My '87 coupe has a brake problem. When using the air conditioning, the brake pedal is firm on the first push. But without the air on, the pedal may need a pump or two before the pedal is firm. Once engaged, the pedal is firm and does not drop at a stop light. The car just passed emissions and runs well.
I think I have a vacuum leak or a bad brake booster. Anyone have this problem, and how did you solve it? How hard is a booster change-out? Thanks for the feedback!

 

Check the booster check valve that is in the large vac line running to the booster. Sounds like it is bad or missing.

 

I will check that tonite when I get it home; the valve and hose are not very old, tho.
The master cylinder does not lose fluid either. Would I hear a vac leak at the booster if the diaphragm was broken?

 

if it is a vac leak you will loose pedal boost, as opposed to a bad master cyl which you loose pressure regardless of boost or not.

A bad master is easy to check, with the key off, press the brakes half dozen times, then press and hold... if the brake pedal continues to move and does not hold solid, you have a bad master or bad hoses.

 

I checked out the vac hose to the booster, and the check valve. They are good. When I removed the hose from the hard line to the engine, no noise. When I removed the hose from the vac booster, it wooshed. Checked the valve again (orally!) and it worked fine. It's oriented properly, too.
I sprayed some carb cleaner on any vac hose end I could find, to no effect on engine idle. Same with brake cleaner....
I'm sure the engine is pulling more vacuum at idle with the air on, or at least that's how it acts. If the booster is okay, and the pedal is firm at a stop, what else could it be?