CMP windshield throwout arm assemblies
 

I started looking at this because the arms shown for supporting the larger flat windshields on desert trucks shown at post 4 of Charlie Downs' thread on Aero-screens bore a visual resemblance to the arms used on CMPs to hold hte windshields open for better ventilation.
I'm more familiar with the arms used on Chevrolet CMPs than Fords as that's what seem to grow best at the Hammond Barn. However, when I look in various parts books I see that although the actual arms aren't shown with both Ford and Chevrolet part numbers, many of the surrounding brackets, frames etc related to the windshields do have dual numbering for the two makers so I would expect that the arms would be very similar (if not the same) between the makes. These parts show * as "unique to CMP" in the parts lists so although they might be similar to an existing part, they weren't identical to anything that existed before CMP. There have been other cases where * CMP parts did get used later for other things.
One set of arms pictured here (yellow, curved, short) did come from an early Ford Cab 13. These arms appear to be the same as those found in a Chevrolet Cab 12 and a Chevrolet Cab 13 (with civilian dash so probably early) sitting at the Barn.
The arms were handed LH and RH and existed in at least three styles:
1. Short (length not stated in parts list but measured as 7" (very close to exact) from centre of pivot pin to center of securing stud/bolt on windshield frame at full extension. Used from serial 184--05003 to 284--13801

2. Long given length of 10-21/32" (same centres as above based on measurement
3. Another long variant of the same length to be supplied as replacement when type 2 depleted (so interchangable).
I have photos of two different "long" arms with the difference being that one of them has an additional detent to more firmly hold the windshield at a 6" c-c opening measured at the same points (i.e. not as open as the short arms at full extension but more than half the full opening of the long arms) but I have no idea which was earlier. A case could be made for the later version being the one with the added stop location as a "product improvement" or just as easily the one without the intermediate stop being a production simplification to remove an "unnecesssary frill". If anyone has very late production trucks that they think aren't likely to have been modified, this might help to decide which was the later of the two "long" arms...
In general, you wouldn't expect to see a truck with a mixture of short and long arms off the production line as the brackets mounted on the cab frame were on the two versions (Long/Short) to accommodate the fact that the short version had the arm mounted outboard of the bracket on the windshield frames and immediately adjacent to the brackets on the cab frame while the long version had the arms inboard of the brackets on both the windshield and cab frame. As a result of the relocation inboard, the cab-side brackets used in the trucks with long arms had longer bolts/studs for the arms to slide along and a hexagonal spacer on the bolt/stud.


First, photos of short arms mounted in a Cab 12

Now a couple of photos of short arms as employed on Cab 13

And some long arms as employed on cab 13

side-by-side photos of long and short arms

With a ruler to give rough dimensions. The width of the arms measured as 1" (almost exact) in the parallel sections (more at the detent section).

And the mounting foot for the windshield frames. As far as I can tell, the same bracket was used for both short and long arms, both right and left handed, just assembled differently. Some of the brackets I've looked at had Chevrolet style part numbers (that don't show as a separate item in the CMP parts listings - so presumably could only be ordered as part of the arm assembly) cast into the part and others are plain, without part number.

My two cents
 

Hi Grant

I suspect that the arms with the mid point hold notch are an improvement to prevent or reduce broken windscreens. The long arms without notch/hold notch are prone to slaming shut as you reach the terminal velocity of CMPs of air speed of 50 MPH. Which maybe reach on flat ground after a twelve minute run, or down 9% grade at mid throttle, but exceeding 50 MPH air speed is more often encountered when hit by strong head wind. When this happens even with the hand wheels tight the windscreen slams shut with real force. If one of hold tight handles works better than the other then the window really gets racked.

This was also a problem on M37 when they are up engined, you had to drive them with the windscreens shut, or breaking the windscreens was a problem.

Cheers Phil

OK I confess. It was me. The reason you can find the arms and not the handwheel clamps that hold them in place is because I have them all. The HUW needs 18 to secure the seats, battery trays and wireless table to the floor and 4 more for the windshield arms. I managed to scrounge them all but realize that borders on greedy.....

An Australian invention
 

Grant,

I think you will find that the long arms (without notch) were originally introduced on Australian GMH production CMPs to allow the w/screen to open to 90 degrees, or be closed shut. I believe the intention was either fully open or fully shut, so leaving the w/screen locked at an angle just by the friction/tightness of the locking wheels was not intended. There were footman loops on the leading edge of the roof to secure the canvas w/screen covers for when the w/screen was in the fully open position, to prevent reflection.

There were also activating arms on the centre pylon to aid in getting the w/screen to 90 degrees but these are not visible in your images, so perhaps these did not make it into CDN production? The levers were also an Australian invention.

