I have a 1971 Cutlass, and I am having a problem when I hit my brakes. This only occurs when I am going faster than say 40mph and I hit the brakes hard. I feel a knocking that vibrates up through the shifter and I hear the knocking noise like somoeone is knocking on your door really fast and the tempo slows as the car slows. I almost feel like it would be my emergency brake pulling tight for what ever reason, but I dont know... Anyone else ever have this problem?

 

This could be a lot of things. Certainly a warped rotor could cause this problem. I'm leaning towards worn steering or suspension parts, however. Have all the moving parts in the front suspension checked for wear.

 

It sounds like it could also be the rear end/differential or universal joints if it's knocking that fast then slows. I would check the U-joints soon, don't want the driveshaft falling off and doing major damage.

 

Busted transmission mount letting the driveshaft hitting the floor?

 

I think the transmission mount sounds like the most logical thing... You are about the third person I have had tell ne that. The next question is how difficult is it to replace?

 

Real easy. Should be 3 or 4 bolts. Get the car up on stands or ramps, loosen the bolts, jack up the back of the trans a little to pull the old mount and install the new one. If you don't have tools or equipment and are in Dallas (assuming from user name) I can knock it out for a few bucks. PM me if you need to.