drivetrain problem

[co5j]

95 formula LT1, first noticed problem friday. was making a turn at slow speed, when i accelerated i heard and felt a thump-thump from under the car, almost like i ran over someting but i knew i hadnt. did the same thing at the next light, immediate thump at acceleration, otherwise you never hear, feel or notice anything, car drives fine. upon experimenting the next day, i have now found that if i attempt to accelerate hard there is a very LOUD and FORCEFUL slam from underneath so i immediately lifted. i thought i was going to see pieces laying on the road, it felt that violent, but there was nothing. car still drives fine under normal conditions, still has the noticeable thump at moderate acceleration but i havent tried to push it again. ideas guys?

[86TATpi]

Have you looked at the u-joints on the driveshaft?

[co5j]

i wasnt really sure how to check them. its my understanding i can jack the car up so that one? of the rear wheels is off the ground and then turn the driveshaft by hand and look for play at the u-joints? could it be on either end? how much play would cause that violent of a slam at hard acceleration? does only one wheel off the ground let me turn the driveshaft?

[PurpleJesus]

Originally Posted by co5j

i wasnt really sure how to check them. its my understanding i can jack the car up so that one? of the rear wheels is off the ground and then turn the driveshaft by hand and look for play at the u-joints? could it be on either end? how much play would cause that violent of a slam at hard acceleration? does only one wheel off the ground let me turn the driveshaft?

One wheel off might let you check the diff.... but jack the rear axel and have someone turn the tires back and forth while you look at the driveshaft... pay attention to the u-joints... esp the caps... Also I feel you might find that the rear transmission mount may be broken or otherwise rotten.... see if the rear cross memember is bolted in tight... if that all looks good... check the motor mounts...

oh their is a slim possibility your drive shaft may be out of balence... look and see if all the weights are there... (should be obvious if one has flown off)

The easy way to check a u-joint is to put into reverse, then drive... if you hear a clunk... the u-joint needs to be inspected... (this doesn't always work though)

[co5j]

turned out to be the tranny mount. it came completely apart. went back with a hi-po polyurethane. thanks for the help.