latest clutch analysis
2000 LT with 5 clutches/seals/slave/oring/pressure & back plates/diaphragm spring etc. in only 23,000 miles. One was highway-only installed in Chicago and shot upon arrival in LA. Another I carefully babied and was shot in less than 3,000 miles. Bike has been disasembled or awaiting funds most of its life, and has cost me over 6,000 in clutch bills though I did one myself.
All previous times there was evidence of leakage at the engine seal and/or trans seal, never any leakage from the slave. We suspected a problem with the engine shaft radial play or bent or something obscure like that.
This time we disassembled after only 3,000 miles with the clutch slipping badly (just rolling on in 5th at 60 mph it would break free), and for the first time everything was completley dry. Lots of sooty clutch residue accumulated at the bottom of the bell housing. Friction disc worn nearly to the rivets.
Engine shaft and seal were O.K. though my technician said it was better to install the engine seal not inserted so far into the block, he had a special BMW tool that installed it proud of flush. Indeed, with the seal flush the seal rode very near the edge of the clutch basket sealing ring.
The technician said that the only thing he could find wrong was that the master cylinder adjustment at the lever (a small accessible screw with paint on it) was mis-adjusted to allow no free play at the lever. Yet I'd think the cylinder must have retracted sufficiently or neither forward nor reverse bleeding owuld have been possible, unless power-bleeding deformed the master piston seal. He thought it was a problem, I'm not sure. Unfortunately, nobody tested the rod/slave action before he corrected the lever freeplay at the master. He saw something he didnt' think was right and adjusted it. Now we don't know whether it was wrong enough to be the cause of all the problems.
After he unscrewed the screw a bit and added free play at the lever:
The only thing I could notice that seemed strange to me was that the throwout rod thru the trans shaft didn't retract very easily or quickly in two ways:
1) I'd expected that once the master lever was released so the piston was retracted fully past the master cylinder fill hole, the line was depressurized and connected to the fill reservour. So I'd expected to be able to more easily push in the rod and slave with my thumb against only the small spring in the slave. But no, with the clutch lever released I had to press the rod with any flat tool, or pressing with my palm or thumb I had to press too hard and it hurt (ouch). But perhaps the fill hole is just very small, perhaps a good thing with the frequency rate of slave failures. Indeed, FULLY retracting brake pistons for service takes time and pressure too...
2) But my bigger concern was this test:
After I pushed the rod in some distance I kept some pressure on the rod. Then I actuated the master lever. The rod and level moved in unison, as they should. However, the rod did not retract as easily as I'd expected. It moved smoothly, but it took more pressure to push it to retract than my familiarity with the slave spring led me to expect. Could be just piston seal friction. On one other previous LT clutch I'd trimmed that slave spring to reduce its preload, but this was a new slave only 3,000 miles ago, the felt on the turned-down section of the rod (2002 rod in 2000 bike) was dry, rod was dry right to the end, fluid level was fine. Action was similar without the felt.
So the technician's conjecture is that the master was mis-adjusted at the factory and didn't have enough play to properly retract the master piston past the cylinder fill hole. Then, with heat or pump-up or whatever, the line never was able to de-pressurize via the fill hole when the lever was released. Not filling, the more common symptom of this kind of problem, would usually cause the lever's clutch release point to move farther toward the bar. But if the slave doesn't leak, another symtom might be constant pressure in the line that's never released when the lever is released. That would mean the clutch rod was always slightly disengaging the clutch, making it slip & wear.
The symptom was always that if I droned in 4th or 5th on the expressway for a while, after shifting from 4th to 5th and letting the clutch 'catch' completely, if I subsequently rolled on the throttle in 5th the clutch would slip. So I always thought the problem was a seal leaking fluid as I droned along, then slip after the clutch got saturated. But if the master was the problem all along, then the symptom probably showed up after heat made something expand, perhaps the friction disc or rod or fluid, whatever, causing pressure in the system.
Now for my questions:
1) He said he put in a current late-model diaphragm spring this time, from the newer engine that makes more horsepower. I wanted to put in dual diaphragm springs, which I liked but shortened the life of the already marginal slave. SO, is the new spring stiffer? Does it have a new number? Is it specified as a replacement number superceding the old diaphragm spring number?
2) The master still has a problem with the cruise-control switch, and the lever has excessive play up and down (cross to the actuation direction). After adding play via the adjsuter screw, the VERY experienced technician (on his second personal LT too) said that the action then seemed normal to him. To me it still seemed sluggish, compared to my Suzuki TL1000R sportbike hydraulic clutch slave/rod. Think I should replace the master, or remove all the lines and banjos looking for a chip blocking a banjo bolt hole somewhere?
Unfortunately, to my thinking the problem was in the hydraulics this time, and I'd have replaced ALL the hydraulics including all lines and banjo bolts, and master. But this shop didn't remove the final drive and frame cross memeber, instead they dropped the engine. This meant they still could not access the slave or line.