The Stovebolt Site Forums The Shop Area Engine Shop Need a new rear end in a 56 GMC

The rear end in my 56 GMC "Frances" short stepside is going bad. I want to swap a late model rear with higher gears because I am on the highway 5 days a week. The old rear end was for the original standard 3 speed. I now have a 350 V8 with the 350 automatic.
Also I want to keep the original 6 lug wheels. I think the current original rear is 55” backing plate to backing plate or 62” wide at the wheel mounts.
SO ..anyone know what year rear end is 6 lug with close to the same width?

Frances

Thanks
Cadman

I've got a '70 Chev 1/2 ton in my AD. 3:08 and 6 lugs.

Go to Tech Tips (at the top of this page) and look under axles. All the homework has been done for you.

Do you have any idea what's going on with it? The '56 GMC used a Spicer 45 rear (same as Dana 44), parts are still available, as are different gear ratios. you may want to consider overhauling the existing rear and do a gear swap while it's apart. That will avoid any fitment issues that may come up by changing the entire rear.

That's good news, Bill. I didn't realize that the Spicer 45 was the same as the Dana 44 or that gear sets were still available. I would like to get some better highway gears for my '58 GMC. Does anyone know of a good source for gear sets? I would like to see what ratios are available.

Randy's Ring and Pinion
http://www.ringpinion.com/PartsList.aspx?SearchMode=Make&MakeID=3&MakeName=GM+%2f+GMC+%2f+Chevrolet+&ModelID=290&ModelName=1%2f2+Ton+GM+Pickup&Side=Rear&DiffID=15&DiffName=Dana+Spicer+D44&CatID=10&CatName=Rings+%26+Pinions&CatType=Sub-Differential

You will find the spicer 45 and dana 44 have very few interchangeable parts. GMC 1/2 tons that rolled out of the factory with a 3 speed most likely had a 3.07 rear ratio. 1/2 tons with 4 speeds or automatics had the 3.90 ratio.