Hunt_U_Down

So idk where this post should go. Feel free to move it wherever admins.

Recently my '89 xj has what i call a rear shake. When i hit around 45 mph-55 mph and stay at a constant speed for a few seconds, I will start to get a rear to front shake almost as if the axle is falling behind and trying to catch up. It doesn't affect my steering wheel at all. Its kind of violent though. If I let off the throttle the vibration stops. Its even hard for me to recreate it because its kind of a semi rare occurrence. But it is driving me insane. Crawling under this xj for months now and I'm at a loss. Everything looks great underneath. Any help is appreciated.

Jeep Details:

1.5" Rough Country lift
235 tires
everything else is stock.

neverenuff

remove your rear drive shaft and inspect both u-joints very carefully. Check transmission mount and both engine mounts with a flashlight for cracks or looseness. The drivers side engine mount likes to crack out first. Checking the drive shaft installed does not tell you very much, so do the work to find the answer.

Hunt_U_Down

I've checked the u-joints, they're solid. I've also removed the drive shafts as well. All fine. But didn't think about motor or tranny mount. Thanks

Hunt_U_Down

I've also had someone say check for weak leaf springs. possibly axle wrap??

cruiser54

Have you inspected all the fasteners for the axle to springs?

Got a rear tire with Slime or fix a flat in it?

Hunt_U_Down

Yes I've inspected all bolts and fasteners throughout the rear of jeep. And no, my tires are still like new.

This weekend I plan on inspecting all the engine and tranny mounts. Also I'm probably just gonna replace the u-joints even though they feel solid. They are original so probably better to get something new anyway.

All tires are balanced as well. That was the first thing I checked.

Hunt_U_Down

Just wanted to update anyone who may have had this issue. It was finally solved. And I was completely dumbfounded when i found a vacuum hose undone going into the m.a.p sensor and a vacuum hose undone going into the charcoal canister. Once i plugged them back in the shaking has not returned. Go figure. Still beats the hell out of me how that was what caused it to feel like it was from the rear and not like it was coming from the drive line. But that was what it was. Thanks for all your help!

cruiser54

Thanks for the update!!

Hunt_U_Down

Yep that black hose in the left image was the one that was off. It had me thinking I needed a new axle lol

cruiser54

Check this out:

http://cruiser54.com/?p=280

Hunt_U_Down

Incredible lol.. You literally just wrote that not too long ago. I will be doing your hose upgrade immediately. Two more weeks and the "Mobile Scout" will be getting a lift and some new shoes. Going with Rusty's 3" and some black steel wheels with some Kenda Klever M/T 30's!!!