Work­shop Ba­sics

Strip, in­spect and re­seal your mod­ern clas­sic’s brake cylin­der

Practical Classics (UK) - - CONTENTS - With Nigel Clark

Re­build­ing your master cylin­der made easy.

You’ll in­evitably need to change your brake master cylin­der seals from time-to-time. They should be re­newed on a pe­ri­odic ba­sis in nor­mal use. Change them as a mat­ter of course if your clas­sic’s been laid up for a while or if it’s a new ac­qui­si­tion with an unknown his­tory.

Sportier clas­sics (and Volvos) were fit­ted with twin-cir­cuit brakes sys­tems from the late Six­ties. The hy­draulics are split into two in­de­pen­dent cir­cuits, so half the brak­ing sys­tem will still work if one of them fails. Within a decade, vir­tu­ally all cars had adopted this safety fea­ture.

The heart of a dual cir­cuit brak­ing sys­tem is a tan­dem master cylin­der. It fea­tures two pis­tons in-line in a sin­gle body, each op­er­at­ing a sep­a­rate hy­draulic cir­cuit. Some man­u­fac­tur­ers chose to split the brakes front-and-rear. Oth­ers opted for a di­ag­o­nal split or a com­bi­na­tion of the two, with twin-cylin­der front caliper pis­tons op­er­ated by one cir­cuit each. Con­sult your man­ual or trace your clas­sic’s brake pipes to work out how your sys­tem op­er­ates.

To let the un­wary driver know there’s prob­lem if one cir­cuit fails, there’s usu­ally a brake warn­ing light on the dash­board. This is ac­ti­vated by a pres­sure dif­fer­en­tial switch with a mov­ing shut­tle that senses if there’s a drop in pres­sure in one cir­cuit rel­a­tive to the other. The switch may be in­cor­po­rated into the master cylin­der or a stand­alone item plumbed in down­stream of it. Af­ter re­build­ing the cylin­der, the switch may need to be re­set to re­turn its shut­tle to the cen­tral po­si­tion.

Chang­ing the seals in a tan­dem master cylin­der is a bit more com­pli­cated than in a sin­gle-cir­cuit item. There are a few more bits to keep track of, but it’s still an easy DIY job. Seal kits are avail­able from mar­que and brak­ing spe­cial­ists, and prices are gen­er­ally low. In­spect the cylin­der closely while you have it in pieces. If the bore is scored or cor­roded, you’ll ei­ther have to find a re­place­ment or get it honed/sleeved.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.