Chevrolet 1533X2 30-cwt trucks

[Tony Smith]

Originally Posted by Charlie Down

MCP and CMP trucks were simple practical designs. the flap is out of character.

But in that case what was the flap for? Have I mis-interpreted the original photo of the flap?

Are there photos of CMP airline connectors fitted to trucks?
Are there specific panels to fit under the door with a flap on them? Sounds a complicated way to fit the kit if you have to remove a panel and weld/bolt a new one in to fit the connector.

More questions than answers! If pushed I would go for the flap arrangement purely because there is evidence for it, but I'm not convinced yet.

There is no evidence for any flap, either in a manual or a photo.

The airline fitting on CMP trucks just bolts through the chassis rail with no additional panels or fixtures. The MCP just passes through a hole drilled in the running board.

[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.

[Charlie Down]

Hi Tony,
I was wondering about that piece. It wasn't painted, meaning it was fitted after the paint job or it was masked to stop paint clogging up machining on the fitting. It makes sense. Simple, effective and quick to mount/repair/use. Very MCP/CMP in character.
However, initially I looked at period photo's of the trucks, and later stowage setups which often involve large wooden or metal ammo chests bolted to the step. It didn't make sense that they would have to unbolt these boxes to get to the airline, then remount the boxes when they were finished.
I then put myself in their position and thought about the problem. What if they drilled a hole in the stowage/ammo box, fed the airline through the hole and attached to the connector and then bolted the box in place. They would then only have to open the box, take the airline out and engage the PTO to use it. It would be quicker and simpler, they would have the airline stowed where they need it (freeing up space else where), the airline would only take up a small area of the box allowing it to be filled with ammunition or other stowage.
The first photo show S1 Patrol in September 1942 ready to go. They all have a chest for 10 x 100round Vickers K gun drum magazines fitted on the step. So a fairly standard fit for this Patrol. If you did the above, drilled and fitted the airline in the box you would still have plenty of room for 9 drums of ammunition.
I really like that idea and have absolutely no evidence for it, apart from that it's easy to do and makes sense! Its exactly what I would do.
The other photo's show (when magnified) the fitting on trucks in the field and at the factory. The rhs is shown to show it wasn't fitted on both sides.

So I have a new theory/idea.

And what the hell is that flap all about!

[Tony Smith]

None of the stowage pics show the airline fitting blocked or covered, the boxes are at the rear of the step, the airline is at the front of the left side step.

You are in a flap about this so-called flap! What on earth are you talking about, what flap?

[Charlie Down]

This photo shows what looks like a flap, which is what I'm trying to sort out. It has generated lots of conversations on here and the LRDG preservation society facebook page. Initially I thought it was the airline connection and started looking for evidence to prove this, which has by a convoluted path led me here where I am sure its not, but don't know what its is. So yes I'm 'flapping' about a flap, but what I really want to work out is how the airline was set up from the pump because it's never really been discussed in LRDG circles, but apparently MCP/CMP forums are much better informed!

[Hanno Spoelstra]

Originally Posted by Tony Smith

On CMP's, the the installation of the the PTO pump involved nothing more than drilling a hole in the floor to insert a screwdriver to engage the pump, and fitting the pump to the transmission. A copper pipe ran from the pump to the air fitting, which was screwed through an existing hole in the frame. An experienced Driver/Mechanic could probably fit it in 15 minutes.

On the MCP, I can't believe there was anything as fancy or elaborate as modified body panels, knockouts or flaps. Too much work. The simplicity of Canadian vehicles was their forte.

I think we've been staring at the fitting all along and not wanted to see it, expecting something sexier than just an exposed fitting, but there it is.

Tony, you're the man! Once one knows where to look, it becomes obvious.

[Hanno Spoelstra]

Originally Posted by Charlie Down

This photo shows what looks like a flap, which is what I'm trying to sort out. It has generated lots of conversations on here and the LRDG preservation society facebook page. Initially I thought it was the airline connection and started looking for evidence to prove this, which has by a convoluted path led me here where I am sure its not, but don't know what its is. So yes I'm 'flapping' about a flap, but what I really want to work out is how the airline was set up from the pump because it's never really been discussed in LRDG circles, but apparently MCP/CMP forums are much better informed!

Charlie, that "flap" may be something else? A small tin with cigarettes, spare tyre valves, or ???

[Charlie Down]

Hi Tony, your are correct about the connector not being obstructed on the trucks early in their use, spring /summer 1942, but by September, as the crews became more familiar with the trucks and they modified and adapted stowage arrangements, the connector was obstructed. The attached pictures are all dated September 1942 or later from S,T and Y patrol vehicles, and all have boxes/stowage blocking connector.
Its interesting that the trucks that retained the POW can racks all had similar boxes, and those that had the larger Vickers K drum chests mounted the rack on the drivers side in front of the other rack.

[Charlie Down]

I thought maybe a note book. Its something though, and whatever it is, it has led us to the right answer. Thanks Tony for solving this. I'm putting this one to bed now, job done.

[Tony Smith]

Originally Posted by Charlie Down

This photo shows what looks like a flap, which is what I'm trying to sort out.

What I see in that pic is the truck has got a flat tyre, and the crew have delegated the Sikh Trooper to be the one to change it. Meanwhile, the rest of the crew have taken the opportunity for a Smoko break, and the Trooper nearest the door has decided to help himself to a tin of Bully Beef.

