How To: 20-cwt GS trailer hand brake

[Grant Bowker]

I was looking at the red 20 cwt GS (Chinese aid contract) trailer frame at the Hammond trailer park and considering how easy/hard it would be to restore/rebuild it.

From the data plate, it should have the all steel body. In some ways this is easier (all one material) and in others harder (corrugated tailgate and pressed ribs in the front face) than the composite body. The trailer is missing the foot loops below the frame but Barry Churcher's similar trailer still has them so perhaps he'll let me measure them one day? Likewise the fenders have gone missing. I haven't compared the part numbers in the manual for the GS trailer to the part numbers for the gas welding, compressor or generator trailers to see whether they all used the same fender. I don't even know where to find a manual for the compressor trailer (if that's what Bob has in the trailer park - green frame with 2B1 body sitting on it) but Bob got fenders with the green frame. The ony issue with them is that they have had their mounting brackets extended laterally by about 1-1/2 inches.

The brake system remains on the axle but the master cylinder, linkage to drive it and the parking brake handle, linkage and cables are missing. The master cylinder is the standard Ford part, easy to source. The overun linkage to drive it could be reproduced using the linkage from the green frame as a pattern since the parts from the green frame seem to fit on the red frame.

Now we get to the point of this post. There were 2 patterns of parking brake used on these CMP trailers. one is the same as used on the Ford CMP trucks, looking like a straight stick with a pushbutton on the tip. The other was a shorter handle with a squeeze handle for the latch. This trailer is set up for the squeeze type. At first I thought this would be a problem to replicate, then I found some eBay listings for same shape handle but with a different base that looked like they could be the basis for a reasonable facsimile of the original squeeze handle assembly. This eBay listing is such a handle.
http://cgi.ebay.com/ebaymotors/1940-...item4ced79389c

Otherwise the chassis seems in good shape and quite complete.

Images are the Hammond trailer park, the squeeze handle assembly from the GS trailer manual and the mounting plate for the brake handle on the trailer frame.

[Grant Bowker]

Step 1 was to buy a brake handle. $9.99 plus postage, the seller had described it as a Fird (easy to see the typo they made... but limits the searchability for the auction) part so I was the only bidder. Once I had the lever I enlarged the manual drawing from the original 2" size to match the length of the handle. All aspects of the handle fit so it seemed like a good start. Then the dimensions of the mounting pattern and cable location were checked against the trailer mounting points, they matched too so it seemed the plan was good.

Images are the eBay handle before and after removing from the original mounting bracket. The pivot rivet had enough length remaining that it could later be peened to make a new head.

[Grant Bowker]

New parts were made to the size given by the "enlarged to full size" diagram from the parts list. The main upright was 3/16" to match the ratchet plate on the eBay handle, stiffening webs 1/4" to match the diagram, base plate 3/8" to match the diagram, sloped plate for cable/rod to pass through and its curved wedge support a mix of 1/8' and 3/16" from the offcuts bin. All parts were welded together and the raised profile of a mig weld ground to resemble the dish profile of the original casting or forging. At this point I still hadn't seen an origina, I was working from a mix of known dimensions, period drawing (wildly enlarged but seemingly dimensionally sound) and thinking about it in terms of "how many ways could the part be made" to fit what I knew.

Images are the welded assembly before and after sandblasting and phosphate treatment. The sandblasting left a quite uniform surface that encouraged me to carry on.

[Grant Bowker]

Not much more to the assembly. After sandblasting the rivet that acts as the handle pivot was peened over and the assembly painted. At this stage I was quite satisfied with the result, it looked like a single piece and appeared dimensionally and functionally correct.

[Grant Bowker]

When we went up to the Dan Caldwell's to pick up the HUP parts for Rob Clarke I took the chance to look inside the FAT bodies they have in the back yard and there was a parking brake handle of the type I'd made staring me in the face. (Aside - I think Christie would like him to sell the FAT bodies if a suitable buyer can be found).
Compared to the fabricated part, the main upright is a bit thicker, all facets of the base have more casting draght than I had expected but unless you know what to look for, I think my fabrication is an acceptable facsimile until an original part jumps out of the bush.
Images are the original parking brake lever assembly.