Two driveline (?) noises, advice needed!

Ok. So, I've had my xj a few years and now that i'm finally fixing all the big things, some smaller things are getting more attention.

First, I should say that it has ZJ rear disc brakes on a 8.25 corporate axle. 4.0, aw4, 231, D30 / 8.25.

The first noise is a clunk when I let off the brakes. Hitting them, no noise. Hitting them gently, no noise. Braking hard, holding, then letting off will produce a clunk from somewhere in the rear end. If I slowly release pressure from the brakes before the vehicle stops, it won't clunk. Has to be bound up all at once & released before any noise. All I can think is trans / engine mounts. Any ideas?

Second, under load it will sometimes make a rattling sound, like a roulette wheel. I run 87 octane. It could be winter gas pinging, conceivably, but my untrained ear thinks it is more likely to be u-joints or...? Common under-load-only noises include what, exactly?

I can get Mopar motor & trans mounts for 150 total through work but really don't want to do it - unless it seems the most likely cause of these noises.

It is stock suspension now but ran it for a long time with a tcase drop.

The clunk you're describing sounds like the front of the rear driveshaft's slip joint is binding then releasing. You can pull the DS and clean and lube the splines with wheel bearing grease (I use synthetic disc brake grease because it's sticky). This is a very common issue with Ford Broncos (I had several). The factory fix was to coat the splines with a blue Teflon coating (that didn't last very long). My XJ just started doing it last week so its on my To-Do list.


You didn't indicate your mileage, but mine has 130K with stock suspension, running 235's. Also, some years the front slip yoke is lubed with TC fluid. I'm not sure which years or whether lubing it with grease would help those.

~120K miles, running 235s.
Greasing the slip yoke - def. next on my to-do list. I'll inspect mounts more carefully at that time.

Long shot, but was one of my similar issues. I found that the bushings for the rear leaf springs (front bushings) were shot. This allowed the entire spring (and axle) to shift slightly rearward during braking, only then to shift back to the "normal" position when the brakes are released and the axle is allowed to move back into place. Worth a look-see? You can probably discover movement through the use of a pry bar applied at the rear spring shackle, or maybe a come-a-long stretched between front and rear axles.

Seems to be fixed. Removed yoke, being careful to mark bearing staps, yokes & splines for location. Not sure why I bothered, I also noticed that my DS threw a weight.

Anyway, though it moved freely and seemed to have enough grease on it, the driveshaft yoke was binding. I know this because I painted everything liberally with a nickel based anti-seize and put it back together. Voilla - no more noise. I'd have used regular grease but reading through some repair forums led me to believe that powdered nickel (anti-seize, really) lubes will work better for this application.

Short version: Cleaned slip yoke & greased with anti seize. Brake-related clunking Problem solved.