Lound bang in 4x4 low in reverse

I was backing over a curb and had it in 4low. when the front tires bumped up against the curb, i gave it a lil throttle and BANG! Then the rear tires broke loose and started turning accompanied with a fast clicking almost buzzing sound that stopped when the rear tires stopped moving. The "part time 4x4" light on the dash went out. The transfer case handle was still in 4 low. I rolled forward and put her in 2wd and gassed it up over the curb. What would cause this type of noise?
Tuck is a 1990 XJ 4.0 AW4 NP242 3" lift 31" tires D30/D35 3.55gears

Thanks

Chrisc321 said:

I was backing over a curb and had it in 4low.

Click to expand...

damn thats hardcore.


was it fine after you drove away? if so i wouldnt sweat it too much. mine makes a horrible noise from the LSD under a heavy load because its old and worn.

My guess is that a vacuum leak or a problem with the vacuum disconnect (bad disco motor, bad switch in TC, could be any of a number of things) caused the axle disco to let go. The 4WD light is controlled by vacuum from the vacuum motor, so the axle must have disengaged first to make this happen.

Does it go in and out of 4WD now, or still make the noise? You should probably start by checking all the vacuum hoses for leaks, and the vacuum reservoir for cracks, and from there, if needed, test the disconnect motor for leaks, and finally check that the vacuum switch in the TC is working correctly.

had it in 4low so I could ease over the curb. :dunce: I have a non disconnect front axle

Hello....you need 4-low to "ease over a curb"?? Curbs are like 6" high...sheesh.

But...never mind...when making noise..need to fiture it out..regardless of the circumstance...right?

Well, then, a second suggestion, which is to check your TC linkage. Because it's the last position in the row, if the linkage is out of adjustment, it will often fail to engage fully, even if all other positions work.

You can start by looking at the lever itself. In 2 high, the lever should be about parallel to the floor. Adjustment is pretty simple. Just shift it into 4 low, get underneath and loosen the bolt on the adjusting trunnion, and then make sure that the lever on the transfer case itself is shifted all the way to 4 low (in other words that it's as far as it will go, and detent engaged). Now tighten the bolt again, and you're adjusted.