TTuren

Greetings,
The factory clutch in my 2009 Cobalt SS sedan started slipping intermittently on the highway at 50,000 miles. The car has a ZZP stage I tune (First gear is ramped for a stock clutch and there are no other engine mods) and I opted to replace the clutch with a KY Stage I clutch kit from Turbo Tech. After the install the car had a nasty vibration and the clutch slipped even worse. I opted to replace the entire assembly again with all new parts and ended up with a Stage II kit from Phoenix Friction that included a new flywheel. I ate the cost of the parts and the shop ate most of labor on the second install. That fixed the vibration but the clutch still slips when the car is given any positive boost. Phoenix Friction indicated that the new Kevlar disk would require a 1,000 mile break in period and I'm about half way there right now. 500 miles at zero boost has not done much to improve the situation and I'm betting that this unit is going to need replacement. I'm not hard on clutches and managed to keep the factory clutch in my old SVT alive for 117,000 miles. It was still working fine when we sold it after 17 years with me behind the wheel.

Is there anything besides the clutch assembly that can cause these types of slipping issues? I'd rather not have to go through all of this again after another install. Anything that we may be missing here?

Each assembly has been a complete kit with a new TOB. This is the same mechanic who replaced the Stage III KY (On/off switch) in my first SS. That car had no issues with a factory replacement assembly but they are not rated for the ZZP tune.
Any help would really be appreciated!

ECaulk

iTrader: (6)

What flywheel did you select when replacing the clutch?

If the clutch is slipping already (the Phoenix Friction one) I doubt a more miles will make a difference.

If you end up not getting the clutch to not slip, I'd recommend you go with the GMPP clutch for the LSJ, it fits the LNF just fine and holds higher torque than the stock LNF clutch. I had it on my car for around 100k when I replaced it (not because of slipping, I had the engine out and was replacing other parts, there was reasonable clutch material remaining)

TTuren

Phoenix Friction shipped the flywheel and said it would be a Luk or a Platinum unit. The entire clutch kit came in one box and I don't recall seeing anything on the flywheel itself that would ID the manufacturer. I suspect that it was from Platinum but I can't be sure and PF uses there own part number on the invoice. I tried ordering a Luk unit for the first install but Carid never shipped it. They spent a month telling me that it was on the way though before I forced them to give me a refund.

I had considered a GMPP the first time but I've had two stock clutches slip on the highway (Both factory units in different cars on stage 1 or GMS1 tunes) and I wasn't sure that the GMPP pressure plate would hold over the long term. I know that ZZP and CED both say the GMPP won't take the torque but that the SS community clearly says that it will. The lack of clarity on the GMPP led me to go with the higher pressure plate on the KY unit and then the Phoenix assembly because it has the correct torque rating. Having looked at both new assemblies the Phoenix unit uses a plate that is identical to the pressure plate from GM and KY clearly uses a different pressure plate (No marks or numbers on it though.). The depth of the disks from KY & Phoenix are exactly the same and both were full face Kevlar units.

The car does have an LSD, ZZP engine mounts and Sport Pilot S4 tires. It gets a solid launch for a front driver. The GMPP will really take the load over time? Any idea just how different the plate is for it?

I was considering a full faced unit from Centerforce simply because I have no idea why the current assembly slips but I wasn't sure about using an aluminum flywheel. I was looking at the South Bend Stage 3 as well but wasn't sure if the new flywheel should be replaced. A new Luk flywheel (If I can get one right now...) and a GMPP kit would be cheaper than either of those options but I just don't want any more issues. My wife will shoot me if the car has to go back again...

Thank you for the advice and the rapid response!

Monieg5gt

You need to continue to break it in and stay out of boost. That's your problem. You more than likely glazed the clutch. You need to continue driving it normally. Also spec clutches are very good for the f35 as well. Im frikkin pissed! "New" Clutch slipping terribly! - Cobalt SS Network

ECaulk

iTrader: (6)

I would strongly recommend either the GMPP or the South Bend clutch.

CED and ZZP say the GMPP won't work because they're concerned about warranty coverage.

I did have any issues with my GMPP clutch holding even when I was spiking 26psi on the KO4+, even at sea level (spent some time in California driving "spirited" we'll say).

I've had good experiences with South Bend, a local got one of their stage 4+ back in 2014-2015 and it held great, but it was def a on/off switch. I would lean towards the stage 4 South Bend over the stage 3.

As far as flywheel replacement, if you have the ability to check wear and know what the stock numbers are to confirm there is no wear or weird. Otherwise grabbing a new LUK from Rockauto shouldn't set you back to far.

TTuren

The new clutches slipped just pulling out of the shop and I called Phoenix about the issue when I got the car home. They remarked that it should be fine after the break in period and I've stayed off the boost. It really never had a chance to glaze before it slipped. The biggest issue I have had though is that the car can't be driven in any normal fashion. Anything beyond feathering the throttle on the highway and the damn thing slips. I spent the first week on the freeway in 4th gear. Around town it's OK as long as it gets a pregnant pause on the throttle between shift, zero boost, and light throttle after lockup. I just don't see a future were this unit will hold even stock boost levels but we will see. This will certainly be the last Kevlar clutch that I put in a car though. 1,000 miles to seat a clutch that wants to slip is 2 months of driving and a dice roll.

What Spec clutch would you recommend for this application?

TTuren

You were certainly putting more power through the GMPP than my car can muster! Say, why the South Bend stage 4 instead of the 3?

TTuren

The clutch slipped long before it had time to glaze. It slipped just pulling out of the shop and a quick call to Phoenix had them telling me to give it a 1,000 miles to seat in. I've been off boost but it still wants to slip on the freeway. Spent the first week in 4th gear on the highway. I won't be opting for any Kevlar clutches in the future but I'll give this one it's seat in period.

ECaulk

iTrader: (6)

Higher clamp force, but still full face ceramic. I'm going off of ZZPs site not SBCs, with the stage 3 unit the clamping force is lower and given the torque rating near what the car is making you have little wear before the clutch derates below your torque.

TTuren

I just realized that you attached a thread link. Thank you for finding that one! If mine had started with any grip at all I would guess glazing as well and I still have the new Kevlar disk from KY that I could slip in for free. I don't think that's the problem though.

Monieg5gt

No worries and yes I agree with you if it was slippin right from the beginning like that without even doing anything out of the normal driving conditions like you said then maybe the clutch is defective from the beginning. Another option I forgot to mention is Southbend clutches but I think it was already brought up in your thread I believe by Ecaulk. Also here is the link to ottp for the SPEC Brand clutches.
SPEC Clutches For Cobalt F35 (overthetopperformance.com)