'87 YJ Build

[One-Eye]

I think that might be it.  Just have to tighten everything down and try but initiall test run was good.  No bad noises.  Drove it like 5 miles today just to stretch her legs.

[One-Eye]

So the T-Case works just fine.  Everything goes the way it should.  I also fixed 4-low (because it didn't work before).  Internal setting was FUBARed.  Now, I do have a pretty significant vibration when slowing down.  It happens a little bit when I get off the gas (from higher speeds) but when I get on the brakes it starts to vibrate pretty good until I am doing like 20 miles/hr.  The only work I did on the brakes was the brake lines themselves.  Didn't touch calipers or drums.  I will try to bleed them again just to see if there is anymore air in the lines but I don't think it will make it shake the way it does.  If anyone has any insight to this I am dying to hear about it.  YJ's unit!!!  I can't be the only one that has had this problem...can I?  Thanks in advance.

One-Eye

[calvynandhobbs]

The last time I can think of something like that happening to me was when I had my CJ7. It was the rear driveshaft. When accelerating everything stayed tight, but when I let go of the gas it would create a void in pressure and the ujoint was vibrating. It was shot and after doing this for about 3 weeks the ujoint gave up the ghost and the rear driveshaft fell out on me while driving it.

[One-Eye]

So did you need a longer drive shaft to fix the issue or was it just a bad U-joint?  The U-joints that I have are brand new so hopefully it ins't that but then again they are cheap so maybe it is better that it is a U-joint.  Now that being said I did notice that when the Jeep is given a little bit a gas (or I guess a lot) the rear axel torques a little bit.  Wonder if that is what is making it do that?  When I get off the gas the axel rolls back down causing the vibration.  Wonder how to stop that.  What you said sounds a lot like what is happening though.  Thank you.  God does it feel good to driver her though.

[gearhead1985B]

So did you need a longer drive shaft to fix the issue or was it just a bad U-joint?  The U-joints that I have are brand new so hopefully it isn't that but then again they are cheap so maybe it is better that it is a U-joint.  Now that being said I did notice that when the Jeep is given a little bit a gas (or I guess a lot) the rear axle torques a little bit.  Wonder if that is what is making it do that?  When I get off the gas the axle rolls back down causing the vibration.  Wonder how to stop that.  What you said sounds a lot like what is happening though.  Thank you.  God does it feel good to driver her though.

what are your angles on your pinion yoke drive shaft and t case yoke/output? (f-ed up angles are the main cause of drive line vibes)

and you have axle wrap it is accepted as a normal thing that happens on a lifted leaf sprung jeep and it will get worse when you are in low range  the only way to totaly cure axle wrap is an anti wrap bar but check your leaf spring u bolt torque i tighten the as tight as i can get them with a 3' breaker bar (about 200 ft-lbs) with used u bolts i have seen that cure mild axle wrap an a cj

what i see happening is when you are on the gas normally the pinion wraps up slightly (probably less than 5 degrees) putting your u-joint angles in a happy place and when you let off the gas the axle wrap goes away making the u-joint angles unhappy and it vibes i know on mine the vibes are worse on deceleration than acceleration

[calvynandhobbs]

On my CJ it was just a bad ujoint that I replaced and never had the problem again. What Adam just stated is also very true. Your vibration is coming from that general area. Rear driveshaft and ujoints are the vibration, but it could be from some axle wrap and loading and unloading the ujoints with the pinion angle you currently have. Did your lift come with wedges or have angles on the plate to account for the pinion angle change from being taller?

[kirksjeep]

When you were over my place you mentioned that the Jeep still had the t-case drop kit installed.  With the drop kit it will throw your driveline angles off with a SYE.  Check out Tom Woods website for some insight on driveline angles with the SYE.  I had to pull the drop kit and go to different rear shims before  I did the 8.8 swap to get the vibrations gone.

[Mr Rock]

The last time I can think of something like that happening to me was when I had my CJ7. It was the rear driveshaft. When accelerating everything stayed tight, but when I let go of the gas it would create a void in pressure and the ujoint was vibrating. It was shot and after doing this for about 3 weeks the ujoint gave up the ghost and the rear driveshaft fell out on me while driving it.

X2 one of your rear ujoints is bad, also double check all the straps that hold the u-joints on.

[gearhead1985B]

you need differnt wedges the ones you have are most likly for a jeep with no sye