Chevrolet 1533X2 30-cwt trucks

[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)

[Charlie Down]

To the rescue again Tony, thank you.

[Tony Smith]

Originally Posted by Tony Smith

The drive for the speedo cable, and therefore the speedo and odometer, comes off the gearbox .......

Note that I mentioned the Speedo Cable comes off the Gearbox, not the Transfer Case, like on all 4x4 CMPs and Marmon-Herringtons.

The 2-Speed rear axle was only ever fitted to 4x2 trucks, never 4x4s, as there would be a catastrophic speed difference between an engaged front axle and a rear diff in "Low" ratio. Catastrophic enough to blow up the Transfer Case. A 2-speed diff was never fitted to a front axle in any application I am aware of.

[Charlie Down]

I've put all the information I think is right to draw up a general arrangement for an LRDG 1533X2 cab. Not having one parked on my drive the dimensions will be estimates. However I am not aware of any drawings of the cab and most people base their knowledge on the Tamiya kit on the basis there is nothing better. So there are bits missing such as the gearstick, handbrake and 2 speed lever as I don't have any decent pictures of what the floor panel looks like and the levers would just get in the way of other detail. I intend to do a plan view drawing of the floor plate separately anyway, as well as side views. The steering wheel is also missing for clarity.
Any feedback, obvious cock ups, dimensions, drawings and photo's to help improve it would be appreciated.

[Charlie Down]

Just trying to confirm features on dashboard.
Any comments please.

[Tony Smith]

Originally Posted by Charlie Down

I've put all the information I think is right to draw up a general arrangement for an LRDG 1533X2 cab.

What is the square panel between the glovebox and leftmost gauges? I've not seen that in pics, and think the space in that gap should be closer and the whole dashboard narrower.

[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!

[Andrew H.]

Originally Posted by Hanno Spoelstra

Thanks Tony for the details on the Eaton axle. Agreed - I hope one day a maintenance manual and spare parts list for the 1533X2 comes out of the woodwork!

Re the Eaton 2-speed diff discussion: There are references in the available LRDG literature about the trucks having a "creeper gear". This may have been an Eaton diff, but from my own experience driving "Te Aroha III" the ratio of first gear is so ridiculously low that we never, use it! I cannot imagine what circumstances might justify an even lower gear. So in my opinion, if the intention was to create a "creeper" gear, there was no need for an Eaton diff. However if it split all of the gears giving a lot more options at all speeds,
that might have been useful in the desert.