The Stovebolt Site Forums The Shop Area Engine Shop 3/4 ton differential search

I have been able to find a junkyard with someone who knows his way aroud on these. A Dutchman, who immigrated as a youngster. He loves to talk, and talk, and talk. I consider it part of the price of his knowledge.

I have found some 14 bolt rears that are 67" between the hub faces, which is about 1.5" too wide. Some with 3.73 gears, but this man told me that you can get 3.42 gears in the newer ones. When I have more time, I will go back and try swapping hubs between the one ton and 3/4 ton to see if we can come up with a narrower combination. The one ton hub is thicker, and could probably be machined and new studs installed, which aren't cheap. There is also some axle length differences in the two, and can possibly find a way to shorten without having to re-spline the axle.

As you may allready know, later 14 bolt axles are available in floating or non floating hubs and I believe the rear axles from 88 up are wider.The full floater style has larger brake drums and ring gear.3.73's with 31 inch tall tires is 2400 rpm at 60mph, you'll have that 3\4 ton AD on the expressway at last.

I've been considering the possibility of a later model rear for my 3/4 ton GMC, also. Have any of you also involved with the 3/4 tons noticed the rear ends under the mid 80's Chevy chassis cab duallies? The full floater axle hubs are the long type like the original rear in my 52 (as compared to the shorter full-floating axle hubs on the rears from the 3/4 - 1 ton pickups of mid 70's to late 80's). The outer tire on the chassis cab rears appear to be nearly in line with the front tire, instead of a full tire width further out as with the dually pick-up rears. I'm wondering if this rear might not be a little more narrow than the later pick-up rears. I see these rears most commonly under small school busses on the C30 chassis. Every time I find one standing still long enough to meassure, the traffic light changes and there I am, laying in the middle of the highway with an outstretched tape measure, looking like a durned fool! I did notice a few of these school busses in a local salvage yard yesterday. When I have a day off and the yard is open, I'm going to get over there and get some measurements on one sure not to drive away. Just a few thoughts I figured I would toss out there for consideration.

I was just thinking last night(I know, beginners luck :p )that we need to send in our demands to a gear manufacturer for a wider variety and availability of gear choices for the 3/4 and 1-ton trucks with the removeable diff style that came in the trucks from at least 48 to 72.There are many of these out there and if we got together and keep hounding the gear guys,we can make it happen!

There are two options for a rear end swap on 3/4 ton trucks from '47 to '72; one is to do a "chuck swap" of the whole front assembly, and the other is to buy one of the newly manufactured 3.90 gear setups from any of the old truck suppliers which we are not longer allowed to post here as it violates the "no selling/no commercial reference rule" of the Stovebolt forum.

The stock setup is either a standard 4.57:1 ratio, or optional 5.14:1 stump puller. Dropping to a 3.90 or 4.10 is an obvious improvement of up to 20% depending upon what you use and what you had to start with.

The two options that I know of are using a rear out of any GM '67-'72 3/4 ton w/AUTOMATIC (coil spings) rear end which is either 4.10 or 4.11 depending and is a bolt in and easy, or using the 3.90 rear gears that are manufactured and are a more involved and time consuming ring and pinion swap.

Soooo...

Here's a link to doing a 3/4 ton rear swap which is on my website.
3/4 ton Rear End Swap 1951 GMC
This data was posted here on Stovebolt but it was purged (when the bathwater, baby, tub, and bathroom were thrown out a couple of months ago) in an effort to manage file size issues with the Stovebolt server. I voiced my disappointment with this at the time and have since redone the information in abbreviated form on my website where we warn before deleting valuable data to give you a chance to save the data! Bitter?...moi?...why do you ask?

Recognizing this be a violation of the rules, here's the link to the source of the ring and pinion source as well as the swap page on my site:
Art Houser\'s
I believe that Jim Carter and Chevy Duty sell these ring and pinion sets also.

Kook,If you roll over on the other violaters,the moderators will find you safe haven in the Stovebolt witness protection program.A new identity as a FoMoCo owner and a job as a liberal union activitist will cover your trail. Actually ,the sites you mention are on the links page ,so you're with in the spirit of the "law" lol
Yes, the swap you mention is good and simple. When I was looking for a 4.10 pumpkin, all the ones I found were hammmered, bad bearings, and pitted gears.I never had the luck to find a good one.The cost of new bearings plus a $400 3.90 ring and pinion set had me headed for the barf bag.Hated to drop a wad of cash into an old rear axle for a work truck.So the rugged 14 bolt became an option.My situation was for a 68 C20, which is sold now.I had a 49 GMC 3/4 ton a while back, with a 14 bolt full floater from a 75 Chevy pu. The axle is on the wide side for good looks but the truck is a beater, and the 3.73 made for less stressed cruising.Good used 14 bolt axles are $200-$300 around here.So maybe the guys above will let us know how they make out.

I looked at a semi-floater under a 3/4 ton van, it measured 70.5. Found a full floater in the rack from truck unknown that was 69. Most of the full floaters that I measured came from 80's pickups, they were 67", whether they were 3/4 ton or one ton dualies. The one ton had a thicker hub spacer. What we will look at is putting the 3/4 ton hub on a one ton differential. This guy surprised me. When I told him what I was wanting to do we first looked over some differentials, then went to the brake drum racks and he started pulling them down to see what would swap. And all that I bought from him was a distributor for a 250. I will go back on an afternoon and see what we can work out.