bike with no service history at all. I've replaced so many things that the clutch didn't surprise me. There has been an improvement in clutch action. It's crisper, not as vague.

I agree with your assessment. When I told the dealer my problem was a grabby clutch, the tech wanted to inspect the clutch. Makes sense. Upon seeing the disc's worn condition, he assumed this was the source of my problem. Reasonable thought.

Unfortunately, the problem only occurs when the bike is good and hot, and the tech only went around the block and pronounced it cured.

So far its fine. Time will tell I suppose.

[Cosmoline52]

You're welcome Flash, just a little bit of my personal experience from over the years, simple things sometimes tend to be overlooked.

That big car-like dry clutch in our bikes especially with the older heavier flywheels can sometimes be a little temperamental. Actually no, it's not car-like, it's much more complicated. I suppose the engineers designed its relative complexity to size down the dry clutch components to motorcycle size.

As a result, that pushrod in there is a critical part of the process. Screeching can result simply because the forward end of the pushrod is bearing onto a dry diaphragm springplate. Now I don't know how those BMW engineers expected to keep a dab of grease at that contact point situated considering centrifuqal force but at spline-grease-time don't forget about it, and those teeny overworked release bearings and seals are cheap enough to replace also...

Happy to see your S is running well, Flash! You mention "only time will tell" but hey that's what airheads are all about, right? Extreme durability and reliability for the duration!

:)