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This summer I bought a '96 CE LT4 at a good price because it needed a few things. One of them was a clutch. It chattered horribly. Worst I have ever driven.
I took it apart today and found some things. It has some issues with the single mass SPEC clutch setup. (I will put in a stock dual mass flywheel and clutch that I have so I can get the car running while I decide what I want to do for permanent.)
This is only a 40k mile car and it has an aftermarket clutch already, so I am guessing not many miles on this clutch.
What I found is pictured below.
The flywheel (SPEC SC05S-2) has some serious heat scorch marks.
The pressure plate (SPEC SC421Y ? I do not see their part number on it.) also has some scorch marks, but not as localized as the flywheel.
The flywheel side of the disc is scorched bad on the inside 1/3 to 1/2 of where it should contact. (sorry forgot to take that picture)
The pressure plate side of the disc also shows contact wear on the inside half but not really scorched bad.
The flywheel bolts have a washer on them. They do not fit the bolt very well and look like they are hardware store bulk washers.
I also looked at the transmission input shaft that looks like new. The pilot bearing also looks like new and is the grooved solid one. It also measures the same a new one that I have.
Now some questions?
1. My logic is that the localized heat scorch on the flywheel and patterns on the pressure plate indicate that the problem was either the flywheel or the pressure plate since they are are stationary relative to the flywheel face. If it was the disc, then the marks would be all around rather than in fixed spots on the flywheel. The chances of a fully machined flywheel being that bad are unlikely, so I am guessing that the pressure plate is bad. My thinking takes me to the pressure plate and possibly improperly torqued when installed.
There is a possibility that grease or oil on the surface could cause the failure too, however the rest of the bell housing/flywheel area is dry. If it was greasy due to installation, I thought it would possibly smear a little more and not be as localized as it is.
So my question is do any of you have any thoughts on the cause?
2. Do any of you recognize the pressure plate and/or disc? When I looked to match up part numbers I couldn't find the expected part numbers on these parts and the disc facing material pattern does not look like the ones pictured on SPEC's web site.
3. Has anyone seen washers used on the flywheel bolts?
Some interchange questions also.
4. Can the OEM pressure plate be used on the SPEC single mass flywheel? (I know you would still need a sprung hub disc like from an F-body) Or does it need the F-body pressure plate? Or only a SPEC pressure plate? Or is there a difference?
5. Can the throw out bearings be interchanged between OEM and aftermarket pressure plates, or are they slightly different in attaching to the plate fingers or different heights, etc?
6. Is there any way to test/check to see if a pressure plate is good or bad, other than obvious visual damage to the friction surface?
I have spoken with both of them a couple times when I started the project, and I expect that I will have Jim do some flywheel refinishing and rebalancing too.
I have talked with both of them recently and did not want to keep pestering them if not needed or at least until I can provide some business to them.
I have spoken with both of them a couple times when I started the project, and I expect that I will have Jim do some flywheel refinishing and rebalancing too.
I have talked with both of them recently and did not want to keep pestering them if not needed or at least until I can provide some business to them.
Yes, you right...
All that i can say you about this... That i have hearded and readed around is that zf trans has some problem with single mass flywheel, but think that this is thing you already know
What is the "fit" of the shoulder of the bolts used to the flywheel bolt bore? I'd dimension both of those certainly. The head and the washer doesn't answer many questions.
What is the "fit" of the shoulder of the bolts used to the flywheel bolt bore? I'd dimension both of those certainly. The head and the washer doesn't answer many questions.
The fit of the bolt to the flywheel holes appears normal, it is just the fit of the washer to the bolt that I question. The washer is loose to the bolt and as installed seem shifted to one direction, closer to the bolt on one side than the other.
The fit of the bolt to the flywheel holes appears normal, it is just the fit of the washer to the bolt that I question. The washer is loose to the bolt and as installed seem shifted to one direction, closer to the bolt on one side than the other.
Generally speaking anytime there's a washer used with a flywheel to crank it's either an external or internally serrated piece. I'm quite sure early L98 cars were done this way and most everything else.
I don't believe though that any of the LT cars with a dual-mass did. Just the bolt. The bolt head signifies it's Grade 8 and I see that the washer appears to have a trademark also. Is the bolt a "thread to head" or is there a "shoulder"? Maybe I should have been more specific when I asked. If it were shouldered and because of it's length it would seem the washer occupies all of the shoulder allowing a "poor fit" of the bolt to the flywheel mounting bores.
