How Stuff Works


Classic Car Weekly (UK) - - CONTENTS - fuzz town­shend CCW’s mas­ter me­ChaniC

Fuzz ex­plains hand­brakes

‘The ad­vent of disc brakes brought the need for a new so­lu­tion’

Fuzz ex­plains how this tech keeps your clas­sic sta­tion­ary

Forms of pre­vent­ing ve­hi­cles from mov­ing when sta­tion­ary have ex­isted for many cen­turies and in­deed, the ear­li­est mo­tor ve­hi­cle hand­brakes were taken straight from their horse-drawn pre­de­ces­sors. These took the form of wooden blocks held against the rub­ber tyres, some­times with a me­tal or can­vas lin­ing for a spot of in­creased co­ef­fi­cient of fric­tion.

How­ever, with mo­tor ve­hi­cles be­ing able to be parked with­out con­sid­er­a­tion of an­i­mal mo­tive power, the need for greater hold­ing power on hills and such­like in­creased dra­mat­i­cally. At the same time, mo­tor ve­hi­cle ser­vice brakes were also de­vel­op­ing into pow­er­ful means of the re­tar­da­tion of greater masses, and so it made sense to use the ma­te­ri­als and, some­times, the same or com­ple­men­tary sys­tems.

Many early ve­hi­cles fea­tured drum brakes on the rear axle only, plus a trans­mis­sion brake, the lat­ter some­times be­ing of the ex­ter­nal ‘clamp’ type, onto a drum be­hind the gear­box, or a more con­ven­tional and mod­ern in­ter­nal shoed drum brake.

There can be a few com­pli­ca­tions here, be­cause the trans­mis­sion brake was of­ten op­er­ated by a foot pedal, this be­ing more likely when it was of the more for­giv­ing ex­ter­nal clamp-type, with the wheel, aka ser­vice brakes, be­ing op­er­ated via rods or ca­bles by an ex­ter­nal, ratch­eted hand lever, in much the same way as many park­ing brakes to­day.

Clearly, this was not an ideal sit­u­a­tion, be­cause steer­ing and brak­ing at the same time could be some­thing of an art, al­though, ar­guably and ideally, the two ought not to have been com­bined in or­di­nary cir­cum­stances, so the ser­vice brakes mi­grated to the foot pedal and gained brak­ing to the front wheels as well.

Cable and rod brakes gave the op­por­tu­nity for the park­ing brake to di­rectly op­er­ate the same ser­vice sys­tem, such as on the Austin Seven, thus act­ing as a ratch­eted, hand- op­er­ated ser­vice brake. How­ever, the ad­vent of hy­drauli­cal­ly­op­er­ated ser­vice brakes meant that the park­ing sys­tem needed to re­tain its own sep­a­rate me­chan­i­cal link­age, and so things started to be­come rather more com­plex within the rear brake drums only, which now fea­tured hy­draulic pis­tons ex­pand­ing the shoes onto the in­ter­nal brak­ing sur­face of the drum in nor­mal use, with levers or wedges ac­tu­at­ing them in park­ing mode.

This sat­is­fac­tory sys­tem con­tin­ues in some ve­hi­cles into the mod­ern era, but the ad­vent of disc brakes brought a need for a new so­lu­tion.

En­ter the me­chan­i­cally-op­er­ated, sep­a­rate disc park­ing brake sys­tem, as fit­ted to the likes of Jaguar Mk2s. These fea­tured cable-op­er­ated clamp­ing pads, sim­i­lar to tra­di­tional bi­cy­cle ‘rim’ brakes, whereby the cable cas­ing acted upon one pad and the cable it­self on the other, thus draw­ing them to­gether. A spring fit­ted in be­tween to keep them apart and away from the disc when not in ac­tual use.

These me­chan­i­cal disc park­ing brakes re­quired reg­u­lar ad­just­ment and were prone to fail­ure, es­pe­cially when the spring weak­ened and al­lowed the pads to wear away as they flopped against the disc when not ap­plied. This led to the reap­pear­ance of in­ter­nal drum brakes, now fit­ted within the cen­tre part of the rear discs and me­chan­i­cally- or elec­tri­cally-op­er­ated.

Cer­tain ve­hi­cles con­tin­ued to use trans­mis­sion hand­brakes, no­tably Land Rovers, be­tween 1947 and 2015 and other com­pa­nies, such as Saab, of­ten as­signed the park­ing brake to the front wheels.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.