Fiesta_Charles

I have a '96 LT4 car and I'm wondering if anyone else has dealt with the transmission/clutch/flywheel saga for these later-year C4 cars succesfully in the past couple of years. I've done a lot of reading on here and everything I read about is that changing clutch components with original parts (read: DM flywheels) is basically impossible since there aren't any and switching to a SM flywheel unit ruins the car.

Anyway, I believe my pilot bearing is damaged and making some noise after I completed a track day at Putnam park about a month ago (when I clutch in all the way and I hear a rotating metallic rattling noise). Clutch grabs fine and the car has 95k miles, no idea on previous service from previous owners (I've had that car about 4 years, 11k miles or so). I'm wondering how much of a pain it is to change the pilot bearing and any other related worn clutch components and master/slave cylinder stuff. I'm not very handy and I don't have a lift or many tools, so it's unlikely I'll be able to do any this myself. Money is less the issue than where to go and what parts to source such that I can maintain the stock character of this otherwise amazing car.

Is it a stupid waste of time to just replace the pilot bearing and friction disc and nothing else? What parts should I replace and who sells them? I don't want to convert to single mass flywheel if my DM unit is bad either. Any shops in Ohio (central or NE) that can do this kind of work? Would a Chevy dealer even touch this as a last resort? Should I give ZF Doc a call? Any advice on this issue would be greatly appreciated.

rocco16

Sounds like a throwout bearing to me. If it is, you're lucky.

5abivt

AGree sounds like the throwout bearing. But yes, if the pressure plate is original it is a higher clamp load than the std LT1 pressure plate. Id recommend a GM disc replacement, new pilot bearing and throwout bearing and youre good to go.

Fiesta_Charles

Yep, this is basically what I'm thinking. Can any independent shop be trusted with this? Should I use a Chevy dealer, or Corvette shop? What are your opinions about Corvette specialty shops versus dealers (for quality reasons, I think we all know why dealerships are called stealerships for cost reasons).

5abivt

Isn't find out if there are any corvette or speed shoppes familiar with the c4. Personally I will sell my cars before I ever go to a dealership. Chances are the guys who are experienced with c4s and care are long gone from there. If you have the tools it's not a bad job at home. Once you do this the entire car is easier ! Saves a ton of labor but then again it shouldn't be all that much vs a c5+ given they have to drop the entire drivetrain from the car .. = very expensive. Just my .02

MatthewMiller

Sorry I'm late to this topic. Agree with the others it sounds like a throwout bearing. But once in there it's minimal extra work to replace the pilot bearing and disk. If your pressure looks decent, keep it! "Decent" means it can have heat colorations but not lots of gouges from the disk rivets (happens when disk wears down), and it is still flat. The original Valeo plates are what you want, and they are very hard to source now. If you like the DM flywheel and it looks okay, reuse it too. If not, you will have to use a single-mass wheel, but you can get a steel one that has more mass for a bit less noise. If you have to go that route, make sure the new disk has a sprung hub! The OE one is a solid hub for use only with the DM flywheel.

On the throwout bearing, I strongly recommend finding an new-old-stock INA brand bearing. I had a "performance" clutch brand's throwout bearing lose its seal and ruin a nearly new clutch. You can try calling Jim at Power Torque Solutions: (641)342-7446.

For the pilot bearing, get a fluted oilite bronze solid bushing. Other solid bushings are suspect. Needle bearings are more delicate - mine came out in small pieces! Don't put any oil on the bronze bearing! It is self-lubricating, and may actually fail if you add oil to it.

Any decent shop should be able to do this. The only real tricks I can think of are getting the stock shift **** off the stick, and dealing with the rubber shifter boot under the leather one. You can look up the tricks on the shift **** (mine isn't stock, so I've never done one). After removing the rubber boot on mine, I recommend leaving it in place. This probably requires a helper when the trans comes out and goes back in, to guide the shifter through the hole in the boot. But it's a real pain to put back over the opening in the tunnel if you take it off. I think everything else is standard procedures.

Fiesta_Charles

This is extremely helpful. A few questions:

1. Let's say my DM flywheel is hosed and I need to go SM. Which SM unit should I use, and, which spring hub'd friction disk should go with it? I'm really not a transmission guy so I had no idea there was all this variation between flywheel and friction disk combinations.

2. Would power torque solutions have all of this information? I'm wondering which vendor has the best reputation for outfitting later C4's because I feel like I need people who know these parts intimately in order for me to get this right.

3. I have seen other threads on here talk about bronze bearings and how they're really what you should get, so this confirms what I read.

4. What other common trans/clutch items go bad? I hear a lot about master cylinders and slave cylinders, clutch forks and this and that. I'm not entirely sure what these are and I'm sure they're hard to source too. Should I replace more items since I'm in there anyway? Or should I not touch them until I know they're bad? Thoughts on this?

Thanks again.

pkincy

I have had a Fidanza SM aluminum flywheel in my 93 Lt1 for 20 years (only 35,000 miles however.) There is absolutely no problem and no noise from it unless you shift to neutral and let the clutch out. Then you get the rocks in a can noise. But normal stopping at a light or stop sign with the clutch depressed it is quiet as a DM.

