CMP's and attaching trailers......

[Tony Smith]

I asked the same question here: Artillery light

Some good responses, but no documented references.

[Jordan Baker]

The Cnd 10cwt trailer came with tail and brake lights. There was a cable on the front with standard US male plug. However nothing on the CMP to plug it into.

In the CMP Service Bulletin book there is a write upon trailer air brake line being installed on the CMP frame.

[Phil Waterman]

Hi Alex

My Pattern 12 C60L had what I believe was original trailer plug unit on it when I got it. Though not in condition to use I have saved it. Will dig it out and photograph it. I don't think it was the same as that used on US military trailer of WWII.

As a practical expedient I have replaced it with US M Series plug receptacle. Though to get meaningful trailer lights I've gone over to a 12 volt powered trailer lights which pick up the 6 volt signal from the trucks through 3 relays which then power the trailer lights off 12 battery on the trailer. When using this system I use magnetic based modern lights, which means I can tow other people's trailers when needed.

On the topic of towing other trailers, remember that CCKWs had a pintle hook that rotated, so the lunet was fixed. The size of the lunets of several WWII trailers I've towed is very tight on my C60S which means when towing on rough ground a lot of twistingredients gets put on the trailer tongue. Not a problem on the road.

As to the safety chains I just cross them under lunet an hook them in the tow eyes on the frame ends of my C60S and C60L trucks.

Most of my trailer towing is of my M5 generator behind my C60S Radio truck, which is narrower than the truck to the point that it cannot be seen in the mirrors and it is light enough that the truck doesn't notice pulling. But is just heavy enough to feel it when braking. Towing heavier trailers with CMPs does take thought, I've towed fully loaded water buffalos and you real know those are behind you.

Cheers Phil

[Patrice DEBUCQUOY]

Hi Alex,

Please find enclosed some infos given in HMSO's "Data Book of Wheeled Vehicles"

l8MxwAF.jpg
https://i.imgur.com/l8MxwAF.jpg

qn84NKv.jpg
https://i.imgur.com/qn84NKv.jpg

xmEuDpN.jpg
https://i.imgur.com/xmEuDpN.jpg

T57bCla.jpg
https://i.imgur.com/T57bCla.jpg

Hope it helps,
Patrice.

[Alex van de Wetering]

Guys, thanks for all your replies.

Tony, I had missed that thread. Interesting info.....especially the pictures that Grant posted of the bracket fitted below the hook. It looks to good to be make-shift if you ask me.....so that could be the proper bracket for lighting of an artillery light.

The Cnd 10cwt trailer came with tail and brake lights. There was a cable on the front with standard US male plug. However nothing on the CMP to plug it into.

Thanks Jordan. So, I am guessing the socket does fit in the connector in the back of a Jeep?

As to the safety chains I just cross them under lunet an hook them in the tow eyes on the frame ends of my C60S and C60L trucks.

Phil, that's also the only solution I could come up with.....I mean without fitting additional parts or modifying things. I can only imagine that towing heavy trailers can be a challenge!

From Patrice's scans I understand that the larger recovery tractors and trucks were fitted with proper brake facilities for the larger transporter trailers, but I still wonder about the 2 axle CMP trailers....the 20cwt single axle trailers, Jordan's 10cwt, but also US or British type trailers like the 1Ton Ben Hur and 1/4ton US jeep trailer.
They can be seen being towed behind CMP's in period pictures, so maybe if there was no standard connection for the lighting, they just didn't bother and drove without lights???

Alex

[Jordan Baker]

Yes the Cnd 10cwt trailer plugs into the socket on the rear of the jeep. The trailer is also fitted out with Ford brakes and a larger master cylinder. Same as used on the big Ford trucks of the time. If I have a load in the trailer and im towing it and stop, Ill feel my jeep brakes first then once the trailer starts to slow Ill feel the serge brakes come on. It tows very very well behind the MB. For being such a heavy trailer for its size, it is so well balanced and i can move it around empty or loaded by my self.

Im planning on having it pulled by my C15a at some. I'll be installing a spare trailer socket on the CMP for the lights.

[Grant Bowker]

On the 4 wheel trailers that look like they have CMP bodies, the lighter ones use hydraulic brakes actuated by the drawbar (similar setup to the 15 and 20 cwt CMP trailers).
My 15cwt CMP trailer came with a few scraps of wiring on it, enough that I believe one circuit would have been to both left and right and the other right only. The wiring stopped before the drawbar so I'm only guessing it was tail lights and brake light (hydraulic pressure switch in the master cylinder).

[Hanno Spoelstra]

Originally Posted by Jordan Baker

In the CMP Service Bulletin book there is a write upon trailer air brake line being installed on the CMP frame.

Here are some photos of the air brake line setup on a C60S in Sweden.

Doe anyone have a manual on this trailer air brake line setup?

chevrolet-4x4-cmp-30-2-st-12616-15882557174_redlined.jpg chevrolet-4x4-cmp-30-2-st-12616-158825572912_redlined.jpg

[Grant Bowker]

From what I can see, I would guess the truck shown above is more likely vacuum brake assist with vacuum brake for the trailer than air (pressure) brake. I base this on the little bit I can see of the lines to the cylinder and under the cab. The flexible connections look like simple hose clamped to tube which is more typical of vacuum than air brakes. Having said that, I believe air brakes of the WW2 era operated on lower pressure than current trucks so I could easily be wrong.

[Jordan Baker]

Scanned copy of

Service Information Bulletin #51, May 3, 1943
Trailer Brake Installation

[Grant Bowker]

I know this is getting picky but that is a vacuum brake system for the trailer as opposed to air (pressure) brakes to go with the vacuum boosted system of the heavier CMPs. It does make sense to use the same power source for both. Also, I'm not aware of any CMP equipped with air (pressure) brakes except some trailers (usually towed by larger vehicles than CMP 3 tonners). As always, happy to learn more - even if it proves me wrong....

[Hanno Spoelstra]

Originally Posted by Grant Bowker

I know this is getting picky but that is a vacuum brake system for the trailer as opposed to air (pressure) brakes to go with the vacuum boosted system of the heavier CMPs. It does make sense to use the same power source for both. Also, I'm not aware of any CMP equipped with air (pressure) brakes except some trailers. As always, happy to learn more - even if it proves me wrong....

Grant, you must be right.

I thought I had seen pictures of the trailer air brake line setup on this forum before. I recalled it was for actuating trailer brakes, not boosting thr truck's brakes.

If it was a pressurised system, the truck would have to be equipped with a compressor but I see no signs of that.

[Hanno Spoelstra]

Originally Posted by Jordan Baker

Scanned copy of

Service Information Bulletin #51, May 3, 1943
Trailer Brake Installation

Thanks Jordan!