Clutch pedal lost pressure

[mslevin]

Hey guys,

I was at the track yesterday and unfortunately had my day cut short due to losing all clutch pedal pressure about 5 laps into my first session. As I was coming into a corner, I downshifted 3-2 and it wouldn't go into second. I figured I just missed the shift, clutched in, and tried again. Nothing- wouldn't go in. I managed to coast into the pits.

The clutch pedal had no pressure at all, and I wasn't able to get the car into gear while it was running. Earlier on the same lap, I did a hard shift 3-4, and it felt slightly "mushy" as it went into 4. I thought my hand had just slipped a little and didn't think much of it.

Looking at the video of when it happened, there is a slight noise (thump/bang) as I shifted into 2nd, and I remember hearing a quiet sounds like metal bouncing around in the bellhousing. I was rev-matching all my shifts and not doing anything weird.

I put a new clutch/pressure plate/flywheel in the car a few months ago (Gripforce Stage 2). I also replaced the slave cylinder at the same time (because I broke it lol) with a remanufactured unit from O'Reilly's.

I haven't had a chance to get the car on stands to check it out yet, but at this point I'm assuming the issue is a failed slave cylinder. There were no major fluid leaks that I could see though, and if the slave exploded I'd expect to see brake fluid everywhere.

Any ideas? Let me know if you need more details.



Gratuitous pic of my car

[E36328Coupe]

All your deductions seem reasonable, have to look when in the air.

[jmo69]

Sounds like a failed slave to me too.

[DarbBMW]

Sounds like the slave or the hydraulic line to the slave. How are you fluid levels? Mine went out and thought it was the slave, but it was a hole in the hydraulic line. Pump it several of times and see if it leaks anywhere, does it return back or stay on the floor?

Sent from my Nexus 5X using Tapatalk

[MazerRackham]

Yeah failed master would have shit the cabin and you would of smelled it for sure. Good luck bro.

[mslevin]

Sounds like the slave or the hydraulic line to the slave. How are you fluid levels? Mine went out and thought it was the slave, but it was a hole in the hydraulic line. Pump it several of times and see if it leaks anywhere, does it return back or stay on the floor?

Sent from my Nexus 5X using Tapatalk

Fluid is full, didn't see any major leaks. If there was a hole in a line I figure I would've seen it dumping everywhere. The clutch does return. Honestly it feels like there's a huge air bubble in the line, but I just don't want to believe that's the case. The clutch worked for two months, with a full track day and 1500+ street miles. Unless something broke and is letting air in?

Yeah failed master would have shit the cabin and you would of smelled it for sure. Good luck bro.

Thankfully I think you're right, not the master. That would really suck, because I definitely am way too big to fix things under my dash lol

[mslevin]

Bringing this back up.

I have replaced the master, slave, hard line, and line from reservoir to master. I cannot get the clutch to bleed properly.

It builds pressure but does not seem to operate the clutch. This is based off me putting the car in gear, depressing the clutch, and having someone try to rotate the rear wheels. (they did not move).

At this point I am going to pull the transmission because I don't know what else to do, and I assume there is a deeper issue here.

What I really cannot figure out is this. Putting it in bold as every time I ask on a forum/FB/in person/whatever, no one seems to pay much attention to it.

I got a fair amount of pressure built on the clutch, almost back to normal. I started the car, and 90% of the pressure disappeared. The pedal still returned by itself after being pushed.

How is this happening? There are no leaks. Fluid level is okay. I have no idea how this can be happening. The only thing I can think of is air bubbles being released from somewhere due to the vibrations of the car starting. I have spent HOURS bleeding the clutch. I've probably run 2 liters of fluid through the system.

Tonight, I am going to try bleeding it again. If I cannot get it working, I will pull the transmission and look for something broken. With the car running, I cannot hear any weird noises coming from the transmission.

Any help is much appreciated. I'm at a loss here.

[mslevin]

Update:

Gravity bled the slave with it out of the car. Bled it with the weird push-in-piston-in-slave thing. Continued to bleed the clutch with the pressure bleeder. Pedal felt pretty good. Started the car and the pedal still felt good.

Put the car in gear, with some resistance. Wheels moving. Clutch in, brakes on, car started to stall. Out of annoyance I jabbed the brakes and the car stalled, and there was a metallic CLUNK. Started the car again, and the clutch works and feels fine. :|

Assumption: an issue with an internal seal in the slave or master, as well as a TOB that fused itself to the pressure plate. Something like that.

Glad its fixed, but again any feedback is appreciated.

[E36328Coupe]

The 328 Slave has the bleed nipple at the bottom, fine for changing fluid and no use at all for bleeding because the air is lighter and sits at the top of the cylinder.
Likely you are compressing the bubbles as part of bleeding and by the time you have the car ready to start fluid has been pushed back past the slave seals allowing the bubbles to expand.

I bleed mine as follows:
Cylinder connected to pipe on car but not bolted to gearbox, dangling down.
Open bleed
Push piston up
Close bleed
Let piston down
Lather rinse repeat until all air expelled from the bleed and new fluid pulled down from the reservoir every time to release the pistons replaces all the aeriated fluid.

[JDStrickland]

I had a clutch master blow out on me once, and the replacement part was defective also. Just sayin'.

You're describing a master cylinder failure.

[mslevin]

I had a clutch master blow out on me once, and the replacement part was defective also. Just sayin'.

You're describing a master cylinder failure.

The master that is currently installed is actually the second new one. First one had a manufacturing defect in the threaded portion where the hardline attaches.

I hadn't ruled it out, but the chances of a second replacement (Febi) master cylinder being defective are very low.

The issue seems to be fixed now. Will update tonight when I can test it again and make sure.


E36328Coupe - I did something similar on my last round of bleeding.

[E36328Coupe]

E36328Coupe - I did something similar on my last round of bleeding.

Need to be not something like but exactly like

[pbonsalb]

I bleed the slave manually. Remove it, hold it so the nipple is up, open bleed, depress piston and close bleed while piston depressed, release piston, and repeat 4-5 times. Hard to do solo and messy unless you can loop a hose from the nipple to a catch can.

Did you change the slave hose? If so did you use the correct length and diameter hose?

To bleed the slave master, you simply depress the pedal about 100 times.