Slave cylinder bleeding woes

[jmile46]

Hey guys,

So in the midst of fixing up my e32, ole reliable e34 decided to give me issues too
—__—. 92 m50 zf 5spd. I noticed when car is cold it no longer wants to go into gear. Nearly impossible. I have to absolutely jam it into first or reverse and it grinds reverse more than half the time. Its gotten worse. I should note when car is off, it rows through gears perfectly fine which has led me to investigate the hydraulics. I checked both slave and master with no visible leaks. Since car was in air I figured hell, might as well bleed slave just to see if it helps. So I had someone in car push clutch pedal in and i cracked bleeder open, then closed, and then released pedal. First time fluid squirted out of bleeder with good pressure. Then second time weak, and clutch pedal stayed to floor. So now the clutch pedal has no resistance whatsoever. It does nothing. So I removed slave and hand bled using rod. I noticed that rod very slowly returns to outward positioning, but doesn’t seem to go all the way out.

After a couple bleeds, all with very weak flow, it seemed like nothing changed. I went back up top and noticed brake fluid that seemed to squirt from somewhere. It was splashed over things. I cant notice where the hell it came from, but possibly top of reservoir? Seems like a tiny hole in it. ( It is a separate reservoir from brakes as this car was a manual swap.) I cleaned it up and had someone watch as I repeated what I had been doing. No new fluid anywhere. So Idk what the hell happened as I don’t believe there is any leaks in any lines and the reservoir still had same amount of fluid.

I guess my main question here is how the hell can I get my clutch pedal to actually work again? Was the slave already bad? And this just broke the last straw? Tomorrow Im going to reverse bleed the system from the slave as I’ve seen people recommend, Im hoping that gets things back to normal.


Here is fluid i found. Circled on left is reservoir and fluid coming from middle.

[ross1]

You could be chasing a red herring.
Does it shift fine once warmed up? If so I'll bet a dollar that someone has filled your gearbox with gear oil. Counter intuitive as it may seem your ZF gearbox is intended to be filled with ATF.
The extra drag of cold gear oil will not allow the synchros to work properly, running it this way and forcing shifts will harm it. Hopefully if this is the case it wasn't done to mask other problems and was only a mistake.

Not sure how you "hand bled" using the slave cyl rod. I suspect you pushed enough fluid backwards through the system to be pushed out the cap vent.
I like to gravity bleed these. Fill the reservoir, remove the slave from the bellhousing and let it hang with the bleeder pointing up. Let it drip until clear, watching fluid level. Re-install and check, sometimes pumping the pedal(bleeder closed) a zillion times purges any remaining air.

[jmile46]

Ross,
I always kind of thought the fluid was wrong as shifting was always sluggish when cold. Once warm it does shift fine. But when car is off, completely cold, it does shift fine. Which Is why I thought hydraulic related, wouldn’t incorrect fluid still give me trouble shifting when car was off? I could be wrong on that.

As soon as I posted this I thought when I hand pushed the slave rod I might have been pushing fluid back up so Im hoping that was the case. I thought I did something wrong with initial bleed, which caused pedal to lose ‘power’. Im really hoping once bled again it works again.

[ross1]

With the car off the gears are stationary so no work to be done by the synchros. I'd be draining and re-filling the gearbox.

[jmile46]

With the car off the gears are stationary so no work to be done by the synchros. I'd be draining and re-filling the gearbox.

Ahh!! Duh. Once I get the clutch pedal back in order that is what I will do!

[moroza]

+1 to Ross' suggestion regarding the cause and what to do about it. With the engine running and the clutch pedal down, difficulty getting into gear the first time could be trans internals, or clutch hydraulics preventing full disengagement. But if you continue to hold the clutch down, take it out of gear, put it back in, and this second time is much easier, the clutch is properly disengaged and therefore the hydraulics are doing their job.

Slave cylinders can seize or bind, but it's rare. Masters can leak internally or externally, but slaves leak only externally. Clutch hydraulics can get stiff at very cold temperatures (my 534i got stiff around -20C) but apart from that, I've never heard of temperature influencing how well that system works, while transmissions very commonly are grumpier to shift when cold. A slave cylinder's internal return spring, if any, is much weaker than the pressure plate and might not be enough to get the pedal back up, or the rod back out, on its own. Sometimes they can be ornery to bleed, in part because air bubbles want to rise, while you're trying to expel them from the lowest point in the system.

Sometimes, pump-crack-pump-crack doesn't work as well as pump-pump-pump-crack.

There should be a small hole in the reservoir for air pressure equalization. If you pushed the slave by hand, fluid squirting out of that hole is normal.

It's not perfectly clear to me what you did and noticed, but it seems likely that your slave cylinder (and the rest of the hydraulics) is ok and might already be bled.

[jmile46]

+1 to Ross' suggestion regarding the cause and what to do about it. With the engine running and the clutch pedal down, difficulty getting into gear the first time could be trans internals, or clutch hydraulics preventing full disengagement. But if you continue to hold the clutch down, take it out of gear, put it back in, and this second time is much easier, the clutch is properly disengaged and therefore the hydraulics are doing their job.

