CMP windshield throwout arm assemblies

[Grant Bowker]

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

[Grant Bowker]

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

[Grant Bowker]

And some long arms as employed on cab 13

[Grant Bowker]

side-by-side photos of long and short arms

[Grant Bowker]

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).

[Grant Bowker]

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.