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Your classic woes solved by our panel of master mechanics.
Q Of all the kit I wish I owned, a set of MOT brake rollers would be the most useful. Is there another way of keeping an eye on the performance of my brakes between Mots?
A One of the best ways to preserve brakes is to use the car regularly. The cylinders scrape themselves clean, mechanisms move around, friction surfaces de-rust themselves and the system heats up, driving out moisture.
Brake defects will often be obvious in normal driving, but sometimes they won’t reveal themselves until the brakes are applied urgently. A good check to carry out periodically is to apply the brakes hard at 20mph. Choose an empty, straight and level road. Hold the steering wheel in such a way that it’s free to move, but you can arrest it if it does anything dramatic. The car should pull up promptly in a straight line. Preferably none of the wheels should lock – though this will depend on the tyres, road surface and weather.
Certainly no one wheel or axle should lock considerably earlier than the rest. If one wheel locks, it’s usually because its opposite number on the same axle isn’t doing much. Maybe the cylinder has seized or the friction material is wet with brake fluid, oil or grease? If its opposite number is faultless, examine the wheel that locked for traces of oil or fluid. Contaminated pads or shoes can have an ‘off-on’ action with little in between. Clean the drums or discs and replace the friction material.
If the car slews to one side, it’ll pull to the side with the better (or grabbier) braking. If the steering wheel tries to turn itself, look at the front brakes – if it doesn’t, suspect the rears. If the front axle locks up prematurely, check the pressure regulator of the rear brakes, if fitted. It’ll either be maladjusted or seized. If the rear axle locks first, then again start by checking the regulator. If it’s fine, then the front brakes probably aren’t up to snuff.
A check that can be done on a weekly basis is to hand-feel the wheels after a journey. Apply the back of your fingers to each wheel near the centre. After a normal run, all four brakes should be about the same temperature. After more vigorous use, the front brakes will normally be hotter than the rears – but there should be no temperature
difference between wheels on the same axle.
To check the system for correct sealing, press the pedal down hard for 30 seconds with the car stationary. If it sinks, look for an external leak. If it passes this test, release it and press it very lightly. If it now sinks gently, the internal seals of the master cylinder are defective. Strip and inspect it. You may get away with a seal set – but there’s a good chance the bore will be pitted.
Finally, check the brake servo. Run the engine, switch it off and press the pedal repeatedly until it becomes firm. Start the engine and the pedal should react – usually, though not always, by sinking a little. With the engine at idle, clamp or fold the vacuum hose near the inlet manifold. If the engine speed changes, the hose or servo is leaking air. Remote servos will fill with brake fluid if their hydraulic seals leak. Puffs of white smoke from the exhaust when pressing or releasing the pedal are a telltale.