low pedal engagement, not bracket, not master, not slave

taiden · Post by **taiden** » Mar 04, 2012 4:22 PM

Hey all,

I spent the better part of the day trying to figure out why my new-to-me 88 535i has low clutch engagement and a stiff pedal.

Previous owner replaced the master and the slave. They look brand new.

The clutch bracket looks to be brand new, so it would seem it was replaced recently as well. No cracking in the typical places that I have seen pictured on here.

The rubber line to the clutch slave also appears to be brand new.

The clutch grabs really hard with no chatter, but it engages about 0.75" off the floor. It is not so much an issue of being hard to drive, I just dont want to lose the other 0.75" some day and have to worry about it.

I spent most of the day trying to bleed the clutch system a multitude of ways.

I tried pumping the slave cylinder with the bleeder shut.
I tried conventional methods (with a partner, like bleeding brakes)
I tried vacuum bleeding it from the bleeder screw. (No fluid came out, DIY vac bleeder kind of sucks)
I tried manually pumping the clutch pedal at least a hundred times as some people said that works for them as well.

The last thing I will add is when pushing on the clutch (engine off), you can definitely hear some noise coming from the transmission area. I'm expecting people to give me the bad news of it being a bad fork or a bad throwout bearing. I really do NOT want to pull the transmission to do this (although, the guibo does need to be replaced...)

Nothing seems to be working. Any thoughts?

taiden · Post by **taiden** » Mar 04, 2012 6:06 PM

Just made up a tool similar to the bavauto or w/e bleeding tool. The one that holds the slave piston in place so you can bleed with the screw at the top.

The pedal is worse than ever.

Also, when I had the slave installed in the tool, there was about 1.5" of free play at the top of the pedal throw before you could feel pressure build. This matches the pedal throw I was noticing when everything is installed. This leads me to believe that it is a bleeding issue of some sort.

Devinder · Post by **Devinder** » Mar 04, 2012 6:52 PM

sounds like it could be a worn out pivot pin. There is a plastic pin in the bell housing that provides a pivot point for the clutch release arm. When that wears down too far, the pedal gets low and much harder to operate.

If you have a high-mileage clutch (100k+), then the pin is definitely worn out.

taiden · Post by **taiden** » Mar 04, 2012 7:01 PM

Is it easier to pull the engine and transmission out the top, or drop the transmission out the bottom?

Post by **mooseheadm5** » Mar 04, 2012 8:05 PM

Dropping the transmission from the bottom. Much easier. You may want to have access to a clutch kit, or at least a release bearing just in case they are needed while you are in there. If you don't want to have to ever replace that pivot pin again, you can use the part from an 850i 6 speed, which is steel instead of plastic.

taiden · Post by **taiden** » Mar 05, 2012 2:25 PM

Any other theories before I drop the transmission?

Post by **mooseheadm5** » Mar 05, 2012 2:30 PM

Have you got access to a borescope?

If not, you may be able to tell if it is broken without pulling the trans first. The pivot looks like a pointy mushroom and is 10 degrees from the slave cylinder on the other side of the bell housing. You can see where the base of it presses into the bell housing. IIRC, it is hollow up to the cap of the mushroom. If the mushroom cap is broken off, you can get a piece of wire or small allen wrench into the open tube of the base until it hits the release fork. If that is the case, you need one, but just because you can't doesn't mean it isn't broken off further up.

taiden · Post by **taiden** » Mar 05, 2012 3:04 PM

No borescope sadly.

The only reason I am skeptical of it being something clutch/fork/pivot related is this...

When the slave was mounted in the transmission, there was 1.5" of free play before you could feel it initiate forward motion on the pressure plate splines.

When the slave was mounted in a solid bracket, there was 1.5" of free play at the top of the clutch. Shouldn't it be solid right off the bat since brake fluid is not compressible?

Post by **mooseheadm5** » Mar 05, 2012 3:15 PM

I'd definitely bleed it more.

taiden · Post by **taiden** » Mar 05, 2012 4:18 PM

I'm going to try to reverse bleed it with a turkey injection syringe. Let's hope for the best!

Slow_Ballin' · Post by **Slow_Ballin'** » Mar 05, 2012 5:46 PM

Definitely make sure you are bleeding correctly. I have bled various clutches in my life but never on an old bimmer like this. When I tried bleeding it to decrease the "sogginess" and low pedal engagement I did it wrong and had NO clutch when I was done.

Ended up just having it done at a local shop since I was sick of dealing with it and could not get a good bleed.

Are the master and slave OEM replacements or auto emporium garbage? The last master I bought from ass-zone turned out to be WAY too long and could not be used.

Good luck!

taiden · Post by **taiden** » Mar 05, 2012 6:30 PM

I just put probably 2 ounces of brake fluid UP through the slave from the bottom. I'm about to find out how it turned out. Just warming up my fingers after the 27° weather.

taiden · Post by **taiden** » Mar 05, 2012 7:18 PM

ended up putting about 10 ounces back bleeding and the pedal is worse.

taiden · Post by **taiden** » Mar 05, 2012 8:38 PM

OK. I'm very confident it's a bleeding issue. I've been playing with pushing in the slave while holding it in strategic positions... and I have made the pedal feel MUCH better that any of my other attempts. I gauge pedal feel by installing my slave piston stop and testing free play. I'm down to probably 0.75" of free play in the pedal, but I'm aiming for less seeing as I *just* released a bunch of air from the slave and it hasn't had enough time to work up to the top.

