clutch pedal on the floor only when the car is hot

[jeycat1985]

Greetings, E28ers. 1985 535i, 5-speed, 280k on the clock.

Once again, I am dealing with a clutch issue. Replaced the pedal bracket last summer, since it was cracked. Clutch slave replaced when I had the clutch replaced about a year and a half ago. Replaced the clutch master cylinder, plastic nipple, and flexible feed line about 2 months ago. Everything has been working fine, until a couple of days ago. Clutch works great until the car has been driven for about a half-hour, then the clutch pedal goes to the floor and stays there. I can bring it up with my foot, but I get NO engagement/disengagement of the gears(any gear). Limp home, let it cool down, it works fine, until I drive it for about a half-hour again...same problem. No leaks, no loss of fluid at all. Is this a sign of a failing brake master cylinder, or what?

I could understand clutch hydraulic failure, but it shouldn't go away after letting the car sit idle, should it?

[Coldswede]

Water in your brake fluid is vaporizing causing bubbles in your clutch master/line/slave?

[jeycat1985]

I could almost believe that, but I bled the system and put all new brake fluid in when I changed out the clutch master. This problem didn't pop up until I had put almost 2000 miles on the car since the clutch master replacement. If there was water in the lines, it would have shown up during one of my 500+ mile jaunts after I replaced the clutch master.

[bmws forever]

sounds like the throut bearing assembly is sticky. Heat is making it worse. I recall years ago squirting some PBblaster in the correct spot, mostly hidden from view. It worked.

[jeycat1985]

So....I presume that this would be inaccessible unless I remove the transmission from the car. Or did you manage to lube it with the tranny in the car.

[bmws forever]

I lubed it assembled. Use a spray tube.

[Coldswede]

I'd be pretty hesitant to spray oil into my bell housing. Is this one of those undocumented tricks?

[smokey+]

i have a similar issue.

the other day car sat in sun all day (parked slightly uphill) while i was at work.

when i got back to the car after work the clutch went to the floor and would not return. pumping resulting in a squishing bubbly sound. would not return to normal. still stuck to floor.

left it overnight. and returned the next day after work. another hot day. same results.

left it overnight again. ditto.

returned late at night after the temperature cooled down a bit. kinda funny squishy but clutch returned to normal after a few pumps and could be driven.

what is going on here? seems to happen when the car is hot. can almost predict it.

[Mike W.]

I vote defective clutch master if the bracket is good. The clutch system will self bleed if you have enough patience, which I never do. So I suspect that is the problem. A bad slave will use fluid, causing the level to do down. A bad master will not use fluid, usually that is. It's possible, but rare. Actually there is another possibility, what kind of shape is the rubber line to the slave? Those can fail and become like a balloon. I've never had that happen on multiple BMWs, but I've heard of it.

The reason it happens when it warms up is the brake fluid gets thinner and bypasses the bad seal easier.

[1st 5er]

Greetings, E28ers. 1985 535i, 5-speed, 280k on the clock.

Once again, I am dealing with a clutch issue. Replaced the pedal bracket last summer, since it was cracked. Clutch slave replaced when I had the clutch replaced about a year and a half ago. Replaced the clutch master cylinder, plastic nipple, and flexible feed line about 2 months ago. Everything has been working fine, until a couple of days ago. Clutch works great until the car has been driven for about a half-hour, then the clutch pedal goes to the floor and stays there. I can bring it up with my foot, but I get NO engagement/disengagement of the gears(any gear). Limp home, let it cool down, it works fine, until I drive it for about a half-hour again...same problem. No leaks, no loss of fluid at all. Is this a sign of a failing brake master cylinder, or what?

I could understand clutch hydraulic failure, but it shouldn't go away after letting the car sit idle, should it?

...and the fix was?

[gfoto]

I have the same problem plus I get leak under the car. The problem started when I left the car on the sun for 2 hours, and when the problem occured the red light by the handbrake light turned on....any ideas???

[Xenocide]

Well, if it's leaking brake fluid get under there and find out where it's leaking from. Replace that part, job done

Likely candidates are the clutch slave or any of the soft lines, but it easily could be a rusted hard line. You just won't know until you take a look.

[ldsbeaker]

The clutch system will self bleed if you have enough patience, which I never do.

So THAT explains why my clutch started acting PERFECTLY this week...

[shagrath]

There's not that many components to a manual transmission brake fluid line setup, so there's not much to inspect. If it leaks, replace the part. Look at all the lines. Spraying MPL in the tranny to lube the throwout bearing makes sense and won't hurt anything.

[Xenocide]

There's not that many components to a manual transmission brake fluid line setup, so there's not much to inspect. If it leaks, replace the part. Look at all the lines. Spraying MPL in the tranny to lube the throwout bearing makes sense and won't hurt anything.

Spraying MPL anywhere near the clutch sounds like a bad idea to me. It doesn't take that long to drop the transmission, I'd much rather do that and replace the bearing.