A longstanding issue with my car has been sub-par braking performance. The GM G-Body suffers from woefully substandard brakes, especially when compared to modern cars. Tiny 10.75″ vented rotors up front with single piston calipers and 10″ drums out back on a 3600 pound car do not inspire confidence.
Piling on with the Grand National came the prospect of positive manifold pressure getting past the vacuum check valve on the vacuum booster. This would pressurize the boost and result in no power assist after a full throttle blast.
GM attempted two solutions to this problem. In the 1984-1985 non-intercooled cars, the used the HydroBoost system, which gets pressure for the booster from the power steering pump. In
1986-1987, they switched to the PowerMaster, a hydraulic system driven by a large electric pump.
The PowerMaster worked great off the showroom floor,
but time was not friendly to it. The unit was immediately involved in a recall where a pressure switch on top of the unit had to be replaced. The original would fail, the pump would run continuously, overpressure the rest of the system, which would leak, and you’d have no brakes.
As time wore on, the internal seals in the PowerMaster all eventually fall victim to the enormous pressures the unit operated under (3,000 PSI or more) and the caustic nature of DOT 3 brake fluid.
Many years ago, my PowerMaster suffered an internal leak, and I pulled it off. Replacing the unit wasn’t practical, as a reman unit was more than $500, and failure rates of the remans were high. So at the time, I converted to vacuum.
The conversion worked around town, but it did indeed suffer from pressurization of the booster when the turbo spooled up, resulting in many almost-didn’t-stop-in-time situations.
My attempts to fix this were mainly stopgaps. I added a vacuum reservoir and finally an industrial strength check valve. The stopped the pressurization of the booster, but the brakes still sucked.
I had two options: switch to a HydroBoost or go non-boosted. After watching my father wrestle with getting a HydroBoost working on his 1968 Cougar (it has a rather large camshaft and doesn’t generate enough vacuum to run a vacuum booster), I decided that simple was better and opted for full manual.