The Stovebolt Site Forums The Shop Area Engine Shop Axle ratios for 57-59 GMC Trucks

I have question regarding the gear ratios for the 57-59 GMC light trucks. I know that the 55-62 Chevy 1/2 tons came with a 3:90 with their manual transmissions. I am told that the 57-59 GMC light trucks came with something closer to the Hydramatic trannys which were in the 3:23 range. Does anyone know if this is true and is there a way to tell without counting the ring and pinion? I have been looking for something to replace the torque tube 4:10 axle in my 53 and one of these is available locally. However, I don't want to pursue it if the ratios were the same as the chevy's. Thanks

The GMCs were offered with several gear ratios. I'm running a 3.07 from a '59 in my '56 Chevy.

To determine the ratio, raise one rear wheel leaving the other on the ground. Rotate the raised wheel twice while counting the rotations of the pinion shaft. This will give you an approximate reading. About four rotations means about a 3.90-4.10, etc.

Thanks, I was told by the guy who owns this axle that it won't work on my 53 chevy without a lot of modification. He said the 2nd series GMC's are wider and longer than the 1st series. Did you experience this in your 57? However, he did say it did have a more friendly highway gear ratio which is what I'm looking for.

There will be modification required, but I'm guessing the two rears will be very close to the same width.

It is possible to get the pumpkin from a 55-59 chevy with an open driveline and swap it in your rear housing. It would still be necessary to modify the axle mounts for this to work. You could order a 3.38 gear set for this rearend. However you would have to swap transmissions in order to do this swap.

Bigdadswingdaddy I have a 1951 3100 panel truck. I will be pulling the inline 6 and 3 speed stick. I an dropping in a 283 with a turbo 350. I am doing the rear end pumpkin swap. My question to you sir is, were to find/order the gear set and any other parts needed to perform this swap.

Didn't those GMC's come with Spicer axles, 44 or 60, lots of ratios for them, diff not separate from axle housing like Chevy.

Ed

From what I see that would have a spicer 45, some theads on forum, hard to find ring & pinion.

I would then replace it with a D44 or D60, or a GM 14 bolt, 6 or 8 lug.

Ed

A 60's-70's Dana 44, 10 bolt non drop out or a 12 bolt will work just fine. The length of a chassis has nothing to do with it. Dana 44's were in early 60's GMC's. GMC transitioned from HO to D44 on 1/2T about then I think. You may have a slight width difference you can either live with or compensate with offset. A 12 bolt is probably the best option. Any ratio you want is available. Just measure your WMS to WMS and then measure a prospective donor. There is no way to tell the ratio for sure without pulling the cover and reading the ratio that is stamped on the ring gear edge. Not a big deal to remove before buying. You want to inspect all the gears anyway. You can by a donor for $200 or you can have one built for $900 up. I just rebuilt a D44 3.92 1960 GMC rear. $500 for parts.
"A lot of modification"? If it fits width-wise, the modification is spring perch and/or shock mounts and work out the e-brake. The drive shaft issue you probably already know about. None of that is major. Even if you find a coil spring rear with panhard bar.
I'm sure there are plenty of members to advise what fits width-wise. Cletis has given you an idea already.

Figure out ratio you want, find a standard Chevy 12Bolt on craigslist with that ratio and get'er done. Some guys use car rear ends also but they will be 5 lug.

https://www.stovebolt.com/ubbthread...ar_end_55_chevy_1/2_ton.html#Post1146544

This is in the part for sale section, should bolt up if it is a 55 2nd series