CMP windshield throwout arm assemblies

[Phil Waterman]

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

[Bruce Parker (RIP)]

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.....

[Mike Cecil]

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

[Grant Bowker]

Originally Posted by Mike Cecil

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?

[Mike Cecil]

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

[Charlie Down]

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.

[Grant Bowker]

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 .

[Jacques Reed]

Originally Posted by Mike Cecil

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

Like these Mike.

Cheers,

[Mike Cecil]

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

[Grant Bowker]

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

[Jordan Baker]

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