Alright people so here is the back story (bit of a read):

Mind you this is a 1994 3.4L V6 (I don’t care if you don’t see the value in modifying a v6 or not, I just need advice on this problem as I have never encountered it before and don’t have money to throw at the problem by replacing all the components out back)

Last week I replaced my clutch with a new Spec Stage 3. Whole kit (PP/Clutch/TB), been driving around no problems. Well on Sat. I had somewhere to go, so I get on the freeway, and slowly get up to 80-90mph. Once I hit 85, I hear a dull "BUM" noise from the back and the car starts vibrating. I'm thinking, “great...flat tire.” So I pulled over and checked...all 4 - no flat tires. I'm like, “hum..maybe a rock or something?” So I check the tires (what I can see) - no rock or nail in the tire. So I'm thinking I'll figure it out later and just keep going. As I accelerate up again, I feel the vibration and do some testing. Push clutch in, no change, rev engine up and down, no change. Put car in gear, take it out, no change. As I slow down it vibrates more till it gets under 60 mph… then it goes away. I thought that was interesting so I noted that the vibration only happened above 60 mph.

I get to where I was going and talk to my friend who also has two Camaros (2nd and 3rd gen) and his dad has a 94 Z28. He says that the same thing happened on his 3rd gen when the U-Joints went out. So I'm like "Alright, I'll change those."

Ordeal CITY!

Had to melt the stupid nylon out of the stock U-joints (GM put it there - LS1 Steel Driveshaft). Anyway - while I'm doing this I check the transmission mount, find that the bolt holding it in is LOOSE! So I checked that, figured out that the bolt hole on the cross-member had to be "dremel'd" out a little (lots of ppl say it might be needed with that particular mount) + got a better bolt + threadlock + lock washer (thing isn’t going anywhere).

While I’m under the car I spin the pinion yoke a little bit, and it moves ok and does what it’s supposed to. However, when I push it lightly, it “bounces” a little. I mean like, when I just give it a little pressure it kind of vibrates a little. So that’s a concern of mine but I don’t know how bad that is.

I put everything back together, after checking the rear gears (they don’t look bad, nothing looks wrong inside. There was some metal shavings on the magnet attached to the rear cover but other than that things look fine, no missing teeth or anything on either ring or pinion), and I tighten it all down, fill the rear end, put in the Genuine GM LSD additive (purchased from Peninsula Pontiac) and take it for a test drive – WOW. Changing the u-joints was definitely needed as the car feels like it accelerates stronger (even if its just my mind playing tricks on me I don’t care it still feels better LOL). Anyhow, I’m going moderate throttle (no WOT yet cause clutch isn’t broken in) and it feels great, no vibration, I’m thinking “sweet!” But as I let off the gas, it comes back – this time at only 30 mph, and only when I’m coasting and the car is outta gear. also if i give the pedal a VERY VERY soft pressure (like barely any gas), it sounds like the rearend is bouncing... So now I’m not sure what could still be wrong. Friends of mine say that the driveshaft may be unbalanced, and while I was changing the u-joints I noted a small nick in the rough shape of a circle that was steel in color (silvery) whereas the rest of the DS is brown with rust. (steel ds).

Any thoughts on the matter?

Thanks.

-R