Single Vs. Dual Diaphragm Brake Booster

by Edmund Gary

Power brake boosters help the driver push the brake pedal. "The Reader's Digest Complete Car Care Manual" states that most designs employ the use of vacuum from the engine's intake manifold to develop power. The vacuum booster is round steel container which is mounted on the firewall and is situated between the brake pedal and the master cylinder. Brake boosters produce line pressure in relation to the weight of the vehicle. Two types of boosters are available, the single and the dual diaphragm type.


Single diaphragm brake boosters are generally less expensive than the dual diaphragm models. A 7-inch diameter single diaphragm brake booster is priced at $129.95 as of 2010 at Parker County Performance. A dual diaphragm model with the same diameter would cost $159.95 as of 2010. Larger diameter brake boosters whether single or dual diaphragm will yield higher prices.

Single Diaphragm Boosters

Single diaphragm power brake boosters can produce up to 950 p.s.i. They work well with four wheel drum systems or disc brake front/drum rear systems. These braking systems are lighter than the four disc brake system. These work best on older cars, because drum brakes were a common feature, at least on the rear axle of these cars.

Dual Diaphragm Boosters

The website of MBM Brake Boosters states that disc brake systems require 1000 p.s.i. to be applied to the wheels. Dual diaphragm brake boosters are need for four wheel disc system because they can produce a higher level of brake assist even if their physical size is smaller. Dual diaphragm brake boosters tend to give extra braking even when the vacuum from the intake manifold is low.

Blue Oval news states that the Mercury Mariner is standardly equipped with dual diaphragm brake boosters for its power assist in its braking system. The vehicle has disc front and rear drum set up.

Booster Sizes

Power brake boosters require 16 inches of vacuum or more to function properly according to Sachs Rod Shop, and smaller brake boosters require more vacuum to perform satisfactorily. Smaller brake boosters may be sufficient for tight engine compartments, but they require a stronger vacuum to function properly.


Power brakes are not required to stop a vehicle with disc brakes, according to MBM Brake Boosters. Power brake boosters provide the driver with greater pedal feel and also deliver shorter stopping distances. Smaller diameter dual diaphragm brake boosters provide the stopping power of larger single diaphragm brake boosters. Mike Harington advises on the Super that one should choose braking parts carefully. Mismatched braking components can make the best parts perform poorly.

More Articles

article divider