Single speed is most common on 1.5 ton (4000 series) AD trucks, although a 2 speed could be ordered.
Most 2 tons (6000 series) trucks had a 2 speed.

What model number truck do you have? ("Loadmaster" doesn't tell us much)

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
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-