The Stovebolt Site Forums The Shop Area Engine Shop 3/4 ton third member swaps

I've been all over Stovebolt.com, and over to chevytrucks.org, and elsewhere, trying to verify information about swapping 1967-1972 3/4 ton third members into earlier 3/4 ton rear ends.

My understanding is that the '67-'72 pumpkin can be swapped into 3/4 ton rears from the late '30s up through Task Force trucks. I can find a number of posts that seem to confirm this for AD trucks, but none for TF. I have access to a '52 3/4 ton rear for inspection purposes, and the pumpkin appears identical in every respect I can see to the 1959 rear my friend wants to change.

I found one post that seems to say the AD and earlier axles are 17 spline while the TF and '67-'72 axles are 30 spline, so if you're swapping into an AD or earlier rear you need to get the later axles and shorten them about 1/2".

But I can't find any posts where the poster flat out states that he did this swap into a TF 3/4 ton rear end, with a '67-'72 pumpkin, and it worked.

My friend has talked to a couple of differential "experts" and a couple of truck wrecking yards, and they all say they've never heard of this swap for any of the older trucks. I know I've read about this many times here and on the OleTrucks mailing list, so I think these "experts" are wrong, but I would like to get some confirmation before I advise my friend to spend $400-$500 for a later third member.

Who's been there and done that?

Thanks.

Joe

I can't really answer your question, but I plan on doing the swap in my AD 3/4 ton as soon as I find a 4.11 third member.
I will say that $400 to $500 for a later third member sounds outrageous. Maybe it's your part of the country, but I can get a complete rear end for about $60 at my local u-pullit which has 67 to 72 trucks quite often. I just missed out on getting one because I haven't had a chance to get up there and the truck went to the crusher.

There's a little confusion here. Seems that some of the info you've got is crossed up, as some of it actually applies to 1/2 tons, namely the 17 vs. 30 spline and the axle length issue. That would apply to the early 12 bolt, which changed spline in '65, and the '63-'70 6 lig vs. the '71-76 5 lug for the axle length.
To answer the question, the 3/4 and 1 ton 3rd member (pumkin, hogs head) will swap from the '47 model up to the '72 models. The desireable one would be the later '68-'72 which could be had with a 4.10 gear. There was at one time a 3.90 gear, and if you get REALLY LUCKY, there was a 3.54 only made in '72. The swap is a direct bolt in.

Bill, I think that straightens out all the confusion. Thanks very much.

Ghostrider, I was including some room to do brakes, replace seals, perhaps buy drums, etc.

We think we have located a 4.10 rear here locally that will probably be quite cheap, but may need all the above.

Joe

Joe,
Your truck is nice! I have a '52 3/4 ton also. What size/kind of tires are on it?
Steve

Now that’s where I always get messed up Bill. Your saying that all of the center sections from the ¾ ton trucks from 1947 to 1972 are interchangeable?
Now did all of the 1968 to 1972 models and engine transmission combinations of have a 4.10? Except for the 3.90 which was in, what model, year and engine-transmission combination? And what model and combination in 1972 would have had the 3.54?
When I go to the junk yard around here he wants to know what model, year and drive train combination I’m looking for, specifically.
Boy it sure would be nice if someone could pull all of this information together in one nice Excel spread sheet or something like that listing all the years, models and drive train combinations that were available and their interchangeability. This comes up so often and I’m sure its because it is so fragmented each time. Like seeing a different part of the puzzle each time but never seeing the complete picture.
I sure don’t know how to do it or I would.

Same kudos from here Joe, very nice looking ¾ ton, and tell us about the tars. Oh, and what are you using for those step plates?
Denny Graham
Sandwich, IL

Before junkyards had computers they used just such a manual called a "Hollander Interchange" book. You looked up your vehicle part and it gave a number, you then looked up that number in the back of the book and it gave EVERYTHING that interchanged with it along with foot notes on any small modification needed. On driveline parts back then Borgwarner, Eaton, and just one or two others supplied to all manufacturers so parts off of other brands would sometimes interchange. Hollander is still in business because I got a like 50-60 interchange book to cover a 54 Olds I was restoring.