Slave cylinders can seize or bind, but it's rare. Masters can leak internally or externally, but slaves leak only externally. Clutch hydraulics can get stiff at very cold temperatures (my 534i got stiff around -20C) but apart from that, I've never heard of temperature influencing how well that system works, while transmissions very commonly are grumpier to shift when cold. A slave cylinder's internal return spring, if any, is much weaker than the pressure plate and might not be enough to get the pedal back up, or the rod back out, on its own. Sometimes they can be ornery to bleed, in part because air bubbles want to rise, while you're trying to expel them from the lowest point in the system.

Sometimes, pump-crack-pump-crack doesn't work as well as pump-pump-pump-crack.

There should be a small hole in the reservoir for air pressure equalization. If you pushed the slave by hand, fluid squirting out of that hole is normal.

It's not perfectly clear to me what you did and noticed, but it seems likely that your slave cylinder (and the rest of the hydraulics) is ok and might already be bled.

Thats why Im planning on doing a reverse bleed(push fluid up towards reservoir because this seems to be the best way to do it and I’ve only heard great things. At this point if its not the hydraulics then bleeding was certainly a waste of my time. Now my main issue is getting the pedal to have feel again. I still have to bleed. But first Im going to install slave back into bell housing. I should install it with rod all the way extended correct?

[bigsixe34]

I had instant success bleeding the slave cyl in my '92 ZF 5spd with the reverse method. Totally night and day over traditional pump & open. Have a friend stand at the reservoir with a turkey baster and keep the level in check. You don't need much to clear the line anyway.

[jmile46]

I had instant success bleeding the slave cyl in my '92 ZF 5spd with the reverse method. Totally night and day over traditional pump & open. Have a friend stand at the reservoir with a turkey baster and keep the level in check. You don't need much to clear the line anyway.

Good to hear!

[jmile46]

I should also note, my slave cylinder rod has a lot of play in it, it can move around a lot. Is that alright?

[jmile46]

Bleeding is done and nothing. I have no clutch pedal still. Clutch has no resistance whatsoever. What in the hell did I do wrong?

And why does in look like the slave isn’t in all the way?

Nuts are torqued as tight as can be. Am I missing something?!

I bled slave while it was hanging, not in place, although I feel this shouldn’t matter. Any ideas guys? Yet another time I should have just left something alone.

Edit: in case you missed it, when I first tried bleeding using pump crack method, first crack let out a lot of fluid with pressure( first indicator I didn’t need to bleed). Clutch came back out and then second pump and crack very little fluid and clutch stayed to floor. Since then I’ve rebled the reverse way and still no clutch pedal. So it was like this before even taking slave out of bell housing,!if that pinpoints anything.

[moroza]

That doesn't look right. Check your installation again; it looks like the bottom (in the photo) of the slave is flush against the trans, but the top isn't. Suspect the rod isn't seated in the pivot fork correctly.

[jmile46]

That doesn't look right. Check your installation again; it looks like the bottom (in the photo) of the slave is flush against the trans, but the top isn't. Suspect the rod isn't seated in the pivot fork correctly.

That was the 2nd time i tried reinstalling. Same result. I cannot push it in any further by hand. Do you need enough force to compress rod all the way? Because with the space I have I cannot do that. Ill try again as I agree it doesn’t look right. 2nd time pulling it out rod fell out of boot. Is that supposed to be able to happen? Rod has so much damn play I don’t know If I could ever get it to line up properly. Is there a sure way to line it up? The lack of space makes it a pain!

Edit: despite not looking installed right wouldn’t it be close enough to at least cause some feel in clutch? There’s absolutely nothing. I should note I didn’t keep bleeding until new fluid was present in reservoir. Just a couple pumps and noticed no bubbles. Do I have to go all the way till fresh fluid shows up?

[moroza]

It's normal for the rod to flop around. When installed, the slave cylinder piston and clutch fork keep it in place.

From afar, not seeing in person can lead to some runarounds with advice, but if I were in your place, I'd start over: open the bleeder screw to drain fluid, install the slave correctly, then refill and bleed.

In general, it's wise to bleed a little beyond the point that air bubbles disappear. If the existing fluid looks visibly older than the new stuff, good idea to flush it all out. The clutch hydraulics don't see nearly the temperature of brake circuits, but water contamination (inevitable over time) can still lead to corrosion, which leads to leaks and other problems.

[bigsixe34]

The rod doesn't have too much travel. In your picture there looks to be enough of a gap that you could have problems at the pedal still. There's a depression in the fork that is a bit of a pain to seat the pin in properly. If it's not in there then maybe that's the difference you're seeing outside?

[jmile46]

It's normal for the rod to flop around. When installed, the slave cylinder piston and clutch fork keep it in place.

From afar, not seeing in person can lead to some runarounds with advice, but if I were in your place, I'd start over: open the bleeder screw to drain fluid, install the slave correctly, then refill and bleed.

