Pinion Angle Help needed

[PCP71Demon]

Hey All,
Need some help/clarification on next steps for setting the pinion angle on my 71 Demon. Car had a 904 transmission, which was swapped out for a 727 after the 904 got destroyed. with the 727 being a couple inches longer i had to get a new driveshaft. I also installed a new rear transmission mount which changed the motor tranny angle.
With the new transmission I got a driveline vibration above 40 MPH.
Current setup is the motor is angled down 1.9 degrees (at harmonic balancer), rear of tranny shows angled down at 2.1 degrees, driveshaft (at front behind yoke) shows angled up at 1.6 degrees, driveshaft (at rear ahead of yoke) shows angled up at 2.0 degrees. Differential yoke shows angled up at 2.8 degrees using a 4 degree pinion angle shim.
What are your thoughts on the above setup and any changes that need to happen to eliminate the vibration ?
Thanks in advance
Mike

 

[doug 371]

I think the shim is in backwards...

 

[33IMP]

I think the shim is in backwards...

Agree. Supposed to look like this. (Front of car to the right, super stock springs)

 

[Professor Fate]

^^ above.
Couple of other things come into play here.
Transmission was installed with all factory pieces, *should* be within factory tolerances for your new setup- factory never changed differential pinion angle (unless there was a production/manufacturing error) between transmission setups, but you're right to check.
*Assuming* you get your pinion angle within tolerances (2 degrees negative- pinion is poiinting 2 degrees DOWN relative to the trans, basically pull that backwards 4* shim out) and you still have a vibration, the only thing left that has changed is your driveshaft. Have balance re-checked, or if a used yoke was installed, it may be excessively worn. Last but not least, people have reported noticeable effects from deleting the bolt-on tailshaft vibration dampening weight on certain year transmissions. Not sure if yours originally had one or not.

 

[PCP71Demon]

Thanks to all the responses. Appreciated ! My shims are in the way the pics above show. Thicker section to the rear. Thinking perches are not well located from previous owner. From the responses i gather that my diff front yoke should be angled down, not up the 2.8 degrees, based on all other angles..... If correct, I would just need to put a 6 degree shim in and remove the current 4 degree shim and that should help ?????. Thanks again....so nice to have knowledgeable Mopar people to help with issues and concerns. Drive Safe my Friends !!

 

[PCP71Demon]

^^ above.
Couple of other things come into play here.
Transmission was installed with all factory pieces, *should* be within factory tolerances for your new setup- factory never changed differential pinion angle (unless there was a production/manufacturing error) between transmission setups, but you're right to check.
*Assuming* you get your pinion angle within tolerances (2 degrees negative- pinion is poiinting 2 degrees DOWN relative to the trans, basically pull that backwards 4* shim out) and you still have a vibration, the only thing left that has changed is your driveshaft. Have balance re-checked, or if a used yoke was installed, it may be excessively worn. Last but not least, people have reported noticeable effects from deleting the bolt-on tailshaft vibration dampening weight on certain year transmissions. Not sure if yours originally had one or not.

Thanks....Appreciate the help. Shims are in correctly, thicker section to the rear. so if my tranny is 2.1 degrees down, my diff angle needs to be 4 negative?? if so thinking a 6 degree any shim, replacing the 4 degree, should put me close ? Thanks again for all the help.

 

[CudaFactHackJob]

Yokes parallel.

 

[crackedback]

Trans down 2*.... for a -4 pinion angle which is about the max for a street car under normal driving, you want the pinion point down 2*.

This CAN NOT be done with the car in the air, axle hanging. Measurement must be done with suspension loaded and best with weight in drivers seat.