Unless you’ve stumbled onto the Holy Grail Sam, the only option you have is to find, as Bill pointed out, a ’68-’72 3/4-ton with the Eaton HO-52 4.10 gear. Believe me when I say that I’ve beat this horse to death. No one makes a replacement gear set for that center section, not GM or any aftermarket supplier whether it’s the early model or the later one.
Even though from the outside the center sections look the same, inside they are different. I’ve had my original 1950 center section and a late model 1970 center section apart side by side on the bench. The ring gear, differential case and cover and differential gear set will interchange but the differential carrier, pinion and it’s bearing are different.
So the later one will, as Bill already noted, bolt directly in because the spacing and splines are the same but you can’t interchange the pinions in the differential carriers.
In the parts books you will find all kinds of wonderful gear ratios that will make your mouth water, but the only gear that will fit your housing is the 4.10 from the C-20’s in ‘68 & ‘69. Then starting in ’70 the C-20 and K-20 both used the Eaton HO52 exclusively and offered a 4.10 ratio. In ‘71 you a 3.54 was offered in the K-20 but it was not the Eaton HO52 axle.
On to ’72 and the C-20 and K-20 could be found with a 3.54, a 4.10, a 4.11, a 4.56 and a 4.57 the 4.10 and 4.57 being the only ones that were an Eaton HO52
And how do you know you’ve found a 4.10? Pull the cover and count the teeth, look at the ratio number stamped on the ring gear, or check the SN located on the top of the center section, passenger side.
Here are a couple of pages taken while I was making the exchange in my 3600.
http://www.pbase.com/dennygraham/eaton_ho52 So there you go, all you ever wanted to know about the Eaton HO52 4.10 availability. That is, till someone else comes up with something new.
Denny Graham
Sandwich, IL
