brake pedal stiff when AC on

[grocerygetter]

I know that's wierd.
If I have the AC on in town (not interstate) the brake pedal is hard and at the top of the travel range when you push on it. If you leave hard pressure it will fall like normal eventually. The hard pedal thing happens when coming of boost hard also...like floor it, lift, and stand on the brakes...emergency type situation.
It looks like the car pulls less vac. with the ac on which I thought was normal...what's your guys opinion.

 

[buickpower]

what type of brakes do you have?

 

[grocerygetter]

stock powermaster

 

[Ormand]

If you have the stock powermaster, then the brakes do not use vacuum, and there should be no reason for any change in braking- boost, no boost, A/C, no A/C. The powermaster is not connected to the intake manifold. It uses pressurized brake fluid from the little accumulator on the side of the master cylinder, so the braking doesn't vary with changes in other gadgets, like the A/C. You sure you have the PM?