Clutch failure following brake bleeding - coincidence?

[vt]

Like I was saying, just bled the brakes yesterday, and lo and behold, the clutch is now dead. Symptoms being:

Depress the clutch pedal without giving it a second thought, not noticing anything different, try to shift into reverse, fail, ponder, try again a bit harder, realize that something is wrong, release the clutch pedal and find it on the floor.

Further investigating, depressing the clutch meets hydraulic resistance. Initially, the clutch returns almost to the normal height, but pumping it reliably brings it to the floor - then I have to pick it up by hand or foot, and it goes back with no resistance whatsoever.

Pedal bracket seems to be fine, but I can't inspect it closely until morning.

No leaks noticed under the car.

Having read threads about clutch failures, I think this can be diagnosed as a hydraulic failure (the morning will tell whether this is master or slave), but here are some alarming details I don't want to overlook:

- Clutch was unusually hard to depress, for a BMW (compared with one E39 and one E46, hope that's enough stats) - but not much different from a hydraulic clutch on RSX Type-S, though.

- According to the seller, the clutch master cylinder was replaced on 7/2008, which makes me wonder.

- When bleeding brakes, I was really surprised by the fact that braking fluid looked as if it was replaced very recently - it was muddy all right, but very light, almost as light as virgin fluid.

- There's no say what fluid was in the system, I put BMW DOT4, wonder if it was compatible with whatever was in already. In different times and places I've heard urban legends about incompatible brake fluids causing catastrophic brake system failures, wonder if this may be the case here - especially if the new master cylinder was only exposed to that other fluid. (this sounds bizarre, let's just say it's a late night and I probably need to go get some sleep)

- (afraid I already know the answer, and it is "no") Is there a chance that I simply let the air into the system, and all I have is to bleed the clutch?

- Bentley says you have to use pressure bleeder (which I don't have yet) to bleed the clutch, common sense says I can use a vacuum pump (which I do have), can I, really?

And - damn, that was a pretty short notice! Do they always fail like that, or there's usually a telltale sign or two?

[wkohler]

Look at the pedal bracket. My bet is that it is cracked, and/or broken. Why? Well, with the master being replaced such a short time ago, it was probably a cracked/broken bracket that wore it out. The natural thought was to replace the the master. Here it is again, worn out from the non-linear force on the piston. A cracked/broken bracket will eat one in short order. It doesn't have to be a serious crack to do it, and the crack is rather difficult to see!

You might be asking, "How can this be when x happened, so surely y must be a result of x?" Maybe not. But, let's say you did ask that. It could just be coincidental. Either way, I think your clutch master is bad.

FWIW, the E39 and E46 have very light clutches compared to an M30 E28.

[C.R. Krieger]

I'd try bleeding the clutch system. Sounds to me like air in the lines. Not that it couldn't be a broken pedal bracket ...

[vt]

Bleeding the clutch is the cheapest option, so will be tried first, of course.

So can it be done with a vacuum pump, or I do have to go get the pressure bleeder? If so, which one is the best for the job, keeping in mind that I have total of three cars to maintain for many years ahead? Since I may have to order the master cylinder anyway, I guess buying the pressure bleeder off Internet is an acceptable option, too.

As for the pedal bracket - when I was replacing the accelerator cable, I noted that it looks alien and hand made. I may be imagining things, of course, but I don't think I'd see such welding seams and obviously filed edges on original parts. (like I said before, this car has a very, very exotic childhood and lots of stupid scars in stupid places).

[mooseheadm5]

You can bleed it with a vacuum bleeder, but you may need to put teflon tape on the bleeder nipple threads. After bleeding, you may find that you still need to pump the pedal a few times to get it to come back. Pull it up slowly and push it down, and repeat until you get a good pedal.

[C.R. Krieger]

The clutch system is small. I always gravity bleed it.

Sounds like your bracket may be at the end of its second life ...

[vt]

Not my day, I guess. Tried to use vacuum pump - seems that either bleeder screw was damaged (pinched) or simply designed that way (not round, easier to grab with a wrench) and the vacuum tube can't get a hold on it.

In addition, seems that as soon as I unscrew the bleeder, it starts sucking air through the thread, so there's no way to tell whether the bubbles are coming from the system, or from outside air.

So what did you say were good pressure bleeders, and where do I get the adapter?

[mooseheadm5]

You can bleed it with a vacuum bleeder, but you may need to put teflon tape on the bleeder nipple threads.

In addition, seems that as soon as I unscrew the bleeder, it starts sucking air through the thread

That's why I said that.

[Rob_K]

I usually pull the slave cylinder from the tranny and push piston in by hand several times to force the fluid (and bubbles) back to the reservoir. Then just let it hang overnight for a final gravity bleed.

[vt]

You can bleed it with a vacuum bleeder, but you may need to put teflon tape on the bleeder nipple threads.

In addition, seems that as soon as I unscrew the bleeder, it starts sucking air through the thread

That's why I said that.

Yep, figured that out between the moment I wrote the message and the moment you did Yes, it does work, thank you.

(thinking aloud)

OK, so I took the slave cylinder off (as I expected, the bleeder screw was mauled almost beyond repair, will have to replace it next time) and pushed the air out of it. Bled the system (several times, for I didn't quite realize that I'm pumping too much and the level in the reservoir falls below the clutch intake). Last time, lost some patience and poured the fluid that was just vacuumed out of the system back into it (for it was crystal clear by that time), hoping that bubbles present in it won't matter much and in any case, they'll bleed up in a few hours.

Here's a funny thing, though - when I was installing the slave cylinder back, I realized that I won't have enough strength to overcome the spring resistance, and bled some fluid from the system to move the piston so I can put it back in (that was after the whole system was bled). It is in place all right, and the clutch action is visible (the pedal is firm, the hose is visibly moving when the clutch pedal is depressed), but... the clutch pedal doesn't go all the way to the top. I thought that the fact that I moved the slave cylinder piston shouldn't matter because the master cylinder piston will grab fluid as necessary.

So I guess there are two options at this time that I can see - one (less likely), there's still some air and it will sort itself out. Two, clutch release is busted (I believe that the pedal popped all the way out when I pushed on the slave cylinder, but don't remember).

/me off investigating other options and waiting for the bubbles to dissipate...

Thanks to everyone for your words of wisdom, they've made the life a bit easier

[vt]

I wonder what would be a more probable cause of the pedal not coming all the way to the top - faulty clutch release, or a sticking slave cylinder?

[vt]

[disembodied thunderous voice] It's air, you paranoid overanalyzing twit!

Thanks again to everyone.