91 Explorer popping and grinding in front hubs

[MiniMe]

91 Explorer 5speedStarted having 4wd problems. popping sound from hubs. suspected hubs were failing. Went to local JY and bought a used set of auto hubs.. Put them on and took it for a drive. when I engage 4wd I hear the same popping sound. I turned sharper than I should have and heard a very loud pop. put it back into 2wd and heard and strange noise sounding like from drivers front almost as if my axle was still turning. got it back home and raise entire vehicle off ground and out it into 4hi and 1st gear. I heard a clicking/grinding sound like a baseball card in bicycle spokes from passenger front and continuous popping from drivers front. I swapped all the hubs around and still same result.

How do the hubs actually operate? by vacuum? could I have a vacuum problem thats not engaging 4wd entirely

Could I have two sets of bad hubs? anyway to test them?

 

[adsm08]

Those old auto hub systems are J-U-N-K. It's very possible you have two bad sets, but you might have two good hubs between the four of them. They are mechanically actuated, not vacuum. The axle shaft is always splined in to the outer portion of the hub. When the axle shaft starts spinning it works a spring that pushes everything together and locks the hubs in. Lots of things can go wrong, the spring can break, the cam can break, my last set just plain stripped the cam out.

You can take them apart, clean them up, re-grease everything, and sometimes they start working again. Sometimes they are just FUBAR.

If you can get it on jack stands or stuck in some mud or snow somewhere, somewhere you can get all four wheels to spin but not grab. Put it in 4-hi, and let it roll in gear, see if you have both axle shafts spinning up front but only one wheel. That will be your bad hub.