First off thanks for reading this and any help would be appreciated.

Car now has about 110k on the stock tranny. Had the rear end rebuilt and went from 2.73's to 3.73. Install was great, getting no noise from the rear and things seem to be good until I hit about 65-70mph and up. At that speed I start to get a "rotational vibration" that seems to be coming from the middle to the front of the car. Only happens when the car is accelerating. When coasting and gradually slowing down it is nice and smooth. No vibration and at all times the rear is quiet with no whine. Recently had a new poly tranny mount installed and also a balanced alum drive shaft. car runs great a speeds under 65mph, shifts great, runs strong. Never noticed a problem till after the gear install, but I know the guy who installed it and he did a great job. Any help would be appreciated.

Thanks,
Jeremy

 

I'm inclined to say you have a balance issue with your driveshaft. I do see that you had it replaced, but it may not be balanced properly. I can tell you that any imbalance in the driveline will be much more apparent when running a poly trans mount. If you haven't been inside the tranny, and there was no issue before, it's likely not a trans issue. As a band-aid fix, you could toss on a stock trans mount, but it would be better to have the 'shaft checked out.

 

Before one of you makes a wise-@ss comment, I realize I said he should have his shaft checked out.

 

I figured it might be something like that. I noticed it right after the poly mount was installed. It made the same vibration with the stock driveshaft and the new alum shaft. Figured it would be pretty well balanced from the factory. Where would I get something like that check for balance and then corrected? Never had to look into that before.

Thanks
JCS

 

Any driveline shop should be able to help you out. They generally specialize in rear ends, driveshafts, and axles. Crack open the phonebook, make some calls, and see if they can check the balance for you. Hope this helps. Me, I was a lazy SOB and just ditched the poly mount.

 

A lot of times it's not much more $$$ to just get a good aftermarket driveshaft. Check out the offerings at dennysdriveshafts.com

 

Thanks for the suggestions. I'm leaning towards the tranny mount. Might switch back to a stock mount and see what happens.