I have a 91 Chevy Astro with the hydroboost brake system. I took my van to a shop because I was having difficulties with the brakes. I was informed that this was due to low brake fluid and I needed a new hydroboost unit (the booster). I bought the part, and took it to the shop again. They informed us that the rear wheel cylinders and rear brake shoes needed replaced, and that the brake booster may not have actually been as bad as they initially thought. Right now, the brakes seem to be working acceptably. At times, the brakes do seem a bit hard and high, but this could just be my imagination (having brake trouble has made me a bit paranoid).
In light of this background, I have few questions.
The brake fluid was only low in the reservoir that delivers the fluid to the rear wheels. This would seem consistent with leaky rear wheel cylinders. Is it possible for a defective hydroboost unit to cause fluid loss only to the rear wheels?
Is it possible for the hydroboost unit to be faulty without causing any trouble with the power steering?
Most of the information I have come across regarding diagnosing brake boosters presumes a vacuum based system. How, in general, might one approach diagnosing a hydroboost system?
I had to order the part and have it shipped to me, so, before I return, I would just like to be reasonably certain that the hydroboost unit was not the source of my problems.