Two speed rear axles are very rare to non existent for trucks under 1.5 or 2 tons.

The 2 ton and larger two speeds generally have a regular gear and a slower one, they were intended to get a load moving, not go fast.

I have heard of a few old two speed small rears, but not actually seen one in person. I think Truckstell is the brand, but check the spelling.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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