How to determine what degree axle shims to use?

Hello all,

so putting weight in the back has helped some reducing the grinding sound that I'm getting when decelerating but it's looking like my pinion angle is off because of the longer rear shackles (2 inch economy lift with new leaf springs
more like 3.5 inches of lift). The spring packs appear to be the same which are heavy duty spring packs. I have read that they also provide some lift as well upwards of 2 inches.

I took some measurements and I'm trying to determine if axle shims are the best method. I need to bring my rear pinion down it angled pretty much straight at the TC and the angles are definitely different.

Bottom of the yoke on the TC is 5* straight to slightly downward

Drive shaft is 11* upward

Top of the Pinion Yoke on the Diff is 10* Upward

My understanding is that i need to subtract the angles from the driveshaft angle and account for some axle wrap maybe a 1 - 1.5*? (11-5=6 & 11-10=1) The total would be 7* minus 1* for axle wrap.

Would a 6 * shim in the rear work to bring the axle pinion angle down or am I doing this wrong?

Any and all help is greatly appreciated.

Driveshaft angle doesn't matter. It's the TC and pinion your trying to get parallel plus a little for axle wrap.

BTW, for the most accurate measurements go off the valve cover and off the flat on the back of the diff housing.
Do not buy aluminum shims.
Shims over 4* tend to make the shock mounts pretty staggered, consider cutting and rotating your perches and shock mounts instead.
If your move the shock mounts consider moving them up/out too.

RCP Phx said:

BTW, for the most accurate measurements go off the valve cover and off the flat on the back of the diff housing.
Do not buy aluminum shims.
Shims over 4* tend to make the shock mounts pretty staggered, consider cutting and rotating your perches and shock mounts instead.
If your move the shock mounts consider moving them up/out too.

Click to expand...

The shock mounts also hang waaaaaaaaaaaaay down with more than 4* of shim.

i just cant imagine with such a small amount of lift i would need to shim my axle. I did the same lift in a 2000 jeep and it didnt require any shimming or TC drop. Then again i didnt do the leaf springs in the 2000.

I'm just getting a grinding sound on decel that is driving me nuts.