'99 GMC Suburban - Grinding Noise?

[dcaves2]

I have a 1999 GMC Suburban with a 7.4 454 with 119,00 miles on it. I recently purchased the vehicle from Texas and do love the truck - but when I push the 4wd but (low or high or auto) it grinds like something is about to fall out fo the bottom of my truck. Its not so bad in 2wd drive - but when I go over a speed but theirs a slitgh grinding for about 4 seconds in 2wd and then it goes away. Does this have soemting to do with the transfer case? or u joint? and is this a spendy repair possbly when dealing with a transfer case problem. Also - is this a urgent matter if I dont use my 4wd?

P.S tranny has been overhauled and shifts wonderful.

Thank you in advance for your ansers and time.

[gregory914]

Last month my 97 Burb did something similar, when I accelerated from a dead stop it would make a high pitch gringing sound like if you jammed a car in park at 20 MPH and all foreward movement stopped. It was the transfer case, there are forks with plastic guides on the ends that move the gears in and out of four wheel drive. Mine was the two wheel drive gear fork, it was popping it into neutral. If I put it in four wheel drive it was fine, but mine is the direct FWD without "Auto FWD" selection so I had to limp it home from Toledo back to Cleveland.

I had the transfer case rebuilt by a good shop that knows these things and it's fine. Costs: remove, disassemble case and replace case=$400.00, Parts (rebuild kit) =$157.00, new drive chain=$162.00. Money well spent only took a day! He told me to stay away from rebuilt units because you don't know who rebuilt them and if you have problems you have to send them back to where you bought it from and they are about $900.00 and then you still have to put it in! Plus he gave me a 12 month, 12K mile warranty.

The guy at the shop told me they usualy go bad at 60K miles or so, I've got 128K miles on mine. GOOD LUCK keep us posted.

[dcaves2]

That helps - does anyone think that this is a urgent repair - I'm thinking like in a couple of months (Do too cash)?

Also, would this be the cause of the temporary grinding when I go over a speed bump?

[gregory914]

For what it's worth, mine did pop out of gear when I hit expansion joints on the turnpike so go from there. If your's is doing that on speed bumps, I'd suspect it's the same thing. I did drive mine for 170 miles or so... puckering all the way !!!

[dcaves2]

Hmmm. Very helpful. I do have another question though - is a transfer case basically like a little transmission????

[dcaves2]

I'm still monitoring for feedback everyone. Thanks

[gregory914]

Yes it is like a small transmission. It's located at the tail shaft of the engine's transmission and that's were the power is redirected to the front and rear drive shafts. There are gears and shifting arms that move the gears similar to a manual trans.

[jj76ta]

Did you check the trans mount. If the mount is worn out or broken it could cause the drive shafts to hit the frame or cross member. It is simple to check if you have a friend you trust to put it in grear and hold the break while you watch undernieth and they steps on the gas. {dont get run over} Just a thought.

[dcaves2]

I will check this. Wowo thank you.