66? 12 bolt ID help
 

I've been digging around all morning and can't find a whole lot.

I just picked up a rough 66 SWB yesterday. It has a 12 bolt rear. It's not sitting in a spot where I'd want to pull the diff cover yet. Axle code is HA 07 15 W. It has a shorter panhard rod that seems to mount closer to the diff, with a larger frame bracket compared to my 64 LWB that Grandpa bought new and fairly certain it's all original. Grandpa's 64 also has a 12 bolt (some places say it's 30 spline, others say that didn't start till 65), but a longer panhard with a larger axle bracket.

I found several code charts online, but they all skip 66.

My plan is to rebuild the frame and bed and move my 64 drivetrain, cab and front sheet metal over. Easier than a chop and weld. I just would like to find out as much as I can.

Thanks!

Re: 66? 12 bolt ID help
 

GM Parts Book info-

Re: 66? 12 bolt ID help
 

Ah, the page I've been looking for. So, appears it is a (or at least was) a 3.73, and probably the original axle. From what I've found in other charts etc, 07 is date code, W is build plant, but not sure what the 15 is.

Thanks!

Re: 66? 12 bolt ID hel
 

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That sheet is data sheet is a great source of info. Someone underlined my rear end in pen. 12 bolt posi 3.73.

Re: 66? 12 bolt ID help
 

This may very well be a dumb question but where can the ID code from the parts book posted above be found? I’m curious what gear ratio I have in my truck myself to be quite honest.

Re: 66? 12 bolt ID help
 

The factory build info is stamped onto the top of the passenger side axle tube. That will only tell you what was inside from the factory 53 years ago. It is very easy to just pull the cover and have a look. I can almost guarantee that the oil needs changed unless you have done it recently.

Re: 66? 12 bolt ID help
 

I tried to clean the axle tube off as much as possible but can’t seem to find any stamps or markings anywhere. I also pulled the diff cover but can’t remember how to go about figuring it out that way either.

Re: 66? 12 bolt ID help
 

No letter stamps on the ring gear even if you rotate it around?
Count the teeth on the ring and the pinion , then divide.

Re: 66? 12 bolt ID help
 

The ring gear has the part number, date made and tooth count stamped on the outer edge. Or you can count the teeth on both the pinion and ring gears and divide them to get your gear ratio.