I have a 1999 GMC RCSB 4.8 with open diff's and 3.42's. I looking to get a locker with 3.73's. But I don't know what numbers to look for when I'm shopping. All I know is that it is a 10 bolt.

I don't know:
7.5" or 8.5"?
Spline #?

Thanks,
Nick

 

You have a 10 bolt, 30 spline, 8.6 but an 8.5 fit just fine in there.

 

If you are getting an Eaton then the 8.5 and 8.6 are the same. For Auburn they are different as well as some other brands. The Auburn Pro is also the same for both. The 8.6 has a larger diff bearing ID and some of the aftermarket diffs incorperate that for the early trucks also. I say get the Eaton, they work great, they are tough, and they are rebuildable.

 

Thanks guys, I'm looking for a used Eaton? Anyone know anyone that has one?

Thanks,
Nick

 

do a search on ebay. you can find good deals on new or used ones...