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Discussion Starter · #1 ·
OK, here's the situation... Been getting some vibrations at highway speeds for a while and finally crawled my butt under the read end and started fixing it tonight, but haven't quite got it licked.

Before I did anything, I would get some driveline vibes at speeds over 50 MPH. No biggie since I mostly wheel it and drive around town. When I did the Skyjacker 4" it came preconfigured with 6 deg. shims, so I left those on. In looking at it, the angle was way too high.

Note: my rig runs a CV shaft.

Tonight I put in a set of 2.5 degree shims and it is NOTICABLY better, at highways speeds it's fine as long as I have pressure on the driveline (i.e. acceleration or up hill). It seems best when the rear axle is experiencing a little "squat" (I think that's the right term).

When I am coasting or going downhill, the vibes come back. Not as bad as before, but they're there.

Is it same to assume that the angle is now too low with these symptoms?

I was going to go buy a couple more sets of shims tomorrow and experiment. What are my best bets? Was thinking a 3.5, 4, and 4.5? Is .5 significant enough to make a difference, or just stick with round numbers?

'83 CJ-7 nothing original but the tub and axle tubes
 

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It sounds like bad u-joints or the ball in the CV is worn or popped. With a worn joint or ball, it will react as if it's tight when there's pressure on it (acceleration or up hill) and will come loose when the pressure is releaved(coasting or going downhill).

As far as angle goes, point the pinion yoke 1 or 2 degrees below the center of the t-case yoke. You don't want it to be straight all the time( even after compensating for axle wrap), the needle bearings need to move alittle in the joint or they'll flaten.

Wayne @ Big Island RockCrawlers
"PYRO" The Rock Crawler
Web Site: http://www.members.tripod.com/surfmac/Index.html
 

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bluesman where did you get your shims? I am looking for a set and am wondering if I have to order them or can I get them at a local parts store(kragen, napa, carquest....)

79 CJ 5, 258, dana 30, model 20, T18, dana 20, 2.5" rancho lift, 1" shackles
 

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Discussion Starter · #4 ·
you should be able to get them the same place you got your lift, rancho makes some. You MAY be able to get them from a local parts store, I know Mr. Gasket makes some as well, and most parts houses have access to that brand.

'83 CJ-7 nothing original but the tub and axle tubes
 

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Discussion Starter · #5 ·
Well, it's not the shaft, u-joints, or CV. I have now tested this by installing my spare shaft (Woods', never even been bolted up prior to this).

Also tried a set of 4 degree shims and they have the same symptoms as the 6 degree, just not as pronounced. I'm looking for a set of 3's now (everybody has 2.5 and 4, but no 3's). If anybody has any ideas on where I could find some 3's or any other suggestions, I would greatly appreciate it.

'83 CJ-7 nothing original but the tub and axle tubes
 
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