A question for anyone that has done a single mass flywheel, clutch, pressure plate, release bearing conversion from AMS Automotive on a 1993 ZF6(part #1610).
All the parts that I have seem to be correct for the application but when installed, the release bearing ends up approximately 1/2" too far back (towards the trans). It is throwing the angle of the fork out so much that the arm of the fork comes in contact with the rotating pressure plate.
I took measurements of the old dual mass setup using the edge of the ring gear and the face of the release bearing, there is about 1/2" difference.
Has anyone dealt with this issue with this kit?

 

Are you sure that the clutch disk is facing the correct way? Is it labeled with a "gearbox side" or "flywheel side" printing on the center of the disk? If not, the part with the longer snout / spline protrusion goes toward the engine, and the shallower face of the clutch disk goes toward the gearbox. This way the TO bearing has more space and is closer to the flywheel, giving the fork more angle clearance.

Only other thing I can suggest is to make sure that the TO bearing is engaged correctly into the fork. The fork often has some spring tangs in addition to the actual fork metal. Check your installation instructions carefully.

 

Thanks ajp01, the disk is facing the right way, the fork is engaged correctly. The problem is the physical dimensions. If you lay flat, the old DM flywheel, clutch pressure plate and release bearing side by side on the bench with the new kit, the new kit sits about 1/2" higher. (the release bearing is higher)

 

Those were my only ideas. Basic research on the product shows that the AMS Automotive kit still appears to be a pull-type clutch pressure plate (same as original) and it appears to even use a LuK / Valeo pressure plate housing. But of course the flywheel itself and the clutch disk are significantly different.

What are the stampings / numbers on the pressure plate housing? Some of the pressure plates are thicker than others (ZR1 for example) by a similar amount as you mention. Does your pressure plate frame have numbers like these stamped into the casting? This is a China-made LuK pressure plate casting which is sold by LuK as a replacement kit for OEM LuK/Valeo parts....



Or is it the flywheel itself that's much thicker than the dual mass OEM flywheel?

 

Yes, that is the number on the pressure plate. As you can see, the damage from the clutch fork. The new flywheel is slightly thicker but the big problem happens when I tighten down the PP. The release bearing bulges out quite a bit. There is about .180" clearance between the PP and Flywheel when the PP bolts are hand tight. When I tighten them down, the bearing moves out. I tried putting a .100" shim between the PP and flywheel and it's still not enough. It's almost like the clutch plate is too thick.

 

Contact the vendor that sold you the kit, and I would also contact AMS Automotive directly. No way that's anywhere near correct - the flywheel and/or pressure plate are somehow wrong for your car year / engine / application.

 

The part where the plate is 0.18" off the flywheel with bolts hand tightened sounds about right. All the rest of the way down with the bolts is where the clamping pressure comes from. I suspect the problem is with the flywheel: there was a flywheel for 4th-gen F-bodies with this same clutch (but T-56 trans) that was thicker than the ones in Corvettes with ZF6 transmissions. Those flywheels can be used, but they have to be machined down, I think. I wonder if they used that flywheel and it's not machined? There are several threads on here where people tried that and the fork hit the pressure plate casting like you're seeing.

 

Thank you for the information MathewMiller. I agree with what you said.
I spoke with the tech guy at AMS Automotive and he knew exactly what I was talking about, He was certain that it was crankshaft endplay that was causing the problem......it would make sense but this is a brand new 383 build, I just fired it until I saw aluminum flakes on the floor. The release bearing is actually sitting .670" back farther than the old DM setup when I use the starter ring gear teeth as a basis point. We concluded that it's the unfortunate problem of quality control from the factory in China.
A couple options, modify the clutch fork, and/or machine down the flywheel.
I modified the fork today and after 3

trial fits, and getting in there with the inspection camera I got the clearance needed when the pedal was fully to the floor.
I've included a picture of the fork at trial #2, The old fork is above it.

 

Oh, I think we all forgot to mention the first thing you should check: that the clutch fork pivot stud isn't threaded all the way into the bellhousing. If it's not, then it will cause the fork to hit the PP. It's easy to check but also easy to forget about. If your kit by chance included a new pivot stud, make sure it's the same length as your old one. Assuming that all checks out, please read on.

Yeah, you should of course double check, but it's not crank end play. Also, as far as anyone seems to know, there's probably just a single mold in China to cast all these pressure plate baskets no matter what brand is on them. I seriously, seriously doubt the pressure plate is that far off. These Chinese clutch kits are known for quality control issues, but not for being 2/3" off on height! But if he thinks the QC on his own kit is that bad, then he shouldn't be selling it!

