BMW Clutch Issue

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1986 BMW 535i. I bought it a few years ago with a bad transmission and only 120k miles, and a friend of mine dropped an '83 junkyard transmission into it
and a new clutch. It's been running well, and I have slowly been cleaning various things on it up.
Starting around 220,000 miles, the clutch began sticking closed. That is, I'd put my foot down, the pedal would stick to the ground, and the clutch would remain engaged. I could pull the pedal up and pump it down a couple times and the clutch would open properly again. It started happening now and then, and then more and more often.
I replaced the plunger on the clutch master cylinder, which was leaking, on the suspicion the seal in it was bad. Didn't fix anything. Took it to a respected BMW indy mechanic around here, who swore I did it wrong and replaced the plunger again. Didn't fix anything. Replaced the whole master cylinder. Didn't do anything. Changed the fluid and replaced the slave cylinder. Still no go.
Now, I am assuming that there is no possibility of the line between the two cylinders being an issue, and no backflow valve anywhere in the system. Is this correct?
Recently it got worse, and I took it in to him again. At this point, we figure it has to be something inside the transmission. He drops it, and replaces everything that looks even a bit suspicious, namely the throwout bearing release lever, the lever pin, the clutch release bearing, and the shift bushings. Everything else looks clean, though neither one of us could see how any one of these would cause the problem.
Putting the thing back together, the problem is now actually worse, since the friction point is closer to the floor than it was before. The car is now doing it almost all the time, making it impossible to drive except on the highway.
Help! Anybody have any suggestions about what could be causing this issue? --scott
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Scott Dorsey wrote:

slave?
nate
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Replaced it, also (and I forgot to mention it) replaced the pedal assembly. --scott
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Gift (Answer) from JoshIII: I have a friend that had exact same problem, on about the same year and model as yours, i.e. mid 80's 5-series with manual transmission.
We replaced the clutch master cylinder and slave cylinder, but problem was still apparent.
I determined the problem was in the clutch pedal itself, and not with the pressure plate or throw out bearing sticking on the transmission input shaft.
You can make this determination just by loosening the two nuts holding the slave cylinder to the transmission and pressing the clutch all the way down to see if it sticks to floor again.
If pedal still sticks to the floor, *AND* the slave cylinder is still under load with tension from the clutch pressure plate springs, then you know your problem is with the clutch pedal itself and not the transmission.
Next, I got on my back underneath his steering column to see how the clutch pedal linkage works.
If you notice there is a spring loaded hinged linkage that connects between the clutch pedal and the firewall (doing this from memory).
Seems like I remember the clutch master cylinder plunger connects directly to the clutch pedal.
Anyway, this linkage should have a little coil spring on it that compresses when you press your clutch pedal.
If you notice the little coil spring also has an adjustment nut and a lock nut on it.
Loosen these two nuts as far out as you can, and still are able to make the lock nut lock on the threads.
The way the clutch pedal linkage is designed, the linkage rotates past top dead center when the clutch pedal is fully pressed down, and will not allow pedal to come back up.
There should be an adjustment to the linkage itself, but there is not. The only other simple alternative is to loosen the coil spring tension nuts as described above.
This *should* resolve your problem.
It did on my friend's mid 80's 5-series BMW.
Please post result in this newsgroup.
Hope this helps resolve your problem!
JoshIII upstate south carolina josh3i at hotmail . com
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Scott Dorsey wrote:

Can't tell what "clutch remains engaged" means? Does that mean the transmission is engaged or does it mean the opposite? If it means the former it is pretty evident that the hydraulics have failed. If it means the latter then there is no clear indication of a problem with the hydraulics and the mechanical linkage would likely be the problem.

What does "clutch would open properly" mean. If you don't do the pumping thing then the transmission will remain engaged? or remain disengaged? or what?

Has your mechanic actually been able to reproduce the problem or is he going only by your description of the problem? If he has seen the car when the problem exists I would take it to another mechanic.
-jim

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It means the former. But all of the hydraulics have been replaced. I don't see anything else that can be replaced. I do not see any sort of check valve anywhere that could be leaking, either.

It will remain engaged, with the pedal stuck to the floor, which is bad.

He has been able to reproduce it while driving but not up on the lift. I am annoyed that he has been trying to fix the problem by swapping things out, but by the same token everything has BEEN swapped out at this point. --scott
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Clutch system is not bled properly. If the hardware is there, and new, the fluid is good, then it can ONLY be that the system is not bled, i.e. there is air in the line. Clutch hydraulics are as simple as it gets, folks.
Get an auto box.
Bill in Omaha '86 535i
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That would make perfect sense, and the fact that it is okay when cold but undrivable when hot correllates well with the air in the line diagnosis. BUT, the system has been bled many many times at this point. I cannot imagine there is still any air in it.

Agreed and that is what makes this so frustrating.

