AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

Despite the relative simplicity of the brake relining procedure, worryingly high

27th August 1998, Page 46
27th August 1998
Page 46
Page 47
Page 46, 27th August 1998 — Despite the relative simplicity of the brake relining procedure, worryingly high
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

numbers of mistakes are still being made. Chris Graham looks at this safety-critical issue.

Cutting corners to save cash is a dodgy business policy and, when it is applied to truck brakes, it can prove disastrous. Call it old-fashioned, but the ability of a driver to stop a vehicle in a predictably controlled manner is a fundamental requirement. All operators have a moral, as well as legal, responsibility to ensure that their vehicles are safe. Correctly maintaining the brakes is perhaps one of the two key factors in this respect. Tyre condition, which we deal with on page 48, is the other.

A truck's drum brakes can only be as good as their linings. Material quality is vital — always fit the OE recommendation and match the material across the vehicle, especially when using asbestos-free. However, you can specify the best, most expensive friction material in the world but, if it is not secured to the shoes, the brakes will not work effectively.

Awareness of correct lining fitting procedures is growing, thank goodness, and I should emphasise that most larger operators now operate responsible relining schemes, often with assistance from friction producers such as Ferodo. But there are many that do not.

Nobody enjoys the messy, boring process of relining brake shoes. but its importance can never be over-emphasised. Strange, then, that the responsibility for this crucial operation often falls on the tender young shoulders of the workshop junior. The fact that there is no official qualification required by those who work on brakes does not help. The nightmare scenario of little Joey Bloggs. fresh out of school, larking about in the lining booth is a real and worrying one.

As with any other branch of vehicle servicing and maintenance, good brake relining must be based on a methodical approach. One of the most basic requirements is that you reline brakes in axle sets only. Do not be tempted to reline just one side to save money or reduce downtime. One-off problems, such as oil leaks, can render the linings unserviceable at one end. Simply replacing the contaminated material is not the answer.

Failure to swap the "undamaged" linings at the other end will cause brake balance problems and affect vehicle stability It will also lead to knock-on wear problems and, in the end, increase rather than reduce downtime.

As always, it is better to take action before trouble strikes. Keep a wary eye on lining con• dition and wear levels. Always make the change before lining thickness becomes too low. Ferodo, like most other premium brake material producers, build in wear step indicators to provide a convenient guide to overall condition. Check these regularly and act on what you find. Ferodo has developed an electronic wear sensor called Brake Alert. This takes the guesswork out of brake inspection.

Wringing out the last vestiges of life from linings is never a good idea. Expensive damage to the drum and extra downtime are the likely consequences.

It is important not to confine your inspection to the condition of the linings. The state of the shoes is vital too. The shoes deteriorate in sev

eral ways and should not be re-used if problems are found. Check for signs of distortion on the shoe platform area. Inspect all surfaces for corrosion, and look for excessive wear, broken welds and operational distortion on and around the shoe web pivots and abutment points.

Take extreme care when removing the old lining. Ferodo says never to drill out the rivets because this may damage the brake shoe holes. The German Standard fully tubular type rivets should be removed using the correct extraction punch. If this is not available the clenched rivet head can be chiselled off carefully.

Detailed inspection

With the old lining removed it is important to carry out a further detailed inspection of the shoe surface. Pay particular attention to concavity—check for this across the width of the shoe with a straight edge and feeler gauges, as well as rivet hole size, general shoe platform condition and corrasion.

Brake shoe preparation is another vital stage which must be completed before the new lining is fitted. Ferodo advises that its linings are made to precise machining tolerances and that correct attachment to the shoe can only be achieved effectively after a "cleansing" process.

Assuming the shoe itself is intact and free from distortion and corrosion, it must be degreased and cleaned. After this it should be shot-blasted (except if it is aluminium) to remove traces of rust and shale. The final stage is painting to help prevent future corrosion.

Lining riveting is a subject in itself and there is plenty of scope for mistakes here, too. Essentially, there are two types of rivet in use: the British Standard (BS3575) semi-tubular, which has a tapered head, and the German Standard (DEN17338C) flat-headed fully tubular type. Both have their specific applications and it is important that they are used correctly. The setting-up procedure for the relining machine is another potential stumbling block. It must always be fitted with the correctlysized punches for the rivets, and it is essential that the machine's anvil face diameter and height are correct.

Air pressure is another variable, as is the order in which the rivets are fitted. Do not work randomly, plugging holes in no particular order.

Although there are hundreds of rivet pattern designs, a typical full-length lining will have n rivet holes arranged in three rows down its length. The basic idea is to work out systematically from the centre of the lining so that pressure builds progressively and the risk of cracking is minimised. Fit the first rivet to the centre hole in the middle row and then add the two either side in this same row.

The outer rows require four rivets each. The middle four should be tackled first, followed by the remaining two at each end. When the riveting is finished the quality of the fixing must be checked. Start by tapping the lining surface with a light hammer. A high-pitched response will indicate that the lining is securely mounted, while a dull thud will denote a potentially weak anchorage.

Pay attention also to the lining/shoe gap, which must never exceed 0.015mm (0.006in) beyond the rivet bole line. Check this with a feeler gauge. Also inspect the rivet turn-over to ensure that the roll-over is neat and secure and look for friction material fractures around the rivet holes.

The likes of Ferodo put significant effort into promoting responsible attitudes to brake maintenance, By adopting a sensible and methodical relining scheme you will save your operation money, minimise unscheduled downtime and help ensure the safe operation of your vehicles.

COMMON RELINE FAULTS (TO BE AVOIDED)

Incorrect rivet length fitted (too long). Incorrect rivet length fitted (too short).

Incorrect rim punch used (too small a diameter).

Incorrect rim punch used (too large a diameter). Da to brake shoes caused Brake lining fractures caused

by 7:114rle or extraction punch. by poor shoe support.

Excessive shoe/lining gaps. Excessive brake shoe corrosion.

Tags


comments powered by Disqus