Air in clutch lines/hydraulics?

[TheBrightSide]

I recently installed a brand new OEM AC Delco (FTE branded) clutch master cylinder; after the clutch pedal died on me and I replaced that as a resort to not replacing the clutch slave cylinder and other related transmission parts (complicated and expensive process).

It’s currently a super hot summer in CA here, with temps spiking well over 100+ F on the daily for the past 2 months or so. I’ve bled my clutch/clutch fluid from the bleeder valve on the slave cylinder, where it sticks out through the transmission bell housing. I also made sure that there weren’t any leaks from me installing the hard clutch line into the new CMC, as well as checking the condition of the lower clutch line at the CSC, and also the clutch fluid hose going to my separate clutch fluid reservoir.

I use high temp, racing DOT 4 brake fluid, that’s well over 500+ F in the dry boiling point. I typically swap out the fluid in the reservoir once every month or every other month, depending on how often I drive. I can see what appears to be either clutch dust particles, or some sort of other tiny debris, settling at the top of the clutch fluid reservoir; which I try to clean out when I do the clutch fluid swap.

Anyhow, my clutch pedal was fine, but I notice that when my engine bay temps spike (esp on hot days), my clutch pedal feels a little softer at the top; just not to the point of actually losing hydraulic pressure and causing “dead pedal”. I have the factory clutch return spring removed, and have rigged up my own DIY return spring (resembling that of a Lingenfelter clutch return spring); but you are still able to feel any play on the top of the clutch pedal regardless.

I sometimes take the cap off of my clutch fluid reservoir and pump the clutch pedal a handful of times, which appears to take away the very barely noticeable “softness” at the top of the clutch pedal. I figured I’d bleed again, but it would simply come as soon as temps spike, and then stay until I’d open the cap and pump the clutch pedal again.

As of today though… I do notice that pumping the pedal actually made the soft spot worse. It’s not generating any loss of pressure or dead pedal, but I think I’ll bleed it AGAIN, and then go from there. I typically pressure bleed my clutch pedal by pumping it, and then jamming a rod/stick between my seat and the pedal; then I go to crack the bleed valve loose on the CSC. This seems to work without issue.

Maybe I’m just not bleeding it enough? The “soft” spot on the very top of the clutch pedal didn’t worsen till about a month in, after I bled it properly a 3rd time. Sometimes pumping it after I put the cap back on the fluid reservoir helps, but I figured that it would typically only work with the cap OFF. I’m so confused now…..

[TheBrightSide]

https://www.camaro5.com/forums/showthread.php?t=537731

Looks like this thread, I’ll link here, has the issue that I’m encountering. I don’t think any gunk should be “jamming” up my CMC though; if that is a potential cause of clutch pedal “sticking”. I’m almost convinced the CSC or CMC seals might be bad and letting in air; unless I replaced the CMC and it’s fine, while the CSC might be going bad….

[TheBrightSide]

Update: Looks like either my CMC is going bad again, or possibly the CSC this time around…. Unless it took 2 months for my new CMC to start going bad, it should also act just like last time. However, the pedal pressure/hydraulics have been fluctuating.

There is no about a solid ~1-1.5” inches of dead pedal/play at the top of the clutch pedal. Pumping it with the cap off doesn’t help; but if the dead pedal gains back a bit of pressure (for some weird, odd reason), then pumping it with the cap off the reservoir, gives back that consistent dead pedal amount.

The fluctuating of the hydraulic pressure is definitely weird. I can tell air is definitely getting in again, since no clutch fluid seems to be leaking anywhere, yet the clutch fluid in the reservoir has begun to rise (usually a sign of air being forced OUT).

I’m going to bleed it from the slave cylinder again tonight, take it for a 25-35 min drive if possible, and then see what happens from there. If either the slave or master are bad, it should begin loosing pressure around that time on a decent length car drive. Other than that, should I bother replacing the clutch line with a braided stainless steel one?

