Leaf shackle and pinion angle

Is there a rule of thumb regarding a lift shackle and pinion angle?

For example would 1" of lift from a shackle cause a 2 degree change in pinion angle?

thanks for any help.

I am not aware of a particular rule of thumb, but I do not think the shackle length has much effect at all on pinion angle, as measured at the pinion. The pinion angle should only be effected by the vertical difference in height at the rear spring eye, measured from the ground. When a longer shackle is put on, it pushes the body up and will likely change where the eye sits horizontally, but the ground to eye measurement should change very little.
Although I have never measured this...that just seems to me how it would work.

For every inch of shackle, just over 1°

Floydargue said:

I am not aware of a particular rule of thumb, but I do not think the shackle length has much effect at all on pinion angle, as measured at the pinion. The pinion angle should only be effected by the vertical difference in height at the rear spring eye, measured from the ground. When a longer shackle is put on, it pushes the body up and will likely change where the eye sits horizontally, but the ground to eye measurement should change very little.
Although I have never measured this...that just seems to me how it would work.

Click to expand...

Longer shackles from stock ones will change the transfer-case output angle relative to the driveshaft angle. If you do not lift the front of the vehicle the same amount you did the rear with the shackles then the body of the vehicle will sit up higher in the back and lower in the front which will alter your t-case output angle. I dont think it would be "that much". Which will make it seem like you are increasing the pinion angle but aren't really. The axle yoke is not "rolling up or down" with shackle change.

Someone else with more experience than I should chime in eventually and school us all.