Please help me diagnose this problem.
 

I have a 94 M6 Z28 with a 3.73 factory differential. I bought a Spec Stage 4 clutch. I brought it to a local shop to have them install it. Everything seemed great at first. I was driving it really easy so that I could break the clutch in nice and easy. I was noticing some unusual vibrations from the shifter, but I didn't think anything about it at first. Then I got going about 35 MPH and was in 4th gear at about 1600 RPMs I gave it a little gas and this huge, loud, vibration came from the transmission. :confused: I used to drive it easy like that all the time at 1600 RPMs in 4th without a problem. I discovered that I couldn't drive it over 35 MPH because of this vibration. I have some meaty, newer BFGoodrich tires on the back and just got this strong clutch. Do you think the guys at the shop took my car out and blew the differential? I took it to a Chevy mechanic that I trust to have them take a look at the differential. Hopefully, I'll find out tomorrow what's up. :(

To me it sounds like a problem with the driveshaft:think:. There's no reason for the diff to "all of a sudden" start vibrating really bad?:confused:

I think it's possible to bolt up the driveshaft and not get it 100% centered in the U-joint, so that would cause a pretty bad vibration if it's out of perfect alignment.

May not be the problem, but it's a thought!:thumb:

I hope it's the driveshaft, but at 35, I poped it in neutral and the vibration went away. So, that's why I was thinking diff maybe, but I don't know what a diff does when it breaks so I'm not sure. If it is something in the differential, can someone suggest where I can get an affordable replacement? I think it has LSD also.

I still don't think it's the diff;). Keep in mind, as long as the car is moving, then the axles are turning, the diff is working, and the driveshaft will be turning:thumb:. SO, if you said that there is a vibration in the car that goes away when you put the tranny in Neutral, since we know the DS/diff/axles are all still moving, then that ISN'T where the problem lies.

Maybe then there is a gear problem? Does the vibration occur only in 4th gear??:confused:

It happens at other gears too but at about 35 MPH. When I was trying to drive up a hill, it vibrates worse. It seems to happen when the transmission is under load. It makes a kind of loud grrr sound too. Maybe some of the teeth are broken

Maybe they didn't tighten the tranny mount properly and it's loose?:confused: Or maybe the mount was getting worn and should have been replaced but they just re-used it anyways?:rolleyes:

OR, I don't know if they would have needed to unbolt the exhaust to make room to change the clutch, but maybe the exhaust is now rubbing up against the transmission or the floor of the car or something, and when you hit the gas and the motor flexes, the exhaust is hitting something and transferring that "vibration" through the car:think:.

Anything's possible dude.....you should get it checked out:cool:.

This is an update to a more descriptive account of what's going on with my car.
I've noticed that regardless of what gear it is in, there is a harsh vibration in the transmission at about 2K RPM. In each gear it gets more and more harsh, but always at 2K RPM. In 5th gear, it is so loud and harsh that it vibrates the entire car and you can feel it shaking you in your seat. On top of that you hear a loud braaaap sound from the transmission. When I rev it up to above 2500 RPMs (in 1-3 gears), the vibration goes away. I have not tried it in the higher gears. Before, with my old clutch, my car would make a small transmission gear whining sound at about 1600 RPM in every gear. This is normal and I wouldn't feel it or anything. I talked to Spec and the mechanic and they both believe that this is all normal because the clutch doesn't have springs in it. I asked the Spec tech if he thought it may be installed wrong. He believed that because the vibration goes away at higher RPMs, that the clutch is probably installed correctly. The mechanic has repaired a lot of things on my car and my parents car and I believe him to be capable of doing this job right.
So, I guess that leaves me with a super loud vibrating transmission. I can't believe it could get this bad just from the clutch change. I'm going to make a video over the next few days so that you guys can hear how amazingly loud and harsh this thing is. I still can't believe it and I am wondering if something was installed wrong.
If I can't figure anything out, then I'm going to replace it with a stock clutch and sell my Spec Stage 4. The funny thing is, I was worried about how hard it would engage. The engagement of the clutch actually isn't a problem. I love the way the clutch feels and the way it engages. However, this vibration is unbearable. I guess my T-56 is just a piece of crap.