4 wheel drive pops

when i engage my 4x4 on my 86 xj it makes a nasty poping sound. i think it has something to do with the vacuum engage but im not sure. any thoughts would be greatly aprecciated.

when exactly does it pop? like when you go around turns on dry pavement?

Leaks in any of the vacuum system can cause the front axle disconnect to pop out, especially under low vacuum conditions, such as accelerating or cresting a hill. Usually this will be accompanied by the "4WD" light going off also. Check the vacuum lines to the motor on the front axle, for leakage. Look carefully at the rubber connector for rot, and also check that there aren't any rust pinholes in the metal sections of lines. Check also the vacuum lines to the reservoir canister. Later ones had plastic canisters behind the front bumper, but I think the 86 has metal ones in the engine compartment. Then check the diaphragm for leakage if you can, using a vacuum pump. If all those check out OK suspect the vacuum switch in the transfer case.

If the popping is on turns, check the axle universal joints.

its straight and and in turns high speed low speed and any time the vehicle is moving. but when i put it on a lift and run it it doesnt happen.

You'll never find it on a lift. A lift removes all stress on the parts. also check all the linkage. where is the pop coming from ?Track bars, tie rods and ball joints will pop too now those pieces are easiest to check on a lift. there is really too many pieces it can come from to have a guessing contest on a post just about every thing in the front can pop ball joints, u joints axle you name it.

on the 86..if you have not done away with the CV joint on the drive shaft you will get a popping sound but it is real consistent clacking popping sound.....

found out my shift motot wasnt holding so im gonna weld it together and throw in some hubs done and done. ive got it set up to keep engaged right now buy sucking it into fourwheel then i disconnected the disengage vacuum and caped it it seams to work now but i dont trust it for durability.