Hey guys, I'm not sure if this is the right forum to post this in or not but here it goes! I have a stock auto with a 3600 stall in my 99 ss. I just got the motor built, and dynoed the car. They only went up to 6,000 rpm because the car was at 139 mph and they said it was vibrating a lot. They didn't go any higher because of the risk of snapping the input shaft. I think some power was left on the table because of that limitation. Is there anything I can do to stop the vibration and possibility of the input shaft snapping? Like a brace or new crossmember? I'd like to get a new dyno tune at max rpm. Thanks!

 

What type of trans mount do you have. Polymounts will transfer vibration when nothing is actually wrong.

 

It's got the stock transmission mounts and all stock braces.

 

Sounds like something is out of balance - most likely the driveshaft or the rear wheels/tires.

 

I've come down to the assumption that it's the stock mounts. I'm going to get solid motor mounts and a poly trans mount to help stop the vibration. I don't care that the car will vibrate more, I just need the powertrain/driveline vibration gone. The wheels/tires are in balance since they were done recently and I worked at the shop they were done at.

 

IMHO, the proper way to deal with a strong vibration is to find the source of it, not suppress it with solid mounts.
There have been plenty of posts here about driveshafts going out of balance. At those speeds a driveshaft that breaks a u-joint can destroy the car and seriously injure the driver. Hence the use of driveshaft loops.

 

Not something to take lightly for sure. The driveshaft is the most likely culprit. The stock aluminum shafts are pretty poor in my experience. It might be slightly bent or out of high speed balance.

 

Ok I'll look into that. I didn't know if it was just a common A4 problem if I had an actual issue.