bad tranny mounts?

[beaver2489]

I have an '88 GT convertible 5speed. When I hit 43-48 the shifter shakes hard, 50-54 is smooths out then 55mph+ it shakes hard again. It doesn't matter what rpm or gear, and the shaking dampens if I let off the gas. I replaced my harmonic balancer a month ago. If I have bad tranny mounts could it do this? If so how can I check this, how hard to replace them? Thanks

 

[NKau]

Kind of odd that it goes away between 50-54 mph, but from what you are describing, it sounds quite a bit like a twisted driveshaft. Many people on here have that problem. If you accelerate hard with your hand on the shifter, does it shake harder? The easiest way to check for a badly mangled DS is to put the rear end on jackstands (with the front wheels chocked) and have someone slip the car in gear and watch the DS under the car as the wheels turn. I'm also guessing the vibration gets worse the faster you go? Sounds like it might be time for a new aluminum DS; at $160 they are cheaper than getting your old one repaired and come with new u-joints.

 

[beaver2489]

cool, thanks! I'm getting $3400 back for income tax So I'll get an aluminum driveshaft. Ya if I get on it and get to 65-70 and let off its shaking hard. If I'm going up hill it doesn't shake as hard though? I'll try the drivshaft first, then if thats not it what would you suspect the problem be?

 

[Blandnuts]

What happens when you push in the clutch or drive the car in neutral at 55+ (whenever it shakes)?

 

[beaver2489]

What happens when you push in the clutch or drive the car in neutral at 55+ (whenever it shakes)?

If I go 55mph then push the clutch in, the shaking dampens but is still there.