*** I believe you actually need to measure the bore and the bolt shoulder. I'd guess the bolt has "none or very little" shoulder. Look at a typical flywheel bolt for 7/16" MT and you'll generally see a defined 3/16" or so shoulder.
The bolt in the SPEC flywheel at the shoulder OD = 0.429" (what little bit of it there is)
The washer ID = 0.470 to 0.475 (out of round 0.005) (the washer does have a marking, but I am not sure what that means)
The flywheel is not "wallowed out". In the picture you can not see the flywheel hole. The bolt head is covering the opening in the washer.
On my '90 flywheel set up the bolt did not use a washer.
The bolt holes on both my OEM dual mass and the SPEC single mass measure about 0.450". I don't believe the bolt to hole clearance amount is the problem. I was just concerned that the washer holes were too large a diameter to keep them centered on the bolts. I also had not seen the washers used on a flywheel bolt before, so they looked a little strange to me.
Yes that's certainly not a flywheel bolt. The '90 having the dual-mass also I believe wouldn't have had a washer since it's the same as the LT flywheel. The 4+ steel wheel I'm quite sure would have.
I believe the bolts are responsible for the issue. There might be those that would argue that but I don't believe that clutch package stood a chance from the get go.
Does/will SPEC do a new plate on their assembly? Snapshots don't answer most questions but maybe a very experienced shop could tell you if there was "any save" to the flywheel. Looks can be very deceiving.
The bolt without the washer likely would have stood a better chance of retaining the flywheel to the crankshaft.
*** Do you have the L98 dual-mass from the '90?
The release bearing is no issue, it can be used with any combination that you could create using the original "pull" system. I guess I answered the is the pressure plate any good/can it be check when I asked if SPEC would do a new plate. The SPEC disc? How much is a replacement? A comparable sprung disc of most any brand would likely do BUT you need to be concerned with the thickness of any other than SPEC branding I'd think.
Why do you think those bolts did not retain the flywheel? They are the same fit on the diameter as OEM, they were not loose on disassembly, and there are no marks on the bolts/flywheel/crank to indicate movement.
I am not yet at the point of talking to SPEC about any replacements. I am not sure of the failure cause yet so I can't guess that the SPEC parts were any of the problem. I didn't buy these so I am not expecting them to help out.
I expect that the flywheel can be saved. There are some heat spots, but it is still smooth to the touch and if needing resurfacing, I expect it would only take a few thousandths to clean up. The picture looks worse than I think it really is.
I asked about testing/checking the pressure plate to see if there was any way to tell if it might have been damaged so it created the uneven pressure to make the scorched spots. I am still trying to confirm what the cause of failure is. But I agree, that for the cost, I am not planning to use this pressure plate since it is cheap enough to make sure I put a good one in. Same with the disc, I am not planning to reuse it either.
Yes I do have the dual mass flywheel from the '90 setup.
All of the washers seem to display the same wear/tear so I don't believe you had a clockwise/counterclockwise issue but the flywheel had a "wobble" like a loose road wheel. The input shaft kept the disc attempting to run true because of it's alignment into the crank-shaft insert and the pressure plate and flywheel were the compensation. I've never had a similar problem and I've never used a "thread to head" bolt anywhere there's supposed to be a shoulder regardless of the shoulder height. I mention "thread to head" often, I've seen many failures caused by just that. There's a reason for the shoulder.
How to check a "pull style" pressure plate? I've no idea.
They stopped making new dual mass flywheels for C4's. If you can find a NOS one they are very expensive. Most people say you can not refinish or balance a dual mass flywheel due to the complexity of all the parts in it, although it sounds like Jim at Power torque systems can do it.
Single mass are readily available and less expensive for new. They can also be refinished normally.
This looks like the same Spec clutch kit I installed in my '94 a few years ago. I can't say for 100% certain that my memory of the flywheel fasteners is accurate, but if it is, those are the bolts supplied by Spec as part of the clutch kit, and the flat washers came with them. A quick phone call to Spec should be able to confirm (or refute) this. The bolts and washers appear in the photos to have been through the same passivation process, which also hints that they were furnished together.
I shot a number of photos during the job, but unfortunately, none of them include those fasteners. Here are a few that I took of the Spec setup before and after installing it:
FWIW, it's a bit hard to come up with an explanation for why whoever installed that clutch and FW would have even bothered to use any incorrect fasteners, as Spec furnished a fresh set of FW bolts and pressure plate bolts with the clutch/flywheel kit. With all of the correct fasteners at his fingertips, I can't think of a reason he'd have chosen to not use them.