Hopefully, some Aussie CMP owner will have an image of this to post?

Mike

I'm not saying you are wrong, but it seems unlikely that an Australian produced arm would have made its way to central Canada. I haven't seen any examples of footman loops on the leading edge of the roof for securing canvas covers on Candaian CMPs (or residual mounting holes that I recognized). Just curious when Australian production began, is the start of Australian production compatible with the 1942 date implied by the serial number given in Canadian parts listing for introduction of long arms, which I think is not long after start of production of Cab 13 in Canada?

Are the arms on the central pillar in posts 2 and 3 the ones you are talking about or is there yet another variation I should be looking for?

GMH document
 

Grant,

I'm not suggesting that an Aust made arm made it to central Canada, but that the mod was also adopted by Canada. My comments were based upon the details provided in a GMH document detailing the changes made to the CMP cab:

'The greatest difference was brought about by the Australian Army requiring horizontal opening windshield and that an inside lever be added to allow the windscreen to be fully opened from a sitting position. Consequently the levers of the Canadian type cab were completely redesigned to meet these requirements. It was noted that the Canadian cab was subsequently redesigned to allow windows to open further, but as our design was finalised, the Canadian alterations were not incorporated." and, under parts added at Army Request, no.5, 'A windshield blind shown on 262-29-18 was required to prevent reflection of light when windshield was open'.

Perhaps both Army's came to the same conclusion independently, but it seems the Aussies got there first - hence the term 'subsequently' (my bolding) in the quote above. The long arms to assist opening, mounted on the central pillar, don't appear to have been incorporated in the CDN mod, only Aust production. They are a scissor-type action with a different shape and action that replace the long slide arms as seen in your image.

Mike

Chevrolet 1533X2 windscreen arm
 

Looking at the reference photos most of the arm components of the 1533X2 are at least similar, if not identical to the CMP versions. The arm itself looks like the short arm, with the upper bracket and the hand wheel clamps looking the same as the CMP equivalents.
The arm length scales out at roughly 192mm/7-1/2" which corresponds closely with your measurements above.
I am mid way through drawing the windscreen, but could do with some help with the following:

Wiper arms
Dimensions of the hand wheel clamps, and photos of both sides.
Photos of the hand wheel bracket on the side of the windscreen, plus dimensions.
Wiper motor photos and dimensions.

In the last photo of an operational truck you can see the motor has been removed, leaving a spaced mounting bracket. Does anyone have any information about this bracket? In post 3 there's a similar bracket visible on a photo, but the 1533X2 bracket looks like it has a lip on the lower edge.
Also of interest is the factory photo of the truck which has a different lower windscreen bracket compared to the much more robust looking brackets of 'later' operational truck. This is the only photo I have seen of this 'early' bracket. This may just be photo distortion, but it does look narrower than the other bracket.

I only have some of the parts to hand right now to measure.
The short arms measure 7-7/8" as overall length.

The hand wheel (part # 5800946)diameter is 1-29/32" including the lumps for grip, 1-5/8" base diameter at rim. Hub diameter 11/16" (greater as it flares to meet the web). Centre hole threaded 5/16-18. Thickness at the hub 1/2". Thickness at rim 5/16". Web thickness 3/32", centred on the rim. (7/64 inset from rim each side).
Regretably, the bracket mounted to the windshield frame doesn't resemble a CMP part that I'm aware of. (but as above the bolt/stud must be 5/15-18) The reason I keep saying bolt/stud is that samples of early Cab 13 CMP brackets mounted to the cab frame were made from bolt brazed to the bracket but I believe later ones were a stud .

Australian CMP windscreen scissor arm holdouts
 

Like these Mike.

Cheers,

Thank you!
 

Thank you, Jacques, that's the image I was hoping for.

The scissor-type action is clearly seen in your image. This allowed the windscreen to be opened to 90 degrees (ie to the horizontal) from the seated position. Apparently not a modification that made it into CDN production.

Mike

Those (Australian) arms are definitely not something I've seen in Canada...

The Australian arms seem to be similar to the windshield arms used in the C15ta

Chevrolet 1533X2 windscreen arm
 

I've been playing around with the images and drawings.
My initial conclusions are that the 1533X2 had the shorter arms, which is sort of confirmed when I overlaid the images after sizing them.
It looks like the CMP arms were a bit heavier duty than the MCP 1533X2 arms, but seem to have very similar profiles.
Whether the MCP arms were made from thicker gauge metal is hard to see or measure with poor quality 80 year old photographs.

Chevrolet 1533X2 windscreen
 

Here's my initial drawing of the front view of the windscreen and components, without wipers as on operations. Some details still to be added.
Need more information /dimensions and photos of wiper motor, wiper motor mounting brackets, and wipers to do rear and side view of windscreen.

