Practical Classics (UK)

On the DOT


QMy Rover Montego's handbook says to renew the brake fluid every two years. I've no idea when it was last done, though everything works fine and there are no leaks. What's the best way to do this? I intend to use the standard DOT 4 brake flud as recommende­d by the handbook.

Roger Peterson, Mold

Nigel says

AConventio­nal brake fluids absorb moisture from the air. This causes corrosion and also lowers the boiling point of the fluid. If the brakes get very hot, pockets of steam can form in the cylinders causing the pedal to go straight to the floor.

The pedal compresses the steam rather than pushing the pistons out. Drain the reservoir as far as possible using a syringe and a short length of tubing. Obtain roughly twice as much fluid as the system holds (see workshop manual). Refill the reservoir and bleed about a quarter of the total volume of new fluid out through the nipple of the wheel cylinder furthest from the master cylinder (usually rear left).

Do the same for the next furthest (rear right); and so on (front left, front right). Top up the reservoir to the correct level.

Bleeding can be done a number of ways. Place a rubber or plastic tube over the bleed nipple, with the end in a jar. Open the nipple a little and tell your assistant to push the pedal quickly down and hold it. Close the nipple and tell the assistant to slowly release the pedal. Repeat as necessary. A one-way bleeding valve costs about £5 and is a solo method.

Place the tube (with jar) over the nipple, open it only a quarter to half a turn and pump the pedal yourself – quickly down, slowly up. When done, release the pedal and tighten the nipple. Pre-loosen the nipples with a hexagon (not 12-point) socket to avoid rounding them. Be careful of snapping them off.

 ?? ?? You'll see the colour lighten as new fluid comes through.
You'll see the colour lighten as new fluid comes through.

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