Random Clunk/Jerk on Wet/Snowy Roads

[SandyNewf]

Help! I have a 2000 EB Explorer and it has started to "clunk" at different speeds - feels like it's coming from rear end - and I can feel it in the steering wheel. Seems to happen on wet/snowy roads - in 4 HI or Auto - and at different speeds (anywhere from 30mph to 55mph). I've described it as feeling as if I hit a hard, sharp bump - but only with the rear end - or as if the rear brakes momentarily engage. I feel and hear a definite "clunk" noise. Any ideas??

 

[SoNic67]

I think is the TC engaging - the 4x4 should have some friction packs (clutches) inside to smoothen the coupling.
Maybe yours are worn out?