Fluid lev­els

Classic Motorcycle Mechanics - - WORKSHOP CMM - RALPH FER­RAND

Do we re­ally pay as much at­ten­tion to what our brake fluid is do­ing as we should? Lis­ten up, says Ralph Fer­rand!

Words and pics:

Many bik­ers who look af­ter their own steeds change the oil and fil­ter, the spark plugs, check the disc pads and check that the lights work. Very few seem to have a clue in a bucket how of­ten other flu­ids need chang­ing, nor the brake lines. Stan­dard stock rub­ber brake lines should be changed ev­ery four years: fact! Given the huge cost of stock items a sen­si­ble per­son will re­place the cheap (to make) OE rub­ber lines with braided lines with stain­less fit­tings. They are less costly than OE and many, such as HEL, carry a life­time war­ranty. Rub­ber lines swell un­der pres­sure, wast­ing lever/pedal ef­fort which should be go­ing into stop­ping the bike. If you lightly grip a rub­ber brake line, es­pe­cially an old one, and grab a hand­ful of an­chor you will feel the line ex­pand slightly in your fin­gers. The power to swell that line should be act­ing on the brake pads! An­other is­sue that few seem to ap­pre­ci­ate is that brake fluid has a fairly short life­span and should be changed reg­u­larly. It is hy­gro­scopic, which means that it ab­sorbs wa­ter. On the whole this is a good thing as it stops the wa­ter col­lect­ing in cor­ners of the brak­ing sys­tem, but you don’t want a very high con­cen­tra­tion of wa­ter as it will attack the brak­ing sys­tem com­po­nents. Wa­tery fluid of­ten sets up cor­ro­sion be­hind the caliper seals and the flaky alu­minium pushes the seal tight against the pis­ton, mas­sively re­duc­ing brake ef­fi­ciency. The wa­ter also at­tacks the chrome of the pis­ton, even­tu­ally hol­ing it and set­ting up rust un­der­neath in the mild steel. For some bikes it is just the has­sle and ex­pense of new pis­tons, for oth­ers you re­ally have a much big­ger prob­lem if you can’t get a new one. At its worst the wa­ter loaded fluid will boil in the calipers from the heat gen­er­ated from the pad to disc fric­tion and that is re­ally bad news. Laser Tools pro­duces a crack­ing lit­tle pro­fes­sional tool for the trade which mea­sures the wa­ter con­tent of the fluid. We bought one years ago and have found it in­valu­able. We not only test the fluid in the bikes but also the new fluid.

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