Fiat panda 4x4 1987.. when driving in 2wd everything seems fine, engage 4x4 and seem to be getting a clunk /knock from the passenger rear wheel? Quite loud.. would this be the rear wheel bearing on its way out as there is more drive going to it in 4wd?

its possible.. however my money would be on the prop shaft.. check its mountings and the UJ's.
its not an issue i have had before but someone on here my be able to help!

Yes didn't think of the propshaft... can we still get the uj's? Also would that make a quite a loud knock? Does sound like it's coming from the passenger rear wheel only

well the reason why i say that is because theres not really much on the back of a panda that can cause a knock. the only time i have come across a knock was when i found the exhaust hitting the leaf spring. try moving the exhaust about see if it knocks into anything with little movement.

check your shock absorbers.. give them a pull and tug, see if the bushes are still good.

ride the clutch and (hand)brake and see if you can replicate the sound while you have someone safely look under the car.

also check the leaf spring bushes/shackles.

like i say, theres not really many things that can knock :/

Would this be the issue? Also can I still get parts to fix this?

i am not sure, it looks like the centre mount for the prop? if it moves in any way other than turning.. it may be the cause of the noise.

if the rubber has come away i recommend Tiger seal.. its all thats holding my one together for the past 2 years. never came away yet and ive had it under some stress!