There is no fixed amount on how much to drop the TC or what size the shims need to be to get the pinion angle correct. You may find people that have the same setup and they can give you and idea where to start with the drop. This will be a job where you need to install, measure, adjust, drive and then adjust again. What you want to achieve is a condition where the pinion is pointing up at exactly the same angle that the TC output shaft is pointing down when under power. This will make both the front and rear u-joints turn through the exact same angle. When they dont turn through the same angle you get vibrations. Dont forget that when you apply power the pinion will rotate up a degree or so depending on the stiffness and condition of your rear springs so static the pinion will be a degree or so low.
You need some sort of gauge to measure pinion angle and TC case output shaft angle. A cheap inclinometer from home depot will do the job close enough. When I did this on my 92 XJ (AW4. 8.25 rear back when I first got it) I used a stack of 1/8 inch thick aluminum bar stock about an inch wide that I got at home depot. If you can find 1/4 inch that will make things easier. I liked this better than using square tubing since I could adjust it easily, it wouldnt compress and I could get the stack thickness dead on.
First step is to measure the angles you have. Disconnect the drive shaft and drop the rear end of the shaft (dont pull the front you will loose your tranny fluid). Measure the pinion angle. Then find a surface that is either perpendicular or parallel to the TC output shaft and measure the down angle of the TC output shaft. You may need to use a piece of angle iron held up against the TC case rear face sticking down to give you a place to measure from. Write the measurements down. Calculate how much change you got per inch of shim.
Once you get both angles you just take an educated guess and put in some spacers. Try an inch to start with. Measure again and see how much of a change it made in the angles. If the pinion is a degree or so lower than the TC output shaft you MIGHT be done so its time to put the DS back in and test drive it. If the angles are not correct or you drive it and get vibes you will need to change the thickness of the shim stack. Use your calculations to make a guess on how much to add (or subtract) and do it all again.
After just a few tries (2 to 4) you will probably have it spot on. You must measure. Eye balling can be deceiving. Since the pinion rotation under power is going to vary so much the final shim adjustment will be a flat out guess adding or subtracting a shim or two.
Its fairly easy but it takes a little patience. BTW dropping the TC can mess up you TC skid position (factory skid) so it becomes real tough to put it back in. If you drop too much you can mess up your shift linkage so it wont engage into park properly. If you have to go over an inch try using shims under the axle to partially correct the pinion angle so you dont need to throw away vital ground clearance at the center of the rig. Ground clearance and the ability to loose a shaft and not loose the tranny fluid were the main reasons I quickly went to an SYE.
John