[Coz3z3]

I've had to replace my Clutch Master Cylinder twice in the Z/28 now. I have also changed the fluid a lot just because I track it. Sometimes after a bleed, I get the same effect as you and have that soft spot that doesn't seem to want to go away. So I will get under and bleed it again and sometimes it helps and sometimes it doesn't. The best thing I have gotten was a cheap Vacuum pump. Like: https://www.napaonline.com/en/p/PTTW87030


I have found a cheaper one, but that is just an example. Hook it up into the clutch reservoir, and pump it up to about 15psi or so. Watch the air bubbles just come pouring out and leave it there for about 10 minutes. Once done, works as it should.

[TheBrightSide]

Originally Posted by Coz3z3

I've had to replace my Clutch Master Cylinder twice in the Z/28 now. I have also changed the fluid a lot just because I track it. Sometimes after a bleed, I get the same effect as you and have that soft spot that doesn't seem to want to go away. So I will get under and bleed it again and sometimes it helps and sometimes it doesn't. The best thing I have gotten was a cheap Vacuum pump. Like: https://www.napaonline.com/en/p/PTTW87030


I have found a cheaper one, but that is just an example. Hook it up into the clutch reservoir, and pump it up to about 15psi or so. Watch the air bubbles just come pouring out and leave it there for about 10 minutes. Once done, works as it should.

For sake of elimination, should I just replace the CMC as process of elimination? It helped last time, but also, the last time, it looks like pressure would hold for the bleed after a while, and then go out after a single 30-35 minute drive.

My current one gave out completely when I started bleeding it; not one ounce of extra pressure building up, and I bled out even more than I probably got back out of trying to build pressure up in it. I usually use the good ole’ “block of wood” method between my seat and the clutch pedal, since I have no vacuum pump and I have no one else to help me push and pump up the pedal (like hell).

If that fails AGAIN, or doesn’t work outright, then I’ll go ahead replace the slavr cylinder… Do I need anything to replace anything else, besides the really recommended clutch/flywheel, billet release bearing support, remote bleeder line, and some other parts?

I’m planning to take it to a shop bc of lack of better tools and a high enough lifting lift/jack. I’m sure prices range like hell nowadays, but is the process mainly just removing the trans/bell housing, trans lines, driveshaft, shifter linkage, trans crossmember, and some other parts?

[fz4k98]

You mention there is a pressure feeling change. Does the pedal travel change as far as where it engages and disengages the clutch? I have chased several clutch issues over several years and it will act different depending on the issue.

Clutch master cylinder seal if bad will allow blow by when pushing on the pedal. This will soften the pressure and also cause the engagement point to change or lower.

Heat in the lines can cause the pedal pressure to feel softer and increase the distance the pedal travels through its engagement and disengagement points. Cold may be one third to two thirds of travel and hot may be on quarter to three quarter of travel between engage and disengage.

I would focus on all you can before the slave as it is much easier and cheaper than the slave. i went back to a new clutch master, new line and put a double thickness of heat resistant sleeve on the line from master to slave which made a big difference.

As far as bleeding, an extension line off the slave will allow you to bleed with one person and also allow you to use your foot on the pedal.

You mention heat but how does it relate to the engagement point and disengagement point of the pedal?

[Coz3z3]

Originally Posted by TheBrightSide

For sake of elimination, should I just replace the CMC as process of elimination? It helped last time, but also, the last time, it looks like pressure would hold for the bleed after a while, and then go out after a single 30-35 minute drive.

My current one gave out completely when I started bleeding it; not one ounce of extra pressure building up, and I bled out even more than I probably got back out of trying to build pressure up in it. I usually use the good ole’ “block of wood” method between my seat and the clutch pedal, since I have no vacuum pump and I have no one else to help me push and pump up the pedal (like hell).

If that fails AGAIN, or doesn’t work outright, then I’ll go ahead replace the slavr cylinder… Do I need anything to replace anything else, besides the really recommended clutch/flywheel, billet release bearing support, remote bleeder line, and some other parts?

