What's this thunk?

[cmohr]

Glen , have you checked the rear lower control arm bushes at the axle. Simple to check, drop em down, you can see if they are torn quite easily if you do. They will give a clunk as they start to tear, then when they get bad, you start to get rear steering on acceleration and braking.

Just a thought.

[Nobster]

Maybe an engine mount ??

[glend]

First I guess I should clarify that this thunk is more felt than heard. My daughter can neither hear or feel it when it happens. I tend to feel it through the controls and pedals.

OK I have checked all the suggestions:

I have tried to test the motor mounts by trying to rock the engine by revving and backing off and repeating (both in gear and in neutral) - no thunk there. I have tried driving with side to side swerving to produce a noise - nothing.

LCA bushing in the front are fine, as are the upper and lower ball joints in the front. Front Clevis bushes, while slightly distorted (compression towards the ground) exhibit no cracking or excessive bulging and no real gap at the top. I should point out there is no noise going over bumps.
Rear control arm bushings seem to be ok, axle and chassis ends appear to be fine with no detectable distortion. The rear boomerang ball joint is fine, not leaking, torn, etc. The boomerang upper bushings do have what appears to be a slight tear on the front side on both of them, and the boomerang ends look to have a permanent rearward bias against the bushing but this maybe normal (comments on that?).

I have a slight amount of play in the rear drive shaft Uni (the one nearest the flywheel). Not sure if this is due to the transfer case output bearing giving alittle when pushing on the flywheel or to the Uni. Two of the Uni end caps seem to be leaking a little black grease. Could this be the problem?

[CRDSTU]

Hey Glen does it happen at low speed only, higher speeds only or every single time no matter what speed?

Does sound drivetrain related.

[glend]

Stu it only happens at very low speed - just coming to a stop or just moving off from a stop, with a bias towards happening mostly just moving off from a stop. No noises, problems, diveline slop, etc at speed. This is why I initially suspected a binding cailper.

[Hunno]

I'm going for upper control arms as I have same problem in the ZJ. With brand new lower arms & I have seen a photo's on a thread here with the bushes flogged out. They found the problem as it was causing DW.
I think mine is the rear top control arm bushes. only feels like a tiny amount of movement after change of direction.

[marach]

I'v had a thunk in my kj since new on mine its backlash in the gearbox, stealership said it was all good, they wouldnt lie.
Greg