Denny,
when you look for that pumpkin, you want to look for a truck with coil springs. In some of those years, a Dana rearend was used and I believe it was mounted on leaf springs. The 4.10 ratio was generally only available with the automatic on the 3/4 ton, according to what I have been told.

So does this contradict or narrow down what Bill said earlier?
I thought that was what you had said before about the automatics. There is just so much speculation with this problem that I get lost in all of the here say.
To add to the confusion I seem to remember something along the lines of, it had to be a Suburban also.
So if the 4.10 was only avalable with the 3/4 ton A/T then what was in a plain old 3/4 ton stick? And what did they use different for the 3sp, 4sp, V8, big bloc, small block, six cyl? Seems like the gears would run the full range with the number of combinations avalable. And then there were the special factory ordered rear axle ratios also.
Can ya see what I mean by confusing and the need for a consolidated listing??
Denny Graham
Sandwich, IL

This is the way I understand it based on posts from this site and and a few other sources....
though I don't guarantee it is all correct.

The plain old stock 3/4 with stick would be a 4.57 ratio.
The 4.10 is found in 3/4 ton trucks with coil springs and auto transmission.
The 3.90 was found in the 3/4 ton suburban with automatic, but not all of them and is quite rare from what I understand and most have never even seen one.

Just because it has coils and an automatic, don't assume that it's a 4.10, though. My Dad had a '71 that had an auto, coil rear, but had the standard 4.57 gear. So make sure to check the #s, adn possibly do a manual check of the diff revolutions when you look at one.
One more thing, I have seen the Eaton diff with leaf springs in a '67-'72, mostly on 1 tons, and a couple of 4x4s. Seems that the Spicers were used more on GMC and the heavy dudty models, like the Camper Specials and tow truck packages.

Ok, first the information, then the question:
My experience has been,
65 283 4sp 4.57 coils,
72 454 TH400 3.54 coils Dana 60,
65 292 4sp 4.57 coils,
66 327 TH400 4.10 coils,
71 Van 350 TH350 4.10 leafs,
All were 3/4 ton or 1 ton single wheel.

Now I have a question; Can I buy a new ring and pinion for that pumpkin style rearend? I know GM made it, but what do you call it?

This is all great info but to go through all of this to change from a 4:57 to a 4:10 seems like a lot of effort for little gain. Presuming you are not referring to 60's trucks with coil springs. How about changing the entire rear end housing. It seems to me that there would be a number of later model trucks with better gears in wrecking yards all over. Of course you would have to get one with the correct width and reposition the spring pads but you would be getting a more modern set up.
Fred

Out of all the axles listed, the Dana 60 has the most ratio options. Regardless of the application, Dana 60 gears and bearings are all the same. My 59 Burb has an 8-lug leaf-spring Dana 60 under it that came out of a mid-70's GMC, IIRC. It's got 3.73:1 Ford gears, and a Dodge pinion flange. International trucks also ran Dana axles for several years. They're extremely scarce, however, and the one I have is slightly too wide for the Burb. When I restore it, I might go back with something a little narrower, or maybe I'll just have a set of special-offset wheels fabricated. I'm planning to adapt a 3/4 ton IFS crossmember and suspension out of a newer Chevy truck during the restoration, and use a Caddy 500/Turbo 400 powertrain.
Jerry

I still have the Dana 60 under a trailer, but it sat too long and rusted the gears so it needs a new ring, pinion, and bearings. It's empty right now with the carrier put away. I want to use the Chevy rear end because I found a Detroit Locker in a 64 one ton dually.

I took a DL out of a 66 Chevy rear end and put it in a 14 bolt Corp rearend in a 73 Chevy, it fit with a few additional shims on the four cross-shafts and I had to use the older coarse spline axles. Also the puller holes in the axles will line up with grooves in the 14 bolt's hub and leak out all your hub oil unless you fabricate a gasket that will cover them.

Anyway, I'm fixing the 65 3/4 ton for my step-son. I want to make it a light duty cruiser for him. I'd like to find 3.90 gears (new if I knew where to look) for the stock rear end and put the locker in for fun.

God Bless.
Walt

Denny Grahams upgrading his rear? Wow, next thing he'll be adding IFS.
Welcome Denny to the HI PO! Won't be long and you'll be one of us Hot Rodders.