Noise when slowing down in 4WD

[northerngmc]

Winter has arrived and I had my truck in 4WD high. I noticed a noise when I let of the accelerator pedal. I put the truck into 2WD and the noise disappeared.

Any suggestions or where to start looking?

My plan is to check the transfer case and front diff fluid.

I did a quick check on the front shafts going out to the wheel and when I gave them a good shake both seemed fine.

Would front wheel bearings only be in use during 4WD?

Truck in a 2004 2500HD lly with 170 000 kms.

I have changed fluid in both the transfer case and front diff in the past 12 months.

[biggsteve97]

Where you on dry pavement when this happened? What kind of a noise? A bang, clunk, rattle, or a grinding type noise. The wheel bearings are in use at all times no matter what. Id start by checking the t-case fluid level if it is a grinding noise. If it is a bang or a clunk Id check the front driveshaft u-joints since it seems to only happen in 4hI. What type of fluid did you put in the t-case when you changed the fluid?

[usmcchevy]

Originally Posted by northerngmc

Winter has arrived and I had my truck in 4WD high. I noticed a noise when I let of the accelerator pedal. I put the truck into 2WD and the noise disappeared.

Any suggestions or where to start looking?

My plan is to check the transfer case and front diff fluid.

I did a quick check on the front shafts going out to the wheel and when I gave them a good shake both seemed fine.

Would front wheel bearings only be in use during 4WD?

Truck in a 2004 2500HD lly with 170 000 kms.

I have changed fluid in both the transfer case and front diff in the past 12 months.

Prabably not your problem, but everytime someone mentions a T case problem in a 2500-3500 I think of this:
http://www.thedieselpage.com/reviews/tcase.htm

I would check the front diff, front drive shaft U joints and T case. CV shafts will start popping if bad and wheel bearings are in use all of the time, most noticable going around a slight curve at slower speeds.

[northerngmc]

Originally Posted by biggsteve97

Where you on dry pavement when this happened? What kind of a noise? A bang, clunk, rattle, or a grinding type noise. The wheel bearings are in use at all times no matter what. Id start by checking the t-case fluid level if it is a grinding noise. If it is a bang or a clunk Id check the front driveshaft u-joints since it seems to only happen in 4hI. What type of fluid did you put in the t-case when you changed the fluid?

The roads up here are now covered with snow, so I was on a snow covered road in 4WD when I first noticed the noticed the noise. I had sped up to 50 km/h and then let off to make a turn. While still going straight forward the truck made a constant noise that was a rattle/grinding noise. The noise goes away if I get back on the power. And the noise does not happen at all in 2WD.

I used GM Transfer case fluid, not the auto trac fluid, but the blue transfer case fluid.

[northerngmc]

Well crawled under the truck this weekend.

First a correction to above, I am using GM manual transmission/transfer case fluid in my transfer case which is red.

It appear that I do have the dreaded 'pump rub' happening and I have ordered a new back half to the case and the update kit from Merchant Automotive.