Can't figure out vibration!!!

[bumblebee03]

Since I did my engine/Trans swap I have encountered a vibration I can't seem to fix. The engine is a 347 and the trans is a G-Force T-5. The vibration is speed related and not rpm related. The car starts to vibrate REALLY bad at about 70mph and continues on from there. It does not go away when I push in the clutch and coast. I had my driveshaft rebalanced, it really was not out of balance, but it seemed to help the problem. When I drove to the track on Saturday it was very smooth over 70 mph so I thought I had licked the problem. But after my 1st run the vibration came back with a vengeance. I have run the car on jackstands without the rear tires and the vibration is still there. Could inproper pinion angle cause this? I don't think I have a bent axle, but I plan on replaceing them over the winter. Any suggestions would be helpful. Thank You. Lee

[BLOWNBY]

When I bent my driveshaft the vibration went away when i'd disengage the clutch. But other than that it was similiar to yours.

[Bobalos]

I had a bearing in the rear end go out on me & it caused a vibration kind of like yours. I changed U-Joints, ballanced the DS, changed the wheel bearings had the tires ballance & all of that & then figured it had to be in the rear end. that fixed it up.

Bob

[speedytang]

If it does not happen when revving in neutral and only when rolling either coasting or under power I would say remove the driveshaft and run the car in gear because it sounds like the output shaft on the transmission and if it does not do it then a bent axle. But I would say since it didn't do it before and now it does the output shaft has play or is bent.

[bumblebee03]

Can you run the car without the driveshaft? Won't all the fluid spray out of the transmission? Im going to re-clock the driveshaft 180 degrees and then set my pinion angle correctly and see if that helps. Lee

[speedytang]

Use a transmission plug like the one you probably used to install if you already had fluid in it.

[bumblebee03]

Tranny was empty when I installed it. Can I get a plug at a typical auto parts store, or is it more of a specialty Item?

[speedytang]

Auto Parts store usually has them in stock. They are usually cheap I paid $12 for a complete plug kit had 8 different plug sizes. The HELP! section at most parts stores have them.

[Paxtu22]

did you put a pilot bearing in the end of your new engines crank?
what type of balancer are you runnin?

Eric

[bumblebee03]

I think I figured it out. When I went to check my pinion angle, I could not get the driveshaft out, it would not slide forward into the trans. I moved there rear enough to get the rear flange of the shaft off and got the shaft out of the trans. The slip yoke was slightly twisted about 1" from the bottom near the driveshaft side. I think because my pinion was set up (+8 degrees) that when I shocked the tires the pinion went up further and pulled the yoke out a bit further from the output shaft of the trans causing it to twist. I got a new aluminum FMS shaft and it slid right into the trans. I have to finish setting the pinion angle correctly so it is - 2.5 to -3 degrees. I think when it is set like that, the slip yoke will move forward into the trans when launching and giving me the correct strength I need. Should know by wednesday if all is ok.. Lee