I’m planning to take it to a shop bc of lack of better tools and a high enough lifting lift/jack. I’m sure prices range like hell nowadays, but is the process mainly just removing the trans/bell housing, trans lines, driveshaft, shifter linkage, trans crossmember, and some other parts?

That I'm not sure of. I replaced mine the first time because the pedal fell to the floor and what not. Then I replaced it again because the same thing. I track it and I believe the heat and stuff breaks the seals. I would go ahead and try to bleed it again, especially with a vacuum pump. I wouldn't replace it before doing that.

[TheBrightSide]

Originally Posted by fz4k98

You mention there is a pressure feeling change. Does the pedal travel change as far as where it engages and disengages the clutch? I have chased several clutch issues over several years and it will act different depending on the issue.

Clutch master cylinder seal if bad will allow blow by when pushing on the pedal. This will soften the pressure and also cause the engagement point to change or lower.

Heat in the lines can cause the pedal pressure to feel softer and increase the distance the pedal travels through its engagement and disengagement points. Cold may be one third to two thirds of travel and hot may be on quarter to three quarter of travel between engage and disengage.

I would focus on all you can before the slave as it is much easier and cheaper than the slave. i went back to a new clutch master, new line and put a double thickness of heat resistant sleeve on the line from master to slave which made a big difference.

As far as bleeding, an extension line off the slave will allow you to bleed with one person and also allow you to use your foot on the pedal.

You mention heat but how does it relate to the engagement point and disengagement point of the pedal?

I was mentioning heat as a potential factor for maybe some sort of heatsoak-related issue(s). I noticed that it would make my clutch pedal has a very tiny amount of play at the top, but not necessarily dead pedal. I probably DID have air in the hydraulics or some other issue, since I somehow was able to remove the reservoir cap, pump the pedal, and get it to become solid again somehow (not normal, right?).

You also mentioned heat wrapping the (hard) clutch line? Would getting rid of the original factory hard clutch line and lower rubber line going to the slave cylinder, help any heatsoak issues? I believe Tick has an upgrade for that, which includes some different sized fittings on the ends.

I also did some research, and it looks like the clutch master cylinder on the manual V6 (RS) models also fit the manual V8 models? This might help me keep costs down… I might as well keep a spare CMC on the side at this rate… I was reading Corvette forums, and it looks like those guys are plagued with clutch issues as well, particularly with the slave and master cylinder…. I’m definitely not trying to keep this as an only car anymore, unless I have a spare car on the side, ready for emergencies.

[TheBrightSide]

Originally Posted by Coz3z3

That I'm not sure of. I replaced mine the first time because the pedal fell to the floor and what not. Then I replaced it again because the same thing. I track it and I believe the heat and stuff breaks the seals. I would go ahead and try to bleed it again, especially with a vacuum pump. I wouldn't replace it before doing that.

Doing it the hard and traditional way, with trying to pump by foot, should work, wouldn’t it? It should still theoretically build pressure if the seals on the master or slave haven’t actually fully blown and/or are leaking clutch fluid out. I was under the assumption that since pumping the pedal didn’t work AT ALL, that the master cylinder at least had to be replaced, to check if a new one would fix the issue.

Also, for the Corvette C6 with the LS3 engine and TR-6060 trans, I believe they had an inferior CMC that was superceded with a newer part/part number. I’ve been using an AC Delco branded CMC, with a clear-colored plastic shaft. Some Corvette forum members mentioned something about their older, inferior OEM part being that same color. I wonder if I should’ve stuck to the GM/Chevrolet OEM part, where the entire part was all black in color.

[fz4k98]

Over a couple years i tried aftermarket cmc and lines that were designed for the heat soak. Eventually i went back to all stock parts with high quality fluid and double wrapped the line from master to slave. The product i used was from heatshield products and called hot rod sleeve. For my situation, this gave best results.

The fluid is still susceptible to temperature swings as pedal is closer to floor on cold days but fine otherwise.

