In the 1950s what are referred to as power hydraulic braking systems were tried by some manufacturers. This system used an engine or gearbox driven pump to circulate hydraulic fluid to a brake valve, which then operated the brake wheel cylinders. There was no air or vacuum system to boost the pressure. These systems were not very successful, although AEC did manage to make it work in their Routemaster bus.
Any possibly hair raising experiences of these systems?
cav551:
In the 1950s what are referred to as power hydraulic braking systems were tried by some manufacturers. This system used an engine or gearbox driven pump to circulate hydraulic fluid to a brake valve, which then operated the brake wheel cylinders. There was no air or vacuum system to boost the pressure. These systems were not very successful, although AEC did manage to make it work in their Routemaster bus.Any possibly hair raising experiences of these systems?
Fodens had them also, Regards Larry.
Lawrence Dunbar:
cav551:
In the 1950s what are referred to as power hydraulic braking systems were tried by some manufacturers. This system used an engine or gearbox driven pump to circulate hydraulic fluid to a brake valve, which then operated the brake wheel cylinders. There was no air or vacuum system to boost the pressure. These systems were not very successful, although AEC did manage to make it work in their Routemaster bus.Any possibly hair raising experiences of these systems?
Fodens had them also, Regards Larry.
I remember my cousin who had a 6 wheeler S18 tipper going for its MOT When the testing lot first started, He had a right carry on with them because in those earley days the engine had to be stopped, Well no running engine no bloody brakes, These Fodens had the pump driven by the engine, IIRC ERF,S Had a similar system but the pump was belt driven by the prop shaft which was a bit poor when moving in slow traffic, the pump wasn’t been driven fast enough, Regards Larry.
On my reference shelf of manuals is one for ERF models 56 TS, 66 and 68. There is a chapter on two different types of full hydraulic braking systems, one with an accumulator and one without. Worryingly it seems that the pressure pump was driven off the gearbox output shaft.
Foden also fitted a system to their PVD model bus. This used ordinary engine oil, fed to an engine driven pump supplying an hydraulic footbrake valve via a boost box, which in turn worked a conventional master cylinder. The vehicle must have been way ahead of its time since it also included a hill holder.
Daimler went the whole hog with their CD650 bus and powered just about everything, including power assisted gearchange and handbrake, from the same engine driven hydraulic system with bag type accumulators.
The surviving AEC bus system overcame the teething troubles with the earlier systems and if maintained correctly works very well.
I have heard drivers’ stories about this braking system and I think that it was Fodens that had a tank in the cab that could back-pressurise and spray oil over the inside of the cab. If it’s true or not I don’t know.
the foden system was pretty good for its era , given that we only had 6 wheel braking and the brake linings were puny . as long as the engine revs were kept up . with a top speed in the mid thirties ( if you were lucky) silent 6th was used at every opportunity , right foot on accelerator , left foot covering brake . the foden handbrake was also quite good , the first yard of the cable was a motorbike type chain which passed over an eccentric gear to multiple the pull on the lever . the handbrake would bring you to a stop in an emergency . all that and 15 tons of handball when you arrived .
I wonder if any ERFs or Fodens fitted with this type of braking survive. I know a lot of the London buses do because I spend quite a lot of time working on their hydraulic brakes.
At the risk of boring people and digressing on a lorry forum to mention B****, I will recount a little of the history of how and why London buses used this idea.
London Transport during WW2 had been involved in the manufacture of components for RAF bombers some of which used an hydraulic braking system. In around 1948 LT’s Albert Higgins from the mechanical engineering department collaborated with Automotive Products (Lockheed) in research and development of a system for their vehicles. Two rival systems were eventually introduced made by Lockheed and Clayton Dewandre. In service there were advantages over air brakes, the complete system was around one hundred weight lighter, the reaction time was faster,pressure build up time was much more rapid, the operating medium was unaffected by below freezing temperatures, and most important of all, since the maximum normal pressure in the brake lines to the wheel cylinders was so high, the low pressure warning device could be set to alarm (750 psi) above normal maximum pressure delivered (650 psi) by the footbrake valve.
The pump is belt driven from the input flange of the gearbox, but since the gearbox is mid mounted and the transmission uses a fluid flywheel, the pump will operate with a stationary vehicle if it is out of gear. In the late 1990s during a second programme of re-powering these vehicles with more modern engines, problems were encountered when the fluid pump was relocated to become engine driven. It had never previously been deemed necessary to incorporate a pressure relief valve; it was found that without this fitted pipes could burst in certain conditions.
