Here is my problem.
I took my ’88 GT with 33,xxx miles in to my local mechanics today to have the clutch bleed, again. (It was bleed before last August by the same guys.)
Once again they said that they got a little air out of the master cylinder, and a lot of air out of the slave cylinder. But they said that they found NO fluid leaking at either the master or slave cylinder. They also said that they ran the line and they said that they found NO fluid leaking on the line either.

I don’t get it. How can you get air into the hydraulics of the clutch and yet not have fluid leaking from the system?

Any ideas as to how this could occur? Better yet any ideas of how to solve the problem? (I’m stumped on this one.)

All input, ideas, explanations, and suggestions would be greatly appreciated.

Thanks, Bob

P.S. The guys at this shop are damn good. I’ve been bringing all of my cars, (5), to these guys for the last 12+ years with absolutely no complaints. I trust these guys, and I have faith in both their ability, and their integrity.

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"Its nice to be important.
Its more important to be nice."

quote Originally posted by FieroBobo: How can you get air into the hydraulics of the clutch and yet not have fluid leaking from the system?

You cant.

The fluid may be leaking into the boot of the slave cylinder, pooling inside of it, and hasnt filled enough to leak. Or, the fluid is leaking from the master cylinder into the interior of the car, up behind the pedal assembly.

[This message has been edited by AutoTech (edited 03-03-2008).]

crawl under the dash and look up, maybe take a paper towel and rub it on the carpet in the clutch pedal area, i'd bet thats where its leaking
but you may not be able to see it on the carpet thats why i say take a paper towel and rub it on the carpet


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AIM:Onefast2M8
MSN Onefast2M6@hotmail.com
86 GT SC 3800 Intercooled
07 G6 GTP

quote Originally posted by sostock: "What you shouldadid was fetch me that shovel from over yonder, now i'm a fixin' to whip your ass ya dick bag."

[This message has been edited by $Rich$ (edited 03-03-2008).]

I had the same problem years ago on my 86 GT. Like others said, (this may be a little uncomfortable to get to) under the dash. Sometimes the MC can leak fluid and drop behind the carpet. Just look way up and / or feel the clutch master cylinder rod for moisture. There should be zero.

fierogt28

I thought bleeding/de-airing was just a normal springtime occurrence.

<sobs> It is for ME, anyhow.

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'86 GT out for a tan.
'86 Gold SE V8 - fully operational, captain.<for sale!>
'85 Silver SE V6 - automatic for the kid!

Down to three - I think that's enough...

I'm going to have to slightly disagree with Autotech. It is possible for your master cylinder to be leaking across the seal with no external leak. The pedal will get soft and bleeding will generally firm it up again, and the amount of fluid is so small you won't ever see it.

On my 84 the clutch loses pressure and although you're not supposed to be able to do this...I can pump the pedal and build pressure back up enough to shift normally.

[This message has been edited by jscott1 (edited 03-04-2008).]

quote Originally posted by jscott1: On my 84 the clutch loses pressure and although you're not supposed to be able to do this...I can pump the pedal and build pressure back up enough to shift normally.

This is what happens in my car as well. Whats happening is while your pumping, your adding more fluid into the system from the resevior and compressing the air until it operates the slave cylinder. I periodically have to add fluid, or it will run dry.

If your system is not losing any fluid, it just needs to be bled properly. The compressed air slowly pushes the fluid back into the resevior, making you pump it after the car sits for a period of time.

This is how I understand hydraulics, that it is a closed system. You cannot have one without the other.

I'll disagree with almost everyone, but this subject has been discussed at length and frequently since 2001, and the conclusions are:
Air is sucked into the clutch slave cylinder, thru the cup seal. I know it sounds hard to believe, but the cup's lip faces inward only with every slave cylinder I've been inside. The explanation I remember was that it is most likely to occur when the clutch pedal is fully depressed, and then released quickly. Air then works it's way back up into the line. If anyone disagrees, that's fine, because I fought this suggestion too, but finally was convinced of it by a whole bevy of Fiero owners who had been around a lot longer than myself.
You can do a search and see what you come up with, but this is what I remember as the explanation.
Don

quote Originally posted by maryjane: Air is sucked into the clutch slave cylinder, thru the cup seal. I know it sounds hard to believe, but the cup's lip faces inward only with every slave cylinder I've been inside.