Now, when THOSE fail, you just buy a new car.... --scott
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You didn't hear this from me, Sctoo, but maybe it is time to let Casey look at it.
Bob
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Scott Dorsey wrote:

How is it being bled? I find that a pressure bleeder is the only way to fly.
nate
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wrote:

Just a thought: you might try blleding it in reverse. Maybe pressurize the fluid and send it into the system from the slave cylinder end. You'd have to drain some fluid from the master cylinder reservoir first and keep an eye on it. OR you could unbolt the slave and shake it while still attached to the hose. Maybe there's just enough air to present a problem eventhough the bleeding appears good. Either way, there's air in the system now.
Bill in Omaha '86 535i
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Bill wrote:

I'd also tap on each cylinder while bleeding with a wrench or screwdriver if it appears like it is possible for a bubble to form and not get pushed out with the fluid flow. Make sure that the bleeder is at the very top of each component, if it is not I second Bill's advice to unbolt.
nate
(never had a problem with the clutch on my 535i... blew up the motor, but didn't have a problem with the clutch.)
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when you step on the brake the fluid is forced to the caliper and stops the car then when you let off the brake the broken piece in the hose swings around and acts like a one way valve effectively locking the brake in the on position.
I assume there must be a similar hose on the clutch system to allow for movement of the transmission. Has this hose been replaced?
Steve B.
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Scott Dorsey wrote:

OK so you push the pedal to the floor, at that point you find that the transmission is not disengaged and when you lift your foot you find that the pedal is not returning? Right?     I think the way it works on these is the hydraulic pressure from the slave pushes the master and thus returns the pedal. You can assume that the problem is not a line blockage or sticking clutch that prevents the return of the fluid because if that were the case the transmission would be stuck in disengaged not stuck in engaged. Anyway, If anything mechanical was sticking or bent or broken it's difficult to see how pulling on the pedal and/or pumping it could fix that, so it would seem that the only explanation is hydraulic pressure is lost between the slave and master cyl. I assume you would look for and notice an external leak? I suppose it is possible that if the line was near the exhaust boiling the brake fluid could be the cause.

Yes there is a check valve. The piston inside the master cylinder behaves as a check valve. This is why pumping restores the lost fluid between slave and master. If that seal leaks while stepping on the clutch then the fluid goes back into the reservoir and you get the symptoms you describe. Assuming a faulty master cyl. is not the cause, I suppose it's possible that the wear on the pedal linkage may be causing a stress on the piston for which it was not designed. A side load or excess travel causing the piston seal to fail.
-jim

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Does "swapped" mean "replaced with new or rebuilt", or just lip service by a half-assed mechanic?
Top down: Fluid reservoir hose to Clutch Master Cylinder (no bleeder valve) hose to Clutch Slave Cylinder (bleeder valve)
Other directly-related stuff: Clutch pedal w/return spring and adjuster to CMC Rod between slave cylinder and fork (part of the slave cylinder) Clutch actual (fork, release bearing, disc, pressure plate)
Notes: The return spring on the pedal is a helper. The main back pressure comes from the clutch pressure plate spring fingers. These guys give more than 220 pounds of resistance when disengaging the clutch. Given a completely hydraulic connection, the pedal would have no choice but to return to full out position.
I'm a little surprised you haven't found a leak yet. Have you noticed a drop in the fluid reservoir level? If the level is below the MIN line, the clutch supply line will suck air. But it wouldn't affect the clutch operation until the air got to the Clutch Master Cylinder (attached to the pedal). Pumping the pedal creates a short-term fix by temporarily compressing the air enough to slightly disengage the clutch disc. I know it's been said, but I'd replace completely the items under Top Down. The reservoir should be OK, though. If this keeps up, your clutch will die. It may even take the transmission with it. Good Luck.
Bill in Omaha '86 535i
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On 14 Jun 2007 21:56:59 -0400, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

Long shot here but is the clutch housing exactly the same depth as the original. If deeper then the clutch springs may be going over centre and dropping off the slider/retaining springs/clips.
Just a thought.
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If it pumps up it can only really be hydraulic related. If you've fitted a new slave cylinder I'd guess the master cylinder needs replacing - not just new seals. Also bleeding these can be difficult - best to use a pressure bleeder, or unbolt the slave cylinder, clamp the piston, and raise it above the master (if the pipe allows)
One other thought - does the pedal sink to the floor after time if the car is just parked up and not started? If so it's got to be hydraulics. If it is fine on this test it's just possible run out on the withdrawal bearing or the clutch parts this bears on etc is upsetting the correct clearance - but that's a long shot, and should be pretty obvious by looking.
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Master cylinder has been replaced twice now. Pressure bleeder has been used.

After replacing all the hydraulics my first thought was the bearing, so we replaced that too. The shaft does not appear worn or have a lip on it. --scott
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But does the pedal sink to the floor after the car has been standing without the engine running? Also, how freely does it move when in this state? An experienced mechanic should be able to 'feel' by hand if it's moving the slave cylinder and withdrawal arm or just the master cylinder piston.
This stationary test should tell all. If the hydraulics work consistently with normal pedal feel after the car is parked up for some time and the engine not started they must be ok. If the excessive 'slack' only happens with the engine running something is pushing the slave cylinder piston too far back. The bearing might well be ok but now about the parts on the clutch it bears on? I'm not sure which type of clutch is fitted to your model but if the type where the release bearing pushes direct on the 'fingers' of the diaphragm spring, are those all at the same height as it were?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Jun 14, 8:56 pm, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

Having read everything else suggested and all you've tried, one last thing occurs to me.
The E28 is subject to cracking pedal brackets. The stamped metal assembly that holds your master cylinder and the clutch pedal cracks from stress and wreaks all kinds of havoc because of it. It can destroy a new master cylinder quite quickly, so check yours as you do this job. You can either replace it with a new one (they aren't expensive) or weld your old one up (with reinforcement in the obvious area where it cracked). Good luck. -- C.R. Krieger Been there; haven't cracked mine yet ...
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