The Stovebolt Site Forums The Shop Area Driveline Need help ID of late 50s truck rear ends

I need help identifying these rear ends. I was told that the one on the left was out of a '54 3100 and the one on the right was out of a '57 3100.

Any help?
Photos of rear ends

It doesn't look like either one came out of a 54. The one on the left has under slung spring seats which would make it an early 55 and the one on the right appears to have spring seats on the top which could be a 57. Both of them would be 3.90 ratio.

Also, neither rear end in the photo Is a 1954 1/2 ton 3.90 ratio rear end, because that rear end has an enclosed driveshaft torque tube.

On the passenger side of the 3rd member, there should be a stamped ID code. If you can post them, they can be decoded to find out what you actually have. I do agree that the one with the spring padns on the bottom is a '55 1rst, and the other is a '55 2nd-'59. The later rear can also be a 3.38 or 4.10 ratio, in addition to the much more common 3.90.

Can you be more specific of where the code is located? I looked on the passenger side of the third member but didn't see stampings. But they are pretty dirty. It is actually stamped into the steel (recessed letters) or do the letters actually stick out from the housing? Does that question make sense?

I really appreciate y'alls help on this!

Here is a picture

Of the third member if you could tell me where to look. Thanks!
Third Member Pic

This is a GM corporate rear. I think they only came in 3.9. The special order ratios were Spicers.

The number would be stamped between the 2 nuts. Here's a pic of mine showing where the code is stamped.

LongBox55 - Thanks so much for your help. I think you went above and beyond to show me where to look! I really appreciate it.

So here is what I've found. The "55.1" rear end has the stamp NK 1221 and the "57" rear end has AF 806

I hope that can allow you to tell me what I've got. Again I really appreciate your help!

How did guys ever build hot rods or old cars/trucks before the internet?

Here's how the codes break down; the Letter part of the code give the year, ratio, and plant, the Numbers are the month/day. In the case of the first diff, it is a '55 1rst, buit at Detroit Gear and Axle, 3.90 ratio, and was buit on December 21. The other axle is a little fuzzier on the year, as the same codes were used from '55.2 through '59. It breaks down as a 3.90 built on August 6 at Detroit Gear and Axle.

Awesome! So it is just as I thought. Do you know are the '55 1st series axle saddles the same location as the torque tube '53 axle saddles?

Now I guess I just need to decide which one is the better of the two for rebuilding and get to it. I'm going to put one of these under my '53 when I add the T5.

Thanks again for your help!

I would think the pads would be the same. If you need to, the 3rd members themselves are interchangeable.

No the pads are not the same. The '53 rests on a hinged pad and the holes in the springs are further forward than the holes in the '55 first springs. Ideally, you need '55 first springs. However I have read of people drilling new holes in the earlier springs. Never tried it myself.

I think my rear end is off a 57, I'm not sure because it came off a frame without a body. The numbers on it are AF724, close to the numbers on HeathIce's. I looked on the search for a source to look up numbers but couldn't fine one.

I know this is an old posting, but finally getting around to rebuilding this rear end. When I look for differential bearings they have different part numbers for the H072 axle -vs- H033or H035 -vs- Dana/Spicer 44 (which I know these are Danas). So do I have the H072 or H033?

Thanks again guys!

I think the HO72 will have a ring gear deflection pad adjustment beside the pinion, looks like a bolt or screw is all.
The smaller axles shouldn't have that.

The HO72 should also have 8 lug hubs, and yours are 6.

The sure way to get the bearings and seals you need is remove the old ones and check the numbers and or dimensions.

Grigg