[TheBrightSide]

Originally Posted by fz4k98

Over a couple years i tried aftermarket cmc and lines that were designed for the heat soak. Eventually i went back to all stock parts with high quality fluid and double wrapped the line from master to slave. The product i used was from heatshield products and called hot rod sleeve. For my situation, this gave best results.

The fluid is still susceptible to temperature swings as pedal is closer to floor on cold days but fine otherwise.

Gotcha, so you went back to ALL factory parts? This is in regards to the clutch hydraulics I’m assuming. I’ve heard the same thing as well, especially from people who either opt for the Tick Performance or Ram adjustable CMC, and even the Ideal modified OEM CMC that was discontinued like 2-3 years ago. Guess OEM brand (AC Delco, GM, FTE, Sach) CMC’s are the best, huh…

I was gonna ask for reference, as it looks like the OEM CMC I removed from my 2010 SS, was a GM model, but branded through FTE (P/N: GM 92199594). I found an affordable AC Delco CMC, which I assumed was OEM as well, since it was also FTE branded (P/N: GM 92067134, AC Delco 174-1179). The GM CMC appears to be all black colored, while the AC Delco unit is pretty much identical, except with an opaque-colored plunger/shaft.

I can’t tell if the CMC was ever replaced on my car, but I possibly think so, due to a wonky, wrong sized washer someone placed on one of the CMC bolts, where it mounts to the clutch pedal assembly/bracket/mount. I guess in that case, it’s gone through at least 1 GM CMC, and 1 AC Delco CMC so far. I ordered the same exact one again, and it’s worked good since last night.

Only concern is that after engine temps go up to 220+ F and the ambient temp is like 90+ F, the very top of the clutch pedal gets barely soft, but not enough to actually generate dead pedal (maybe around ~1/8-1/4” of play at most). I opened the reservoir cap and pumped the pedal like 5 times with the car off, after driving, and it came back to a fully solid pedal. Was okay on the 30+ min drive to work, but got the little softness back during the 30+ drive home in the hot evening today. I’ll check to see if the pedal will get solid again after it cools down, and w/o having to pump the pedal with the reservoir open. How do the clutch pedal hydraulics act in super cold weather (sub-30 F weather?)?

I was planning to get one of the aftermarket stainless steel, braided clutch lines. There’s some going for around $75-80, and then the Tick one going for $100-140; only difference is that the Tick clutch line, has a 90-degree fitting on one end (which idk goes to either the CSC or CMC; preference maybe?). The Tick one has the rubber-coated thermal wrap, similar to what’s around most oxygen sensor wires. I still plan on doing what you recommended, and getting either some fiberglass or titanium based heat-resistant wrap/tubing. I actually bought about 4-5’ for my aftermarket oil cooler lines, so this should probably be relatively easy to do.

[TheBrightSide]

Originally Posted by fz4k98

Over a couple years i tried aftermarket cmc and lines that were designed for the heat soak. Eventually i went back to all stock parts with high quality fluid and double wrapped the line from master to slave. The product i used was from heatshield products and called hot rod sleeve. For my situation, this gave best results.

The fluid is still susceptible to temperature swings as pedal is closer to floor on cold days but fine otherwise.

Sorry if I'm grave-digging, but I wanted to kinda input my experience, as my car has gone through what appears to be it's FIFTH CMC... And no, I wish I was actually exaggerating; but I recently just put my 3rd CMC replacement in. The other 2 that failed were the original parts numbers that I posted in this topic thread (GM P/N #174-1179, AC Delco P/N #92067134), and the one that was replaced and came on my car when I got it, was GM P/N #92199594.

The same BS happened again, where my clutch pedal would start dying as I would be driving, and I'd be lucky if I had any clutch hydraulic pressure to disengage the clutch fully and get me home (without needing a tow). I even took your advice and sheathed my new stainless steel braided clutch line, with a fiberglass heat-resistant wrap. Just the SS clutch line alone actually made my clutch pedal feel good in general.

