When I go from a standing start there's a slight clunk sound coming from somewhere in the rear of my XJ. I don't feel any major drivetrain jerk when it happens. Any thoughts as to the cause? Possibly an axle bearing? Maybe the differential or drive shaft? It is a 96 4.0 4x4 with 191k on the clock.

 

crawl underneath... you may need to eat a diet of rice and water for a week or two to pull off this feat...

grab driveshft just before it yokes to ujoint and couples to pinion...

bench press it... try to pull yourself up on it.. move it side to side like it's a lever to a huge manual water pump...

if it wiggles, even a little... you need a new ujoint... ujoints first demonstrate issues by clunking- then, they start chirping... then they squeal like a west virginian piggie.. then they finally stop doing what they're intended to do, and you ain't going nowhere...

 

Especially if your rear leafs are shot. I was scraping my ears on ground and gas tank trying to access my diff plug on Thursday

x2 on the u-ies. Bearings grind, u-joints clunk. Unless you went over a bump with your upside down leafs. Then that clunk is the bump stops crushing your new brake line that you ran along the top of the axle where the bump stops hit... Happened to a guy I know...

 

The most common cause of a clunky/thump from the rear drive line is a rear drive shaft slip yoke in need of lubrication.

It sits just rearward of the transfer case, prior to the upper rear u-joint. It is covered with a protective rubber boot.

When that slip yoke gets dry, instead of sliding forward and backwards as the rear end compresses and extends due to acceleration, it clunks in and out.

It is a very easy job, and they are many youtubes and write up for it.

Google "jeep xj slip yoke lube" or something like that.

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If you hear more of a metallic clank in the clunk. It is likely that the rear drive shaft u-joints should be replaced. Also an easy job.

 

u joints can make a clunk sound when bad or loose.

 

Try the driveshaft/u-joint check mentioned above first, but I bet your slip joint is in need of lubrication.

 

Not so common, but a bad tranny mount will clunk on take off. Put a pry bar in there and lift up, it will be obvious if it is bad.

 

My rear leafs are ok, at least they aren't inverted. I know I probably need a set of shocks as well. I will check out the slip joint and drive shaft. Thanks.

 

Could it possibly be backlash (noise emanating from rear diff caused by ring/pinion gear being too far apart).

Backlash

 

A loose pinion nut will cause clunking, but on accel and decel throughout the driving range.