Brake points to watch
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THE COMMITMENT given by brake manufacturers in research, development and production of components and systems can be wasted over the years by failure to maintain systems in line with manufacturers' recommendations. To assist operators in seeing that this does not happen, the South Wales Maintenance Committee for Goods Vehicles has produced a booklet with fold-over cover for workshop use.
Its first chapter consists of an introduction and summary of defects recorded by the Department of Transport; it has others on brake maintenance — present and future; Construction and Use Regulations, legislation and type approval; Commercial vehicle braking — looking to the future; Anti-lock braking systems; Air-brake couplings; List of vehicles and their brake systems; and Useful references.
The Maintenance Committee was very disturbed by the reports from the Department of Transport on a National Traffic Area Fault Analysis. The defects recorded on the first inspection of goods vehicles at their annual test, feature braking system defects as the first five items on vehicles, and similarly as the first four items on trailers. This led the Committee to look into a simple guide to assist operators in braking systems maintenance, and to also give a deeper understanding of commercial braking systems.
"The Committee," says John Gibbons, chairman, who is Western BRS company engi neer, "have studied this problem at length and visited Lucas Girling, who as a company have been very helpful in assisting to produce this booklet. They have also drawn on the experience of the members of the Committee and on vehicle breakdowns recorded by BRS Rescue. We have, I hope, been able to produce a booklet that is a working assistance to commercial vehicle operators."
The booklet puts forward first a number of practical and proven recommendations on preventive maintenance advice aimed at helping the operator: 1, Regular adjustment (where applicable) and inspection of the lined shoe will ensure maximum lining Life, maximum efficiency and probably avoid drum or even brake damage. 2, Always use the lining material grade recommended by the manufacturer. This was chosen to achieve overall vehicle performance. Modern technology and legislation is demanding original standards be maintained. Totally unnecessary problems are constantly being generated purely by incorrect lining material. 3, With hydraulic brakes, regular overhaul and replacement of hydraulic units should take place every two years or 50,000 miles, whichever occurs the sooner. For air it is recommended that the valves and diaphragms be overhauled or replaced at 100,000 miles or once a year, thus avoiding potential faults possibly leading to brake failure. 4, As the effectiveness of hydraulic brake fluid decreases with age, changing fluid every 18 months is recommended. 5, Shoe return springs perform a very important function in ensuring immediate shoe movement away from the drum on release of the brake. Shoes hanging on result in excessive lining wear and increased fuel consumption. Fit new springs at each lining change. Correct potential fitting of the springs is essential to avoid contact with hubs and wheel cylinders are the linings wear. Another important factor is vibration, culminating in squeal, reducing shoe spring life. See also next paragraph. 6, A drum in poor condition, eg having ovality, excessive grooving or having been excessively skimmed out, will create many problems often blamed on the brake. Always check drum conditions. 7, Steering and suspension wear, chassis damage and tyres all have an effect on braking characteristics. Defects in these areas may be accentuated but not created, by a brake application. 8, Lubrication of metal to metal contact surfaces with
the approved brake grease i! of paramount importance a: dry, sliding or rotating compo nents can result in efficienc, losses of up to 30 per cent Shoe tips are a particularl. critical area together with bell crank lever trains. 9, Finally, check the shoes, a they are subject to constantl changing forces and generall much abuse, deformation c the shoe platform and we and Brinelling of shoe tip may take place. Ultimateh their effectiveness will b minimal and they will gene ate other brake problems. The following information 1-1.4
been broken down into thrE main categories: 1, Hydraul operation; 2, Cam operation; Wedge operation.
Within those types it is po sible to discern two-leadin! shoes, leading/trailing-shoe ar duo-servo configurations, whit may be clarified by the three di grams.
Individual types of brak( have their own service requir ments of perculiarities and boo let has attempted to select ti most common problem areas.
The booklet is copious supplied with illustrations at explanations about specif problems. Its aim is to explain operators the basic principles booking maintenance witha going into to much detail t each type of brake because ti detail is usually available manuals. Exploded diagrar rather than sectional ones used so that a fitter in t workshop can work from t booklet.
It has a section on fun trends and suggests, that, ap from inspection, maintenancE becoming minimal b specialised. There is, howevei big part to be played by 1 operator, it says. This lies accepting the new technolo and adapting or even discard traditional thinking to encc pass this. A number of import points need to be borne in mit
• Set up the brake corret using genuine replaceml parts only — failure to do so result in wasteful, expenf. downtime which will have bi self-created. Complaints of ii
'lye braking will also result.
o not meddle unnecessarily brakes. Providing the run clearance are maintained reasonably stable, this is icient indication that the :es are efficient.
o not attempt to standardise irances. Manufacturing -ances will vary and dictate t those clearances will be; e could differ for all shoes n axle.
