IN YOUR OPINION
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Nothing But the Best j FOUND the discussion on brakes in your February 8 I issue extremely good reading (perhaps a little hard going in parts, where certain technicalities were discussed); some very meaty stuff, and it will certainly stand re-reading.
Brakes are of vital importance and it is my opinion that in recent years there has not, in many cases, been sufficient emphasis placed upon this aspect of vehicle performance by manufacturers and purchasers—particularly in view of the great improvement in such things as power/weight ratios, steering and chassis and tyre design, all factors tending to encourage maximum loading and, in many cases, overloading.
I don't suggest that brake designers and manufacturers have stood still; rather is it my impression that there has not been sufficient " get-together " between commercial vehicle manufacturers (or "assemblers "0 and brake and brake lining manufacturers and vehicle operators. Individual brake designs are here and there very good and one or two commercial vehicles have always enjoyed an excellent braking reputation. But it seems that too often a commercial vehicle has developed over some years, with higher power outputs, better gearing and the availability of motorway-type tyres, while much-improved trunk routes enable higher speeds to be maintained, yet brake drum diameter and lining width probably haven't been altered; I don't think it is much good improving the brake operating system unless you give the better system larger drums and better linings at the same time.
My personal experience with regard to two types of modestly priced (not the most popular) four-wheelers in recent years has been that you can improve your stopping power no end by specifying (and paying for) the optional brake system, at the expense of a much reduced liner life, and probably much increased fade.
I have to endorse John Moon's remarks about wheel locking. I cannot agree that wheel locking is some sort of "necessary evil ". Surely it is possible to design and produce, and build into, any size of commercial vehicle, a system which will give good braking distances, without wheel locking. And, if you closely analyse the experts' reaction to this suggestion, it seems to me that all you get is an attempt to blind us with science, a lot of technical chat about "envelopes of fore and aft ratios ", "maximum retardation ", centres of gravity being moved about, and so on, but I couldn't find an answer to John Moon's question from any of the gentlemen in the discussion.
Of course, a very important aspect of the whole problem is one that was just very briefly hinted at once or twice; I refer, of course, to the problem of educating, training, and generally putting your trust in the one man whose experience, ability, judgment and reactions affect, one way or another, the whole situation: the driver. The human factor is so important. Here you have a situation which may well be unparalleled in any other industry. A manual worker, paid a quite modest hourly rate, in charge of a piece of expensive (and lethal) mobile machinery, probably loaded with someone else's goods, worth perhaps three or four times as much as the vehicle itself; unsupervised hour by hour, and sometimes for days on end, who, if he has confidence in his vehicle, and particularly his brakes, and knows how best to use them, will probably stay out of trouble and produce an excellent life from his brake linings. If for some reason he is not happy, or does not like his machine, or does not -understand what happens every time he presses the pedal, or, worse still, doesn't care, then you are going to have skids, collisions, possibly fatal accidents, and expensive repair bills anyway.
So you have certainly got to give every commercial vehicle driver the best possible system, the most foolproof operating system that can be designed and built. In other words, I suggest that there is no margin for anything at all. We must have the best obtainable, even if at extra cost.
Thinking along these lines, why on earth can't we have some sort of retarder, at least as optional equipment, such as Mercedes-Benz fit, I believe, as standard? Your panel did just touch on this, but seemed to get off the subject a little 'too quickly. I am told by friends in the trade that the best exhaust brakes give much more than a moderate amount of assistance, and moreover appear to be relatively trouble free.
And I can't for one moment understand why disc brakes are so slow in appearing on, at least, medium-weight fourwheelers. I would certainly buy a truck with front discs, if the specification and price were reasonable, and certainly this front-disc, rear-drum system does just what seems to be required in the way of producing more braking on the front than the back.
thought John Moon's observations about unsuitable linings, and discounts, most pungent. This sort of thing, I am sure is widespread, and, of course, we are back to another facet of this human element again. Overloading is probably the biggest single factor affecting brake performance once the vehicle is bought and operated, and you are so right when you question whether operators really appreciate this danger. There will certainly have to be a satisfactory answer found to the overloading problem, and quickly.
London, S.E. I . STEPHEN MANSFIELD,
Director, John Harris (Cartage), Ltd.
A Future for Disc Brakes I WOULD like to comment on your discussion on com mercial vehicle brakes (The Commercial Motor, February 8), which I have read with great interest as braking problems have played a very important part in my livelihood as a haulier.
I read that Mr. Moon has driven a 12-ton-gross rigid vehicle and a 24-ton-gross articulated outfit, both fitted with air-pressure braking, was able to stop very quickly from 30 m.p.h., without any wheel locking whatsoever; whilst appreciating this, I would like to say, however, that we have 'vehicles that do the same but unfortunately they have a very short brake lining life and frequent drum failure.