[Charlie Down]

Hi Tony

Hopefully last question.

In this compilation view, are these levers for the PTO, or for something else such as a 2 Speed axle , as has been suggested elsewhere? (no mention of a 2 speed axle in the LRDG specification, but it does have details such as the rear axle ratio, so would have thought it would be mentioned if fitted)
Earlier you said that a slot was cut in the floor (photo attached of a floor for a LRDG conversion project) that allowed a screwdriver to be inserted to engage the PTO, but the drawings of the parts diagram shows a lever as part of the PTO compressor kit. Did the screwdriver fit into the end of this lever or was there an extension lever up into the cab?

Just seeking clarification.

Thank you for clearing this all up

[Tony Smith]

Originally Posted by Charlie Down

Hi Tony

Earlier you said that a slot was cut in the floor (photo attached of a floor for a LRDG conversion project) that allowed a screwdriver to be inserted to engage the PTO, but the drawings of the parts diagram shows a lever as part of the PTO compressor kit. Did the screwdriver fit into the end of this lever or was there an extension lever up into the cab?

Thank you for clearing this all up

Those levers are for the Eaton 2 speed rear axle.

There is no "lever" in that parts diagram. The pump has a fixed vertical shaft with a screwdriver slot in the top, and the lower end has a fork. This fork engages a sliding gear. When the shaft is rotated with a screwdriver, the fork pushes the gear rearwards to mesh with both the countershaft in the gearbox, and the crankshaft of the pump.

[Charlie Down]

Thanks Tony,
Perfectly clarified!
Thank you for your patience and help.
Hope you have a good day down there, stay safe.
Charlie

[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?

[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.

[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!

[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.

[Tony Smith]

As far as possible, the components on Canadian Chev (and Ford, Dodge, etc) were kept as standardised as possible and used across multiple vehicles.

Features on the dash are common with the detail pics of the Chev Cab 12 CMP components in THIS THREAD (although located in a different arrangement), and from that we can see the enamelled "GM Canada" dash jewel and the Inspection Light socket are also on the 1533X2 dash.

That thread will give you an indication of what the Ignition Switch, Choke and Throttle knobs should look like.

[Bob Carriere]

The current issue of the rectangular civilian instrument panel was a civilian style much like the first year it came out on trucks in 1940..... 1939 had the round gauges....... I would expect all of the original 38 or 39 Cairo modified LRDG to have been built with the round gauges....... round gauges may have been carried forward for the flat cowl conversion but would expect all 1942 factory 1533 to have the rectangular civilian style gauge cluster.

Lots of retro fitting and field modifications can be expected once the trucks saw action in North Africa......for example some of the factory rectangular folding windshields were removed, bumpers were dead weight...... at least half the waterfall grill was cut out...... and factory pictures do not show the huge water expansion tank on the driver's side.....spare(s) inside or outside the cargo box and I suspect machine gun mounts were field installed based on availability and ammo supply....... hard press to see two trucks similarly kitted side my each!!!!

In the various official messages reproduced on MLU of what they wanted never was it mentioned to have a 2 speed rear axle...... they made do with what they could get or scrounged from the battlefield.

That what makes them so interesting ......... the challenge is to make one that is plausible.

Cheers

[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.

[Hanno Spoelstra]

Some original documents referring to the Chevrolet 133" wheelbase trucks. The "W.B." in these documents caused some confusion, but these are in fact Chevrolet WA trucks.


(via Brendan O'Carroll and John Valenti)


From the “Desert Chevrolets” article in Wheels & Tracks magazine no.8 I copied the technical details of the 1940 Chevrolet WA.



Edited to add: the above information refers to the Chevrolet WA 30-cwt truck used by the LRDG before the 1533X2 was taken into service

[Bob Carriere]

Hi Hanno

The "W.B." refers to wheelbase and not to "series WB.....by coincidence the 1940 WA series is the 133 inches and the WB series the 158 1/2 inches wheel base.....

On the first memo they refer to 113 wheelbase which applies to cars or at 113 1/2 for the 1/2 ton trucks.

Precious documents ........ and the magazine documents makes mention of either 900x13 ot 10.50x16 .........

Any idea which Heavy duty front axle they were requesting from General Motors....? GM did list a std front axle for the 3/4 ton Commercial KD with 11 inch brakes and the Heavy duty axle for the 3/4 ton Commercial KE with 14 inch brakes .......BUT with 123 3/4 wheel base........

Frame wise all 113 and 1/2 ton trucks had a curved frame above the rear axle......
.....all larger trucks 123 and larger the rear frame was flat from the rear of the cab to the end of the frame.

.....and GM also had the HD Maple Leaf front axle same as the HD Cab Over Front axle.

TONY........ I have a 1543X2 parts list, issued November 1940 ( no 167) and it does list the Eaton 2 speed axle....... but blank luck on the 1533!!!!!!

Two front axles are listed for the 1941 model....... one with ball bearings and one with cones and bearings for the "X" HD front axle using 10.50x16 tires. To me cone race /bearings denotes a model similar to the Maple Leaf HD or the COE......... The front wheel hub on HD is unique in having a small domed bolted cover instead of the recessed screw on cap ......

So much to learn........ so little time.

Cheers