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Practical Classics (UK) - - CONTENTS - Tommy Wil­son, Dun­geness

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.

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