I have a 2000 C5 with a big cam and bolt ons making 390/360. I have the LS7 clutch setup and was pretty happy with it until the end of the drag race season. I let someone who actuall CAN drive make a pass in the car hoping for an 11 second time slip (about 20 passes on the ls7 setup). Instead I got a 13 second slip and a clutch burnt to #@#!. After that I didnt really run again but I did notice on high speed runs the clutch pedal would stick. The clutch fluid was black so I sucked it out and did the easy fix (it never fixed it). I noticed it got MUCH worse after I installed a short throw shifter. So this weekend I bled the system the old fashioned way, took it all down and really flushed it. Afterwards I did a couple of high speed runs and the pedal stuck AGAIN and the fluid is black AGAIN (also some black flakes in it).
Does anyone have any suggestions? Could the short throw shifter be causeing it? Can it be the clutch slipping under the heavy load of the WOT runs? It doesn't feel like its slipping but I dont KNOW for sure. I am not launching it hard just running WOT thru third gear. It sticks every time I do this and only made the first high speed run after the flush before it started again.

Thanks guys!
-Ken

 

No-one has been able to post with 100% certainty what causes the famous black fluid or sticky pedal. Some feel its clutch travel (put a block under your pedal or move your seat back so you don't depress the clutch all the way during shifting) to test that theory. Many have claimed it solved the sticky clutch 100%. Others feel that its the slipping clutch or drilling the master will help.

My personal opinion is that black fluid and/or sticky clutch is caused when the clutch slips and/or generates enough heat to affect your slave and/or fluid. Rapid expanision of the fluid due to heat could explain the sticky clutch also.

I did lots of research before chosing a clutch. Lots of guys swear by the LS6/LS7 clutches, but the FACT is that they're both ORGANIC based clutches and do NOT like being slipped! Once they've slipped a few times, they are easily glazed and will continue to slip! I saw my stock clutch when the Tex was installed by CT Corvette and it was definitely glazed and burnt from only a few failed launches (and 120k miles of normal use). Interestingly there was still plenty of clutch material, it just was glazed.

I have a textrailia OZ700, which is more of a metallic/ceramic puck design which doesn't allow for slippage, its more of an on/off style. My fluid hasn't changed colors even after starting in 2nd gear a few times (testing launches) and I've NEVER had the sticky clutch after my Tex install.

JMO.

 

I've got the same problem on my 01 Z after a H/C install last week. Let met say that I don't know what the problem is but I'm having a hard time believing that it's heat. My car does it cold or hot - I realize a slipping clutch will build heat instantly. It's totally RPM based for me. If I drive the car easy, I have no problem. At high RPM it just can't snap back. I don't think my clutch is slipping...it just seems that it's not up to the new power level.

 

GM has a tech bulletin out on this. They say the black leaches out of the rubber color and is NOT bad.

 

Doubt you can recover your clutch. Once it gets really hot the disc material is ruined so it will slip again and get hot again. Some say you can bleed it every day and nurse it, but good luck.
Once the LS1/6/2/7 Luk clutches start sticking it is the beginning of the end. I have experienced this at least a half dozen times with these.
We put a LS7 clutch in a ~525 hp rear wheel LS7 conversion and it was all over in <200 miles. Just a stupid move in retrospect.

 

Contaminated hydrolic fluid CANNOT be good no matter what GM's tech bulletin says... Its not really the color thats bugging me its the sticking, but they are definently related.

-Ken

 

I was getting tuned at Tom's last week and saw your car, very nice! Great numbers for the mods too, has convinced me that a cam is the next thing on my list...

 

Me too.

Recent heads/cam, clutch now sticks to the floor shifting anything over 6k rpm. Have a good friend who is also experiencing the same identical issue after recent heads/cam.

When pushing the car hard, I tend to very lightly rest my foot on the clutch pedal in anticipation of the next shift, and I can feel the pedal almost "growing", pushing back at my foot at 5k+ rpm....based on that, it seems something with the pressure plate is definitely moving/flexing, the wrong way. I have had no feeling/evidence of the disc slipping, the clutch is grabbing and holding just fine, just the pedal feeling goes way weird. After 2 or 3 high rpm shifts, the pedal remains glued to the floor when clutch is pressed, even if the car has coasted a long time, and I don't clutch it till the rpm's are very low..

I originally thought this had to be a hydraulics/heat related issue, but now after experiencing it enough times to sort of test and analyze it's actions, I strongly suspect it's actually a pressure plate issue. The plate has no problem grabbing the clutch (and holds it fine once grabbed), but once released under high a load/inertia situation, temporarily loses it's spring action and doesn't want to grab again, hence, nothing to push the pedal back.

Just my observations..but the reality is no one has ever come up with a true solution, short of going to an aftermarket clutch.

It's not a fluid quality issue.
It's not a pedal overtravel issue
and I don't think it's a slave or master cyl issue.

 

The clutch slips slightly in higher gears when in the max torque band, particularly with new power (torque) mods. This is when the load is greatest just before the shift. You can't necessarily feel it slipping but it gets hot in a second or two due to the clamping force and friction.
Once it has slipped, gotten hot, incurred lots of rpms plus centrifugal force it is too much for the system so the soft street friendly disc fries, never again to have sufficient friction.
After market HP clutches use harder less forgiving but less heat sensitive materials. When a HP clutch chatters it is not graciously slipping smoothly it is jumping between engaged and disengaged, thus the hard starts particularly with a cam that is not happy at low rpms.

