Bad 4x4 noise

TheMythofUtica · October 9, 2006

Anybody sick of me yet? Yeah I've been living with some problems with this truck.

It's a 1999 OBS Yukon with 'autotrac' or whatever they call the pushbutton style system. OK, when I engage 4x4 my truck sounds like the t-case is going to implode. It grinds badly - I can feel vibrations in the floor and steering wheel. It works, but just makes really bad sounds. Problem has existed since last winter, just let it go all summer because I don't use 4x4 during the summer.

Checked the t-case and it's full of fluid. Front diff is full of fluid. The truck has 104,000 miles and it's probably the original fluid. But could that be the cause of the noise and vibration?

I mean it really feels like the t-case is going to fall out of the truck, however I can't isolate the problem. It may be the front axle, I can't tell. Anybody have any ideas for this one? U-joints appear tight, wheel bearings are tight. No play in either driveshaft and the problem virtually disappears when in 2 wheel drive (still a little bit of noise though even in 2wd).

Thanks again guys.

bobcat5544 · October 9, 2006

does this happen when the truck is just sitting in gear no movement or when the truck is moving. also how do you know the 4x4 is fully engaged / working

TheMythofUtica · October 9, 2006

It only makes noise when I'm moving and it doesn't change based on whether or not power is being applied (on the gas or off, still makes the same noise).

The 4 wheel drive works. How do I know that? Because in 2wd my rear tires just spin in deep snow and ice and when I switch to 4 wheel drive the truck actually makes forward progress.

ZZ327 · October 9, 2006

i think your transfer case isnt engaging all the way so it just grinds but the 4x4 still works. DONT put it in 4wd untill you get that fixed!

bobcat5544 · October 9, 2006

Ok so when you are not moving at all in 4x4 there are no noises, but when you are moving is when the noises are present, does the noise change in sound the faster you go?

TheMythofUtica · October 9, 2006

Not really, the noise kind of gets louder with speed but the pitch stays the same. It's a deep tone grinding/growling type of noise along with vibration in the floor and steering wheel.

bobcat5544 · October 10, 2006

If you can feel it in the steering I would be looking at the front diff. like the pinion bearings or the front hubs

You can also remove the front drive shaft and engage the 4x4 if you get the same results then it is in the transfer case.

TheMythofUtica · October 10, 2006

OK, I'll give that a try. Thanks.

95Sierra2500 · October 10, 2006

My truck was just making this same kind of sound/vibration. Double check those U-joints, and spin your driveshaft around a few times, or if you're brave enough, put the truck up on jackstands and have someone put it in 4WD and put it in gear, letting the tires spin. Watch and see if either of the U-joints is just kinda flopping around. It definately sounds like one of your U-joints is shot (just fixed mine this morning), or you have a problem in the transfer case. A CV joint or a differential problem would make noise all the time as your front half-shafts and the diff are always spinning.