Guys, I'm reading this thread because I'm having an issue right now. Since May, I've been running a Spec Stage 2 clutch on a Fidanza 13.5lb SMF. The assembly has always felt balanced, but it has chattered pretty badly. Today at an autocross it started slipping. I didn't smell anything and was able to drive it home (just had to be gentle with throttle). It also feels like it is taking up at the top of the pedal travel.

I am wondering if the pivot stud is loose. But the other possibility is that the pressure plate is dying. This clutch kit only has maybe 2000mi on it, and just autocross runs with no abuse. If it was the pressure plate, and if Spec is no longer supplying quality parts, then what other brands of clutches should I be considering?

 

I don't have a whole lot of experience with SPEC clutches other than the one that has been described in this thread. However, my SPEC stage 2 chattered really bad, so to me it seems like it may be somewhat common with this clutch disc.

I don't think the pivot stud being loose would cause the clutch to slip. It would need to be pulling on the release bearing to get the pressure plate to relieve pressure on the disc and I don't think the stud being loose would cause it to be pulling the bearing.

I would think the the stud being loose would move the stud towards the flywheel making the slave cylinder rod extend further to function. That would make the clutch engagement closer to the floor than the top of the pedal.

I am not an expert on this, but that is where my thinking takes me.

As for brands of clutches, I have not used many aftermarket ones, but I have used the stock ones with good results. The stock ones are getting hard to find though.

Good luck.

 

I think you're right about this. When I was mulling this over in my head, I was forgetting that this is a pull-type p/p. So yeah, I doubt the fork or pivot is the issue. It's low miles on this Spec setup, so I can't imagine that the disk is worn or the friction surface on the flywheel is ruined (the flywheel has a replaceable friction surface, and it was replaced new in May). So it seems like it's narrowing down to the p/p.

Assuming this turns out to be a p/p issue, I would buy a stock Valeo p/p if I could find one. I could use it with a beefier disk (my engine is a 396 that makes C6Z levels of power, so a stock organic disk may not hold up well). I found a few "Valeo" kits on ebay (this is the Valeo kit I see online, part number 52802203), but I really can't tell if they are legit and/or the "good" made-in-US parts from 20 years ago vs new made-in-China stuff that was just still branded "Valeo." Any tips for a reliable source of Valeo pressure plates?

 

The one you linked to is the current Valeo parts. They are the overseas ones. They look almost the same as the originals except for the cast in markings for "Valeo" are a little different. Although these are the made in China ones, I expect I might try them if I can't find originals for my next clutch change. (note that Rock Auto is about $50 less than your link)

I don't know if any of the originals still exist, but if they do my guess is that Jim at Powertorquesystems.com might have them. His web site shows them.

My personal opinion is that finding the best throwout bearing is important. I am not a fan of the design of the pull type clutch we have. The throwout bearing's two halves are moving in relation to each other whenever the engine is running. One side is anchored to the pressure plate and the other is anchored to the clutch fork. I am surprised that a bearing can spin all the time without failing for very long, let alone 100k miles or more. If any of the original INA throwout bearings can be found I think they would be worth the cost. I am suspicious of the China bearings lasting very well and they may be the only options. Again Jim may still have some of the INA bearings.

Good luck.

 

FW bolts are typically shouldered to locate the bolt hardware stuff with washers like that....correct me if Im wrong cheesy not to mention imo dangerous. Thats a LOT of weight spinning around.
Look at the T56 PP bolts very long shoulder only a few threads but thats the way its supposed to be. IN PLACE and postively located at all times
Like to see SPEC come in and straighten us all out.

 

If you're running a single-mass flywheel, you'll need a sprung-hub clutch disk. The OEM disk has a solid hub.

I'm skeptical that your pressure plate has failed so quickly, unless it has seen some pretty serious abuse. I'd carefully examine such things as the pivot, etc, before even thinking about ordering replacement clutch parts.

Live well,

SJW

 

I installed a SPEC Stage 3 plus clutch and their 22 lb "lightweight" billet steel flywheel, along with all new associated everything;

I am very pleased with the results, but it was not a simple "plug and play"

I was shipped the wrong flywheel, one for an F body with a t56 trans, and while it would bolt in, it never would have worked properly; it was exchanged for the right flywheel without any hassle...however. if I had installed it....?