 

This sounds like the issue to me too. I REALLY doubt it is slipping, I know the car pretty well and the RPM's are in line with the speed/acceleration. The PP is just not pushing back. I hate to have to toto another clutch but it does look like I am going to have to.

-Ken

 

Everyone is gonna argue with me , but its not heat related. It will do it even if you start your car and bang the gears in the first 30 seconds in the morning. I had 2 cars do this.
Its the pressure plate.

 

The GM tech bulletin is marketing hyperbole. I have never seen any brake or clutch system where black leaches out of the o rings or seals.

It just makes no sense and I don't believe it.

What are these biodegradeable seals that dissolve in brake fluid?

As soon as mine starts to change color I purge it. Just cannot be healthy for the clutch performance.

Give me a brake, no give me a clutch!

 

I saw my Tex pressure plate and it looked like a beefed up LUK clutch cover. Anyone else see the same? Maybe one of the vendors of the Tex can comment on what pressure plate Textrailia uses. I'm just saying I don't get the sticky clutch, but I am pretty sure I have a similar pressure plate as many other kits, including the LS6 style clutch. The friction DISK is the issue (heat generator when slipping) in my opinion.

As far as the black fluid, I have a brand new GM LS6 slave and master and my fluid slightly discolored when my clutch was breaking in (I felt it slip once or twice when it was freshly installed) but hasn't since. This still sounds like a heat issue to me...my clutch doesn't slip (generate heat) and the fluid doesn't discolor.

Remember, in our cars the slave is in direct contact with the pressure plate fingers, not like most other designs where the slave actuates a clutch fork and is nowhere near the pressure plate. If the pressure plate heats up, the heat goes directly to the throwout bearing and slave thru direct contact and convection from surrounding air.

 

Scoundrl,

I just keep posting it over and over and those that want to cure the sticking pedal, cure it with the Protocol. And those that prefer some one-shot cure, fail at it and continue to complain.

Here is the Protocol. Keep at it until the fluid remains clear and clean. If you do that, your clutch pedal won't stick anymore.

The Protocol: check/change the clutch fluid

A single full bleed of the clutch will usually not get rid of the accumulated crud in the hydraulics. That's why your fluid turned black again immediately after you bled it.

Check with any road racers you know. See if they'd run a session with black fluid in their brake hydraulics. They'll say no.

Ranger

 

Exactly.

Ranger

 

It is absolutely heat related. Heat cooks the clutch (brake) fluid. The degeneration accumulates and is made worse by the absorption of water. Once the fluid reached that state, it boils at a much lower temp than shown on the can it came in. Boiling produces gas. Gas will compress under pressure, unlike liquid. Gas in a hydraulic line reduced the delivered pressure. That in turn makes mechanisms that depend on an expected pressure malfunction. Ergo...your pedal sticks.

Solve the problem. Ensure the brake fluid in your clutch is clean and therefore doesn't boil below spec.

Where does the heat come from? Slave is inside the bell housing, in close proximity to the rotating parts that produce friction when they function, eg the pressure plate, the rotating (clutch) disc, the flywheel.

When you launch and do a sequence of strong shifts, burst of enormous heat are emitted from that friction. Degenerated fluid boils, gas is emitted, and the hydraulics fail to function properly.

Fluid cools. Gas is re-absorbed. Things are fine again...until next time.

Clean up your fluid.

Ranger

 

Ranger, I saw your post when I was researching my sticky pedal. I did it 10 or more times before I decided to flush it. This issue is not going away with clean fluid, as soon as I make a high speed pass it sticks and the fluid is black again. There cannot be this much "crud" in the lines, it has to be something making it black. I am torn between heat and the pp malfunctioning. I will just have to spend another $1500 and get the textralia. I am really miffed about it though, this clutch should easily hold my 390 hp. I am going to flush it one more time and re-install my stock shifter, it did seem to get much worse after the short throw was installed. If no luck I'll just eat the money and get the new clutch.

-Ken

 

I can tell you I did not slip during shifts (I slow shifted on purpose) and had pristine dot4 synthetc fluid in this last time. I did not launch the car, took off normal and nailed it around 20mph. After third gear the clutch was sticking again and I had black fluid with little chunks/flakes in it. I want to belive its heat as it looks like it but I have slipped my share of clutches over the years and this thing IS NOT SLIPPING. It holds tight, I can roast the tires dumping it at 60, the rmp's are in line with the speed/acceleration. There HAS TO BE some real explanation for this.

 

^^^ Ken, If the fluid is black and contains particulate matter, it is corrupt. You cannot go from pristine to corrupt fluid in one pass through the gears.

I recently went from pristine to the start of pedal woes in 1200 miles of highway driving with a lot of strong 2-3 and 3-4 shifting but no launches. Six flushes with pedal pumps in between and I made passes at MIR with a normal clutch pedal. LS7 clutch 450 rwhp with 11K street miles and 73 passes at the drag strip, more than half on DRs.

390 rwhp should be fine with Pristine clutch fluid. Pristine means clear and clean after 20 pedal pushes.

Which brand brake fluid are you using in your clutch?

Ranger

 

All strong shifts at elevated rpm entail slip when the clutch pedal is released. I'm not referring to intentional slip.

If you analyze video of a stock Corvette (M6/M12) drag strip pass filmed in HD, you will see "smoke" expressed from the car's tail center on each shift. That smoke is particular matter coming from the clutch friction surfaces. That friction produces heat as a by-product.

Ranger