2nd Gen Non-Engine/Transmission Brakes, vacuum, and loss of power assist

[CRSmith]

A week ago, I posted with a groaning power steering and brake vacuum pump. That was low fluid that showed itself on a 5 degree morning. I filled the pump with fluid, and no more groaning.



Now, sometimes, when I hit the break pedal, I'll feel a sudden "pound" or hit. This is followed by a lack of power assist. The problem is intermittent. Sometimes the brakes work without a problem, other times it feels like I've got a 5000lb trailer on board.



Could it be air bubbles?



I tried searching for about a half hour, but found only hints about the 'pressure relief valve', but searching that doesn't find much brake info.



Thanks.

 

[bmoeller]

The booster is powered by the power steering pump (Hydro-boost). No vac. involved, as in the '96 and older trucks. There is a blue cylinder on the booster that is an accumulator. It could be going bad, if the sytem doesn't need bled.