Clunk out of 4x4...HELP?

[SMorneau]

I have one that baffles me. My 4 wheel drive seems to work perfectly except after shifting out of 4x4 into 2wd I drive for about a mile and I get a clunking noise and sensation that is similar to the rear end clunking. It is not violent but it never used to do this. I had the tranfer case rebuilt last summer after a snap ring broke and except for this it seems to work well.



The truck will shift into 4x4 hi range just fine at speeds up to 60. No clunking just slips right into gear. It doesn't whine anymore than it used to and the indicator light comes on almost immediately. I will drive for a mile on the interstate and shift it back into 2wd. The 4x4 indicator extinguishes almost immediately and all seems well. After about another mile of driving I get the afore mentioned clunk/sensation. Sometimes it is very pronounced, but not violent, other times it is almost imperceptable.



I was under the impression that when the light went out the axle was definitely disconnected and the front output shaft from the xfer case was disconnected when the lever moved. If this is the case I am stumped! It has done it in both 4th and 5th gears so it doesn't seem to be the transmission.



Any ideas would be appreciated. Anyone else had this problem?

 

[baby.driver]

The light is not accurate. Look for a vacuum leak on the disengage hose.



Jay

 

[Matt42]

4wd Thunk

I agree with Jay. The light will just tell you that the signal has been sent to the mechanical thingy that does the disengaging. This sort of odd partial disengagement problem is why I prefer manually locking hubs. Wish I had them.

 

[illflem]

Originally posted by SMorneau





I was under the impression that when the light went out the axle was definitely disconnected and the front output shaft from the xfer case was disconnected when the lever moved.

You are right, the light sensor is located to trigger the light when the locking collar is engaged. The position of the vacuum actuator has nothing to do with the light. The clunk should come at the exact same time that the light goes out. I can see why you are stumped, I am also. If you let up on the throttle when shifting the collar will engage/disengage faster and easier. If you keep on the throttle it can take a mile for the collar to move, the load is holding it in place, but the light will indicate were the collar is.

 

[baby.driver]

When I first installed the BD 2lo kit, before they fixed it to draw vacuum on the disengage side, the collar would float enough to cause the clunking noise. Scared the poop out of me knowing the forces involved could break something. It was LOUD. At the time it was banging around the light was OFF. The light is on only for a fully locked collar.

I still say look for a leaky hose first.

In fact I will go so far as to say that if you can shift into 4hi at 60mph, " it just slips into gear", " light comes on instantly", that your collar is already partially engaged and you've been spinning that driveshaft all along.



Jay