In general, it's wise to bleed a little beyond the point that air bubbles disappear. If the existing fluid looks visibly older than the new stuff, good idea to flush it all out. The clutch hydraulics don't see nearly the temperature of brake circuits, but water contamination (inevitable over time) can still lead to corrosion, which leads to leaks and other problems.

Yeah. I think Im going to baster out old fluid from reservoir and restart. When you say open bleeder to drain you want me to let as much fluid as I can just drip out of bleeder? And then when I do final bleed should i have it already installed? Or can I do it with it hanging because its so tight its hard to bleed when its installed.

[jmile46]

The rod doesn't have too much travel. In your picture there looks to be enough of a gap that you could have problems at the pedal still. There's a depression in the fork that is a bit of a pain to seat the pin in properly. If it's not in there then maybe that's the difference you're seeing outside?

Even if not in the indentation I find it hard to believe it would keep the slave from sitting properly? I don’t know how I can be installing it wrong. Wouldn’t cranking down the nuts pull it in? Im cranking with a half inch socket wrench and both times it stopped at that point.

[moroza]

Yeah. I think Im going to baster out old fluid from reservoir and restart. When you say open bleeder to drain you want me to let as much fluid as I can just drip out of bleeder? And then when I do final bleed should i have it already installed? Or can I do it with it hanging because its so tight its hard to bleed when its installed.

What I meant was to install the slave without any (pressurized) fluid in it. Bleed when it's installed, difficult as that may be.

[jmile46]

What I meant was to install the slave without any (pressurized) fluid in it. Bleed when it's installed, difficult as that may be.

That makes much more sense. To relieve pressure in slave, im just going to want to crack bleeder and let it drip?

[jmile46]

All fluid drained from system. Same result. The slave will not go in beyond this point. As you can see in pictures, the mounts are completely flushed with bell housing but center is still hanging out. Im losing my mind. I don’t see how else this bastard can go in an further. Unless this is proper, which it definitely does not look proper. Its almost as if this is the wrong slave, but its the same one that was working fine in the car 4 days ago. I am truly at a loss here.

[bigsixe34]

Can you remember if the gap was there before you removed it?
I have seen one or two anomalies with slave cylinders. When helping a friend change one on an Elantra years ago, I remember having to reuse the pin from the failed unit in the new one because an "OEM replacement" was off in length by about a centimeter.
Hmm... I just remembered this is not a new piece i.e. above story is not applicable.

[jmile46]

Can you remember if the gap was there before you removed it?
I have seen one or two anomalies with slave cylinders. When helping a friend change one on an Elantra years ago, I remember having to reuse the pin from the failed unit in the new one because an "OEM replacement" was off in length by about a centimeter.
Hmm... I just remembered this is not a new piece i.e. above story is not applicable.

I hate myself for the fact of not taking a picture beforehand. I can’t remember, the piece that seems like it should go in further appears cleaner, as if it was once in there. But I just cannot see this thing as going in any more. It is literally bottomed out.

[jmile46]

Alright so I have a couple thoughts currently.

1. Im still waiting on more opinions on the fitment of the slave. Looks off to me but It truly cannot mount further. The “wings” that go around studs are flush with bell housing.


2. This led me to wonder if the clutch fork, or whatever the divet that the slave rod sits in was broken or out of place in some way. Based on shoving my phone up it appears to be centered and in place. It has little movement up and down which seems good. Im no longer thinking there is an internal issue.


3. I may have neglected to mention but one time when pulling slave out, the rod fell out. I shoved it back in and seemed it worked fine. But I now heard that once this rod comes out of slave, it is no good. Is this true? If so Id say thats my issue and slave is no good.

4. Assuming all else is alright and I need to bleed, I watched a youtube video where someone said if after bleeding clutch pedal still does nothing, they said to push in clutch pedal all the way and hold and then go under pull out slave and hand bleed it. Is this a possibility assuming The master has air in it?? Is it worth a shot despite doing a whole reverse bleed? Can I reverse bleed with the clutch pedal pressed. ?

https://youtu.be/xl5WQCgUjDc

This is video where guy bleeds slave by hand. At end he talks about pushing in clutch and bleeding. This method by hand is a pita when under car with no room so I would like to reverse bleed whole system. Right now there is no fluid in the system. It is completely drained.

I need advice from you gents!

[moroza]

The ears are flush with the bellhousing, really? Both of them? If the rod were too long, bottoming out the slave would result in the clutch being disengaged all the time. That happened on my 544iT (E31 clutch and slave, whose pin was a few mm too long). Something else is wrong with the fitment.

[jmile46]

The ears are flush with the bellhousing, really? Both of them? If the rod were too long, bottoming out the slave would result in the clutch being disengaged all the time. That happened on my 544iT (E31 clutch and slave, whose pin was a few mm too long). Something else is wrong with the fitment.

Both ears are flush yes. Its unbelievable to me, and baffling me. At this point of tired of the frustration especially now wondering if it even works. Im ordering a new one tonight. Im going to install and reverse bleed the system fresh as there is no fluid. Fingers crossed I didn’t mess up the master with all this.