[onpyramid]

Swapped the C-4 auto for a T-5 manual. Shortened the drive shaft 3/4" and balanced it. New u-joints front and rear. Speed related vibration from about 58 mph on up. Up to 70 mph the vibration is liveable, but noticeable. Any speed north of 80 mph and it vibrates quite prolifically.

I measured the drive line angles while the car was resting on level ground, with these results -

Output shaft is down 5 degrees
Drive shaft is down 3 degrees
Pinion is level at 0 degrees

As I understand it, I should shim the rear axle to raise the pinion angle, correct? Assuming the pinion angle will change under acceleration, should I set the pinion angle at "up 4 degrees" while it is on this same level ground?

I should also note that the T-5 was a used unit, and I fear the tailshaft bushing may need to be replaced. The slip yoke seems too move to much in the wrong directions.

All help appreciated.

[JohnTN]

From what I understand, you currently have the worst configuration -- "U" shaped line from trans to pinion.

If you raise the the pinion angle you will decrease the driveshaft down angle and get out of the "U" configuration when the pinion up angle becomes greater than the driveshaft down angle. Going to 4 degrees up should help significantly.

How much the pinion angle will increase under acceleration depends on whether you have leaf springs (more windup) or coil springs. You will need help from someone with much more expertise than me to answer that. At constant high speeds I don't think you have much if any windup. Rear axle windup is maximized under hard acceleration, such as drag racing.

John

[onpyramid]

Changed the pinion angle to "up 4 degrees" and the vibration seems to have gotten much calmer. I even shimmed the transmission up 1 degree to match the pinion exactly. I still have minimal vibration at higher speeds....at 75 mph you can tell its vibrating, mainly from the rear view mirror, although you can feel it, a bit. At 80+ mph, the vibration is back strong enough to be noticeable.

I think my next move is to replace the tailshaft bushing in the transmission, and to put on a new slip yoke, just to be sure.

Wish me luck.

[NEW INTERIORS]

If the Output shaft is down 5 degrees,, then set the pinion angle to 5
degrees up.. and give that a try..