jmgtp

I've been battling a clutch hydraulic issue for over a year. I don't know what to do to get it right.

I can pump the pedal up and achieve a pretty good pedal and driveable car, only to let the car sit for a a few days, a week, and come back to a mush pedal and a clutch that won't properly disengage.

I've bled it numerous times, same problem. Achieve a good pedal, come back a week later and its mush. I'll mention the fluid level in the reservoir never changes and there are no signs of fluid leaks or wetness.

Last year I replaced the master and release cylinders. Same exact problem. Most recently I used a compressed air powered vacuum bleeder. It achieved a great pedal feel and a properly disengaging clutch. Sure enough, a week later and its not right again. Pump it a hundred or so times and the pedal comes back to acceptable.

The only thing that has not been replaced is the hydraulic line between the Master and Release cylinders, though I don't quite see how that could be the problem.

What can this be? It truly seems that air finds its way back in while the car is not in use. Yet I never see a sign of fluid leakage or a decrease in the fluid level in the reservoir. I even removed the flywheel inspection plate to look for wetness in the bellhousing, nothing there. I don't know what else to try or replace.

I find it hard to believe that the master/release cylinders that I replaced and the new ones are all defective and showing the exact same symptoms. Do I replace the hydraulic line at this point just to cover my bases?

This is a 94, LT1, ZF6.

hcbph

Been there, wrote the book. You still have air is the system. If you want to try the 'simple trick' a former GM mechanic told me, it won't cost you a penny.

Engine off, reservoir full & cap off, pump the clutch about 10+ times rapidly and the last time hold the pedal down. After about 5 minutes, slide your foot off the clutch and let it pop up on it's own. You may have to do it more than once, but then again you don't have anything else to do

Here's the idea behind it. While you're holding down the pedal, any air in the system works it's way back up the line to the U over the reservoir. When you slip your foot off the pedal, the fluid comes back with enough speed to push any air out of the line and back into the reservoir.

I've done it, it works. Good Luck.

jmgtp

Hello and thanks for the reply.

I've also tried this method, I even set my cell phone over the reservoir and recorded video so I could see the bubble burp. The video is on the forum somewhere (last year).

What I found was indeed air bubbles, big ones, then as I repeated the process smaller and finer bubbles until none were observed and the pedal felt good. This produced good results and the car drove fine, but again, some time later (week +) air found its way back in.

I'll try this method again. As I recall, I had to put a plastic bag over my sneaker. Without, there was too much friction between the pedal and the rubber sole to 'slip' my foot off.

hcbph

If you're getting air back into the system, assuming you keep the fluid level up, you have a leak somewhere. I've read where some have gotten bad or leaking slave cylinders. Bad seals or something from what I remember but I can't swear to that. When I had mine done the master and slave came from Napa and it's been fine.

jmgtp

Well, I can't find any evidence of a leak. No wetness, nothing in the bell housing or on the ground. The reservoir level remains the same. I heard about the bad seals in the release cylinders, it look like that problem stretches back at least a decade. These are new parts, its always possible they sat on a shelf that long but this is the 2nd master and 3rd release cylinder I've put in the car, and it always comes back to this same problem.

I might just replace the hydraulic hose as well. If I'm going to throw parts at it, that's' the only thing that hasn't been changed out. Hate to do that, but not sure what more testing or bleeding I can do.

PG-LT4

I just tried the bleeding method and it worked great. I had my slave rebuilt about 2 years ago. I didn't drive it much over the winter. when the weather changed everything was fine until a couple of weeks ago. I thought I was going to have to pull the entire unit. The fluid level was a little low and I'm hoping it was because there was air in the line, there is no sign of a leak.
Thanks for the post

whalepirot

I've lost faith in almost all new parts, whcih is taking most of the fun out of this older car thing.

Hence, I had Jim at Power Torque Systems rebuild with GOOD seals, not the crap in the aftermarket, including NAPA.

Last I checked, that hose wasn't cheap and you see no evidence of leakage.

jmgtp

Can the aftermarket cylinders be rebuilt by Jim or only the originals? My originals are long gone. The after market units are a bit different, they give you sense of being heavy duty because they are cast iron and not stamped steel like the oem pieces.

The fact that I can pump up to a good pedal makes me thing the master cylinder is allowing fluid to bypass. It's just so weird that lack of use is what seems to cause the pedal feel to degrade. If I drove the car daily I'd probably never know there was a problem.

whalepirot

Probably, but he much prefers not. I sent him one from a local yard, that turned out to be too pitted for use and a waste of $50, so after a short wait, Jim got another from a trusted supplier and redid it for me. Therein lies a lesson if shopping for one in a yard, as either type can be found. The dishonest seller in Placentia, CA told me the cast ones were OEM, but a different design...NOT SO!
Also, when the cars sit exposed to the elements, often the cylinders are too pitted for reliable rebuilding and the seals are getting too rare to waste on a poor candidate. The local yard gets littel rain so wetter climes , beware. Jim buys freshly removed ones that are backed, as rebuildable, by his source.
Sure, for a while!

The short lesson for me was to let the expert, Jim, do what he does best. It was the shortest path and least troublesome and expensive over time.

