Rear Brake Rotor Size

[Spoolmak]

I'm going to replace the rear pads and rotors after six years and 140,000 km (85,000 miles) as the pads only contact the rotors to a width of one inch on both inside and outside rotor surfaces. Ouside of that one inch the rotors are seriously rusted to the point the rotor surface is lower than the parts that still make contact.

When I called the parts store, I was told there were two different rotors listed for my truck.
One is a 330.4 x 90 mm, the second is 330 x 76 mm. The second number is the critical one as it refers to the height of the rotor when it is lying flat. The difference in height is 14 mm, or @ 5/8 of an inch. Seems odd to me. I'll measure the exisiting ones before I buy the replacements, to make sure I get the right ones.

Does anybody know why there are two different rotors listed?

Thanks,

Tor

[Quack_Addict]

I'm not certain on this but I think one rotor goes on the 'small' 10.5" full float axle GM put in the HD trucks equipped with the 6.0L and the other rotor goes with the 'big' 11.5" full float axle GM put in the 8.1L and Duramax trucks?

Most part shops around where I live get the 2 HD / full float rear axles screwed up all the time. I bought 2 different rear differential cover gaskets for my axle at local shops (got the wrong one both times; the guy SWORE it was the right one the second time) before I finally had enough and got the proper gasket at the stealership.

[Spoolmak]

Thanks! That makes a lot of sense.
I'll get the bigger rotors from Lordco to start with. If they are the wrong size, I'll just exchange to the other one.

Tor

[Turbo Al]

EBC brakes have rotors that are zinc coated that inhibit the rust that we are getting on the rear rotors from salt spay etc.
Al

[Spoolmak]

The job is done. Great prices on parts from Lordco. Both rotors and better quality ceramic pads cost $225 Canadian. A 30 inch extension bar made short work of the bolts and I had no trouble getting the guide pins out with a good quality t-55 Torx. I also adjusted the parking brakes and everything works as it should.

Feels good!

Tor