I recently put in the RE 4.5 short arm lift on my 1988 XJ. Ever since I have been noticing a clunking noise coming from underneath the car near the rear. The noise happens when getting on the throttle while moving and right when I get off the throttle. If I hold the throttle in just the right spot it will make a rattling sound.

Today I climbed under the car to take a look and it seems to be coming from the inside of the transfer case. The rear driveshaft has a bit of rotational play if I try and turn it side to side.

I have not yet installed an SYE or longer driveshaft but I did do the transfercase drop that came with the lift kit. I know it is not a permanent solution and plan on doing the SYE and driveshaft.

Has anyone else experienced this? What could be causing the clunking sound? And would it be safe to keep driving it like this until I get a SYE and driveshaft (if thats the issue)? Really don't feel like potentially killing my transfer case!

Thanks

Check your transmission and motor mounts. Check your exhaust hanger that hangs off the crossmember. Lifting and a TC drop can expose issues with the mounts and make the exhaust clunk on its hanger.

Check the ujoints too.

Ujoints... you just changed the angle of your drive shaft so bad ujoints may show up worse... i would also check your u-bolts to make sure they are tight...

I will check all of the above and the U Joints again. But is it normal to have a fair amount of play in the drive shaft at the transfer case? The play doesnt seem to come from a U joint.

Search youtube for videos and you can measure your play against others.... when you move your rear driveshaft and get play, does the yoke from the tcase move as well??? If not, then its the ujoint connecting the 2... if so, then you do have other issues... your driveshaft should have very little play if any...

Also, somebody else with a 4.5 lift can chime in here, but im thinking you may need a shim.... when you accelerate, your rear axle twists a litte which makes it "further" and closer to your tcase.... if the lift made that angle too severe, then that may be the noise and a shim will help.... thats also why i suggested the ubolts to minimize axle wrap

So the Ubolts are tight but I do notice a slight amount of axle warp occurring.

I put the car up in jack stands and had someone run the car up and get on and off the accelerator so the noise would occur. The noise is for sure coming from within the transfer case. The Slip yoke does not have any vertical or horizontal play, only the rotational play. I do believe it is this rotational "slack" that is causing the knock when you step on the gas.

What could cause this excessive slack? It's not the chain because that is only active while I'm 4wd correct?? It's the 231 case btw.

When you "wiggle" the driveshaft by hand, does the yoke coming out of the tcase wiggle the same amout?? Or does the driveshaft move more than the yoke? If you can wiggle your driveshaft and the yoke stays still, then its ujoints... otherwise, may need to rebuild the t-case????

The Ujoints don't seem to be the issue. They do not have any wiggle.

The play is coming from within the transfer case or transmission. I am not sure which. I am 90% sure that this play is what I hear knocking when driving. I am just not sure what would cause this amount of play and if it is a bad idea to keep driving the car like this. Could it be bad splines or gears in the transfer case??

Any other input is greatly appreciated!

Here is a video of the amount of play. The noise sounds just like this while driving and hitting the accelerator.


In the video the car is in park but it also makes the same noise while in neutral.

Rotational play is normal, its just part of the design

It shouldn't be doing it constantly though. You might check your motor mounts or trans mount, they could be allowing the powertrain to shift and bump the driveshaft.

Look here:

yeah, friend of mine has a broken hangar there, and the exhaust dribbles on the crossmember

It was extremely common on almost new XJs when I worked at the dealership. very little clearance was part of the design. As the clock ticks on 25 years, very likely a source of vibrations, clunking etc.