What's this thunk?

[glend]

I have a new 'thunk'. Symptoms: I remove my foot from the brake and shift to the accelerator = thunk! Occassionaly coming to a stop I can feel a thunk. This is not something I hear so much as feel through my foot. The KJ CRD has only 50,000kms on it.

What I have done recently or in the past few months to try to locate and solve the thunk:

Pulled the rear drive shaft and greased the slip yoke, pulled all the brake calipers off and cleaned and regreased (with silicon grease) all the slides, clips, and pins. New pads on the front brakes as well.

I have crawled around underneath and checked every suspension related bolt and component that I can find. The control arm bushings look ok but hard to tell. The front ball joints seem fine.

I know my vehicle well and check it regularly so this is really pissing me off.

I have a hunch the thunk is coming from the rear end somewhere but no evidence that this is so.

Ideas?

[billy the kid]

G'day glend,I get that "thunk" occasionally. Mine seems to be coming from the front end.I'm not game to tell the stealership as they will diagnose it as a $2000 repair.Not lol

[Auberon]

Might I suggest from your description of a decelerating or braking thunk that you think seriously about lateral unis rather than longitudinally acting ones - probably needing a good lube - any play? Otherwise twould be indicative of other possibilities.
Otherwise it points to suspension like the LCA bush which can thunk before going metal to metal like allowing the clevis bracket to occasionally contact the LCA under acceleration or deceleration.

I found my LCA issue by lifting and dropping it slightly with just my shoulder and a mechanics stetho.

Rotten noises like thunks travel and are deceptive little buggers.

Typically in any engineering diagnostics thunks imply excessive backlash - it is primarily a matter of deciding if it is lateral or longitudinal for diagnosis direction or I also use one of those parabolic listening devices that JayCar sell to listen for those odd noises as you can record them for about 10 seconds and play it through an oscilliscope - writes volumes once you get a wave form even when rotating by hand BUT first things first:
QUESTION 1: Longways or across?
Good luck
Remember those lateral unis are always turning even if not driving. Have they been done?
Good luck
Auberon

[glend]

I suppose it could be a drive shaft Uni but I have been under there with a pry bar trying to move it around and can't generate any offset movement at the rear diff. I can however get alittle vertical movement at the end where the flywheel and slip yoke join the transfer case. It could be the transfer case output bearing I suppose but its a young vehicle for that to go (but I do have a 3" lift).

[Fouros]

could be rear upper ball joint, on the boomerang

[JEEPaul]

When you greased the slip yoke did it stop the 'thunk' in the short term? First time I greased the slip yoke in my old XJ it stopped the thunk for a couple of months, but then returned. Regreased it with almost half a container of grease (ie, half filled the yoke 'sleeve' with grease) and it never returned. Used a similar amount of grease on my KJ after it developed a thunk a few months ago and still all good.

[glend]

Paul it seems to be a different problem. Yes the slip yoke thunk did go away after the regrease, and I did use a fair amount of grease. I was amazed at how little there was on there from the factory. That was all before the Jeep Jamboree, this thunk has surfaced after I returned from the Jamboree.