The Stovebolt Site Forums The Shop Area Driveline GM 12 bolt rear end id

Can anyone decode the axle housing stamping for me?
I already figured out it's a 3.73 rear end by the Mph,
Tach reading and the tire height.

THD 0217K


Thanks.

The quickest and easiest way is to pull the rear cover and read the part number on the ring gear if it has a rear cover. It will give ratio and date code, at the same time you can see if it has a posi-trac third member. Any idea what it came out of?

It's in a 70 gmc half ton.

You might try on the 67-72chevytrucks site. They have a very active forum.

Being a GMC could be a Dana 44, check for tag on cover bolt.

Pretty sure it's a GM truck 12 bolt. No tag and the cover matches a GM 12 bolt and the numbers are stamped front of passenger side right where GM would put them. It's a half ton so I doubt a dana would have been put in it. I'm just curious how the numbers decode. I know by driving it, it's a 3.73 gearing. I'm not at a point where I can pull the cover at this time. Most sites I look at address a lot of car number decoding but not truck and I can't find the THD suffix on any of them.

May not have been original to the truck? Sorry but I can't find that number anywhere or any sequence even close to it in my notes.

Have you felt or looked up on top of the tube on the passenger side? The rear I'm using came from a 1969 Chevy 1/2 ton and was stamped up there. I had to look around to find it, actually. I think the axle codes for the 12 bolt break down like this:

B, W, G or K tells you where it was produced (K which shows up in your number might mean it was built by McKinnon or it may mean it was built in November...can't uscramble that egg) B means Buffalo, W for Warren and G for Chevy Gear & Axle

A through L tells you the month it was produced (A for January, L for December) if it was made between 1964 and 1970. If your rear end was made after 1971, 01 for January through 12 for December.

If it was for a 69 or 70 truck, it will have a panhard bar ear cast into it. This will be on the passenger side. You can see this below.

The gear ratio codes are always two letters or one letter followed by one number. I'm not going to post all of them because it is a long list, but you can probably find them online somewhere. I will tell you if yours is a 3.73, my notes say it will either be CC, CI (if it is positrac) or also could have been CU (for posi), K4 or K5 (positrac). That's all the id codes used for 3.73. I've never seen any 12 bolt which didn't follow this ID sequence, but that's not to say one didn't happen somewhere. Good luck.