The Stovebolt Site Forums The Shop Area Engine Shop Need Help on this 3/4 ton rear end question

To the 3/4 ton guys:

I was of the understanding that I can swap the pumpkin out of my
1953 Chverolet 3/4 ton truck which has a stock rear end and a 4.57 gear
ratio with one from a 67-72 Chevrolet/GMC 3/4 ton which has a 4.11 gear
ratio. I was of the understanding that all 3/4 rear end were the same from
1947 to 1972 except that the best ratios were in the 67-72 trucks.

But, as I have been shoping around I get a response like this one
below! Are these guys right, what book are they looking at? I talked with
Jim Carter's and they say a 67-72 c20/c30 pumpkin is what I want to improve my highway speeds. I am
inclined to trust Jim Carter but I am hopeful for more definitive
advice from others who might have already done this.

Dear Sir,
Two things: one, we cannot help you with your request for a higher gear
ratio as all we have left at present is lower ones. Two, our books say that
you have to stick to Chev or Gmc 20 or 30 series in 1961-4, or in 1965-6 the
20 series 3/4 ton with coil springs to find the 4.10 ratio. The 67-72
pumpkins do not work and the highest gear ratio you can get in the ones that
do work is 4:11. The others available are 4.57, 5.14 and 5.83. Good luck,
Elfros Autowreckers

Thanks,

Dennis Oland
1953 Chevrolet 3/4 ton

I have a 68 C-20, it has a noisy 4.57 gear set. Some have 4.10's . Not famolar with the swap but I believe you may have to chage something in the pumpkin to make it work properly. Try Randy's Ring and Pinion web site or this guy rear man

Oland, Do a search, this topic has been covered here. I helped change the pumpkin in Old Car Kook's 51 GMC 3/4 ton from a 4:56 to a 4:11 . The 4:11 came from a 72 3/4 ton. He bought the chuck from Tom Myers Truck Parts in Oklahoma 918 542 3871. It was a direct bolt in.

Kook posted some pics here on the page of the conversion. If you can't find the pics , E mail him at [email protected] ..

Oland, This thread will lead you to it,,,

3/4 Ton Swap Pics

Unbolt the drive-line.

Remove the bolts holding the axle shafts in(they are out by the wheels on the end of the hub).Remove the axles(pull out)
Remove the bolts holding the differential unit in the housing.
Remove the differential.
Clean out the housingand clean (if you already haven`t ) the new donor differential.
Install your new differential.
Install your axles.
Fill with oil and hook up the drive-line!

You may want to remove the hub and brake drums so you can clean and inspect the bearings and seals.

Have fun and remember to recalibrate your speedometer!