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Measuring runout accurately

Although brake replacement is a daily task for many mechanics, one process that is often overlooked is checking lateral run out. All mechanics are aware of the importance of this check and routinely carry it out, but how can this be made easier and more concise in garages? Scott Irwin, head of technical training at Textar, discusses how important it is to acquire accurate runout measurements.

Firstly, it’s always good for garages to take part in refresher courses to ensure that every technician is up-to-date with best practice techniques. This is something Textar takes very seriously and carries out regular garage visits and training session to ensure best practice is being adhered to. Nevertheless, one process that is often overlooked is checking the lateral run out.

A DTI gauge gives a precise reading on how much movement there is once the brake disc has been fitted back onto the hub. Run out should not exceed 0.07mm, any reading above this can have damaging consequences to the entire braking system and cause vibrations through the steering wheel and brake pedal, which could result in a returning, unsatisfied customer.

During brake work, the bolts or nuts need to be tightened to make sure there’s minimal movement in the disc, but most mechanics will reach for spare bolts or nuts to do this. These can damage the wheel bolts or nuts and cause scoring on the brake disc itself, leading to problems when the wheel next needs removing. These bolts or nuts need to be kept in good condition as they play a key part in holding the braking system together. One way to eradicate this danger is to reach for a conical washer as opposed to a spare bolt or nut.

The shape of these washers encases the wheel bolts or nut to avoid causing damage to the bolt / hut head, and they are the perfectly machined to lay flush against the disc. They provide the ideal solution to measure run out as accurately, with the disc sitting tightly to the hub.

Brake judder is another problem often encountered when working on this area of a vehicle, usually caused by disc thickness variation (DTV). This can stem from improper practice when cleaning the braking system. A hub cleaner should be used to remove deposits while keeping the hub intact. Taking the time to clean the system properly to remove any debris can prevent numerous faults and flaws.

In an industry where downtime can cause a backlog of jobs and consequently income loss, it is imperative that mechanics are aware of these tools and processes to continuously perform to a high standard, ultimately helping with customer loyalty. Extra diligence during the brake replacement process can save a lot of time. Instead of a trial and error approach to determine if poor results are based on the tools used or uneven surfaces, this can be eliminated as a cause so the mechanic can quickly get to the root of the problem.

About Autotechnician
Autotechnician is a magazine published nine times a year, delivering essential information to independent garage owners and technicians in the UK. Delivered both digitally and in print, autotechnician provides readers with technical, training, business advice, product and news, allowing our readers to keep up to date with information they need to run and work within a modern workshop.
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