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December, 2004
Requirements
Power brakes are required to assist with braking of the vehicle (especially with the added load of Lead Acid batteries).
Typically a vacuum system is used to power the existing vacuum operated power brakes. However, there are other alternatives.
Design Alternatives
- A vacuum pump to power the existing vacuum operated power brakes
- An electro-hydraulic brake system. GM put these in cars in 1986 under the name "Powermaster", and cost around $600-800 rebuilt. There is also a unit called "Grand Master".
See Dual Diaphragm Booster Upgrade for more information.
- A hydraulic brake booster, which uses hydraulic power from the power steering system to boost the brakes.
- A variable solenoid on the brake booster and eliminate the vacuum system (this is experimental)
Vacuum System Design Notes
- Using a vacuum reservoir will help to ensure the vacuum pump is not constantly cycling. This can be built with 18" of 3" PVC capped at either end.
- Putting an in-rush surge limiter in series with the power of the vacuum pump, will make the unit quieter.
- Always put a diode across (in parallel, cathode to +) any inductive device (pump in this case). This keeps the back emf spike 100's of volts from frying your contacts and not to mention and uP controls that may get glitched when the pulse goes through the wiring.
- The "man of great ideas", Lee Hart has a great suggestion to keep the pump quiet: put the pump inside the vacuum reservoir.
Noise does not transmit well through a vacuum. Given that 1 ATM is approx 15 psi, and that a typical vacuum pump works to about 9 psi, we need a box that can hold 6psi.
If looking for a waterproof container, you will need one that be submerged to 4.5m (15 feet) - this is the depth at which the pressure is 21 psi. (15 psi (standard air pressure - + 6psi = 21 psi)
Electro-Hydraulic Brake Boosters
In the 1980s GM made the "Powermaster I" an electro-hydraulic brake booster.
Supposedly there are two models, one which is angled, and the other which is straight.
See Dual Diaphragm Booster Upgrade for more information.
A picture of the wiring diagram
My unit came from: 1982 Custom Cruiser Station Wagon p/n 18011369
Hydraulic Brake Boosters
Hydraulic brake boosters were used on:
- FORD GRANADA 1976 2 Wheel Disc 2700145
- FORD GRANADA 1976 4 Wheel Disc Hydro Boost 2700192
- 96 Astro Van
- 94 grand caravan
- 85 BMW 535i
An are also available in kits : Prior Reman Hydraulic Brake Booster
There are several sites which show how to install a hydraulic booster, often used on off-road vehicles:
www.stu-offroad.com/hydroboost
www.off-road.com/~jweed
www.members.tripod.com/surfmac
Selection
As of Nov, 2004 a power brake system has not yet been selected. An MES-DEA 12v vacuum pump has been purchased as well as a
used electro-hydraulic brake booster from a 1982 Custom Cruiser Station Wagon.
Preferably the electro-hydraulic unit will be used, as this results in less parts, plumbing and noise. However, this option requires extensive modification
to the brake system.
Update, Dec 2004: Due to difficulty obtaining parts for the electro-hydraulic brake booster, it has been decided to use the MES-DEA vacuum pump with this existing power brake system.
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