However, it seems to be a hit and miss, as some of my other CMC's have died in one go, and others take days to a week. And once again, there would be no clutch/brake fluid leaking anywhere, simply the seal(s) in the CMC failing (which I'd discover as I replaced the CMC through process of elimination). I also replaced my transmission fluid as well, and would notice the shifting quality decrease over the span of the first month into the next few months, after I replaced the CMC.

My latest CMC that I replaced, actually kept coming back to "normal", for the next few days, after the car would cool down. "Normal", meaning that you would think that air would get in and stay stuck; but no, the clutch engagement point was fine, and the clutch pedal would act like no air had ever gotten in. It wouldn't actually replicate the issue of letting air in, until the car would get up to operating temps (driving for 25-30+ mins or letting it idle during that time).

I got sick of going with OEM parts numbers and decided to take a chance on a Dorman CMC, P/N# CM640176. But as you know already, FTE and Sachs all supply parts for all the other companies that rebrand and sell/distribute the parts. I inspected the markings on the plastic composite CMC, and noticed the difference in maybe like 2 different things, with one being the time/date stamp of production, and some other production or serial number of some kind. Not sure what's even defective at this point, as it seems like my CSC is still obviously fine.

Now... with how weird my very last CMC acted, I decided to take it apart; which basically just included using a flathead to press in the main lock ring, for the plunger to the CMC assembly. Now, I noticed nothing out of the ordinary, except two things; one being that there was what appeared to be silicone lubricant stuck at the end of the CMC, and two being that that same lubricant was what came on the metal part of the plunger and it was now bone dry (which seemed typical).

I didn't initially think the dried out plunger was super important, however, the other spot that I noticed where silicone lubricant had gone, was around the main seal that the plunger used (separate from the main o-ring that is after the lock ring). I'm not sure if maybe the heat soak maybe softened the rubber(?) seal in the CMC chamber, and the combination of contamination with the silicone lube against the seal, maybe caused it to intermittently lose pressure. I was thinking this might be partially important to consider, since I have a remote/separate clutch fluid master cylinder reservoir, and I would notice remnants of what appeared to be clearish debris (resembling silicone) at the top of the reservoir and clutch fluid.

I cleaned the inside of the CMC out, as well as the seals, and then lubricated the metal shaft on the plunger with high temp grease. I actually planned to test the CMC I had put back together, out on another car. I'm kind of confident that it will work again; I just don't know if it will fail, is the issue. Although, I am sort of confident in my theories, this still doesn't give me any sort of comfort or reassurance whatsoever, for the available quality of parts for our mass produced, domestic American cars... Oh, and I was also too afraid to take apart my new Dormant CMC, to check the inside and maybe clean some of the silicone lubricant out..? If this current Dorman CMC goes out.... I'm gonna be at a loss of thoughts as to why. I'm also curious and probably won't ever find out, but I wonder when my bone stock CMC from the assembly line had actually failed...

[bsn]

You don't want to use grease any petroleum in the system will destroy the seals. If you have already put it back on the car you need to pull it back apart clean every remanent of grease to try to salvage the CMC and thoroughly flush the system. Going through that many CMC's make me think someone may have accidently added some power steering fluid in the past.

[J35Y2]

Originally Posted by bsn

You don't want to use grease any petroleum in the system will destroy the seals. If you have already put it back on the car you need to pull it back apart clean every remanent of grease to try to salvage the CMC and thoroughly flush the system. Going through that many CMC's make me think someone may have accidently added some power steering fluid in the past.

I have no idea. The seals looked absolutely fine on the very last CMC I took apart, and there was silicone lubricant residue that was pretty much all at the end of the CMC and around the rubber plunger seal. Seeing as how it contaminated into the clutch fluid, how would you appropriately and adequately lubricate the CMC?

I’ve also flushed the hydraulic system many a times before, and also on the time that I swapped in the new stainless steel clutch line. It definitely is something odd… The new CMC has been doing fine, but I’ve been weary about it and watching the clutch pedal closely, as always…

I figured the brake fluid would technically lubricate the seals and whatnot, although I noticed friction around the plunger. I didn’t know if running something dry like that or without some form of lubricant, would cause excess wear and tear?