As many Grand National owners will attest, when the Powermaster braking system works-it works well, however when it fails ... all hell breaks loose. Complaints often consist of a fading brake pedal, a hard pedal, or a spongy pedal, any of which can be caused by any of the components within the system. The Powermaster system consists of a master cylinder, accumulator ball, pressure switch, and an electric motor. The electric motor supplies the pressure to assist in braking much like the brake booster in a vacuum-operated system. However, the Powermaster system has a high rate of failure due to a potentially faulty pressure switch, the electric motor crapping out, or a bad accumulator not storing enough pressure. A rebuilt Powermaster unit can be had for anywhere between $400 to $600, but who wants to lay out that kind of dough every year or two? Better yet, who wants a braking system with a high rate of failure?
The reason behind utilizing the Powermaster system in a turbo vehicle is simple, when under boost vacuum is not present, hence a vacuum-assisted braking system would be rendered useless. However, many GN owners have retrofitted their braking system to a vacuum-assisted brake booster setup, with additional vacuum assistance coming via an electric vacuum pump. While the addition of a vacuum pump works well, it takes up more room and once again makes the driver rely upon an electric motor for assurance when braking.
After much thought we decided to retrofit our turbo-propelled G-body to Hydroboost braking. General Motors utilized Hydroboost on many of its trucks, vans, and heavier cars touting its strength and reliability. Hydroboost uses power steering pressure to assist the master cylinder instead of a vacuum-operated brake booster or Powermaster. The power steering pump supplies pressure up to the Hydroboost then loops down into the steering gear (steering box), finally returning to the fluid reservoir, awaiting re-entry into the pump. While this system does rob a bit of horsepower, it's only during braking, so not a problem for us power junkies.
Additional advantages of the Hydroboost unit are its package size, which is much smaller than a big ol' brake booster, its ability to provide anywhere from around 1,200 to 2,000 psi of line pressure giving the brake calipers more than enough clamping force, and near instantaneous braking compared to the lag generated from a vacuum-assisted unit. The Hydroboost is also beneficial to a non-turbo vehicle running a big camshaft. Bigger bumpsticks don't fare well in the vacuum-generating department, so a Hydroboost setup may be the way to go there also.
Depending on your budget many Hydroboost system components can be found used at a local salvage yard or sourced from the internet. To lessen our chances of acquiring any failed components we called Powerbrake-Drivetrain, which provides a complete retrofit kit replacing the vulnerable Powermaster. All-new high pressure and return lines are provided along with a rebuilt master cylinder, power steering pump, and Hydroboost unit. Instructions are fairly easy to understand and we pulled the conversion off in a single weekend for around $525-driveway style!