The Stovebolt Site Forums The Shop Area Engine Shop Changing the gears of a 3/4 ton

My 3/4 ton will only go @40---45 mph. and that's pushing it. I would like to change the gears in the rear, but C. D. only has 1/2 ton gears. I don't know if they would work , if not what is my best recorse? I've goten a lot of help in the past and always was happy to get it. Paul

There are some threads on this subject. The rearend gear assembly (known as the front loading style pumpkin) from a 67 to 72 3/4 ton GM truck with automatic has a gear ratio of 4.10. These will bolt right in in place of your original. There were some Dana axels in that period which don't apply here. Your original ratio should be 4.57, so changing to 4.10 is not a big change. You can also put 235 x 85 R16 tires on to give a reasonable rolling diameter.

Some vendors like Jim Carter sell the 4.10 gear set but they can only be used in the modern gearsets mentioned before.

Search for Eaton 4.10 in the archives - that should give you more information than you need.

truckernix - that ratio was most common behind automatics, but there were some stick-shift trucks with the 4.10 pumpkins.

Additionally, the 1970 BB 3/4-ton trucks used that axle with a 3.90 gearset, but good luck finding one...

Sorry, I should have sad it was a 53, 3/4 ton. Don't know if that has any berring on the hole project.

Chevy used the same basic carrier design in their 3/4 ton (and 1 ton, iinm) pumpkins from 1946 - 1972. The actual gear parts are different but all carriers work in all pumpkins.

As it was stated before, the 68-72 style carrier came in a couple of different ratios: 4.57, 4.10, and 3.90. 4.57's are by far the most common, followed by 4.10's. I'll repeat GMCPanel's wishes of luck on finding a stock 3.90.

The good news is, you can purchase 4.10 and 3.90 gear sets from Jim Carter that will fit the 68-72 carrier, if you can't find one with stock 4.10 gears.

The only thing is, they're pricey.

Good luck in your search!

The 4.10 gears that are (supposedly) available are a TOTAL ripoff and waste of money. You still need the '64-'72 carrier to install them. You might as well just get a '67-'72 carrier from the boneyard. Even if you have to have one shipped, the maximum for a ready-to-run unit with shpping should be $200-$250. I got a good one at the pick-n-pull for about $60.

GMCpanel,
I did not know about the stock 390, that would be pretty nice. I have noticed that Jim Carter doesn't seem to offer the bearing and shim kit for that gearset, but he does offer it for the closed drive rearend. I am wondering if the bearings are still available elsewhere. I don't need one myself because I now have the 410.

Bearings, etc. should be available through your FLAPS - just tell them it's for a '72.