Noises with 4wd engaged

Richard Carrino · December 4, 2019

I have a 2002 GMC Sierra 2500z, just bought it last year. It’s been a project truck with a hand full of problems. This is my first time using the 4wd since we just had snow this week.

It engages and works in high and low but there’s some noises coming from the front end that although I’m no mechanic, can’t be good. There’s squeaking thats on and off that will increase with speed. Also some chirping and vibration that will also happen on and off.

The front left CV joint was recently replaced. Front right has a tear in the boot, maybe it’s going bad as well? I was luckily able to plow and get it home but I don’t want to keep driving it and cause more problems. Can anyone help me out on where to start troubleshooting? I have time today, I can get out there and start messing with it.

Thanks,

rich

davester · December 4, 2019

tear in the boot isn't good, as CV joints need to stay clean and properly greased. If you catch it early enough, you can just remove the old boot, clean all the bits really good, reassemble with new grease and boot, and if not soon enough, new halfshaft.

does the front diff have correct fluid level?

after you shift the truck into 4wd, try lifting one of the front wheels off the ground and see if you can rotate it (you shouldn't be able to).

If you can't, great (that's how it's supposed to work)

If you can, then reach under the truck and see if you can rotate the front driveshaft.

If you can rotate the front driveshaft, then the transfer case isn't working right (it's not in 4wd or the chain is busted)

If you can't rotate it, then the front axle isn't locked, either the actuator isn't working for whatever reason (more likely), or the locking gear or passenger side stub axle is broken (less likely), or something else is wrong with the diff (much less likely).

If the above checks out, I would next try getting all 4 wheels up on jackstands, put the truck in 4wd, and put it in gear and see if it still makes that noise. And maybe carefully use a mechanics stethoscope to narrow down where the sound is coming from if necessary.