This makes sense, but it doesnt.

You are correct about the seal inside the slave. Just like the compression rings on a piston, it seals with pressure. When you disengage the clutch, the fluid is pushed againt the face of the seal, spreading it to make it seal, and in turn pushes out the piston.

Now when you engage the clutch, the force of the springs of the pressure plate pushes the piston of the slave cylinder back. When its doing this, the seal is now pushing against the fluid, spreading it to make it seal, and forcing the fluid back into the bore of the master cylinder.

So either way, there is supposed to be pressure on the seal.

This is how I understand it, but I didnt design it

[This message has been edited by AutoTech (edited 03-04-2008).]

quote Originally posted by AutoTech: This makes sense, but it doesnt.

I agree-it makes no sense, & I don't understand it, but was finally convinced of it. It doesn't happen all at once, very tiny amts of air at a time till small bubbles are formed, over a relatively long period of time. I remeber it was pointed out to me, that no cup seal can seal 100%-they would wear out in no time if that were the case, because there would be no lubrication of the seal at the smallest part of the sealing surface. Air molecules being smaller than fluids, the air can get in.
I won't argue it, I have just come to accept it.

You know what I just thought of...

When you engage the clutch rapidly, maybe the master cylinder is now actually sucking the fluid back into its bore, rather than the slave forcing it back in....like the springs on the pressure plate cant keep up. Doing this just might create some kind of very short, very low amount vacuum?

[This message has been edited by AutoTech (edited 03-04-2008).]

Could be. Been off the internet for nearly 2 years so I may have it a bit askewed.

Well, I dunno why it is, but I do know that I seldom go more than a year without bleeding, and seldom more than three without replacing my slave. The genuine GM parts DO last longer though...

I presently have the same problem , no leak , and i have to bleed maybe once in 2 weeks with the car standing still in my garage .
The slave is 2 years old coming from Fiero Store .
There are a small amount of little bubbles coming out off the slave .
I bleed the gravity way , lifting the car on one side , and after it goes fine for a few weeks .
That problem is usually the master cylinder . Even if you don't see any fluid leak .
I'm gonna do a search today later on .

[This message has been edited by Robert 2 (edited 03-04-2008).]

Im going to have to agree 100% with Maryjane. Infact, I have seen it happen countless times. It's just the nature of the umbrella seal. It can seal against incredibaly high pressures in one direction. But, if there is ANY pressure on the wrong side, or even the slightest vaccum on the pressure side, I can guarentee that air will enter the slave.

Heres where I tell you exaclty what I do with slaves that do this:
First I have to say that I have only seen a couple of slaves that needed to be replaced. Most just need a rebuild.

When I rebuild a slave,
I take the assembly apart.
I remove the umbrella seal, you have to be careful when doing this. One tear and it's over.
I thoroughly clean the seal with WD40 and a rag, inspecting it in the process.
I also clean the piston with a solvent and a wire brush.
Then I put the seal back on the piston.
The slave bore is where the problems occurr. Brake fluid is hydroscopic, It absorbs water which pools up in the slave and causes rust spots in the bore. To clean this up, I take a "brake hone" with my drill and plenty of WD40 and have at it for a while. This is where the problems are really taken care of, the instant that the enitre bore is clean and fresh is where I stop with the hone.
I use a solvemt and some rags to clean out the residue.
Then, I always make sure I apply a really light fresh skin coat of grease into the bore. You don't want much in there, as the more you put in there, the more it can contaminate your fluid.
I put the spring onto the piston and insert the piston into the bore and put the snap ring in.
I push the piston in all the way and add a touch more grease to the inside of the bore.
I found that the light coating of grease is pretty important, it not only allows the installation and free movment of the piston, it acts as an air seal, and keeps air from penetrating past the piston to the umbrella seal where It can begin to give you trouble.
I always install the bleeder with a little bit of grease on the threads, this way air doesn't leak past the threads when you are bleeding the slave. This is a necessity if you are using a mityvac to bleed the system.
I put the pushrod and the boot on the slave.
I wrap my slaves in heat reflective fiberglass tape. This protects and prolongs the life of the slave for years to come.

