Hello all,

I'm pretty new to the forums, but not necessarily cars. I picked up my 6 speed C5 this past summer and so far has been a great car. Last night a friend of mine asked me if I could get on it; so I did. I don't abuse the car or anything like that, but I do enjoy a good rolling takeoff every now and then. That being said, this one seemed to be more than the clutch could handle. I turned the TCS system off and basically nailed the gas at about 10 mph with the clutch all the way out. As expected, I got some tire spin and so I shifted into 2nd at about 30 and spun through 2nd; everything seemed fine till I hit third and then my clutch pedal seemed to have lost some pressure/ got sticky and I got an immense burnt clutch smell. I did not ride the clutch at all so I was a little confused why I was getting such a strong clutch smell. Immediately I let off and shifted into neutral and parked the car. The car only has 48k miles and never appeared to be abused or mistreated (always serviced on time and all of the fluids were changed before I purchased the car). Nor have I ever noticed any unusual clutch wear. I drove the car later that night and tried to replicate the issue, however the clutch held without any problems. Has anyone ever experienced anything like this?

Only mods: American Racing headers, SLP LM catback, and Blackwing intake.

Any input is much appreciated

Matt

 

No expert by any means but the stock C5 hydraulics suck. My pedal gets funky every time I rip through more than 2 gears unless I keep my clutch fluid changed very regularly.

I wonder if the smell was just the tires and the clutch problems are normal. U usually need to pump my clutch a couple times after a 1-4th gear run just to get it to release at its normal position.

 

pressure plate may not have re engaged thus not putting enough clamping force on the disc allowing it to slip. don't worry, organic discs can take that, you just ground off some material

you need to flush the clutch system as the biggest reason this happens is the sub par hyd system that goes non existent when dirty

use a very high quality fluid like ate super blue or motul 600 for the flush

 

Ahh, that all makes perfect sense gents. Thank you all for the replies! I'll be sure to get the fluid all flushed out with some high quality fluid!

Matt

 

Clutch fluid flush is definitely in order. Check fluid color in clutch master cylinder reservoir, I'll bet it is black signifying contamination. Search for the "Ranger Method" of flushing. Use a top quality hi temp fluid. If the flush does not fix the problem, maybe the previous owner was abusive to the equipment. Hope not, then you are in need of replacement.

 

Mine gets stinky at the track under hard acceleration.

 

Appreciate the responses guys! I went ahead and used the ranger method and flushed the fluid about 3 times. The fluid was pretty black initially so I think that was the source of my issue! Clutch response is much more positive. I think I'm going to have to flush the fluid a few more times, but I think the clutch itself is in good shape!

Thanks,
Matt

 

takes about 20 of doing the ranger method before it remains clear for awhile.

i started with a clear fluid, think it was prestone. once i was able to get most the grime it was only then i switched to super blue.

i managed to revive my clutch back to more or less like stock after enough flushes

 

I wouldn't say they completely "suck". There are inherent things that cause what you're describing and unfortunately the forum response is "crappy hydraulics".

While the factory hydraulics are not the best in a C5, and only slightly improved in a C6, they are a decent setup comparatively speaking. The thing that kills the slaves/fluid is the clutch dust that is contaminating them. This is caused by the dust getting between the seals and body of the slave cylinder and then mixing with the fluid. This is the reason that GM thought to put a rubber boot around said piston/seal assembly on the C6 units. This helps slightly, but, high dust conditions can be a pain.

That said, the reason the clutch pedal sinks to the floor under spirited driving in a factory clutch is, in most cases, NOT the hydraulics. The clutch is slipping, this heat from the clutch slipping builds in the diaphragm spring assembly of said clutch and causes the spring to go "limp". When this happens the setup cannot maintain pedal height as the spring has lost it's tension. When the spring has cooled enough, IE you've stopped beating on the car/it's not slipping as bad, the spring regains it's tension and the pedal functions once again as it should. This, as you can see, has absolutely nothing to do with the hydraulics. The organic materials used in factory clutches are improved from the older version, but, as with any organics, they do put off a lot of dust and the smell is from the heating of the material. Our recommendations to customers are always to make sure you maintain your hydraulic fluid and keep it clean. This, along with a clutch that is designed to hold your power rating, will allow for long life and crisp/clean shifts.

I apologize for the long post, let me know if this makes sense to you or not.

 

I question the heat thing, because I didn't get this on the road course this summer. Happens more when I bang gears repetitively. Now that it's cold out, it seems much worse. I too burned the clutch good once passing a line of slow driving @$$holes, I did a WOT 3-4 and the clutch slipped when I banged 4th. I pumped the pedal back up and all has been well, that was about a year ago and I've tracked the car a half dozen times since then. When I was at sea level in September, the clutch was still good enough to burn through 2nd and give a good scratch into 3rd.

 

There have been some very positive posts about the clutch working better and holding more power after removing the plastic close-out covers on both sides of the bell housing to allow more fresh air into the bell housing. Helps keep the clutch cool and the dust out. I'm thinking I'll be doing that in the spring.

 

If shifting a clutch aggressively you are intentionally causing more heat. Generally most guys aren't power shifting in Road Racing, so only if the clutch is being overpowered would it come to light. Clutch material generally doesn't grab as well when it's cold, so when it slips you are heating it faster which is why I believe it is more noticeable if that makes sense. Higher gears, which offer less torque multiplication as well as increased aero, put more strain on a clutch. Any fluid contamination will also cause slippage. The self adjusting pressure plate in the stock single disc can act funny as well if it hangs up varying plate load, which can happen too. Hope that helps.

I agree that can work as can running without the inspection cover, but you don't want any debris getting in the bellhousing.

 

what exactly is the hp rating for a stock clutch? i am making 424hp/383tq and mine starts slipping around 5500 rpms in second and every gear after if i got onto it in first. At what point is the stock clutch useless? i picked up the car bone stock with just over 30k and the car has only been modded for about 5k they have been "spirited" miles but i have never drag raced the car.

 

There isn't an exact rwhp rating as aerodynamic drag, gearing, weight and traction put different strains on a clutch. Also a clutch holds the most amount of power just after being broken in when new, it goes down hill from there as it wears. Chassis numbers can of course vary depending on calibration and correction factor, so actual hp at the crank in given environment is more important and how the driver actuates the clutch as power shifting/launching a clutch is not the same thing as static fully engaged holding capabilities.

 

If you've slipped it a lot then it's likely done. The LS1 was rated for 350hp. If your number is 424hp at the wheels then your engine power is way over what the clutch was designed to hold.

You could try taking the plastic bell housing closeout covers off on each side of the engine but I doubt that would fix it this late into it slipping.

 

It could also be an oil leak from the seal at the back of the crank. Happened to me after I replaced the clutch the first time, which ruined the Z06 unit.

If you are in 4th about 60-70 and goose it without any clutch action, does it slip?