Chevrolet 1533X2 30-cwt trucks

[Tony Smith]

Originally Posted by Charlie Down

Are there photos of CMP airline connectors fitted to trucks?

This is the Left side chassis rail of a 12 Cab Chev.

You can see the PTO port on the side of the transmission (Dark grey, no pump fitted), and the pre-drilled holes in the frame. A short copper pipe runs from the pump to the inside of the frame rail. The airline fitting bolts through the lowest of the 3 holes, connecting directly to the copper pipe.

[Tony Smith]

Originally Posted by Charlie Down

Are there photos of CMP airline connectors fitted to trucks?

Originally Posted by Tony Smith

This is the Left side chassis rail of a 12 Cab Chev.

You can see the PTO port on the side of the transmission (Dark grey, no pump fitted), and the pre-drilled holes in the frame.

Jaap De Wit has posted some good pics of his 12 Cab Chev which clearly illustrates the relationship between the position of the Transmission gear lever, the Air Compressor engagement shaft, and the Air Fitting hole on the Chassis in THIS THREAD

[Hanno Spoelstra]

Next topic on Chevrolet 1533X2 configuration: the rear axle. The requirements document of the LRDG posted by John J. Valenti specfies a 6.17:1 differential ratio.

From the “Desert Chevrolets” article in Wheels & Tracks magazine no.8 I copied the technical details of the 1940 Chevrolet WA. This had a differential ratio of 5.43:1, or 6.17:1 as an option.

I’ve read the 1533X2 was fitted with a 2-speed Eaton axle. Can anyone show the technical documentation to underpin this?

2B188792-D663-4F75-A854-7F96B31ADE73.jpeg

[Charlie Down]

My research has led to a website http://chevy.oldcarmanualproject.com/index.htm
which has lots of old manuals on it.
I have attached illustrations showing exploded diagrams and parts lists of a 2 speed differential, a standard axle for comparison and diagram of the linkage to the cab although it doesn't show the cable connector to the speedo adapter.
Its not clear to me whether the 2 speed unit bolted on to replace the conventional axle differential casing at the front of the axle, or it came as a complete replacement axle. I haven't yet found a good clear photographs of either axle for comparison.
The front axle was 100mm wider than the normal axle to allow for the extended fenders and sand tyres. I presume the rear axle would also be extended. Would this be a new axle, or would they just have extensions to the standard axle?

[Hanno Spoelstra]

There’s a lot of info to be found on the Eaton conversion. But where do we find documented proof of the assumption/fact that the 1533X2 was fitted with a 2-speed Eaton axle? Is it only the handle in the cab?

Would there be a need for a 2-speed axle? Or would the LRDG have more benefit from a limited slip differential as fitted to the CMP C15?

[Charlie Down]

From what I've gathered from reading around, the 2 speed axle gave alternate 'half gears' so the 4 speed box became effectively an 8 speed box offering a lower crawler gear and better economy over a range of terrain as a more suitable gear ratio was often available, both very useful to LRDG Patrols.
However I would have expected it to be detailed in the specification, with the only possible reference being the 'Speedo adapter' which would be necessary for more accurate navigation during the day, until a star fix could provide accurate co-ordinates at night.
Looking at period photos of LRDG trucks the 2 speed handle shows up whenever there is a suitable angle of the cab, which admittedly isn't often!
So until proved wrong, with the photographic evidence, and the obvious advantages of having this feature on the trucks, a reference to speedo adapter (which could admittedly be to do with the larger sand tyres) in the specification, Tony Smiths very positive identification of the feature ( and other features!) I am happy that 2 Speed Axles were a standard and beneficial feature of 1533X2 trucks.

[Tony Smith]

The Eaton 2 Speed diff was a very widely used diff in both military and commercial trucks from the 1930's right up to today. Methods of engaging the diff have ranged from a lever and solid rod, cable, pneumatic and electrical controls. During the war, they were fitted to Chev, Ford and Dodge vehicles in large numbers.

The adapter is a necessary part of the installation. The drive for the speedo cable, and therefore the speedo and odometer comes off the gearbox and is geared to read accurately when the diff is in the "High" ratio. When the "Low" diff ratio is selected, the gearbox drive will still be reading the higher speed for a certain gear/rev range. The adapter is switched with an actuating cable from the lever, and reduces the cable speed by a similar reduction ratio to the diff (which I understand is a reduction of 39%, ie a ratio of 1.39:1)

[Hanno Spoelstra]

Thanks Tony for the details on the Eaton axle.

Originally Posted by Charlie Down

So until proved wrong, with the photographic evidence, and the obvious advantages of having this feature on the trucks, a reference to speedo adapter (which could admittedly be to do with the larger sand tyres) in the specification, Tony Smiths very positive identification of the feature ( and other features!) I am happy that 2 Speed Axles were a standard and beneficial feature of 1533X2 trucks.

Agreed - I hope one day a maintenance manual and spare parts list for the 1533X2 comes out of the woodwork!