Bleeding the new clutch master and slave was one huge b**ch; finally forced the fluid up into the slave and then into the master and viola...clutch bled in five minutes....not hours;

Before reinstalling the transmission, I left the clutch all hooked up with the pilot bearing tool locating the clutch disc and proceeded to measure the travel of the throwout bearing with the clutch pedal depressed...and the travel was inadequate; at least according to the info supplied by ZFdoc. This required removing the spacer between the clutch master and the firewall and replacing it with a thinner spacer approximately one half as thick. A thinner spacer effectively increases the travel of the piston in the clutch master cylinder and ultimately provides more throwout bearing travel; a side benefit was that the clutch pedal is now at the same height as the brake pedal.

So while everything worked out well in the end, I can only suggest that you check everything and don't go from one step to the next without verifying the fit and function of everything up to that point.

Also check two often overlooked measurements, the radial play at the edge of the outer rim of the flywheel...a small burr at the crank can throw the outer rim of the flywheel off (in my experience) 0.040 inch; and the end play on the crankshaft; excessive play here will definitely impact clutch performance; sometimes a new rear main (#5) bearing with its associated crankshaft thrust surfaces may be needed.

 

Right, I've been running sprung hub on this SMF setup all along.

I have some of the same skepticism. So I took it all apart yesterday. With so little miles on it and non-abusive use, it shows very little wear. What I can see is:

• A minor rear main seal leak that I will certainly fix. However, this has existed for at least 2-3 months with no problems at all, and is no faster of a leak now than it has been before. There were no signs that it soaked the disk material or anything like that. So I find it hard to believe that it caused a relatively fast failure.
• Signs that the p/p wasn't applying even pressure around the full 360* of the friction surfaces on both the flywheel and p/p itself. Most of both surfaces show normal very minor heat marks, but there is about 90* of their arcs that shows no heat marks at all.
• The flywheel side of the disk shows even and normal wear. But the p/p side of the disk appears to only have wear on the inside half of the friction circle. The outside half of the circumference looks like it was never even touched.

None of this explains the clutch takeup moving high in the pedal travel. The friction material was still very plentiful. The fork pivot ball is in good shape and still tight. Throwout bearing seems fine. I don't know if the wear patterns I observe are really indicative of problems or not. The slave cylinder seems fine, and I can't think of a failure mode that would result in the pedal disengaging the clutch at too high a portion of its travel - everything I can think of going wrong there would result in the opposite problem. And the fork did not seem to be applying any force to the throwout bearing - I was easily able to wiggle the bearing around before I took the bellhousing out. I had my son operate the clutch while I watched from underneath, and I saw nothing abnormal.

So my concern is that I'm not really sure what's wrong. I certainly don't want to throw the same parts back in unless I can verify they are good. I don't know any way to bench test a p/p. Does anybody else? I am willing to try a cheap replacement set just to see if it works properly, which would rule out everything besides the current the p/p and disk as a cause. What I can't do is have this car out of commission for weeks. Any suggestions?

 

gotta start somewhere

a small oil leak? any possibility some of it migrated onto the clutch disc? That's one reason I prefer to run a metallic disc; they are not affected by oil contamination...

signs of uneven wear? put a straight edge across the surface of the pressure plate and the flywheel face, either can be warped by friction and heat (usually generated by slippage)...done it myself

and check the axial and radial runout of the flywheel.

Now there are two possible throwout bearings, one for a black tag ZF with a larger I.D. and a second for a blue tag ZF with a reduced I.D., usually reduced by a plastic nylon sleeve (but maybe not always); the black tag throwout bearing will install on a blue tag (but not the other way around) but will not performed as expected since it's larger I.D. does not stay centered on the transmission input shaft housing.

 

Dimensionally everything checks out fine. There are wear signs that indicate uneven clamping pressure around the disc, both on the p/p and flywheel surfaces. I think it is very unlikely that any oil got onto the surfaces at all.

I didn't know that until I saw your post! But I measured and I had the correct bearing.

I am hoping to hear back from Jim at Powertorque. If that doesn't work out, anybody have any experience with McLeod Super Street Pro kits?

 

Also be careful when installing it.

I believe the pressure plate can be damaged during installation which might be why both you and I had uneven clamping. I have seen some shops actually drive them on with an air impact wrench.

The manual says to use a criss cross pattern and tighten the bolts only a turn at a time until it reaches proper torque. (see below)

Good luck.

 

Putting the Zf6 back in is almost a surgical process. First and foremost, as Woolford said, the flywheel mounting area needs to be medical room clean.

