Brake Components

Q: Brake Components

What the heck is the difference or use for all the valve components for the brake system?

A: The round cylinder next to the master cylinder is the “METERING” valve, necessary for allowing the rear drum brakes to make full contact before the discs start to work, by holding back pressure to the front discs. ALL 69-70 disc brake GM cars have this.

The “PROPORTIONING” valve is a little SQUARE inline valve under the driver’s seat in the line going to the rear brakes, to slightly reduce the rear wheel braking on nose-heavy cars. On 1969 ‘birds, it was attached to the subframe’s left rail. NOT ALL 69-70 GM cars had this.

All 1969 and 70 GM disc brake cars have the “metering” valve, but not all have the “proportioning” valve.

All 1967 and later brake systems (dual braking, including 4-wheel drum brakes) used a warning lamp switch that also served as a distribution block, where the 2 lines in from the master cylinder become 3 lines out, one to the rear, and one to each front wheel.

In 1971, all GM disc brake cars went to a single component that combined the distribution block, warning lamp switch, metering valve, and proportioning valve and it was called (imagine this!) a “COMBINATION” valve. They were usually mounted on the frame and are hard to see from underhood.

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