Pinion angle help needed.

[Kent mosby]

My 1973 scamp is almost ready to go, or so I thought. I have a completely rebuilt 512 RB, 727 trans, 8 3/4 shortened rear. SS springs. Competition engineerings drag shocks..
During hard acceleration there is not much vibration but cruising at 3500 rpm, 72 mph there is tremendous vibration coming from the driveline.

My measurements are relative to gravity on a lift. The transmission output shaft is pointed down 1-2 degrees. The pinion is pointed down 7 degrees as well. I understand that the rear end pivots up during hard acceleration and that may be why I do not get the vibration.
View attachment 1715533907

Is the only way to make this better to redo the perches? Can shims help this?

 

[mopowers]

You're only a couple degrees off. Shim it and be done with it.

 

[pishta]

your way off! if your trans CL is -2 down..your pinion should be like -1 down so under acceleration is my go up to +2, and that would be perfect parallelism to output shaft.

 

[mopowers]

On a street strip car with a 512, 5-6ish negative will work fine. He's at -9 now. Shim it a few degrees and go.

Lakewood Traction Bar Wedge Kit

 

[67Dart273]

Seems to me the pinion should be damn near zero (level) so when it comes up it matches the tailshaft.

 

[Tooljunkie]

I use an app, its a pain,but i level driveline with my jack under the diff, then point diff to get the number i need

 

[Kent mosby]

@Tooljunkie very nice app. Thanks

Would using a 6 degree shim be good to get me into a working setup? That would get me to -1 relative to ground but more important 6 down relative to the driveshaft. which is what the "Book"says to be.

 

[DoctorDiff]

Your pinion angle is 9 degrees negative. I consider 4 degrees negative, maximum.

 

[famous bob]

My 1973 scamp is almost ready to go, or so I thought. I have a completely rebuilt 512 RB, 727 trans, 8 3/4 shortened rear. SS springs. Competition engineerings drag shocks..
During hard acceleration there is not much vibration but cruising at 3500 rpm, 72 mph there is tremendous vibration coming from the driveline.

My measurements are relative to gravity on a lift. The transmission output shaft is pointed down 1-2 degrees. The pinion is pointed down 7 degrees as well. I understand that the rear end pivots up during hard acceleration and that may be why I do not get the vibration.
View attachment 1715533907

Is the only way to make this better to redo the perches? Can shims help this?

View attachment 1715533924

Too much when not under load ---------------

 

[teringer]

I would raise trans to 1 plus you may not be changing your pinion angle much depending on your rear suspension ,also check fan ect after shiming

 

[AJ/FormS]

Easy to prove;Feed it gas and brake simultaneously, while traveling in the vibration zone.
I run about your angles but with softer springs, and a 367 with a manual-trans. It has no vibration traceable to the pinion angle..

 

[Kent mosby]

I placed a 6* shim and now my measurements are that the transmission output is 1.5* down, driveshaft level and the pinion is 2 degrees down. So under acceleration it should be good. I had it up to 100 mph and there is still some noise or vibration somewhere but very slight. I will continue to evaluate.