MJ Rear pinion angle for SOA

I'm going SOA in my MJ, I pulled my D35 and I'm installing a 29 spline 8.25. Now, before you get all "get a slip yoke eliminator" on me, I've done enough reading to know I don't need one for my MJ, contrary to what XJ's need for 5-6" of lift. Because of that, I'm using my stock driveshaft. Now, I'm getting ready to weld on my new spring perches and I want to make sure I've got the pinion angle correct before I weld everything up. With the stock driveshaft I want the pinion angle to be parallel to the t-case output correct? Do I want it exactly the same or should I compensate for the twist of the axle under load? In which direction, pointing the pinion up or down?

4% of pinion up or so because of the extra length in the Driveshaft the angle is not as critical

The only issue with using your stock DS is that it will be right on the border of being too short

I have a friend who did the same thing netting him 8.5 inches of lift with his 4 inch packs. I asked him and he said he set it at 3 and used a long bed drive shaft (his is a short bed) and to watch out that you quadruple check everything before welding

Your pinion should point DOWN about 1.5-2* less than the transfer case output angle(which stock is about 4-5*)

talk to BrettM, hes been running it forever

I currently have 4.5" or so of lift in the rear of a LWB MJ, using the stock driveshaft.
The 8.25 snout is a fraction longer than the D35 correct? So you'll pick up some yoke travel there.
Worst case scenario you'll have to get your driveshaft lengthened, or you can find a longbed shaft and have it cut down.

As far as the pinion angle:


The pinion angle at the differential should be equal and opposite the pinion angle at the T-case, so that the u-joint harmonics cancel eachother out.

rockwerks said:

The only issue with using your stock DS is that it will be right on the border of being too short

Click to expand...

It's been awhile since I did SOA on my shortbed, but yeah I set the angle to 1.5* lower than parallel to the TC output. The drive shaft was about 5/8" further extended at the slip joint. I never had any problems running it like this. I didn't change the rear shaft when I swapped to an auto vice manual, so now its compressed a little more than stock.

Is the pinion face on the 8.25 further forward or backward than a D35?

With a CV shaft (SYE kit installed) you would want to point the pinion at the transfercase output (or 1 degree down to account for wrap).

When setting pinion angle with a non CV shaft (driveshaft just has one u-joint on each end) you want the pinion angle (rear axle angle) to mimmick the output shaft angle on the transfercase so that both front and rear u-joints share a common angle in relation to the driveshaft just like in "87Manche's" pic above. That way each of the tow u-joints cancells out the others vibrations.

Phase also becomes more important when not using a CV shaft.