General Maintenance & Repairs - Violent shaking/vibration 3500-5000 rpm?

I'm not sure what is causing it. As you climb higher than 3k rpms the car becomes shaky, you can see the shifter stick vibrating. I might try to get some film of this later today. it seems to smooth out above 5k, but honestly lately I don't really beat on the car because this issue is freaking me out.

It is a LT1, I'm running the dual disc Mcleod in it with the steel flywheel. T56 I purchased used about 3 summers ago was supposedly rebuilt to level 2 specs by this shop owner in Tampa, yeah I know, kind of big gamble there.... Driveshaft is a Denny's Nitrous Ready. 12 bolt Moser rear with Eaton posi and 4.11 gears.

I notice I get a fairly nasty vibration on deceleration also if I let the car coast. Under load or braking I do not notice this other vibration.

Any ideas?

Edit: Just thought about this, it is especially noticeable in 3rd and 4th gear, it is still there in 5th, don't know about 6th. I haven't exactly been doing any high speed runs with the thing with the way it is behaving.:lol: I think the issue is there in 1st and 2nd but it isn't as noticeable, due to the gearing maybe?

Sounds like a trans mount if the shifter is shaking around like crazy.

Sounds like a trans mount if the shifter is shaking around like crazy.

Check that and u-joints and driveshaft for dents, bending, and missing balancing weights. Does sound a lot like the trans mount. Shifter shouldnt move that much. Make sure the cross member is tight to the body too.

Shifter mount is a three year old prothane, but I will check it out, maybe the bolt holding it to the crossmember fell out? I'll check this out.

I used blue loctite and those nuts with a bushing in them to secure the brackets on the u-joints, but I will also check those for looseness.

Also to note the faster I raise the revs the worse it gets, if I ease it up through the rpm range it isn't nearly as bad.

I had the same problem w/my car. After changing literally everything out...It turned out to be the tranny.

And that is what I fear.:lol:

I got under there today, I was able to tighten the crossmember bolts maybe 1/2 to 1 turn with a ratchet by hand (no cheater bar), having to really put some ass behind it. Same deal for the stud in the Prothane trans. mount. U bolts weren't loose on the U-joint in the rear. Not sure if any weights have fallen off the driveshaft or not, doesn't appear so. I can't move the driveshaft side to side or up and down, so I assume the u-joints are in decent shape.

SuperSam, what had gone wrong in the transmission?

Bump!

It is less noticeable now after tightening those items up, but it is still there.

Any input on possible transmission issues? I would assume input or output shaft bearings?

Could I be lucky and it is the driveshaft? Any recommendations for places that could check and balance the driveshaft in northeastern PA?

Does it shake when you rev the car in neutral?