I just added some shims on my 8", went with a 6* shim, and still have some vibes (greatly reduced), I think I may add on a t-case drop.
*=degree
Shims are not too bad, and if you are doing shackles with them that will help as well for about 1* or so. Before doing this I would suggest going to Home Depot and getting a gravity protractor (~$10) to measure the differance bx your pinion ange and driveshaft. It has a magnetic bottom that will hang from your drive shaft nice, but use an extention (socket ext) for your pinion as not to trust the housing surface. Say the drive shaft is at 20* and the pinion is at 14*, thus giving you 6* differance. Stock is at 0*, keep in mind that as you step on the gas you pinon will rotate up 1-3* depending on thrust. Someone may chime in here, but I think you should be OK with a 1-3* differance.
I'm not sure what you know so I'll start from the beginning.
Remove the wheels in the rear and place jack stands.
place a jack under the axel to sepperate it from the spring pack.
I would suggest removing the entire spring pack since you will need to make the shims part of the pack. The front spring eye may be a bear to remove. If it breks there is a good chance you broke the welded nut inside the frame rail. There are ways of fixing this e-mail me if it does.
To be safe use three 10" c-clamps on your spring pack. One next to the center pin, and the other two on either side just outside the clamps that hold it together. It can be done with one c-clamp but those springs are under lots of compression. I broke the c-clamp when I used one.
There is a center pin that holds together your pack that can and probably will break. I used a pair of vice grips on the bottom and the correct size socket for the top. Then pound out the broken pin with a screw driver or drift punch.
This pin will need to be replaced with a longer ones, about $7 at a local 4x4 shop.
Place the shim with the fat part to the rear of the pack on the bottom and insert the new center pin through the shim and pack and replace new nut. Hacksaw or grind off the excess center pin.
You can now remove the c-clamps slowly.
install your new shackle on the vehicle by using the stock bolt hole to the rear. The shackle now becomes your mounting point for the spring pack in the rear.
Now loosen the other spring pack and repeat the same steps above so you can move your axel a bit to help re-align the center pin nubs.
Line up the new center pin nub with the hole on the spring perch. You may have to move the axel a little to line things up. replace the u-bolts and the plate like it was before on top of the spring pack. You may need longer u-bolts to do this, also from the 4x4 shop. Sometimes the u-bolts have a hard time lining up with the plate holes. you can use a c-clamp to compress the u-bolt in, above the axel to line things up, now reinstall the u-bolt nuts. You should see your pinion angle move up as you tighten down the nuts on the u-bolts. Thats about it.
During this make sure not to strip the threads on the u-blots or center pins, or else you be back at the 4x4 store.
This is long but detailed to include problems I ran into, which may not happen to you. I still consider myself a learner as well, but I'm sure someone with more experience will chime in with other strategies. This is what worked for me. Good luck and keep us updated.
Dom
