The Stovebolt Site Forums The Shop Area Driveline Rear end for 69' GMC 3/4 ton

Would like to swap out for a posi- trac. Can that be done? What should I be looking for?

A '69 GMC 3/4 ton should have a Dana 60 (I have seen some with Dana 70s as well), a limited slip carrier or locking differential (Detroit Locker, which was a factory option) will be readily available for it. http://www.ringpinion.com/

What is the basic difference between a 60 and a 70?

The overall design is essentially the same, the difference is the size. The 60 has a 9.75" ring gear, the 70 has a 10.5" ring gear. Both will be full floating in a 3/4 ton, while I have seen semi float 60s (Hemi Chryslers, GMC/Chevrolet 1/2 tons, many late model 3/4 ton vans from the Big 3), I have never come across a semi float 70. The easy way to tell what you have is to look for a "60" or "70" cast into the center section. Usually, it can be found either on the top of the pinion snout or on the rear face of the housing, next to where the cover mounts.

You guys are really impressive with your knowledge. Thanks for sharing. I'll have it home next week and get it on the lift for inspection and ID. I know there is an issue: the drive shaft rotates 1/2 turn before take up, and clangs pretty loud going from reverse to drive - the reason I didn't drive it home.

So I'm thinking I'd replace with an upgrade more suited for here on the farm. If I can replace as a unit, like the third member in a F...., my only experience, that's the way I'll go. Otherwise it seems to be a really solid old truck with plenty of umph. Input appreciated.

I've only found two 3/4 tons with the D70 in it, one was a '69 Chevrolet Camper Special my Grandpa bought new, the other was a '72 GMC Camper Custom I looked at buying from my Uncle. Could possibly have been an odd option, certainly rare for sure.
On the Locker, I could have sworn that I saw that listed for the Danas in GM trucks, perhaps it was in a different brand (Ford maybe?).

I had the 69' GMC on the lift this weekend and got the casting numbers off the differential housing - C30255. But I couldn't find anything on Google to help understand the numbers. I did find an article on GM RPO numbers, and looked as directed, but no info on the differential. And there was not tag on one of the bolts. Doesn't look like a complete assembly swap, but no history.

Also have another question; say the plug to check oil level, but how do you drain it for a fresh oil change?

Thanks Barry. I sure hope they saved a bunch by deleting that drain plug. Sorry, but I was not a Chevy guy until we bought the 41', so the cover is all that the 10 bolts/nuts hold? Looks like I better start looking for a shop manual!