QCVette is absolutely accurate about PP installation. It is a tedious process, but very important, especially on these externally balanced set ups.

The pivot stud assembly can be tricky as well, and this is the part made me pull the tranny and start over three times. You said you checked it for wear, I have found that it likes to groove where the clutch fork contacts it. I greased this area really well with a solid axle grease. The other part of this installation, and very important part, is the backing plate. This little piece has a very light torque load, and will snap very easily. However, the pivot stud, being reversed threaded, can slowly back itself out little by little over time. The backing plate prevent this. Also use at least a blue loc tite on it, I used red.

The other part is installation of the trans. It has to go in smooth and clean and all the way before being bolted in. If you try to pull it to the bell housing using the mounting bolts, there will be issues as some point.

Then there is the hydraulic system. Once the factory slave goes, unless you have Jim at Powertorque rebuild it, the aftermarket ones are questionable at best. I was changing them annually until I got one from NAPA, it was their house brand. It held up well for the couple of years, sold the car, it may still be good, IDK. My clutch master was leaking pretty bad as well, you'll know this by greasy carpet under the clutch pedal.

You will get pretty significant chatter at idle in neutral, especially with the 13.5 wheel. This is the ZF trans, and well documented on this forum. It's just the way the gears are cut and that is part of the reason why this trans is almost bullet proof. So take the good with the bad, however, if yours is a bluetag, I think there is a shim available from ZFdoc for the countershaft that eliminates this.

 

Thanks for all that info. FWIW, my engine is internally balanced - no weight in the flywheel. I will double-check the pivot. Yeah, I am used to the loud transmission with my flywheel. It's been on the car since I've owned it. No worries there. I have pondered that shim kit from ZFdoc (mine is a blue tag). I am a little hesitant to mess with the internals of the transmission, but now is the time to do it if I'm going to!

FWIW, I am now pretty sure that my throwout bearing's seal went bad and it spewed its grease onto the friction surfaces. Other than an NOS bearing (which is serious money), if anybody has any other ideas for a better-than-Chinese-quality release bearing, I'd love to know about them.

 

First call I would make would be Jim Jandik at Powertorque or Bill at ZFdoc. I bought my clutch kit from Carolina Clutch, that bearing seemed decent.

 

JMFC that would explain a lot.

so what was the brand name and where did you purchase this fine presumably Chinese product ?

 

I talked to both gentleman, and I am working on a parts purchase for what I hope will be my "forever clutch." I will update.


At Jim's suggestion, I check a couple things on the pressure plate that came out. It looks like there is a slight height difference in one or two of the bolt tabs/legs that mount to the flywheel, which caused uneven pressure around the circle. Wear patterns bear this out. That is probably what caused the clutch chatter. I'm still not 100% sure what caused the slippage - the t.o. bearing grease is one theory. It is also possible that the p/p overheated due to the uneven pressure, and just won't maintain full pressure anymore. This was SPEC Stage 2 kit (including the bearing). It's probably not fair to single them out, since all new OE-style clutches (plates and bearings, at least) seem to be sourced from China and have issues.


It turns out the search for good parts has been harder than actually pulling the clutch out! Quality parts for our pull-type clutches are very hard to come by. I hope I have a solution in the works!

 

Yeah, depending on how uneven the pressure is, if you didn't have full clamping force, that was probably your slippage, especially if it was higher rpm/torque situations. Combination of time and heat. There's really not much of a margin of error on these things. lol

 

Update: Original Valeo LT4 race pressure plate (the fancy factory-specified part for the GM factory race effort, ~2lbs lighter with higher clamping force) and an original INA release bearing are on the way from Jim, to be combined with a Centerforce Dual Friction disk. With any luck at all I'll end up with a smooth-engaging clutch on the street and a little margin of safety on power holding ability for autocrossing and other hoonerific activities. I will update.

FWIW, one of the other interesting options I ran across in my searches is a RAM push-type conversion kit. It uses their hydraulic throwout bearing and comes with a flywheel for under $1k (single disk version - they have a twin disk version for mo' money). It requires some extra steps for setup, but this may eventually be the go-to option if/when the NOS parts supply runs dry. In the meantime, if anybody has a US-made or Brazil-made old Valeo plate, Jim advised that they can be resurfaced and the bolt legs made true and even. For those plates, it may be worth calling him to ask about doing that rather than shopping for replacements.