i have a 2003 GMC Yukon SLT 5.3L that when i put in reverse or drive it makes a loud grinding noise and it does not move. what can cause this to happen?

It's hard to say with the description, but if the vehicle moves fine in your forward gears, you may have lost your reverse gear. It doesn't say if this is a manual or automatic, but either way it isn't good. I would get it somewhere for a professional to look at right away.

Sorry, all it does while in gear is a grinding noise and when I step on the gas pedal the engine revs up and it does not move, the same thing happens when in reverse. Its an automatic.

Unfortunately you have catastrophic transmission failure. I would look at possibly trading it in, or start looking up used transmissions.

Actually... There may be a problem with the transfer case. Your 2003 would be an electronic shift correct? If that's the case you could be stuck in neutral, or your transfer case chain is broken.

Well before it happened it made a loud grinding noise from the back of the vehicle.

I also found out that my vehicle does not have the Electronic Shift.

Ok...so there is a manual shift transfer case in a 2003 Yukon? Will you please take a picture of the shifter to put the Yukon in 4wd?

my vehicle has the push button 4wd option which is located on the left side of the dash board

Ok. So it does have the electronic shift 4x4. If the transfer case indicates that it's In 2hi. First look under the vehicle. Is the drive shaft connected? If its disconnected from the rear end, or transfer case its the drive shaft. Possibly a u joint? If it is, try selecting 4x4 on the shift pad. If you still get no movement and experience the same problem, you have found your culprit. The transfer case or drive shaft. I changed direction when you said you have to put a rock in front of the wheel to keep it from rolling away even in park. Sorry for the initial confusion.

But when I put it on 4wd the vehicle won't roll at all.

I'm also able to drive it in 4wd. Also I was told that it could be the spider gear as well.

Did you look to see if your drive shaft was connected? It's either the driveshaft went bad...or the transfer case.

Did you look to see if your drive shaft was connected? If the drive shaft is connected, if you are able to drive in 4x4. If the noise is coming from the rear end, and the drive shaft is indeed turning, then it's the rear end.

The noise was coming from the rear end, we are able to drive it but not far. The driveshaft is connected.

The whole rear went bad or just the spider gears.

Then it's the rear end. We've figured it out!

It's hard to say specifically without taking apart. Could be the pinion shaft, the ring gear. I've pulled these apart with high mileage and had the entire diff just fall to pieces. You can find a complete used rear differential easy enough and fairly inexpensive.

Am I able to replaced the gears on the rear end or do I have to purchase a whole rear end

Yes it has high mileage as well. I think I'm going to take tge cover for the differential off and look at the gears.

Gears can be replaced if they aren't damaged, and the pins weren't damaged,...there are several factors to look at when you pull it apart. if you just buy the Diff you just pull out the old one and replace 8t with a good used one. It makes it kind of plug and play.

Thank you so much.

No Problem! Happy to help

Pinion bearing gone to pieces ring gear rides off of pinion my friend just had all this replaced also with the axle bearings price was 654.00

I got a 2000 gmc yukon an it do the something won't go in reverse its makes a grinding noise I can move it in park but its coming from the front is it the tranny help me