I'm also having a bit of trouble conjuring a way that the FW bolts or the flat washers would have contributed to such a huge chattering/hotspot problem. Here's a thought: Since you conveniently still have this all pulled apart, why not bolt the FW back onto the crank, reinstall the bellhousing, and set up a dial indicator to measure the axial and radial runouts of the FW relative to the transmission interface surface and centerbore of the bellhousing? If it's running true axially and radially, I think you can discard any thoughts about the FW or its fasteners being a contributor to this problem.
I would agree that if the disc had axial runout that causing this problem, you would see indications of heat and scoring distributed around the surfaces of the FW and plate, and that's not the case here.
My money's on a fault in the pressure plate. Most likely, uneven pressure of the clamping springs.
I'd email these photos to Spec, and get on the phone with them to see if they can offer any insights.
I don't think the OEM plate can be used with a sprung-hub disc. I don't think it has adequate clearance for the larger hub. Spec should also be able to confirm this.
Thanks for posting all the pictures of your clutch.
I did not find any pictures of the disc that looks like ours on any of the web sites. Yours looks exactly like mine, so I expect mine might have been the SC422Y (stage 2) also. Not that it matters since the disc and pressure plate are bad enough I don't think they can be reused.
Interesting that the flywheel bolts sound like they came from SPEC with your clutch and look like mine as you remember it.
It might be interesting to run a dial indicator on the flywheel to see what it is now. If it is still good, it would rule that out as a cause although if I reuse the flywheel it would be after refinishing.
My guess is still the uneven clamping of the pressure plate too.
The sprung hub disc has the springs to the flywheel side so I don't think there would be too much difference. To me the OEM pressure plate fitment looks pretty close to where it would work with the sprung hub, but I agree that someone like SPEC or other vendors could give a confirmation or not. I suspect that talking to SPEC might be a good idea and help to identify the cause.
It certainly might be interesting to check the bell-housing offset while checking all of the other dimensional checks. Misalignment of the bell-housing generally creates issues with release bearings, input shaft retainers, crank-shaft pilots etc. I can't imagine it relating to something like what you've experienced. The housing to block hardware all seemed to be correct?
I can't imagine any vendor supplying bolts like you removed with any package that included theoretically "everything". I've never seen a SPEC package fresh out of the box but those bolts seem unimaginable.
Did the PO mention he did the clutch or was it a "for hire" shop job?
The bell-housing seemed correct. The magnesium one with all the right spacer shims.
I am surprised with the bolts too. I am less surprised by the bolts than I am a with a washer that does not fit tightly around it.
The PO gave me little to no indication of what all was done. He did not do any of the work on anything.
The shop he took it to (a Chevy dealership) screwed up several other things I found on the car too.
Like the front shock top nuts were not screwed all the way down to compress the bushings. There was a 1/2" gap from the top of the bushing to the nut. It made a racket on every bump. The PO said he took it in for that and they didn't find it but looked at sway bar bushings.
On the clutch job, they missed several things on the job too. They didn't put any nuts on of the lower shifter boot retainer ring, so it rattled. They damaged a couple pieces of the interior trim by tightening too much.
They adjusted (or rather misadjusted) the hood. It wouldn't close right. It was easily fixed by adjusting the latches/pins.
And a bunch of other stuff. Their work is one of the reasons I am leaning towards improper tightening of the pressure plate leading to uneven clamping.
I think the PO sold the car because he couldn't work on it and was getting taken by the stealership. He did not know anything about the car. He even stated that it didn't have the "big" engine 350. He said it was a 327. I suspect because his mechanic told him it said 327 on the block (which is the last 3 digits of the casting number) It is an LT4 and all the right parts are there.
For me it makes for a good project, and I think it will turn out as a very nice car for a decent price. I just have to sort it out a little bit.
That is a *likely* a Chinese copy pressure plate (the original Valeo's are not available anymore). You also appear to have a SPEC stage 2 Kevlar clutch disk.
SPEC may tell you otherwise, but I suspect they get that pressure plate from somewhere in CHINA. Just like many other or replacement parts for our vintage cars now come (even those bought from the dealer and that come in AC DELCO Boxes)
Aftermarket and OEM should use the same throwout bearing (unless you are using that new clutch out there for us that is a push-type).
The only difference in throwout bearings depends on the transmission. The black tags use the larger guide tube which requires a bigger ID throwout bearing. The blue tags use the smaller diameter guide tube which uses a smaller ID throwout bearing - it also has a white plastic ring inside the inner diameter.