This is probably old news for most of you guys on here, but for what it's worth I feel as if most of the problem with bleeding is not just that the bubbles rise as you bleed, it's that a huge air pocket gets trapped in the slave. It's pretty hard to get out due to that strange bend in the hardline that screws into it.

taiden · Post by **taiden** » Mar 05, 2012 9:45 PM

Just another update. Pedal throw (with slave piston stop on) is really low now. About 1/2 inch. But I can still feel a bubble moving around when I squeeze the slave by hand (with slave piston stop removed). It wont come out. It's a decently sized bubble and I'm hoping that will do the trick.

The bubble is worth about 3/8" inch of throw at the slave. That's quite a bit imo.

taiden · Post by **taiden** » Mar 05, 2012 11:29 PM

OK. I'm 99.999% sure it's a bleeding issue. There's a good sized bubble in there that keeps moving in and out as I pump the slave. The pedal is soft now because of it, yet the clutch actuates better than before. If I can get this final bubble out I'm good to go.

I've been pumping the slave. Has anyone figured out a way to promote the bubbles moving up to the top using this method?

Slow_Ballin' · Post by **Slow_Ballin'** » Mar 05, 2012 11:30 PM

I thought I read something somewhere about bleeding with the slave not mounted so that the bend in the hard line is not an issue...

Can't remember what exactly I read or where it was??

kevink00 · Post by **kevink00** » Mar 06, 2012 10:03 AM

I recently went through 2 master cylinders from Bavauto that were defective. The first one had low pedal to start and within a week or so the pedal would go to the floor if I kept constant pressure on it. I checked all over for leaks, but it was the master bypasssing internally. I replaced it with another from Bavauto, and that one still had a low pedal but didn't leak down. I thought, "Well, this is how my clutch is going to feel." It failed catastrophically on my way to work and bypassed completely, becoming completely useless. I sent that one back too and got a refund. I bought a master and slave from Autozone, (yes, Autozone) and now have a high pedal,easier shifting due to quicker clutch disengagement, and months later no problems. Also, I have never had the problems bleeding these systems that some people have. I find that if I can get it drivable, by the second or third day it bleeds itself completely just by driving motion, and frequent, low travel(just to the point of resistance) pumping. You might not want to rule out your m/s cyl, even if they are new.

taiden · Post by **taiden** » Mar 06, 2012 10:35 AM

Thanks Kevin

I've tested for internal bypass by holding moderate pressure over a long period of time. It passes this test, thankfully. But it's worrying to hear that you had a bad master that would have passed this test...

I'm going to the hardware store to pick up an oil can to try reverse bleeding it one last time. If this doesn't fix it, I'm going to be very frustrated indeed!

Previous owner won't pick up his phone to answer simple questions. I can appreciate that he doesn't want to deal with the car, but a 5 minute conversation could save me hours later down the road.

kevink00 · Post by **kevink00** » Mar 06, 2012 10:40 AM

The other thing that may be going on is that the PO might have used a MC or Slave with mismatched diameters. That would also cause a low pedal. Hope you get to the bottom of it. I know how frustrating "simple" things can get.

taiden · Post by **taiden** » Mar 06, 2012 10:43 AM

Well, the previous owner does run a business selling OEM bmw parts... so I would HOPE that he bought the right stuff! We are all human, however...

taiden · Post by **taiden** » Mar 06, 2012 6:00 PM

Hooked up the power bleeder and got the system completely bled. Pedal feels so good now.

The only issue is... clutch is still not disengaging 100%. Horribly hard shifts and on a slight incline in 1st gear with the clutch on the floor, it rolls significantly slower than with the car in neutral.

I adjusted the eccentric bolt that the master cylinder's clevis attaches to. Got a bit more throw, but not enough to get it to disengage fully.

It feels like there is a lot of throw that is not fully engaged but not disengaged. You know how a lot of cars have say 0.25" - 0.5" throw between fully locked clutch and fully open? This has 1-1.5".

Post by **mooseheadm5** » Mar 06, 2012 6:48 PM

I'm still thinking you might have to check that pivot pin. How far did the slave go into the hole before you encountered resistance? The pushrod should pretty much be fully compressed by the time the slave is bolted down. You can check this by tightening it almost all the way down and inserting a feeler gauge into the gap between the slave and the trans until it hits the pushrod. Then, press the clutch pedal. This will leave a little mark on the pushrod. When you pull the slave (again, I'm sure you are sick of that) the mark will tell you where the travel starts and ends.

taiden · Post by **taiden** » Mar 06, 2012 7:08 PM

I used the scribe method as you described it. The mark ended right against the boot when the slave piston was completely relaxed.

Post by **mooseheadm5** » Mar 06, 2012 8:58 PM

How long was the total mark?

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MyE28.com

low pedal engagement, not bracket, not master, not slave

low pedal engagement, not bracket, not master, not slave