I have an 86' cj, 4.5" Rubicon Lift, 44 Front, 9" Rear, 36" TSL's, 6cyl, NV3500, Dana 300, CV Rear Shaft. At about 40mph and up the jeep is not shaking and not necessarliy vibrating, but the whole rear driveshaft and tranyy is rotating constantly. It doesn't feel like it's the tires, but I guess it could be. The driveshaft has been recently balanced and the rear is set up correctly (2* below directly pointing at rear of tranny yoke). I thought it might be a lose motor mount, but that isn't the case. The shifter is motioning left to right. doesn't seem to be as bad when its cooloer outside, but still there. Any toughts? I haven't installed my front shaft yet (not arrived yet), so I can't pull the rear and drive in front wheel only to see if it stops. Any help would be apprecitaed.

With the information you've given, it seems unlikely that the problem is the rear driveshaft. You did install a new U-joint in the rear of the rear driveshaft when you got the CV joint installed and the shaft balanced, right?

It could possibly be a pinion bearing in the rear differential. Could be the transmission/t-case mount, if you've already checked the engine mounts.

Could be an out-of-balance tire. Could be a loose wheel lug nut in front or rear. I'd chack all that stuff.

If you still can't find it, you might want to put the vehicle on a hoist and run the engine with the tranny in gear and see if it does it then.

new u-joints. The 9" rear is a brand new unit from currie ent, so I don't think that is it.

I did notice the transmission stabalize bushing & bolt was not tight. You know the where it is bolted on the drivers side through the belly pan. Do you think that not being bolted down securely could cause this? I have new parts & bushings I was going to install, just haven't gotten around to it yet.

I'd get those mount parts replaced and then see what it does.

I had a tranny mount go out on mine. it can be hard to move by hand but with the engine torque it will. Hose down those belly pan bolts with PB blaster for a couple days before you drop it. I busted a bolt off mine and that was a PITA getting it out when lying on your back with drill shavings fallling on your face!!
Josh

That's what assistants are for! <img src="/forums/images/graemlins/smile.gif" alt="" />

Off Sunday so I am going to swap out the bushings and replace the stablizer bolt that holds it all togther and see if there is any change. Right now you can spin the bushings by hand b/c the stud that comes through the belly pan is stripped, so it is definately loose. hoping that makes a difference. Will let ya know Sunday how it goes.

also you might want to check your control arm bushings.. could be part of the problem <img src="/forums/images/graemlins/kewl.gif" alt="" />

Update - Dropped the belly Pan and replaced bushings and stabalizer bolt and hardware and the motor / trans seems nice and solid now. I think it is time to replace my tsl bias ply tires though. They flat spot really bad and take a good 10 minutes to warm up and reduce the vibrations. At first coming out of my driveway its so bad the whole damn jeep is shaking (Think paint mixer). After a bit it got much better. However, this is my dd/weekend wheeler. So I need some real world advice here. 37" SSR's, 36" TSl radials or 37" MTR's. I need to keep to my 15" x 10" rim so Krawlers are out. We do a lot of back country wheeling. Mud (yep), Rocks (of course)but mainly all around trail riding with a mix of everything. Want to get tires tomorrow, so any real world advice you can offer would be much appreictaed.

The flat-spotting you describe is a well-known problem with bias ply tires. It's much worse in winter because it takes them longer to smooth out. Some guys I know use bias ply tires in the warm months and radial tires in the winter.