(((**Note: The guide tubes from a black tag will bolt to a blue tag ZF trans (and vice-versa). Mine, for example,was a remanufactured 'blue tag' but had the black tag guide tube on it and required a 'black tag' throwout bearing. Confusing huh? I converted mine back to blue tag guide tube (and throwout bearing)....)))
Ive done a clutch swap no less than 3x in my 93, using SPEC parts, so I will give my $.02
1. First clutch job... in 2002... SPEC stage 2 kevlar. Worked great until one day the sprung hub center separated from the disk requiring a flatbed tow home. This happened on the highway in the middle of a 3rd gear pull. Note the SPEC supplied components (throwout bearing and pressure plate) appeared to be high quality - except the disk which separated as mentioned in 2006. Note a machine shop balanced the plate and flywheel together and the assembly required minimal balance weight. It was at this time I first installed the alum flywheel.
2. So now the year is 2006: So next I put in a SPEC stage 3+ clutch. This time the SPEC supplied throwout bearing was 'sloppy' with off-axis play in it. It was marked 'CHINA' and was not as good as the original one and the one included in 2002. The SPEC supplied pressure plate still appeared to be high quality requiring very little balance to match it up with the aluminum flywheel. I ran this combo until 2011, when one of the disk's sprung hub springs broke out of his retaining cage on the stage 3+ disk, causing an unusual pulsation, 'feel' in the clutch pedal - so then I had to put in a new clutch AGAIN
3. 2011....I bought another SPEC stage 3+ clutch and noted the clutch disk was slightly thicker (by design) than the stage 3+ disk I had bought in 2006. This time, the SPEC supplied throwout bearing appeared to be something entirely different. It appeared to be a high quality machined bearing of the exact dimensions as the stamped and 'put together' AC DELCO throwout bearing. This time though, the pressure plate did not appear to be as high quality. It had some different stampings - just like yours does (namely that C#####) code on the front. The other SPEC supplied pressure plates didn't have that marking on it. The other ones (From previous years) looks like it had 'VALEO' on it, but that SPEC had gouged the VALEO markings off of it. This C##### pressure plate required quite a bit of material removal to make it balance with my lightweight alum flywheel.
I was also in contact with power torque systems. Jim 'hates' SPEC. I understand he does not sell their products, so I have to take his 'hatred' with a grain of salt. He wants you to buy his products (sometimes via. Carolina Clutch). In my case, SPEC had a superior product for my 520 rwhp supercharged corvette, so I had to go SPEC.
He has had some valid points against SPEC.
He has pointed out that their so-called 'balanced' flywheel pressure plate assemblies are so often 'out-of-balance' that they should NEVER be trusted .
ALWAYS take to a machine shop and get the flywheel/pressure plate assembly balanced to each other (don't forget to take off the counterbalance weight when having this done. lol).
He also is rightly suspicious of SPEC's claim that their pressure plates have more clamp force than a stock valeo pressure plate - yet it looks just like a valeo designed pressure plate (or Chinese knock-off)...just painted a pretty blue color.
I have questioned 'Jerami' of SPEC about this and he swears SPEC either has these made special (or modifies the available replacement pressure plate??) to improve clamp force and he is not about to share whatever secrets they use.
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One thing I always do is compare the 'stack height' of a stock clutch/throwout bearing/disk/pressure plate/flywheel assembly to the 'stack height' of the aftermarket unit I am installing. If I notice big differences, I get on the phone with the manufacturer and ask questions, WHY
I suspect your line of thinking is correct about the pressure plate possibly being the culprit. IF you read my post, you likely noted that the 3rd time I installed a SPEC, the pressure plate appeared to be not as high quality. Their were different casting codes (as yours has in place of where there used to be a VALEO cast mark)
One of the concerns about the overseas pressure plates is that the fingers are more brittle (metal not as high quality) and might not last as many cycles as the VALEO units. I have no idea if this is true or not.
I would CHECK the pressure plate fingers and look for any cracks in the fingers that could cause uneven clamp force. Push down on each one with a tool and see if any of them seem to take more or less force to move.
I am using that pressure plate like you have. Mine is working fine right now. Fingers crossed.
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Oh, I do have a NOS LT4 valeo pressure plate (back when they were made in USA) and a stock (unsprung) clutch disk if you are looking for stock parts. I do NOT have the throwout bearing. PM me if interested.
10-10-2015, 05:58 PM
LT4 Clutch Chatter