MatthewMiller

For stock or near-stock car, I wouldn't obsess over it too much. If you want your car to rev and accelerate faster, you can get a light aluminum flywheel. Like pkincy, I also have the Fidanza 13lb flywheel (vs 40lb for the DM flywheel!), and it makes a real difference in performance. But...it is harder to modulate on the street when you're trying to get rolling from a stop, and with our tall first gears it takes a bit of getting used to. With a stock-type organic disk, it isn't hard - it's just a bit different. When you upshift or downshift, it's actually easier to be smooth and cool with it! It will be noisier at idle in neutral than a heavier steel wheel, but with a stock cam this is ameliorated somewhat compared to what I'm hearing. A 25-30lb steel flywheel will drive more like stock, and be quieter although not as quiet as with the stock DM wheel. So it kind of depends on what you're wanting, exactly. Fidanza also makes a heavier flywheel, but so do several others. I imagine they are all fine. I only have experience with the light Fidanza.

For a stock or near-stock power level, and especially if you want to retain good modulation on the street, go with an organic disk. I had an organic disk in my 396 with probably ~500hp at the crank, and it lasted for many years. I wish I'd put another organic one in. RAM and Centerforce seem to have good quality disks. Again, make sure you stick with full organic and not a dual-friction type of disk. I am no expert on best brands, but this is what I've gleaned from my experiences so far.

Yep, for sure. Jim there owns and races C4s of his own. He knows the ZF6 drivetrain like the back of his hand.

I wouldn't mess with your original master or slave cylinder unless they are actually malfunctioning. They are higher quality than the replacements you can buy now. I would inspect your fork and the pedestal for wear at the pivot point mainly. Chances are they are okay. The pedestal - a good one - is getting hard to find. Not sure about the forks. Again, I'd just add a bit of grease to the pivot point (I used a high quality grease for brake pins) and call it good unless there is obviously a problem.

If you end up replacing the flywheel, you may want to consider ARP flywheel bolts and the special washers that go with them. Make sure to get their special assembly lube for the bolt heads and use Loctite on the threads. They have very specific directions about all this on their website. You'll probably need to refill your trans fluid after all this. You can check out about a zillion threads on this forum regarding what's best. I'm using a fluid that nobody else uses and I don't think you can get it anymore anyway, so I won't be much help on this topic.

MatthewMiller

I wanted to add something to make the search for a disk a little easier. If you keep your DM flywheel, just look up disks by your vehicle application (96 Corvette). Make sure the item description says "solid hub" or "non-sprung hub" or something like that, as there is a lot of assumption these days that most clutch jobs will involve the switch to a single-mass flywheel.

OTOH, if you are going to switch to a single-mass flywheel and therefore want to buy a sprung-hub disk, looking up the disk by your actual vehicle will either not get those search results, or it will get you a mix of sprung and non-sprung disks. The easy way to search for sprung-hub disk is by looking for a replacement disk for a 96 Camaro V8 (Z28). Those cars had a completely different transmission that wasn't noisy and didn't required a DM flywheel, so they came with single-mass flywheels and sprung-hub disks. But they were the same diameter and the input shaft was the same diameter and spline count (26). IOW, the only difference in the disk for a Z28 and Corvette was that the hub was sprung on the Z28 but solid on the Corvette. So that search will get you the correctly sized disk with a sprung hub.

9T3VETTE

As and FYI Jim at powertorque has retired and sold off his remaining stock. Another wrench to throw in the mix.

MatthewMiller

I knew he'd shut his website down, but didn't know he officially retired and sold off his stock. That's too bad. Maybe ZFdoc has some OE parts, or a line on some?

Fiesta_Charles

This has been extremely helpful! Thanks guys, I knew the forum would come through. I will likely do this repair at the end of the season and until then I won't do any more HPDE's or anything else until this issue is fixed. There is a Corvette shop in Cleveland that has done some frontal engine work on the car before, it is possible that they can handle this is well. If not, a reputable transmission shop. Thanks again for the advice and I'll see if I can come back with a success story!

Charles

MatthewMiller

If you were happy with that Corvette shop they may be the better bet. I get a little leery of some specialty shops like transmission shops. If you were needing the transmission rebuilt then maybe (maybe). But any mechanic can do this job, and the Vette shop will have done them before and is probably pretty familiar with the DM flywheel. One thing I forgot to mention that is unusual on a C4 is the C-beam that has to come off with the driveshaft. It's actually not hard, but it's quite different from a typical crossmember. A shop that's used to working on these will know exactly how to zip it out quickly, whereas a transmission place may not. So again, check with the Corvette shop first. If they tell you they've done these before, and especially if they are willing to try to keep your DM flywheel (if that's what you want to do), then I'd lean toward them.

Please do let us know how it turns out!

Christi@n

There's a difference in clutch disk...

Dmf clutch disk doesn't use coupling springs
Smf kit has clutch disk with coupling springs

Am i right?

MatthewMiller

Correct. That's what I was referring to in post #10.