Clutch hydraulics failing multiple times?

[TheBrightSide]

As the title states, I’m wondering why/how my clutch hydraulics keep having issues. I still have about 10-20% clutch pressure left, which normally if it died, it would’ve hit 0% about, and I wouldn’t have any way of getting into gears without the car/engine off.

I’ve replaced the master cylinder twice already, with OEM parts (GM/AC Delco, Sach, FTE), as well as even replaced the factory clutch line with a stainless steel braided one. Replacing the line I thought, was a great bonus, as it kept the clutch pedal always feeling solid. I sheathed the clutch line in a titanium heat-resistant wrap, to prevent heat soak as well, for an extra measure.

I’m hoping that maybe something random, like the clutch slave cylinder bleeder bolt somehow came loose… But then wouldn’t it constantly be leaking, loose all hydraulic, and leave me stranded..? It doesn’t seem like so, because once again, my clutch fluid/master cylinder reservoir is chock full, and the clutch pedal is having issues. I have a clutch return spring as well, but you can immediately tell that all the clutch travel on top is pretty much just dead pedal.

Has anyone ever had clutch hydraulic issues this bad?? That’s gonna be my 3rd CMC within a year and a half since I got my 2010 SS. It still does have the bone stock CSC, I’m most likely assuming. I was debating on whether that was having issues. But usually after I bleed the clutch slave cylinder, it will give me a final tell on whether the clutch master cylinder is bad…

[TheBrightSide]

I just came back after letting the car cool down, and the clutch pedal pressure has come back?? I wonder if it’s actually back fully…

I tried pumping the clutch pedal with the cap off of the clutch fluid reservoir (I have the separate remote Pontiac GTO reservoir), but it didn’t do a whole lot earlier…

[bsn]

Sounds like air in the system.

[TheBrightSide]

Originally Posted by bsn

Sounds like air in the system.

Welp, it continued doing that for 3 days, which I thought was abnormal. At one point, I thought it was finally the clutch slave cylinder too… I guess not, once again.

For about 3 days, once the car would get up to operating temps either idling or driving for 30-40+ minutes; the clutch pedal would start to gradually lose pressure, leaving me with about 15-25% pedal pressure. When I’d notice it start to “dead pedal” and have slack from the very top down, I try to use the clutch as less as possible, so I didn’t get rid of the remaining hydraulic pressure I had (to get home or wherever).

I would then turn off the car/engine and let it cool down for anywhere from 30 mins to 2-4 hours, come back, and the clutch would either have been right back up to normal, or I’d give it one push (or two) and it would be perfectly fine. Somehow, the air would be pushed back out somehow, cause there was still bo brake/clutch fluid leaking anywhere. And I usually see the clutch fluid level rise if air gets in during a failure like this, and it didn’t rise, and there were also no tiny air bubbles.

Well, yesterday, it did it again during the drive home from work. And like clockwork, I went to check on the clutch pedal after letting the car cool down, and it wouldn’t return. Went to go finally bleed the slave and it wouldn’t hold pressure, even after like 20+ pedal pushes. After about 50+ pushes of the clutch pedal, it finally started getting up to about 75-80% normal pressure, but that wasn’t normal and I wasn’t gonna chance driving the damn thing.

Now… this is an GM “Genuine” CMC, part number 174-1179. It has an opaque-colored pedal/plunger adapter piece. Not sure if that’s related to the older “recalled” or TSB part that the C6 Corvette CMC’s had a revised, superceded new part (number) for. Most of the other CMC’s are either all black in color, or they seldomly have that opaque-colored plastic part on the plunger to the pedal. Not that it’s connected (maybe), but the C6 superceded, revised CMC was also fully black, even up to the clutch master cylinder/fluid reservoir.

I ended up getting a Dorman CMC, and of course, they’re all either supplied with parts from FTE, ATE, or Sachs. I have “some” faith that maybe this CMC won’t shit the bed, unlike the same one I’ve ordered like almost 3 times (and have all failed) by now. Hopefully someone sees my Amazon updated review, and stays away from that.

[TheBrightSide]

Updating this again since I took apart the other CMC that kept failing (GM P/N #174-1179), and found absolutely nothing wrong whatsoever… Only thing that needing some “care”, was the shaft that moved up and down with the plunger/pedal attachment.

I guess the silicone lubricant wears off and somehow ends up making it’s way into the hydraulic system, where remnants stick inside of the CMC. Idk if that was an issue, but there was some silicone lubricant along all of the seals, except for the main o-ring that goes after the locking snap ring in the CMC.

My new Dorman CMC P/N #CM640176, pretty much acted like a brand new CMC. Like any other PROPERLY working CMC, it gained full pressure after about 5 to 10 pushes of the clutch pedal. I pumped it between 30-40 times in between each bleed, and made sure enough air got out. I was even tempted to bleed it again after the car heat cycled, but I checked the pedal and the fluid reservoir with the cap off, and it’s been amazing.

Probably still going to change out my trans fluid soon, since I feel like there’s metallic gunk in there.. Not a whole ton, but more than “normal”, since my shifting quality deteriorated as the other CMC started failing over time. 7-8/10 shifts were always notchy, and I believed it was either inferior ATF that I had filled the trans with, or that the synchronizers and blocking rings or other gearbox parts, were somehow prematurely failing (even though I’ve been babying the car the past 10k miles or so).

I guess we’ll see if I update this by Thanksgiving or Christmas time… I’ll update this as soon as possible, if the shifting quality begins to deteriorate. Normally, I do a trans fluid change and sometimes bleed the clutch, and it will start to feel crappy again within a day or week, so…