4hi shift clunk

CanadianHD · December 24, 2004

Hey guys, just registered after cruising the site for a while. I just bought a new to me 2000 gmc 2500HD CC/SB and my problem is there is quite a clunk when I shift from 2hi to 4hi. The sound seems to come from right under my seat. The truck has the push button transfer case, 5.7 auto all stock. I checked the fluid today and it seems a little dirty but it was full. Also the previous owner rarely ever used the 4 wheel and it has 110, 000 kms (canadian eh).

My question is does anyone think that switching to the new autotrac II fluid would be beneficial. Sorry for the long post and thanks in advance.

496 CUBIC INCHES · December 24, 2004

Mine clunks going into 4hi as well. I don't know if the auto-trak fluid will help,but it won't hurt to change it. I went with M1 ATF when I changed mine out last year. I didn't change it for any reason other than to get all the fluids to synthetic. As far as I can tell the clunk didn't change.

Mighty HD · December 24, 2004

I have an 04 2500hd and it slams hard into 4-hi from 2wd. When I am on the gas going a steady speed, and shift--as long as I am accellerating some and shift to 4-HI it's quiet as a mouse, but if I'm coasting and not on the gas..shifting sounds like the transfer case is going to drop..

CanadianHD · December 24, 2004

Thanks for the replies. I am going to change to the new blue stuff in the transfer case and MightyHD I will try giving it a little gas when I shift to see if that helps. Hopefully it doesn't explode, haha.

Shaners · December 24, 2004

My T-case was replaced under warranty. It would bang into 4wd so hard, that it felt like the entire driveline was going to fall out from under the truck.

According to the area rep, my T-case had an improperly machined shaft in it.

CanadianHD · December 24, 2004

Shaners, mine doesn't bang that hard, its more like if you put a manual transmission into reverse without putting it in second gear first, if that makes sense lol. Its just a quick clunk/grind as though gears are meshing. Any thoughts that this could be caused by the previous owner not using the 4x4 very much and are there any servicable components of this t/case, such as actuators ect?

8100 Power · December 25, 2004

Mine makes an a clunk too, give gas or not it does it......but goes in and out real quick, im happy

CanadianHD · December 25, 2004

Tried giving it some gas when engaging today and it went in smooth as silk. Go figure. Now to try and get it to do it that smooth all of the time....

Mighty HD · December 25, 2004

Exactly what mine did. I was thinking with only 5,000 miles it shouldn't be sounding like this. All of my other trucks I usually could coast or be stopped and put it in 4-hi. This is the first where it specifies to be on the gas while shifting.

Be SURE your rear wheels arent spinning while you press it into 4-hi. That's almost as bad as slamming it into reverse while you're driving..lol

dcalex · December 27, 2004

Think of the t-case as a standard trans without a clutch and you can see why the little tricks with the gas pedal to relive the strain will allow it to shift easier. I kinda like that clunk......no question that it made the trip to 4WD