Getting back to this "clamping range" thing you discussed here:

...don't forget that the new disk is supposed to be a lot thicker than the old, worn out one. So that .180" clearance should be more than with the old disk, and the bearing should push out quite a bit more. I really don't think that's your problem. Here are some things you can measure to rule out causes:

• Try the same test above with the new flywheel/PP/bearing but the old disk. You should have less than .180" of clamping range now, and the bearing won't push out nearly as much.
• You can verify your "clamping range" is correct by measuring the distance from the end of the legs (where the PP mates to the flywheel) to the PP friction surface when it's off the car. Just lay PP on a bench, transmission side down, lay a straightedge across two of the six legs, and measure down to the friction ring. You should get a distance of between .195" to .205". If so, then the pressure plate is fine.
• Just to be sure, you can compare it to your original: lay both PPs (without flywheels or bearings) down on a table, flywheel side down. Measure the distance from the tips of the diaphragm fingers (where the bearing rides) down to the table surface. They should be very close. I bet they are not 2/3" different: again, there's no way that QC is that bad, even in China!
• While you're at it, do the same check for the two throwout bearings by themselves, making sure they are the same heights from where they hook on the diaphragm fingers to where the fork pulls on them.

Once you have verified that PP and bearing by themselves are close to the old ones in height, you will have eliminated all possibilities except the flywheel.

I am almost sure they sent you the wrong flywheel. Here's just one thread on the differences between the Camaro and Corvette flywheels. It's fairly common from what I've seen. I'm going by memory here, but I think if you lay the flywheel down on a flat surface with the pressure plate side down, then you can measure the distance from the crank mounting face down to the flat surface. That's the "thickness" measurement that matters: effectively, the distance from the crankshaft flange mating surface to the flywheel's friction surface. I bet you're going to find a significant difference there.

If the flywheel measurements also end up being the same as the stock ones, then you have the right parts.

There is absolutely no way in hell I would clearance out the fork and call it good. That thing is seeing a lot of load and it needs the rigidity the edge rails provide to that stamping. Also, I think you're just putting a bandaid on the real problem, whatever that turns out to be. There's no reason you shouldn't have a clutch kit that is correct in all dimensions and doesn't cause the fork to grind on the PP.

 

MathewMiller Thanks again for the information and link. I have measured everything and made comparisons to the old DM setup and it's the new single mass flywheel that is .133" thicker. Are all of the Chinese flywheels for the Corvette like this? and do they all need machining or did I just get the wrong one in the kit?
BTW I have another clutch fork to use once I get this problem figured out.

 

I don't know that fair to mention all Chinese but past experience with any and all SM flywheel replacements it needs to be 'confirmed' before the install. Using an AMS catalog I didn't see 'KITS/packages' but separate part #'s for clutch and flywheel.
You definitely DO NOT want to modify a C4 fork (they fail regularly). A clutch from AMS could be a valid purchase but a flywheel I believe needs/deserves more thought!

*** Does your flywheel actually display a 'Country of Origin'?

 

Okay, based on everything I've read, that .133" is enough to cause the problem you have. I'm not at all sure about the situation with flywheel manufacturing. Luckily for me, I never had to mess with that part because my C4 came to me with a nice Fidanza flywheel. I am going to guess that some flywheels are home-grown, since they can be made for the F-body applications and machined...but that's just a guess. Maybe the Chinese flywheel factory makes them all to F-body spec and then machines the Corvette ones down - again, I don't know. I do know that AMS has different part numbers for the Camaro (167533) and Corvette (167426) flywheels, so it's not like they are sending a common part and expecting you to machine it. I also know you can go to places like Carolina Clutch, SPEC, RAM, etc and get solid-mass-conversion steel flywheels that actually fit correctly. I also know they are going to cost a lot more.

I see that you have three options:

1. Put all this crap back in the box and send it back for a full refund. That's probably what I'd do, because this isn't a legit kit of parts. Then you have to spend more for a decent kit. Probably Carolina Clutch knows the most about these.
2. Have this incorrect flywheel machined down to the proper spec for your C4. I know others have done this with F-body flywheels before. I don't know how advisable it is. Maybe it's fine, maybe not, but you shouldn't have to spend the extra money on it. If you do this, take your old flywheel to the shop so they can match it.
3. Buy a flywheel from somewhere else and use the other parts that came with your kit. Obviously this adds a lot of cost. Maybe you can get a partial refund since AMS (and Rockauto) sells the same kit sans the flywheel for a lot less.

While we're at it, you need to check the disk and make sure they sent one with a sprung hub. That's required for the solid-flywheel conversion. And yeah, I would definitely use a non-clearanced fork if you have one. Sorry you're having to go through all this!