Spent a lot of time getting the side arm curves right. The 1533X2 arms look to be finer than the 'later' CMP arms.

Any information and feedback welcome.

I seem to recall my former 1944 Chev CMP windows would open to 90 degrees but arms definitely did not reach up to touch cab roof wnen closed.
Can't remember if there was a half way stop...might have been, but memories...sigh.


Ps in retrospect, I'm pretty sure there were half way stops on the arms.

Hi Charlie,

Not sure if this is what you need. These are vacuum wipers and mounting bracket to the windscreen bracket. From a Ford CMP but maybe common. If they are what you need I can get you the dimensions.
Note: Small lever on windscreen side to allow manual operation of the wiper just visible in top view.

Revisiting your photos I think yours are completely different make/type. Anyway, I will leave this post up for interest sake. Sorry I could not help.

Cheers,

Thanks Jacques,
I think you are right about it being the wrong type, but interesting all the same. I don't think the 1533X2 had a vacuum supply to power the motors, I presume it was electric, but to be honest I have no idea! The photo shows a cable or tube feed to the motor.
On the operational vehicles it was removed anyway, but I just like to know what should be there, and it might help with what sort of bracket should be on the inside of the windscreen to mount the motor onto. Grant's photo shows a very simple bracket on a later CMP, but looking at the LRDG photo the bracket seems to be more complicated.

Certainly vacuum. There were a small number of car makers that provided electric wiper motors in the 40's, but usually on high value, low volume models. Certainly not on a Chev (or Ford) Truck, and not for a military model.

I think they both look the same, as simple as it needs to be. What complexity do you see?

This is getting off topic, but didn't at least one Canadian jeep contract have electric wipers? I'll have to check parts lists but hopefully some of our jeep experts will be able to give a quick, definitive answer.
More later on what I believe would be a typical Canadian CMP (Chevrolet) wiper setup.

There are lots of variations in vacuum wipers, up into the later 50s (particularly British cars, often with a vacuum tank (with the hope that you might get at least one wipe as you climbed a hill) These were mostly mounted under the dash so had a separate control.
There were larger units (cylindrical bodies) in the M series trucks that were new (to the N.Z. Army) after the Vietnam war (70s) (e.g.M816- M818)
These were fitted in Wagner logstackers up to 2000. These big units, as I recall were pressure rather than vacuum. (still available?)

I have seen as thread on here talking about Canadian contract Jeeps with electric wipers.

Wipac is a common brand with British units appearing to have a "shield type cover (pointed at the bottom end) and U.S. ones having a cover shaped like a horse racing oval.(e.g. WWII WC Dodge. _ these were small units early on and were larger like the CMP ones later in the war)
The CMP ones like the Dodge ones had an operating lever (assist) as well as a push pull (on off knob) The CMP cover is more square with a rounded bottom.
I have a couple of them still sealed in their Ford V8 marked LV* CC15 17505. I do have a use for them.
I think they were extensively used as Tony said. I hope that helps a bit.

Thanks for the info, learning every day!
So what generated the vacuum? Not come across anything on the various drawing and photo's that indicates a vacuum generator on the truck, so was a vacuum generated as a by-product of the engine to power the motor?
Tony, I hope it's a simple bracket, I'm not looking for complicated, I like simple. But more importantly I love accuracy and details! In the period photo with the arrow you can see what looks like a lip on the bracket. This could just be something in the background 'photo-bombing' the image. Looking at other components they are as simple as possible, so it's most likely a simple flat bar with 3 holes, just seeking confirmation.

Vacuum is drawn from a threaded port in the Intake Manifold.

When younger, I owned a M135CDN 2-1/2 ton truck. Being gasoline powered, the truck would have been capable of generating vacuum to run wipers but the truck definitely used compressed air to run the wipers, taken from the system that provided air pressure for brake boost, trailer braking and also had an outlet under the dash for a hose to inflate tires. I presume other trucks of the same vintage may have used similar components. One advantage of using air pressure is that if there is a small leak, there's no chance of drawing water into the engine (recall that they made a big thing of the early M series being sealed to run under water).

At the moment it looks like a simple mounting bracket, although reading around it could have 4 mounting holes on early brackets and 2 on later ones. Phil Waterman photo illustrates this nicely
I'm also beginning to understand the variety of motors available for the MCP/CMP range with this Lynn Eades photo showing just a few of them.
So far though not matched any motor to last photo, which appears to have a block on the rear of the assembly at about 45 degrees. Or is that just an optical illusion?
Is it safe to assume they would be Trico motors?


http://www.mapleleafup.net/forums/sh...t=wiper+motors