Grinding cltuch cable when hot?

[Ross]

When my engine is cold the clutch cable is slilky smooth in its action. When hot the cable feels like it is grinding in it's casing. Anyone had this???

[Ross]

This might be the reason???

BMW motorcycle with a grabby or jerky clutch
by Duane Ausherman


This page is about the /5 BMW motorcycles and later.
Is your clutch OK when cold and gets really grabby after warming up? It isn't that you are clumsy. A grabby clutch usually means that the input shaft of the transmission has excessive end play. It can grab even when cold, on a bike with a really loose input shaft. The shaft is moving and engaging the clutch by itself.

I recently learned of another reason for a grabby clutch from Dave. His bike had a grabby clutch and it was due to a broken clutch rod. It was broken at the felt and the edges were at an angle. They would alternately make the rod longer and shorter as they "turned" against one another. Replacing the clutch pushrod fixed the symptom. Thanks to Dave.

It is also possible for the spines to need to be lubed, but that is far less likely. It also does not vary with temp.

To reduce this end play means removing the transmission, opening it up and re-spacing the shaft. While one is in there, several other things should be checked and replaced. This job is not trivial and should be left to an experienced /5 BMW mechanic. In my opinion, very few persons exist today that are capable of properly rebuilding an old BMW tranny. Some will say that only the splines need greasing. It may be true that they need grease, but greasing the splines to allow the clutch plate to float, and therefore not grab, is the wrong solution. The shaft shouldn't be moving in the first place, fix it. The splines should be greased, but only so that they don't rust and wear prematurely.

The end play may be checked without opening the transmission. It takes a dial indicator and a way to hold the transmission down. Get it all set up ahead of time. Heat the transmission up to about 180-220 F and put the dial on the input shaft. Grab the shaft and push and pull on it. The end play can be measured more accurately than with the cover off. BMW calls for the end play to be .004," but I like to set it at .001 or .002 when cold. The end play increases when warm and you may well find .004" when the whole case is heated up.

To correct the end play one must open it up. That means several special tools and is not for the faint of heart. To measure the end play I use a homemade tool. It is an old ruined rear cover. It has been machined off until the bearing surfaces are revealed. Then the bearing holes are opened up by hand sanding a bit to allow it to drop over the bearings without heat. The "tool" cover surface must be very good and clean. It holds the shafts in perfect alignment and allows the depth gauge to reach the bearings. A bearing that isn't "held" will tend to cock to one side and that is why the method shown in the BMW workshop manual won't work well. It uses parallel bars and a depth gauge.

The number stamped into the cover is the resulting thickness of the cover. That number is used in the math for calculating the shims required. One must then measure the depth of the bearing cavities in the cover to be used. I suggest that one also check the surfaces of the case and the "real" cover for dings that may cause a leak. After that it is all addition and subtraction.

While this input shaft spacing needs to be done, one should strongly consider replacing and servicing other parts while one is in there. Whenever the tranny is out, I suggest that you check and service the clutch, rear main seal, oil pump cover O-ring and the tranny input shaft seal. Learn more about the clutch.

I hope not as the gearbox was overhauled 3 years ago and has only done 40k kms.

[Ross]

The more I look into this the more I think the gearbox is going to have to come off. Think the first I need to do is check the input shaft splines to check if it is lubed.

[ME 109]

Maybe the bearing on the end of the clutch pushrod is stuffed?

[chasbmw]

Remember that much of Duane's advice comes out of his experience with /5 and /6 models and this advice may not apply to later bikes.
In your case there have been many reports of the plastic housing of the clutch release bearing expanding when hot and causing the symptoms you report. Usually resolved by fishing it out of the back of the gearbox and lightly sanding the outside of the bearing holder. With luck youahould be able todo this without removing the gearbox.

[Duane Ausherman]

chasbmw said, "Remember that much of Duane's advice comes out of his experience with /5 and /6 models and this advice may not apply to later bikes."

I wish to agree totally. Also, since "my day" we have learned even more about those bikes of that era. New materials have been developed too.

My website should not be considered as any gospel, just a starting point for consideration of an issue.

I am pleased to see that someone is still going there. I haven't checked the traffic pattern for more than a year, but it was then still running about 1400 unique visitors per day. About 400 are looking for porn and about the same for other technical things, but over 1/3 are actually looking for BMW motorcycle information.

Big brother is watching you........... or could if I had the time.

[Ross]

Thanks guys. I did read Duane's website last night at work between calls. So didn't have a chance to fully sit there and digest all the info.

So would the part that needs sanding down be part No. 2 in the below??? Or is it No.3?

[Garnet]

Big brother is watching you........... or could if I had the time.

I heard that he's retireing (getting new tyres) soon, then we'll all be in trouble.

[Ross]

I have pulled the clutch control assembly out. Removed the clutch thrust piston. If I put my finger on it and press down while turning the clutch thrust piston the bearings feels good. But I can move the bearing in this part from side to side and it feels rough when I do that.



Can I assume this may be the part that is causing the clutch cable through the handle to feel like it is grinding? As this pushes on the clutch pushrod. Which when you look at the parts diagram above this clutch thrust piston seems to have replaced parts 2 & 3 and MAX BMW Parts says this does in fact replace the older throwout bearing AND piston. So I have answered my own question me thinks???

Also of note is that when I pulled the boot off this control assembly water came out. Not good.

To add to this. The bearing in the middle will move not side to side. It moves to one side all the way and the other side no movement at all. Looks like the bearing has collapsed on one side.

Mortorworks in the UK will get an order for this part as they are $100 cheaper than getting this part here in Australia. Which sucks as I do like to try to keep my money on shore with guys here. But when I can save $100.

[Ross]

Packed the clutch thrust piston with grease. Fitted it back in. Adjusted the clutch and all feels way better for the time being. Took the bike out for a ride to get some beer and clutch still feels good even when hot.