factory 3.90 Eaton rear end???

[Gary66]

So a buddy of mine is updating his 64 k20. Came with a 292 4 speed and he says a factory Eaton rear end...anyone rang across one of these?

[mattbert56]

Yup. There a good solid rear end. There rumored to be one of those hidden gems for 4x4 and crawling stuff. But shhhh. I guess people like to keep there secret. I k of drums can be a pain to find. And same with spring kits for the brakes. I think I bought a brake spring kit for a 71 c20 and they were the same.... not entirely positive I'll have to check and get back to you.

[evan396]

We have the Eaton rear end in our k20 and it was hard to get the brake parts. We also used some of the springs from a c20 brake kit. Drums are also hard to get, and we are going to swap out the front for a Dana 40.

[RedRoad]

I guess I got lucky as the the brake parts for the eaton in my 72K20 were all available at Oreily and fairly inexpensive (shoes, springs, drums, slave cylinders). All the hub bearings were available at Autozone and were around $100

The only problem now is the bearings for the third member. The seals and carrier/pinion bearings it will be around $450 (even more if you have a ball bearing pinion set). If the ring and pinion is toast you are out of luck as there are no new replacements available. I will also put in a detroit locker from a 14 bolt with the 14bolt axles. If you want to use later 14 bolt brakes that is an option as are the 14bolt disk brake kits.

[RedRoad]

as for the R&P, factory ratios were 4.10, 4.56, 5.13. Randys used to sell an aftermarket 3.90 set but it hasnt been available for years now.

[Tito19]

I have an Eaton under my 69 k20 and have had the same experience as RedRoad. New drums did cost me a pretty Penney.

[special-K]

I got everything to rebuild my corporate rear, including brakes, at Napa. 3.90 was never a factory option from GM. Hardly any different from 4.10