Ranger

On 2002 C5Z06 with stock LS6 clutch (Luk-made) I avoided clutch pedal issues through 350+ passes on two such clutches by following a rigorous and continuous procedure of changing out the fluid in the master cylinder reservoir.

With that in mind, here are three clutch fluid issue threads to review:

Clutch Pedal Woes--Fluid Impact

C6Z06 Clutch Hydraulic Fluid--the Chevy Spec

Clutch Pedal Woes--Fluid Changing Kit

On the LS7 clutch (also Luk-made), following the same fluid swap procedure, the pedal is completely normal on the shifts through 33 passes, but will hang mid-way up on any launch over 3800 and on launches involving any clutch slip.

So the LS7 clutch is proportionately much less slip-tolerant than any previous LS1/2/6 I've driven.

Ranger

5 Liter Eater

Good reading Ranger. I have begun the regular maintenance on the CMC reservoir. I have changed it out twice now in ~2 weeks and plan to do it every week or so. I will say I have noticed a bit of an improvement but it's not what I would call fixed yet. We'll see with more changes. I am using a mitivac to suck the fluid out of the reservoir and suck as much out of the hole leading to the CMC as I can with the mitivac. After cleaning and refilling I apply vacuum to the hole to suck out any air that I can. I will keep everyone informed on my progress.

I'm sure I could use a complete bleed to get everything out to start fresh so to speak but I am not in the mood to drop the exhaust, drop the tunnel plate with it's numerous bolts and cut up my knuckles cracking the bleeder right now. Damn my cheapness for keping me from spending another $100 on a remote bleeder.

DRR

Unfortunately, the remote bleeder needs to be installed with the clutch out. The remote bleeder allows you to get all the fluid out. I bleed mine once a month, which is obvious overkill, but that is the way I like it. Plus it takes less than 15 min.

5 Liter Eater

Does it? Seeme like you could drop the exhaust, tunnel plate and bell housing inspection cover and be able to unbolt the slave so you could rotate it to unscrew the bleeder. Maybe I'm being overly optimistic. I may contact LAPD and see if they've ever heard of it being done.

5 Liter Eater

OK, yesterday, on my test track, :P I ran out first, second and third gear. The clutch was firm throughout and even when I pushed it in to go to neutral after rapping out third. Normally it would become squishier and/or firmer throughout the WOT redline shifts and if I were to push it in to grab 4th it would go to the floor, maybe stay there, maybe come back up but 4th would most likely have grinded.

So I am starting to become a believer in the boiling fluid theory. This is with only two changes of the reservoir fluid. The first was with a big bottle of DOT3 that I have had forever but remembering that the fluid absorbs moisture I got a smaller bottle of Prestone DOT4 and used that for the second fluid change (DOT3 and 4 are compatible, DOT5 is not) and will use this for all subsequent changes.

I haven't put my foot on the clutch while the RPMs are coming up so I don't know if the slave is still being pushed back.

I plan to change out the fluid this weekend again.

Warp Factor

The "boiling clutch fluid" thing makes sense, but leaves one question unanswered.
Why don't aftermarket clutches seem to have the same problem?
I've only heard of the "sticky pedal" with GM and LUK clutches.

5 Liter Eater

In one of Ranger's threads above he talks about the mode of failure in detail (slave hanging up) but what if we are both right? So the boiled clutch fluid makes it easier for the pressure plate fingers to press the slave back? I may be reaching here.

You can't argue with results though and I apperar to be getting results.

5 Liter Eater

Anyone know where I can get some "Kool Sleve" or the like? I don't want to have to disconnect the CMC-slave hydraulic line to insulate it.

Ranger

This is the product I used on the clutch hydraulics on my 2002 Z06: Koolsox

Threading the Koolsox onto the lines is easier if they're disconnected.

An alternative would be to cut them and sew them in place under the clutch master cylinder and slide them down. Would take patience and good hands.

Ranger

5 Liter Eater

Why use several of the sox rather than one of the sleeve? Could tap the roll pin out of the bottom of the CMC I guess to install it in one piece.

