大象传媒

BRAKING SYSTEM - DESIGNED AND INSTALLED IN THE FIELD.
Recalled on tape in 1985 by Edmund Ralph Wilmot BEM S.A.E.C

I recall the time in Italy, when Monty鈥檚 caravan was brought in for repair and modification work. I was not with the South African Engineering Corps while they were in the desert, where they had actually converted an old Bedford truck chassis to build this caravan for Monty. I was an Infantryman at that time. I believe these Engineers also built other similar Caravans to this one.

When the Caravan was brought in, they weren鈥檛 grousing about the towing mechanism so much. It was the fact that it never had any brakes that was causing most concern. It depended entirely on the towing unit to hold it going downhill, on some of those Italian hills it took a bit of doing and was quite a thing to keep under control. So he wanted some sort of brake, others had messed around with this thing and decided that they couldn鈥檛 do it. Eventually they got me working on this. My idea was to build a braking system for the Caravan and link it up with the towing trucks own braking system. Monty also had it brought in because they had problems with the steering mechanism, which was unreliable and unsafe.

The trucks had vacuum servo air brakes. The old Bedford chassis had a liquid brake system, though this was removed when the caravan was built. I was puzzled with these problems and wondered why they had removed the original braking system from the chassis and had not made use of it. I was convinced that I could do something to solve these problems.

I took a piece of three-eight mild-steel plate, as I remember it might have been up to 18 inches long and about nine inches deep. I attached onto this a vacuum servo cylinder that operated a lever through a fulcrum. This was then connected to a standard master brake cylinder, as used on the trucks. The critical thing was to determine a fulcrum point that would give you a mechanical efficiency, sufficient to more or less allow you to break both vehicles equally. The brake applied on the axle tow unit had to be adjustable, so that the trailer itself didn鈥檛 skid or exert excess strain on the tow-bar. Also if the brake on the Caravan wasn鈥檛 working as effectively as the Truck, it might as well not have been there. The brakes on the Caravan had to be applied and be synchronized with the braking operation of the towing unit.

I built this braking unit on to the inside of the chassis of the trailer. Connected up the vacuum servo so that it could be linked or unlinked with the towing truck, just like a standard coupling that you see on trains. I connected up the master cylinder, bled the lines and we went out for test. As it happened the weather was dry and we found a sandy stretch of road. I told the chap driving to bring her down at such and such a speed and when he got opposite to where we were standing, apply the brakes gently to see what happens. We carried out a series of tests and it was quite amazing to see this thing almost skid together with the towing truck. It was beautifully synchronized and really quite amazing. It surprised me, that it worked so well first time out. We couldn鈥檛 do a lot of mathematics on it at the time as it was something just done in the field.

This braking system pleased the Army, although I did it myself. I have always thought it was extremely clever, to be built under those circumstances. Having done that I thought I would do something about the bending tow-bar business. The steering mechanism had a turntable arrangement, built underneath the front of a standard Bedford chassis. The chassis wasn鈥檛 stepped, nor did it have a proper platform turntable. They had evolved a steering mechanism that was operated by the steering tow-bar itself. There was a drop-arm with a ball-joint connecting link and this functioned on the standard set-up through the front wheels with an ordinary track-bar. This had one disadvantage in that its movement was limited. It tended to bend the tow-bar if moved to an excessive angle. The bloke towing this Caravan really had to be careful with it. To try and back it was quite a dangerous operation, though they got along with them in the desert it. It was much more difficult once we got up in to those Italian hills with mud and what have you, they gave a lot of trouble.

I began work in my dugout by making cardboard models of the tow-bar assembly. I worked out at what point it had a lost motion and if taken beyond that point, would have no further action. I eventually went on and made modification to the tow-bar assembly. This wasn鈥檛 altogether ideal, because if you were turning very sharply the trailer was certainly going to swing out farther than you did. However once the critical limit was correctly adjusted, any motion was lost after that critical point and she started returning to its forward position again. We found this worked very well and did away with the trouble we had with bending tow bars. We ultimately went on to re-build over twenty flat deck trailers for the Army and had comparatively little trouble with them after that.

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