Rear End Numbers and Ratio
 

I am in the middle of servicing the rear diff. on my 64 1/2 ton GMC. It has a tag on it that say "46-13" on the top and "3.54". Now i'm thinking 3.54 gears....What is this thing and whats it doing under my truck?

It has patent #'s on it twice and the only other # was C90294 at the top right rear and 44-1 at the right bottom rear. Its a 3 rib on the driver side and 1 rib on the passeger side of the carrier. Any idea what I'm looking at without seeing a pic?

Re: Rear End Numbers and Ratio
 

Sounds to me like you are looking at a Dana 44 rear axle with a 46 tooth ring gear and a 13 tooth pinion that would calc. out to a 3:54 rear end ratio. What it is doing under your truck is probably pushing it down the road with power from the engine and trans.
All kidding aside, GMC's came stock from the factory with Dana rear axles. 1/2 tons had Dana 44's and 3/4's came with Dana 60's.

Re: Rear End Numbers and Ratio
 

Nicely put...

Re: Rear End Numbers and Ratio
 

That explains it. I couldnt find anything that would help on the GMC. Everything point to 3.55. Thanks for your help!