BRAKE FLUID is a grey area for the home main­te­nance per­son. What many don’t un­der­stand is it, like methanol, at­tracts wa­ter. It’s hy­gro­scopic. So when you get into the en­gine bay of your old car and you find the un­der­side of the mas­ter cylin­der lid is rusty or cor­roded, it’s be­cause of this.

When you drive the car, the wa­ter in the lines will get hot and may even boil. It does this at a much lower tem­per­a­ture than brake f luid, which isn’t good. It’s ad­vis­able to change the f luid at worst once ever y three years. You can test it – but we’ll get onto that in a mo­ment.

Peo­ple get scared of bleed­ing brakes, but it’s not a dif­fi­cult task. You’re try­ing to achieve a cou­ple of things: re­fresh the f luid, and re­move any air bub­bles, as air com­presses eas­ily and will make your spongy pedal worse.

The first step is to pull the old f luid out of the mas­ter cylin­der. You can do this ide­ally with a sy­ringe, though it can sim­ply be soaked up with a rag (but don’t let it drip on painted sur­faces!). Do this un­til it’s dry, wipe out any crud and crus­taceans, then top it up with a freshly-opened con­tainer of f luid. Don’t use the one you’ve had sit­ting half empty on the shelf for months or years, as that de­feats the en­tire pur­pose of the ex­er­cise. Keep the con­tainer handy, as you’ll be top­ping up as you go.

The eas­i­est way to bleed brakes on your own is first to leave the lid off the mas­ter cylin­der. Then go to the fur­thest bleed nipple – usu­ally at the rear, on the op­po­site side to the mas­ter cylin­der. Open it up and let Mother Na­ture take over.

Grav­ity will roll fresh f luid through. Use a hose and con­tainer to col­lect it and leave it open un­til you see fresh f luid com­ing through. So long as you don’t touch the brake pedal, you won’t pull air back into the sys­tem.

Close that one off, top up the mas­ter cylin­der and go to the next fur­thest away. Re­peat the process un­til all the wheels are done. This takes time, but it works.

With a friend on hand there are quicker method op­tions.

Brake f lu­ids are a bit of a mine­field, as there are lots of op­tions out there. The best rule of thumb is to stay with the older DOT 3 or 4 on older cars. And don’t mix up f luid types. Un­der no cir­cum­stances should you put sil­i­con f luid in your older car – it just won’t be com­pat­i­ble with the seals and hoses and you will end up with a com­plete dis­as­ter.

One tool we use in the trade, that’s be­come much cheaper as time has gone by, is a brake f luid tester. It’s an elec­tronic ma­chine with two probes and gives you an in­di­ca­tor of when it’s time to lose the f luid. It’s a great lit­tle gad­get to have in the tool­box.

Happy brak­ing!

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