Chevrolet 1533X2 30-cwt trucks

[Tony Smith]

Originally Posted by Colin Alford

Transmission,

While the transmission was visually similar to other CMP and MCP types, ... only 1533X2 and 1543X2 used the same speedometer drive gear.

Because the Speedo Drive gear ratio has to be related to the specific Differential Ratio and tire size.

1531 and 1541 had 6.16:1 gears and 17" wheels
1542 had 6.16:1 gears and 20" wheels
1533 and 1543 had Eaton 2 speed diff and 16" wheels.

The Eaton final ratio was dependant on the particular ring and pinion gears fitted with a fixed reduction in the 2 speed gears. Typical ratios of the 40's were 5.83/8.11 and 6.33/8.81 ratios. Note that the Hi ratio in either of these combinations is not the same as the 6.16 of the Chev differential, so a unique speedo drive gear ratio has to be use with the Eaton.

Now if Bob Carriere would be so good to look in his 1543X2 parts manual, we might determine the actual diff ring/pinion ratio.