,Iways refer to information ad by vehicle or brake menuirers when meeting a new of brake. Technical service irtments will normally be too willing to assist.
le days of the "big hammer" oach are numbered; a more iking" approach is essential. len disc brakes come into ce, says the Committee's :let, it is to be expected that ceability will follow the line ei by car disc brakes, with the offs of less time-consuming ce and fewer service prob stem options, it says, is an which has seen some deof neglect in terms of serunderstanding and is iy of consideration. The inct term "dual-line" should illed "split-braking system" 3curacy as it encompasses a ber of options.
ginally air or air/hydraulic fils were of the single-line utilising a single actuating The major disadvantage lay with a single leak or burst causing complete system failure.
The front/rear split followed utilising a tandem master cylinder and/or tandem air actuators. As technology and legislation improved, so alternative systems evolved utilising "L" and "H" splits giving greater vehicle stability and safety in the event of a partial brake failure. To match these systems air valve and master cylinder designs are improved. Finally, cost as always, must figure in vehicle design and serviceability and a very recent development is the use of two single master cylinders, mounted through the chassis, operated by two individual air chambers.
The regulations that cover the design and use of air brakes on road vehicles must comply with the Construction and Use Regulations and the European Economic Community Regulations.
These lead to the Type Approval of a whole vehicle, discussed in the booklet.
A simple explanation of what is required under the C & U Regulations is followed by an explanation of EEC Regulations and incorporates some recent important changes.
The three-line braking system, which became the system adopted by UK vehicle and trailer manufacturers, is later explained. Operators will have to adapt vehicles manufactured after October 1, 1982, and first used after April, 1, 1983, and if necessary connect "three-line" vehicles to "two-line trailers (and vice versa) without making the vehicle trailer combination unsafe.
"A warning should be given that most conventional threeline drawing vehicles need modification in order to safely draw a two-line trailer. This is because if the auxiliary line of the drawing vehicle is not linked by a fourth coupling or internal connection to the service line, the trailer brakes will not operate should the drawing vehicle's brakes fail."
Under the scope of this booklet no further detail is given and it is recommended that the excellent publication by the Department of Transport is ob
tained, entitled Braking Connections for Goods Vehicles and Trailers, obtainable from: DoE/DTP Publicity Stores, Building No 3, Victoria Road, South Ruislip, Middlesex HA4 ()NZ.
It is also recommended that the driver's leaflet and wall poster accompanying the booklet is obtained and explained to the drivers; they are the ones who will have to couple the rvehicles/trailers and an understanding is vital. Also it is recommended that a notice is displayed on all drawing vehicles first registered before April 1, 1983, which are not built to the requirements of the EEC braking Directives, to indicate to the driver whether or not the vehicle is suitable for drawing two-line trailers.
Manufacturers are responsible for complying with the legal construction and performance requirements, in respect of the relevant vehicle system or component in the new condition. The authorities have to confirm that the Regulations are satisfied.
The Type Approval procedure demands that a representative vehicle or component is submitted to the designated national "Technical Services" for compliance testing.
In the UK the Technical Services function is carried out by the Vehicle and Component Approved Division of the Department of Transport.
Skipping forward to the chapter "Looking to the Future", and quoting the booklet: "There is a clear indication that the day of the disc brake is near as far as trucks are concerned. But, having said that, it is also clear that the development of disc braking on heavy vehicles will not happen overnight.
"It is likely to begin at the lighter end of the weight range, say 6/10-ton vehicles and then gradually make inroads into other categories. Probably the 14/16-ton area would be next, as the 10/14-ton category suffers from the small wheel sizes used in relation to the size of the vehicle and this poses problems in relation to disc size.
"Indeed, some of the chief reasons for disc brakes not being adopted previously has been the size of commercial vehicle wheels and the room needed for the right size of disc required to efficiently do the job. Clearly, careful installation engineering provides the key to this problem, but this is more easily solved in the categories we have already indicated.
"Once the installation problem is solved, the heavy-dutydisc brake shows some clear advantage over its drum-brake equivalent. The most obvious of these is weight saving, since the combined weight of a caliper and disc is a good deal less than that of the equivalent drum with shoes, wheel cylinders, actuators, etc. Secondly, we should look at the performance aspects and as was found in the private car and van categories, discs do not distort in the same way as drums when they get very hot, and brake fade should not be experienced to the same degree.
"The third advantage that disc brakes provide, is that of stability, since the compact instant action of the caliper on the disc provides a consistent form of control which the more complex operating mechanisms involved in drum braking do not.
"Application and release of the friction in the braking mechanisms are therefore rather more effective in the disc brake assembly. Finally — and of particular interest to operators — disc brakes are generally easier to maintain.
"Clearly there are four very good reasons for tackling the installation difficulties in fitting disc brakes. It should also be notable that the swift application and release of disc brakes lends itself very well to anti-lock systems."
The UK's Maintenance Advisory Committees put in a lot of work in servicing and associated fields (CM September 4) and can advise large and small operators alike. Its list of vehicles using various brake types and its list of references will be useful too, to many operators.