Grabby BMW clutch
By Duane Ausherman
Is your clutch OK when cold and gets really grabby after warming up? It isn't that you are clumsy. A grabby clutch 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.
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 way to hold it. Get it all set up ahead of time. Heat the transmission up to about 180-220 F and put the dial on the 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.
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 a bit to allow it to drop over the bearings without heat. It holds the shafts in perfect placement and allows the depth gauge to reach the bearings. 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. It is all addition and subtraction.
While this single job 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.
Last edited 27 Dec, 2001 Visit our web site at http://www.softcom.net/users/w6rec/