DGXR

On your recurring issue, maybe you can snug up the line fittings a little more to be sure the air isn't seeping in at those joints... unless you've already got them tightened down good.

Jim Jandik reconditioned both my clutch cylinders a couple years ago. Of course I got back the same ones I sent to him, but I seem to recall he had a few rebuilt units on his shelf ready to go. He does not deal with the aftermarket stuff (or at least doesn't hold onto it) so I'm sure the units he's holding are OEM units. Give him a call, hopefully he still has a few.

1993C4LT1

Hope you figure out the issue OP. I want a ZF6 C4, but I've heard of the mostly bad new parts zf6 clutch cylinders. I asked Jim through email if he still rebuilds. He said yes, but only the original Lucas Girling parts. Then he was pretty douchey after that, for whatever reason I'm not sure. Seems I'm not the only one he has spoken douchey to.

DGXR

This is really surprising to hear. Maybe he was just having a bad day.

He went out of his way to answer my calls. And when I made a stupid mistake trying to remove the master, he was very supportive and understanding, and steered me in the right direction. I came away from that whole experience convinced that he is an awesome human being.

whalepirot

When I first called him he was distant, then, as we began to laugh and he learned that I called to listen to him, it changed. He explained that way too many guys call to argue, not listen.... not sayin' ya were, but many do. There is no shortage of pretenders in this hobby, but Jim is not one.

Can anyone blame him? Time is money and he knows his stuff. Why call an expert and then argue about him being wrong?

He went overboard to help me, then sent a fantastic unit. BTW, we laugh a LOT and share interests in other pursuits.. like vintage audio gear and great music.

1993C4LT1

OP forgive me for going off topic. Let me know if you want me to stop replying. Wasn't arguing with him by any means. Just asking simple questions, because I am doing my due diligence before my 93 A4 Ruby sells, and I get a zf6 c4. I have a screen shot of his email. Would post it, but didn't mean to go off topic. Again, hope OP figures out his problem. We would all benefit from it.

DGXR

You might have a different impression of Jim Jandik if you picked up the phone and called him. Email (and all text-based communication) has a way of leading to misunderstanding and misinterpreting the other person's tone. But also you could very well be right, we haven't seen the email It doesn't really matter. He is a good guy and has been extremely helpful to many C4 manual trans owners.

Also, when GM decided to sell all the tooling, machinery and other specialty equipment for producing these clutch hydraulics, Jim bought it. To my knowledge, he is not producing new parts but I guess he could if it was really necessary.

jmgtp

Hi everyone - let's reel it in a bit! We certainly don't need to be bashing any of our C4 experts!

My plan as of now is to remove the master cylinder and install a slightly shorter spacer. Actually, I have a spare space that I want to "slot" and section so I can add/subtract width until I feel like the clutch is releasing in full. Now, I know this won't solve an air in the system problem but this is something I've wanted to do for a while.

When I reassemble I'll be sure the lines are snuggled up good, thought I don't believe that to be the problem.

Lastly, I'm going to bleed the heck out of it again.

If this all fails I see two options. First, try to warranty out the master cylinder with Rock Auto. If they won't honor it or the replacement fails then I'll be searching for a used oem cylinder to send off for a proper rebuild. Wish I didn't throw out the original all those years ago!

jmgtp

I tried something different today. I applied a vacuum to the reservoir.

I was as inspired by this thread:
https://www.corvetteforum.com/forums/c4-tech-performance/3178556-c4-hydraulic-clutch-issues-with-solution.html

I hadnt thrown out the master I recently replaced so thankfully that meant I had a spare reservoir cap. I put a small hole in it and then used the suction cup size adapter from a MightyVac. I plumbed in a catch can and hooked it up to an pneumatic powered vacuum bleeder. I teed in the MightyVac because it has a gauge on it so I could see how much vac I was pulling but the air powered unit did all the work, not the MV.

So, I was able to pull about 17" vacuum for as long as I wanted. I had enough hose length to sit in the car and pull vacuum while operating the clutch, holding the clutch, popping it. You name it, I tried it. Over and over and over again.

The result at the moment is a damn near perfect clutch feel. I didn't drive it as the roof is off and it's raining. But going by pedal feel it is just right. Will it last I don't know. I'll let the car sit till the weekend and fingers crossed the pedal is still there. Hoping it was just air I couldn't get out before.

The theory of vacuum in the reservoir is that any air bubble pockets would expand, move easier and be expelled. Here are some pics.

1993C4LT1

Hope the clutch pedal still feels good Keep us updated

hockeyhead019

Interesting fix! I wonder if you could plumb it into the existing car vacuum system?

Definitely curious to hear the results on this one.

Side note: +1 for dealing with Jim. Spoke with him on the phone after shipping my cylinders to him yesterday. Very pleasant guy who was happy to chat. If you end up needing a rebuild I would send them his way.

jmgtp

If this doesn't work I'll need a new master cylinder. If I can get a replacement under warranty I will. If not, then I need to track down a rebuildable oem one to send to Jim.

As novel an idea it is to use engine vacuum - in a properly working system vacuum is not necessary in the reservoir. Plus an inevitable slosh of the fluid would get picked up by the vacuum and ingested by the engine. Not in my intake manifold! Letting the car sit parked till Saturday. Will drive it then and report back here. Hoping for a long term result.