your mind is still stuck in SYE mode me thinks...

 

You know what, I think you're right to be honest. I've been on 750 mg of naproxen the last week for headaches, so bear with me here. Just thinking out loud....

Lifting the jeep does not affect the actual pinion angle. it only affects the driveshaft angle. This in turn puts pressure in the u-joints as they turn, possibly binding them up. A shim with the fat and forward is going to point your pinion down, causing more binding on the axle pinion u-joint. So really, why run shims at all?

 

because I effectively lowered the rear mounting point

 

Kind of but not really. Yes, you "lowered" your pinon by increasing the height of the t-case, but that shouldn't have changed the angle of the axle pinion( which is determined by how it sits on your leaf springs), only that of the driveshaft. This is what causes vibes due to u-joints binding. The output shaft and pinion should still be parallel (within 2*) with each other. Pointing the pinion down will require an increase in driveshaft length and will also create more binding on the u-joint, so how does that help? Like I said, my brain is a bunch of fuzz right now, so I may be looking at this all wrong still and need it explained better.

 

I thought about this last night while fixing vibes on another jeep, I did not have vibes with a slip yoke DS and pinion almost in line with DS at ~4.75". The s10 leafs, relocation boxes and lift shackles were perfect at putting the pinion a few degrees below DS to account for axle wrap. I drove like this for a few months around the country before swapping tcase's with a SYE. I know the premise behind why tcase and axle should be paralleled but at that height, your putting so much strain on the u joints and honestly I think they would bind if you lowered the pinion. I was always told by geezers that a DS should have a offset from end to end to allow the needle bearing to spin and disperse load and wear among them to increase the life of the Ujoint. Hench why some older cars have the motor offset

btw dukie, why are you against SYE's on older XJ's? Its nice pulling rear busted rear DS and driving out in fwd and not worrying about losing fluid.

 

not against them at all - just don't have the cash for one right now, and i know the stock slip yoke DS will work on my XJ at ~4.5". Thanks for the input tho - I talked to another friend that was at ~5" with no shims and said it was fine, so i'm just gonna let it ride and adjust after if necessary.

And i always carry a Gatorade cap for that reason lol - fits perfectly in the TC output to seal the fluid in.

 

lol I have to remember that, I alway use gatorade bottles for spitters

 

same reason i carry one in my jeep. No $$ for an SYE yet.

 

so just to update - installed the lift - ended up with about 5-5.5" in the rear, no shims, no sye, NO VIBES!

took it up to 85mph without issue.