Offroad-Express

I have just brought a 99 Wrangler Sport. I engaged 4x4 tonight and instantly heard knocking coming from left front. Stopped as soon as I disengaged 4x4. What should I do?

I would check the front axle U/J's first?

Can you explain it a bit more. Is it when 4H or 4L is engaged and you moving straight? Or when turning? It could be the double cardan joint in the front driveshaft or as already said axle u-joints.

Can you have a look at the u-joints and see any signs of rust/spinning caps etc.

I am assuming nothing knocks when in 2H (normal driving).

Sorry yeah no noise in 2wd, put in 4wd high and knock knock knock at about wheel speed going straight and turning, back to 2wd noise stops. Didn't try 4 low.

Ok, first test would be to remove the front driveshaft and do the same test again. If the knocking goes away, you know what needs rebuilding/fixing - its fixable.

Noise comes from the left side because that is where front diff and driveshaft is.

Removing driveshaft is easy, four bolts on the diff yoke and four bolts on the transfer case yoke.

Hey All
Heads up time, I took my newly acquired Rockster (as named by my son) to the hospital and it turns out it is the driveshaft bearing down by the front diff that has poo'd itself. Here's hoping it can get fixed in time to go and play this weekend?
Thanks for all your help.

Driveshaft has u-joints. There should be no other bearings in the driveshaft. If it's the u-joint then they are easily and chapli available. Easy to fix too. Stick with Dana Spicer u-joints.

I may have it wrong buy it was definitely a bearing as the guy said it's best to go heavy duty, may be one in front diff, not sure, all the 4x4 guys said to take to him as he specialises in 4x4 and is in the local club too.

If it was the bearing, then Timken would be the best option (used by factory as well).