Workshop Basics

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

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.