Buckshotram

If I am idleing in traffic like creeping up to a redlight my brake pedal gets hard to push like the master clyinder isn't working. But what does the brake booster or something like that do. Also the brake light comes on like the park brake is set. What kind of problem does this sound like???

infidel

Common problem with pre '97 trucks with vacuum assisted brakes.
What's happening is the vacuum pump can't keep up at idle with repeated brake applications.
Best course is to be aware of it, idle up if need be. If you want to get fancy plumb in a vacuum reservoir tank.

Buckshotram

Is it also normal for the brake light to come on? Thanks for the info.

infidel

Yes, there is a low vacuum sensor.

ScottN

A lot of people press the pedal harder than they need to when they are stopped. This uses extra vacuum. If you're just creeping along, you shouldn't have to push the pedal very hard.

Note that the vacuum pump works somewhat opposite of a gas engine in generating vacuum. Gas engines have a bunch of vacuum at idle, when the throttle plate is closed. The vacuum pump is turning slowly, so pumps little air.

I suppose if your idle was exceedingly low, that would make a noticeable difference.

Buckshotram

Yes my idle seems a little low 600-650 in drive im going to bump it up about 100rpms this weekend and see if it helps. thanks for the info guys