Guys,

I am swapping an LT1 T-56 into my '87 Camaro.

I understand the LT1 pressure plate uses special bolts with an extended shoulder. The shoulder is designed to go all the way through the pressure plate and slightly into the flywheel. Based on pictures I have seen, the stock flywheel seems to have a counterbore for the shoulder to fit.

I have no stock parts to compare. I have the SPEC steel flywheel, SC85S. It does not have a counterbore for the bolt shoulders. The SPEC does come with standard grade 8 pressure plate bolts, but common sense tells me GM designed the extended shoulder for a good reason. What are people's thoughts on this? Maybe SPEC forgot to dill the counterbores on my flywheel? Do others have aftermarket flywheels with the counterbore?

There are pictures of the bolts and the stock flywheel counterbore here:
http://www.zr1.net/forum/showthread.php?t=8306

Thanks,
John

 

Here's a CF 700107. It has the feature for the shoulder.

I wouldn't put a clutch together without that. That's what centers the clutch on the flywheel. Look how much slop the bolts have in the holes in the clutch; not good. It doesn't take much off-center-ness to create ONEHELLUVALOTUVA vibe.

If I had one like that, I'd almost be tempted to drill the counterbore myself.

I couldn't find the right clutch bolts when I did my swap. I went and found some Grade 8 bolts, that were too long, but had the shank behind the threads LARGER than the threads, rather than SMALLER, like alot of em are; and I cut the extra threads off with a die grinder & cutoff wheel, and chased the threads. Might have been like 3" bolts, and I cut off ¾" or 1" of threads, don't recall exactly. I think I also used a Grade 8 washer under them, because the clutch seemed like it was made for a washer head. Anyway, ended up with about ½" of thread left, which went basically all the way through the FW ± 1 thread or so, and left about ¼" of the shoulder in the FW, and tightened em to a reasonable torque for 3/8"-16 hardware, like 30-35 ft-lbs. Basically a perfect fit.

 

Mcleod Sells the pressure plate bolts P/N 1502.

 

Yes I am extremely temped to take the flywheel to a machine shop to drill the counterbores. Of course SPEC claims they are unnecessary and even provides bolts with only a short shoulder.

I have found a source for the real bolts, Carolina Clutch. They claim they have been manufacturing them now that GM has discontinued the originals. We'll see when the package comes Tuesday.

 

I am not looking for the bolts. But thanks.

 

I have done the t-56 swap myself. I may be crazy, however, I think(I'm no engineer) if the shoulder on the PP bolt is the same as the bore on the PP then the PP can't move. Say the bolts had no shoulder and they were 3/8ths (all thread) and the bore of the PP was 7/16ths. The PP would be able to move that fraction of an inch regardless if they shouldered to 3/8 into the FW. (think 3/8ths through the PP then shouldered to the counter bore of 7/16ths) I think that in theory that if you had 1/4" FW holes and the PP was bored to 3/8ths and the shoulder of the 1/4" bolt was 3/8ths there should be no movement of the PP around the bolts. FWIW. ATA I also have the same Spec FW with their stage 3 PP and clutch. Maybe GM added the counterbore to lessen the stress on the threads..(7/16ths counterbore with a 3/8ths thread engagement, more meat there.)

 

Exactly. I suspect the bolt shoulder extending into the flywheel is to react the shear stress. Typically the shoulders are used for locating where you don't have high bolt torques. I believe these bolts are only torqued to 22ft lb or so.