R.H.A. and 'CM' Handbrake Figures for Ministry
Page 19
If you've noticed an error in this article please click here to report it so we can fix it.
BY JOHN F. MOON A.M.I.R.T.E.
OR many years now the Road Haulage Association has been very concerned about handbrake inefficiency on oods vehicles, and most of its members have been equally loftier]. In view of the imminent introduction of annual !Sts for all commercial vehicles over five years old which as been promised by the Ministry of Transport, the ehieles committee of the R.H.A. is to meet Ministry cpresentatives some time after January 20, 1964, in an ndeavour to persuade them that well-maintained but not ew vehicles will be unable to meet the Ministry's requirelents for 25 per cent handbrake efficiency, particularly as lost of the vehicles that fall into this age group ars* .nown to have been unable to produce 25 per cent leceleration-ineter readings when new.
To lend some support to the R.H.A.'s argument. I 'arried out some braking tests on old vehicles last Saturday, using a standard Tapley meter. The vehicles :oncerned were made available by g T. Redburn Ltd., Enfield, Middx, dr. Harold Redburn being the chairman if the R.H.A. vehicles committee. The tedburn fleet enjoys a high standard of naintenance. so it can be assumed that
he figures obtained last week are among he best that could possibly be expected *slam the particular types and ages of ,ehicles dealt with, despite which five of he six lorries used were unable to meet he 25 per cent requirement.
Only One Satisfactory
The results obtained are detailed in he accompanying table, and it is signifi:ant that the only machine with a satis!actory handbrake preformance was the 3edford TK tractive unit, which has a usc transmission brake as standard. With t sharp application of the handbrake ever a meter reading of 35 per cent was 7ecorded, albeit with locking of the nearside rear brake for a total distance of 15 ft.. whilst even a medium application af the lever unaccompanied by wheel 'ocking produced 25 per cent. Although standard so far as its braking specifica,ion was concerned, this KHA unit was non-standard in that it had an Eaton two-speed axle and Scammell automatic coupling. this work having been carried out specially in co-operation with the Arlington Motor Co. Ltd. and Seammell Lorries Ltd.
The 1953 semi-forward control and 1957 forward-control Leyland Comets did not show up well, whilst the 1962 Comet in lightly laden condition had a performance comparable with that of a 1962 Super Comet tested at seven tons greater gross weight but having larger rear brakes. The 1958 S-type Bedford put up a surprisingly good performance; but the Cornmer 8-tonner was disappointing, although the 2-ton overload could not have helped.
During the course of these tests, Mr. Redburn told me that he felt it was unreasonable of the Ministry to expect as high a figure as 25 per cent for the handbrake efficiency of old vehicles when it was obvious that most of these vehicles could not have reached such a figure when new, and that hauliers could hardly be expected to modify all their vehicles— even assuming that this were physically possible– to meet the proposed requirements. He felt that the trouble lay with the Ministry for not having made the vehicle manufacturers adhere to a given minimum handbrake performance years ago.
So far as the manufacturers are concerned there is still a divergence of opinion as to whether a handbrake should be regarded as an emergency brake or merely a parking brake capable of holding a vehicle at its designed gross weight on a certain gradient. One of Britain's biggest brake manufacturers is currently designing rear-axle brakes to give a gradient-holding performance of 1 in 4 (or 25 per cent efficiency), but
whilst their brake units are claimed to be capable of this, they are still in the hands of the vehicle maker in that they are not responsible for the efficiency of the handbrake linkage.
It is quite obvious from these tests, however, that if the Ministry's 25 per cent figure does become a legal requirement, very few five-year-old heavy vehicles will be able to pass the test, irrespective of the standard of fleet maintenance practice. The need for good handbrake performance is recognized throughout the industry; but it is unfair suddenly to expect hauliers to provide this when vehicle manufacturers, generally, have been skating round the problem all the time, although some handbrake efficiencies have now been improved.