My biggest concern with the slaves has always been heat. My 88 didn't have the magic heat shielding on the "Y" pipe, and never came with the little heat shield that the 85-87's did. The heat killed the slave every 6 months, each time the problem was the same. I would start to lose the disengagment of the clutch, I would constantly have to let the air out of the slave to keep me going till I could rebuild the slave, yet I wasn't losing fluid. And every time, I would rebuild the slave and be good for another 6 months. Fixing the heat issue, and limiting the amount of grease I used in the rebuild has solved the problem. I never replaced the slave to this day.

I also have to agree with maryjane.
I had this happen on my 85 until I figured out what was happening IN MY case. I tried to explain it here.
https://www.fiero.nl/forum/Forum2/HTML/082567.html

Basically, if a small amount of fluid leaks past the master seal or valve (depends on the type of master) you loose some volume in the pressure side of the system without loosing any total system volume. When releasing the peddle, if the valve or seal has not opened the reservoir fill port then the pressure side goes negative once the slave has returned to it's rest position and will pull air into the slave past the seal. I was able to reproduce this on mine until I rebuilt the master replacing the fill valve seal as shown in the link.

[This message has been edited by Dodgerunner (edited 03-04-2008).]

quote Originally posted by Fierobsessed: When I rebuild a slave

OK so where do you get your rebuild kits for the slave??? master???

On your slave, if you have this type of seal you could try the fix sardonyx247 did that worked for him.
https://www.fiero.nl/forum/Forum2/HTML/076049.html

As far as rebuild kit, I got my slave from Oreily's.
They did not have a rebuild for the master (Gen1 model) but I found one at a clutch/brake store. (for a Jeep Cherokee clutch)
I know others have found them at other parts stores.

I've never had to replace any parts, just clean them. Still, if I could find rebild seals, I'd do it that way.

quote Originally posted by jscott1: I'm going to have to slightly disagree with Autotech. It is possible for your master cylinder to be leaking across the seal with no external leak. The pedal will get soft and bleeding will generally firm it up again, and the amount of fluid is so small you won't ever see it. On my 84 the clutch loses pressure and although you're not supposed to be able to do this...I can pump the pedal and build pressure back up enough to shift normally.

JS, is that on the master side? We are seeing exactly that on Rundlc's DOHC conversion. You can pump the pedal fast four times and have plenty of stroke to shift but if you move it slowly you get nearly nothing.

Terry

Your slave is sucking in air. I have seen this happen many, many times.
Look at the fluid in the resivor over time, if it goes down you have a leak, if it goes up, you are sucking in air.

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"DRIVE IT LIKE A FIERO"
'84 Fiero, engine to be determined
'87Blue GT 3.4L Swap Completed!!!!!!!! Boosted!!!!!!!
Las Vegas Fiero Club
Fiero Road Club Of Northern Nevada

my 2 cents
make sure your slave is not getting to hot next time you feel the air in the line check to see how hot your slave is can cause hyd vapor to form

quote Originally posted by AutoTech: You know what I just thought of... When you engage the clutch rapidly, maybe the master cylinder is now actually sucking the fluid back into its bore, rather than the slave forcing it back in....like the springs on the pressure plate cant keep up. Doing this just might create some kind of very short, very low amount vacuum?

Yes, this happens.
The solution is to make a new double-seal (these are available, though they are somewhat expensive and would require making a new piston) or to add an o-ring next to the existing seal (not possible on the aftermarket pistons/rebuild kits) to allow it to seal without pressure.

Gentlemen,
Thanks for all the valuable info, and the diverse range of opinions and plausible explanations. I will be printing out this thread and reading it carefully during lunch time tomorrow.

