OK.. maybe someone can help me out here..Last year put new motor mounts and tranny mount in our car..its a 71 Olds Cutlass S..everything worked fine.. Now this year got the car out and been driving it around and now the driveshaft is hitting the bottom of the floor at the front ujoint..All i have done over the winter was put a new exhaust under it..Any suggestions why this is happening.. it really hits going down the road when you have to apply the brakes and also hitting bumps...could it be shocks or weak springs in the front causing this?? Or possibly wrong tranny mount making it sit to high in the rear of the tranny...Any suggestions would be greatly appreciated.....

 

First, get under the car and check the u joint and yoke for play.

 

Barring collapsing floor braces from rust or overloading, I'd take a look at the body to frame mounts - 42 yrs. in the 'rust belt' can take a toll! Could be all of the above.
Jack it up and take a look.

 

This is a long shot, but when you put in the exhaust system, where on the frame did you jack the car? On my 70, a previous owner had jacked the car under the frame rail at the unreinforced part near the trans crossmember. This bent the lower flange of the frame upward, raising the crossmember and causing the driveshaft to hit the floor occasionally.

 

I had it sitting on jack stands when i did the exhaust..and when i did jack it up i used a floor jack under the front crossmember under the engine and the rear i jacked up under the the center of the rear end..

 

Tranny mount possibly split apart?

 

This probably will not be applicable to your situation, but when I took delivery of a new 1965 442, it had a similar problem. The dealer found a small wrinkle in the drive shaft tunnel sheet metal. After removing the wrinkle with a hammer and punch, the problem was resolved.