I'm having some issues with my 97 formula firebird, I believe the problem to be routed to the driveshaft. I've owned the car for almost 2yrs, and in them i have replaced the universal twice. The car runs smooth and accelerates hard up until i hit around 90 mph, then the car shakes violently underneath the shifter (6spd). Would it be a good idea to replace the shaft, or are there other possibities for this problem? thanks Dan

 

cheap easy solution is locate stock LS1 al ds and replace. typically under $100. common problem for LT1 cars with even aftermarket steel ds. i know, i paid $225 for scratch built steel ds(i was in a bind), had it balanced 2x and still no good. it was stock length but all other dimensions were diff to GM OE ds. i then paid $125 for LS! al ds shipped to my door and problem solved. i don't know what the issue is, harmonics or whatever, but the cars just prefer aluminum

 

I have the same problem around 85-90 then above 95 it is better but the vibration is still noticable even more when i decelerate. I bought a brand new ls1 driveshaft (not the discontinued one) and still have the same problem but not as noticeable still bad tho. i can't figure it out

 

had that prob too, the poly tranny mounts make it worse, but switched to a 3rd gen al driveshaft with spicer u- joints and problem solved

 

so that explains my whole car shaking like crazy at 110 yesterday..

 

if you replace the driveshaft and still have "bucking" issues, then its inside the rear axle, i went through 3 driveshafts and 4 u joints before i noticed this..... just an idea to remember if the problem still exists!!