Well I got yukon 4.56 gears pit in 2 weeks ago and I hit 520 miles on new gears. Its making grinding noise and rattling. sounds like I'm dragging something heavy on the ground. Taking it back tomorrow where I got them installed. Its running ok. It has factory posi rearend. and posi works.any ideas??

 

could be anything. id try not drivng it as much as possible.

 

Sounds like you may have overheated and destroyed the gearset. Did you follow the break-in procedure to a T? They don't give you those instructions for nothing.

 

I followed break in. The first 300 miles. I took short trips, But betwwen 300-500. 70 miles then half hour break, then drove another 70 miles home. I took it easy and didn't beat on the truck. It nows has 580 miles on gears. Its at the shop now getting looked at. I'm getting the oil changed. I'm running royal purple oil (i think thats what its called)

 

Well the break in was done correctly and you're using some of the best oil out there. I'd say it was probably set up wrong. But be careful, because if it was overheated, the shop may try to blame it on you.

Does it make the noise when under load, when turning, when coasting, etc? Does it do it at certain speeds or at all speeds? I blew my ring and pinion the other night and it made similar noises only while coasting. Bad pinion bearings can make a similar noise as well, but in my experience it does it most while braking heavily.

 

It did it all the time, starting, cruising and stopping. The strangest thing happen. always my luck It stopped making the noises 4 miles before I got to the shop. They are going to check it out and change the oil I just don't understand something: Why is when you buy the truck brand new,You never have break in period with the gears. Whats the difference.

 

You know, I've always wondered the same thing. Good luck and let us know what the shop says.

 

Well we think it was rust build up on the rear rotor. Just like how drum brake gets built up at the edge. When I pulled the wheels I noticed the rear brake guard had scrapes on it. I thought maybe axle bearing or something shifted causing the axle to shift inward and causing to hit the guard. So they sanded the corner edge and changed the oil since it hit the 500 mile mark.

 

In order to make them run cooler and quieter, new gears are lapped at the factory. However, they are not lapped under the same pressures that driving creates. The loads generated while driving, force any microscopic high spots on the gear teeth back into the surface of the metal. This is called "work hardening". Work hardening is similar to forging in the way that it compresses the metal molecules into a very compact and hard formation. This can only be accomplished if the metal surfaces are lubricated and the gear temperature stays cool enough that the molecular structure does not change. If the temperature of the metal gets hot enough to change the molecular structure, it will soften the surface instead of hardening it. This may seen like a balancing act but it all happens easily & passively as long as the oil keeps the gear cool while it is breaking in. Some of the synthetic oils on the market today can help a gear set live longer. These oils will continue to lubricate at temperatures where many crude oils break down.