65PonyLove

So I put new poly mounts in and I have ran into yet another problem. I put the car on jacks and put it in drive....the driveline bounces up and down, and the leafs shift from front to back. The spot on the leafs towards the rear jump up, inturn moving the rearend up and is hitting the bottom of my car. There is fresh markings down to the metal so its definately hitting it hard. ALL THIS IS CAUSED FROM NEW MOTOR MOUNTS AND TRANNY MOUNT??? What do I do??

JMD

No, you have some other issue, is the driveshaft bent? do you possibly have a broken U-joint? could you have a broken spring or spring perch? Is it possible that you have a dragging rear brake.

There is a serious bind , bend, or imballance somewhere...

I am assuming that the rear of the trany points pretty close to the yoke on the rear axle..... I can not imagine that the driveline is so misaligned that simple misalignment could be causing this... There is not enough room for this serious a misalignment....

67mustang302

It could be axle wrap-up as well. Add that to any of the above listed problems and you'll get some mean vibration

fast66

Did you remove the driveshaft when you changes the trany mount? If you did, it sounds as though you have not bolted it back up properly. Check the U joint is central in the diff yolk.
Other than that, I agree with JMD ragarding a bent tailshaft, you didn't jack the car up by the tailshaft while doing the mounts did you?

65PonyLove

It is def not a bent drive line. I used jacks under the frame when I installed the mounts. (and the drive line was left on also). It is possible that the deteration of the old mounts allowed so much play that when I installed the new poly mounts it caused the"shifting/play" to move towards the weaker point (the rear of the car). This is the only changed I made. It drove fine before this. So what else could it be?

JMD

Itpossible that the tightening up of the mounts caused the movement to go somewhere else, but, you still have a problem somewhere, and the way you are describing the situation, a big problem.

Doesthe driveshaft slip yoke have room to move back and forth in the transmission?

Does your car have shocks on it right now? If not, the axle may be hanging low enough while the car is on stands that the drivshaft may be in a bind.

scouttrooper

The nose of the differential and the tail shaft of the transmission must be parallel for a pair of U-joints to work correctly. This took me a while to get my head around. I thought a U-joint was for turning angles, so two joints could turn two angles... right? WRONG! The two must be parallel. If they were pointing directly toward each other, that works... because that too is parallel. If changing the mounts raised or lowered the front of the engine-transmission unit, it would fulcrum off the transmission cross member thereby changing the angle and taking them out of parallel. If this is the case, use wedges to alter the rotation of the rear end (lift or lower the nose). Hope it's that simple for you.

65PonyLove

It does have shocks on it right now. And if I need to add wedges/shimms, where would I put them to make the angle correct again?? It sounds to my that the rear end needs to move up to match the mount moving the driveline up??? RIGHT???? Then would I put wedges etc in the springs.....I dunno but I feel like I'm getting closer....THANKS!

65PonyLove

HEY ....TROOPER.....could I check the angle of my driveline with a construction level?? It might sound weird but from what ur saying where it connects to the tranny and rearend need to be at the same height so a level would tell me how much it needed to go in a certain direction, RIGHT??