Ranger

It seemed to me that the loose fit of the Koolsox would do a better job in keeping the heat away, just like they do on plug wires.

That was my sense; I didn't do any pre-test.

The clutch hydraulic lines in the C5Z06 were not insulated on the stock LS6; But after all the clutch hydraulic issue on that car (caused by cooked nasty particle-filled clutch fluid), Chevy took two steps on the C6Z for the first time:

(1) they delivered the car with DOT4 fluid in the clutch hydraulics, an upgrade to the DOT3 in the C5Z and a higher temp fluid than is used in the C6Z's brakes
(2) they insulated the clutch hydraulic lines.

So retrofitting these steps to C6s and C5s seems prudent. And when I have an opportunity, I'll further insulate the hydraulic lines with coolsox.

Ranger

5 Liter Eater

I'm confirming Ranger's fluid swap process is a complete success!

I changed the fluid for the third time. This time I actually did it twice. I used the mitivac to suck the reservoir dry and wiped it out. Lots of sediment in there. Filled with new fluid (synthetic Prestone DOT4) and immediately saw sediment coming out of the hole to the CMC drifting into the new fluid. I pumped the pedal and more came out. I left the fluid in and stuck the Mitivac in the hole and pulled ~25 "Hg and pumped the pedal. The pedal got lower as I pumped because of the vacuum being pulled on it. I had to lift it up with my foot. A lot of bubbles came out and also more dirty fluid while under vacuum. I sucked it all out and filled with fresh fluid and pulled a vacuum to get any air bubbles out.

On the way to work I romped on it plenty and did not feel the pedal being pushed back up and the pedal felt very solid throughout all the shifts. No stuck pedal or mushy pedal or firm pedal. I don't know if the Mitivac'ing is adding another layer of protection by helping to suck out more fluid than would normally come out via turley baster and also by getting any air out of the system but since I use the Mitivac to suck out the reseroir I might as well use it for that too. I do know that pulling a vacuum alone without changing the fluid does not cure the problem. I tried that before, thats why I have the mitivac.

I still need to insulate the hydraulic line which should cut down on the fluid change frequency but I definitely have to say that regularly changing the fluid has solved the pedal to the floor problem for me.

Since changing the fluid resolved the problem that debunks my pressure plate theory so I'll have to defer the technical explanation to Ranger, he goes through it well in the links previously posted in this thread. Many thanks to Ranger for contributing to this thread and others relating to this problem. For me at least, I consider this mystery solved.

Ranger

Hey 5 liter, Glad it worked for you. But keep after that fluid whenever it changes color.

And when you get a chance, please post a pic of that "mitivac." Suspect some folks here would consider buying one to help resolve their issue and perhaps avoid the cost of a dealer bleed of the clutch hydraulics.

If folks get the clutch fluid changing religion and keep it, there'd be a lot fewer unnecessary clutch swaps with all their attendant unpleasant follow-on vibration issues.

Ranger

5 Liter Eater

Double post, please ignore

5 Liter Eater

It is not as effective as a full bleed via the bleeder on the slave but it is handy. If you're going to be changing out fluid regularly it's a good idea IMO.

Kschwamy

Just replaced my LUK Gold with an RPS for the exact same reason.

Ranger

Thanks for the pic and comments, 5 Liter Eater.

Ranger

keliente

Gonna give the fresh fluid a try today...

My pedal sticks randomly. I haven't been shifting hard or at WOT at all - just sometimes I will push in the clutch while creeping around the neighborhood and it won't come back up...

Z06ufgrad2002

The fluid changing method works almost every time.

mowton

Hopefully not a stupid question or one that has been asked a million times, but if I'm using the "Turkey Baster" approach to partial change out, can I begin re-filling with DOT 4 Synthetic even though the balance of the fluid is standard DOT 3?

I have seen a marked improvement since starting this routine. Must say after 2 years, the initial change out fluid was quite black.

Thanks

Ed