From what I read in your discussion I would say that you have all the ingredients for a better braking system. All hauliers who operate vehicles in this day and age are still confronted with the serious problems of inadequate braking: there is always the human element creeping into braking systems especially in goods trucks that are over 14 tons. So far as I can see the braking designs inside the drum have not changed much for the past 30 years and we always get the same old story of the operators overloading. Surely when designing a vehicle one knows what the overloading capacity is by its tyres; if a vehicle's carrying capacity can be judged by its tyres then surely a guide can be taken from this.
Perhaps if the Ministry laid down a standard of efficiency, say 60 per cent, even on vehicles that are capable of being overloaded, this would cut down the margin of error. Also, if this was law perhaps we would not hear any more of " the customer is not prepared to pay "; this is completely untrue. I think this gets involved with the cost-cutting that takes place largely with the manufacturers and they simply blame the operator. If a definite standard was laid down this excuse would not be used.
There was a mention of trailer handbrake controls that operate the trailer brakes independently of the tractor. This is a fitment that we have on our fleet but it is unfortunate that drivers have a tendency to drive on these, thus overworking the braking of the trailer, and fade takes place, causing the whole system to break down on both trailer and tractor. It is very important that these vehicles be fitted with this type of equipment in the event of icy weather or wet roads and for the prevention of jackknifing; but a driver, not involved in an emergency, may because of his reaction apply his brakes too rapidly and, because very little manual pressure is required, could create a disastrous stop and cause a fatal accident.
With regard to air brakes, I consider the whole system has become one gadget looking after another and although I like the hydraulic system, unfortunately we have to leave this at about 14 tons gross because of its limited application. Also [feel that air brakes are invariably designed for the full load and when the vehicle is empty they are very delicate brakes indeed to operate; driving is thus inure nerve-racking and fatiguing for the driver.
1 see there was very little mention of a dual braking system which would still operate in the event of one of the systems breaking down. I should like to see a vehicle equipped with a dual braking system, for instance air/ hydraulic, mechanical/air, each working independently.
It may be true that many operators do not realize that their vehicles' brakes are dangerous until it is too late but there are a good many operators who are aware of the bad braking system from the start but have no other choice but to accept what the manufacturers have to offer. Please don't lay all the blame on the operators.
Regarding the fitting of retarders, could it be that pit2
the fitting of these would be more of a supplement to the brakes than to get a good braking system in the first place?
There was mention in the discussion of pedal effort and braking efficiency, and that they did not give a true indication of a vehicle's stopping capabilities; of course this is very true. Where application is manual the more pressure applied the greater the retardation, and in this way you take away a lot of thinking from the driver by giving him a little more physical effort; I am sure it would cause him less mental strain than he has to suffer with the present system. I am speaking, of course, of air pressure—full air pressure --and again I would like to see automatic adjustment. This, it is said, cannot be fitted to the drum because of the expansion rate, and we hear about the disc brake being a long way off because of the need to get a mechanically acted version which could be operated by air pressure. I am all in favour of automatic adjustment which, though it cannot be operated on the conventional drum, could possibly work on the disc. So far as heat effect is concerned, here the operation would be in reverse: when the disc cooled down it would retract away from the pads.
As to compressors and servos, I think the manufacturers have taken it too much for granted that these are on hand, and yet they rob us of power and cause engine problems. Enormous power lies in the movement of the vehicle, for instance a 30-ton-gross weight free-wheeling at 50 m.p.h.; this power could be harnessed to retard the vehicle.
My conclusion as an operator of heavy goods vehicles, like many others who have been greatly perturbed by the lack of efficiency of the present brakes, is that drum brakes are nearing the end of their usefulness and that a perfected disc brake is the answer.
My efforts towards this aim have led me to design and make a prototype self-energizing disc brake which is fitted to one of our semi-trailers. This brake is designed to take several forms of applications—air, hydraulic, vacuum, electrical and mechanical.
Bedfont, Middlesex. F. J. HOPE,
Director, Hope Transport Ltd.
Rather Odd?
IREAD with great interest your article in The Commer cial Motor of February 8 on braking problems. Near the end of the article John Moon stated that Continental makers have satisfactory brakes, and he continued: " I see no reason why British manufacturers cannot do the same ". This to me sounds rather odd coming from a man of his experience. I seem to remember that he tested the A.E.C. Marshal 6 x 2 last summer, which stopped from 30 m.p.h. in 45 ft. Surely this is a remarkable figure for a vehicle grossing 20 tons!
FeItham, Middlesex. R. HARBAR,