 

Thanks for all the help and suggestions with this problem. With me being in Canada and buying the kit from Rock Auto back in October, it would cost me an arm and a leg to send it back. They would require the entire kit including the pressure plate which is now scored from the fork. BTW the kit is part #kit1610, it includes the 167426 flywheel (at least that's what's on the box) and the 04-213 clutch and PP.
There isn't a machine shop near me that can machine the AMS flywheel so I have ordered another flywheel today, a Platinum Driveline FW426 and hoping that it will be the right size, if it's not, I can send it back no charge and then I'll get my original one machined next week.

 

If you paid with a 'Credit Card' I'd certainly initiate a dispute through them. You have what's considered obvious issues and snapshots so you could very well potentially realize 'something'. Being in Canada I imagine a RA purchase also incurs additional fees! I stick with the 'dispute' and comment back here regarding how it proceeds.

I'm an admitted RA hater ..............

 

This doesn't help the OP other than I feel his pain, doing a clutch job twice sucks! I know I went the SMF route and had bad results as well. I purchased a new SPEC SMF flywheel and the hydraulics that Bill Boudreau had recommended to me.
I purchased all of the other parts; TO bearing, remachined PP, clutch disk, pilot bearing, short throw shifter and shim for the transmission from Bill Boudreau. He has a wealth of knowledge and seems like a nice guy, but I had no luck with this setup.
The clutch disk slipped and chattered from day one. I was in contact with Bill several times and I tried everything he recommended to get it to stop slipping but it just kept getting worst. I finally pulled out the junk and went with the RAM Corvette conversion kit. It didn't cost any more than the junk Chinese parts that I purchased from Bill (no ding to Bill at all as he doesn't manufacture this stuff and in fact he did give me a bit of monetary compensation to ease some of the cost for the parts I purchased from him).
It is unfortunate that GM installed a half *** Pull type style clutch/Dual mass flywheel for the '89-96 C4 and then sold everything off to China for replacement parts.
The RAM is made in the USA and it does work very well! I may purchase a spare setup from RAM in the near future just in case they decide to discontinue the conversion setup.
Good luck to the OP I sincerely hope he gets it figured out and working.

 

I sure wish I had done this when I redid the clutch in my 96. Did you go with the single or dual disc?

 

I went with the single sintered iron 900 series disk 90-0810NS. It is a bit aggressive and does chatter a bit when starting off from a dead stop (pretty typical for sintered iron disks). It would be ideal with 4:10 rear gears (it is in my future). But it does not slip at all, engagement is quick compared to the stock Pull type setup shifts are very smooth compared to the stock setup.
Clutch take up is just a bit higher than stock. Clutch pedal effort feels like the stock setup.
The dual disk and the single 300 series organic should engage more like a stock clutch with no chatter.
I kind of knew what I was getting into with the 900 series setup and I almost pulled the trigger on the dual disk. It was a tough choice and I did contact Mike Norcia at RAM for his recommendation.
I decided to not drill into my bellhousing, you can align the new hydraulic throw out bearing on the input shaft from the cut out where our clutch fork use to reside. It takes a bit more fiddling than if you did just drill a hole like the instructions showed, but I didn't want an extra hole in the bellhousing.
It really is a good setup and it is very complete other than the clutch alignment tool (I purchased a steel one), flywheel bolts and Teflon tape.

 

Just giving an update regarding the issues with the clutch fork shaving the PP upon start up on the ZF6 SMF conversion:
1. I purchased another flywheel and it was the exact same thickness as the AMS flywheel. (I shipped it back and getting a partial refund)
2. The original DM flywheel was so worn out that I could actually wedge 2 flat screwdrivers across from each other and pry the two halves apart to the point that it measured the same thickness as the new SM flywheel! (originally I measured and thought the new SM flywheel was much thicker)
3. The probable cause of the issue: The shape and dimension of the new clutch fork.
I purchased the fork from a Corvette vendor on ebay but it seems that there are at least 2 different "stampings" or suppliers of the fork, one of them being somewhat thicker . I didn't use my old fork that I had because the seat where the slave cylinder rod sits, was worn. I modified the new fork that I bought, for clearance


and it now looks similar to some of the forks for sale online. I've attached a couple pics but it's hard to see the slight differences in the critical areas where the contact was being made.
I've fired up the car on the stands and now have no contact between fork and PP. All seems to be good.
Thanks to everyone for the help and suggestions especially MatthewMiller for providing some critical dimensions needed for diagnosis.

 

Hey just from curiosity; When you say your DMF was so worn out you could pry apart the halves - How many miles did you have on your original dual-mass / OEM clutch setup by the time it wore out to this point? Did you also measure the rotational play in your DMF to understand if it was within spec - say 1 5/8" or so?

 

The LT1 had multiple oil leaks including the rear main and made it to the clutch area. I don't know exact mileage but most likely over 200,000. I believe the pressure plate and flywheel were original to the car but the clutch plate had been changed previously as it had "made in China" on it. The flywheel had in excess of 1.75" of rotational play and the surface had many hotspots.