One of the things that I like most about this forum is that the breadth, and depth of knowledge and expertice is really quite remarkable. And the willingness of so many to offer up help to a relative newbie is most gratifying.

Once Again, Many thanks to all for your help.

-Bob

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"Its nice to be important.
Its more important to be nice."

I had nearly the same problem... I had no pedal, couldnt figure out what it was, no evidence of leakage... i guess i got lucky when i replaced the slave cylinder and it took care of the problem...
good luck

quote Originally posted by TK: JS, is that on the master side? We are seeing exactly that on Rundlc's DOHC conversion. You can pump the pedal fast four times and have plenty of stroke to shift but if you move it slowly you get nearly nothing. Terry

Terry,

I'm not sure, I have replaced the master, the slave, the pedal, and have an adjustable banjo, yet the pedal goes soft after a few days and I have to pump it up before I take off. Yet the reservoir is still on full and hasn't dropped a bit, and the master is dry. From what I understand only a faulty master can behave that way.

I may replace the master again and see if it improves. By the way, I don't believe the genuine GM parts are available any longer.

[This message has been edited by jscott1 (edited 03-04-2008).]

I had this issues years ago. There was air, no leak. New slave, and master cylinder. It ended up being a bad "new" slave cylinder. I stumbled on it when I had the slave nipple in the closed position, and the clear hose on for bleeding. I found the when I wiggled the nipple, air bubbles started to come up into the hose where I could see. The slave wasn't holding the pressure there. Everything else was perfect, so this was a lucky find. I exchanged the slave cylinder for a new one. Has worked great since.
(with a steel clutch pedal too)
Try this out, see what happens.

I was constantly rebleeding my clutch system until I heard about packing grease in the slave boot and piston. No problems since.

quote Originally posted by AutoTech: This makes sense, but it doesnt. You are correct about the seal inside the slave. Just like the compression rings on a piston, it seals with pressure. When you disengage the clutch, the fluid is pushed againt the face of the seal, spreading it to make it seal, and in turn pushes out the piston. Now when you engage the clutch, the force of the springs of the pressure plate pushes the piston of the slave cylinder back. When its doing this, the seal is now pushing against the fluid, spreading it to make it seal, and forcing the fluid back into the bore of the master cylinder. So either way, there is supposed to be pressure on the seal. This is how I understand it, but I didnt design it

The problem with the slave is not so much as the u-seal but the fact that there is no o-ring in addition to the u-seal to help 'stabilize' the piston within the sleeve. I have never seen a hydraulic cylinder that uses only 1 seal before (or since) the slave on the Fiero in the industrial industry.

Using only the 1 seal allows the piston to move in an axis perpendicular to the motion of travel – which in turn affects the way the u-seal seals. Plus the fact that the piston can rub on the side of the cylinder and thus creating a wear patch so that the bore is no longer round. Every slave I have taken apart you can see the ‘rub’ marks. A little wear on a hydraulic cylinder makes a big difference in how well the seal works.

Now if someone was to machine a groove near the outer end of the piston and install an o-ring it should solve this problem.

Back to topic – as mentioned, they could be leaking (either or both), pull the rubber boots off both so you can see them better – if it is just weeping a bit, it may be hard to see with the boot on. A hydraulic system is sealed, if you are getting air in you have a leak (also check the bleed valve as NickD3.4 meantioned) – if the line has a pinhole, it will be easy to see – have someone press and hold the pedal and look for a spray (wear safety glasses – and DO NOT put your hand/etc over the stream. Fluid under pressure can be injected under the skin – not sure if there is enough pressure in the clutch system to do this, but better safe than sorry).

I recently ran into a situation on mine - kept loosing fluid (no air, at least until the master ran dry), couldn't find a obvious leak, but then I attached a clear hose to the slave bleed valve and drove for a few days. Found that there was fluid in the hose afterwards - seems the valve seat ended up with some pitting and was not sealing very well. It was leaking enough to drain the master after about 3 weeks of daily driving, but not enough that it cause a noticable leak in the bay (not sure if what really happened to the fluid that leak out).

[This message has been edited by Mickey_Moose (edited 03-05-2008).]

