99 Tahoe won't shift to 4lo + a clunk

[Ikillrinst]

i just did the same exact thing, after putting the new rear end in this weekend the clunk was still there and worse, so after reading older posts on this forum i pulled the shaft cleaned and greased it, and for the first time in 6 years its not clunking, who would have thought it was just that simple:smilielol:

 

[spero]

How do you repalce the transfer case motor? Were you able to remove the old TC w/out removing the driveshaft? How do you Retrieve any trouble codes from the data link without a scanning tool? In short. can you just align and bolt the new TC and expect it to work w/pout any technical difficulties?

 

[loulblades]

Recently had to replace my 4WD switch because the 4WD wouldn't engage properly and that took care of the problem.

As far as the "clunk" is concerned, the recommended lube for the yoke is GM's Special Lub(e)ricant (I kid you not). That worked for me.

 

[jnicks01]

As for the clunk, I have it once in a while. I put on new shocks and spare tire was in the cargo area, so those are not the reason.

4x4 low. I acutally just had the same issue yesterday. I shifted into 1st gear and it ingaged when I was moving at about 2 mph. Had to be in neutral for it to shift back into 2wd, if I remember correctly. Kind of worried me when it wouldn't go back into 2wd right away. Thank god for the owners manual.

 

[98 Yheti]

The Clunk
I have a 98 GMC that I had the same clunk in a while back, until I figured out the problem. After wrenching around for a while, I finally got it. The problem was the U-Joints on the rear drive shaft. What happens is when sitting still, there is no pressure on the u joint because the drive shaft being turned. As soon as you push the pedal, there is instantly pressure put to the shaft. When this happens, there is pressure put on both the U-Joint between the Transfer Case Yoke and the drive shaft, and between the drive shaft and the differential yoke. As soon there is the pressure, the U-Joint is no longer loose in the Yoke and “slams†against the sides of the yoke. It will only do it one time because after that there is plenty of pressure to hold it up to the side due to centrifugal force and the motor turning to turn the wheels. Therefore, when you stop again, the pressure is taken off of it and it will give the “clunk†again. This is especially common in lifted and lowered vehicles due to the fact that the angles are changed at the U-Joints placing more pressure and strain on them. U joints are not too difficult to change and a shop will charge a lot of money to put them in for you. If you have the time and the right tools go for it! Hope this helps!

The “4Lo issueâ€
Currently, my truck is still not functional in 2wd and 4wd. About three months ago, I was driving on the interstate and my transfer case shorted out and dropped me into 4lo. This then caused the tcase, the transmission, and the custom rear driveshaft to all “explodeâ€. The trans and the tcase have been replaced along with the driveshaft, but there is still a problem. I have gone through and replaced every part of the tcase TWICE now and it still does not shift out of 4lo. What I have narrowed it down to is the wiring harness going to the tcase. Somewhere in the wiring, it is grounding out which is shifting it down into low range. I am going to test the wiring and see what I can find. Not sure if this helps you or not, but just thinking that it may be similar to you, just in “reverse†of what I am experiencing.

Long post, but hopefully someone will find it helpful!

Best of Luck!