So is it just trail an error and keep replacing new hardware until it works??

Gven that I'm not losing fluid I don't see that I have a measureable leak. I don't know 100% that I have air either, I just know I'm losing pressure, and I'm able to build pressure back up enough to drive.

quote Originally posted by jscott1: Terry, I'm not sure, I have replaced the master, the slave, the pedal, and have an adjustable banjo, yet the pedal goes soft after a few days and I have to pump it up before I take off. Yet the reservoir is still on full and hasn't dropped a bit, and the master is dry. From what I understand only a faulty master can behave that way. I may replace the master again and see if it improves. By the way, I don't believe the genuine GM parts are available any longer.

Ok, I'll let you know what we find. My dealer has "restoration parts" but I suspect they are Wagner.

quote Originally posted by jscott1: So is it just trail an error and keep replacing new hardware until it works?? Gven that I'm not losing fluid I don't see that I have a measureable leak. I don't know 100% that I have air either, I just know I'm losing pressure, and I'm able to build pressure back up enough to drive.

If this is the problem you are having (no air and no fluid loss), I would suspect the master cyclinder - the seal between the primary and the secondary is probably leaking.

quote Originally posted by Mickey_Moose: If this is the problem you are having (no air and no fluid loss), I would suspect the master cyclinder - the seal between the primary and the secondary is probably leaking.

That's what I suspect too. Last time I was master cylinder shopping I couldn't find a GM and settled for the Wagner. It never has worked quite right...maybe another one might work better.

Generally, the piston seal on the master is leak free. but there is a little plunger inside the master that has a little rubber seal on it. If that leaks, then it will let the pressure from the piston to pass directly back to the reservoir. So if that seal goes, you will not lose fluid, it would just bleed back into the reservoir. you might have to pump the pedal to get the pressure high enough to force the seal closed, or perhaps the clutch will only disengage for short periods of time. The only solution is to replace the master.

quote Originally posted by TK: Ok, I'll let you know what we find. My dealer has "restoration parts" but I suspect they are Wagner.

I have purchased the parts from the dealer and promptly returned them when they turned out to be cast-iron Wagner replacements.
Then I bought an AC Delco brand master cylinder from a local auto parts chain... and low and behold, it was a black powdercoated welded steel replacement that was identical to the good original GM ones with the exception of having a slightly thinner mounting flange. I don't know if I got the last of them or if AC Delco is actually making and selling good ones.
I tried buying an AC Delco slave but it was just a Wagner or other cast iron slave in the box.

quote Originally posted by Fierobsessed: Generally, the piston seal on the master is leak free. but there is a little plunger inside the master that has a little rubber seal on it. If that leaks, then it will let the pressure from the piston to pass directly back to the reservoir. So if that seal goes, you will not lose fluid, it would just bleed back into the reservoir. you might have to pump the pedal to get the pressure high enough to force the seal closed, or perhaps the clutch will only disengage for short periods of time. The only solution is to replace the master.

That's exactly what's happening with my car!!

I foresee a new master in my future. I really wish I could get lucky and find an AC Delco master but I came up empty last time I looked.

quote Originally posted by jscott1: That's what I suspect too. Last time I was master cylinder shopping I couldn't find a GM and settled for the Wagner. It never has worked quite right...maybe another one might work better.

Which vehicle is this for jscott?

quote Originally posted by jscott1: That's exactly what's happening with my car!! I foresee a new master in my future. I really wish I could get lucky and find an AC Delco master but I came up empty last time I looked.

Looks like you can get them here still.

No one has commented on packing the slave cylinder boot and piston with grease. Even if you don't like the idea it is a diagnostic technique to see if the slave is pulling air.

You can get rebuild kits for the one with the small seal on the plunger. They are available for about $24+. That is what I just payed for one to have on hand last year.
They are not listed for a Fiero but are used on other cars.
Look up a kit for an 87 Jeep Cherokee clutch master rebuild kit.
(this if for the master with the line coming off the middle not the end)

[This message has been edited by Dodgerunner (edited 03-07-2008).]