Brake problem..

Whenever im at a light and i got my foot on the brakes, it goes all the way down slowly, goes down even faster when my a/c compressor kicks in. Wtf could it be? When it goes down, i pump it once or twice and it comes back up but will eventually go down again. This only happens when im at a complete stand still.. thanks To yall, i do all the repairs myself, so i need u guys again..

you got a leak somewhere ur getting air in your lines. my clutch has done this twice. check for lose hoses and check your master cylinder and check your bleeder valves and caliper line. you might have a lose one. youll see fluid wherever its leaking. i wouldnt drive it too much unless u have anunlmtd supply of brake fluid lol.

Ive checked every where and no fluid leaks, even my fluid level is where it needs to be.

check under the dash where your pedal pushes the stud into the master cyl. and see if its leakin there unless u already have. that is weird tho. if its not leakin out of the lines or calipers maybe one of your rear cylinders r leakin alil did u check them (under brake drum).move the rubber boot around, squeeze it or somthin and c if fluid comes out of the rubber boot cause that boot will hide leaks. if not them id get a new master cyl.

oh and you might could test your ebrake. if it barely slows you down it may tell you there is brake fluid on the pads and or drum. never tested that theory tho but u never no

I'd first suspect air/leak in the system, or could be a master cylinder that's bad internally.

Now - when the AC is on, does the engine rpm drop a little? That could affect engine vacuum, used by a power brake booster....

I will agree the master can not leak and be weak.Can be the push rod,or bushing internally are sticking(and yes not leak).Also your rear wheel cylinders on those drums are prone to leaks and or loosing pressure.Granted my master leaked at the resivour and even had a leaky wheel cyldr to add drama.Just some ideas being most of our trucks are over 20yrs old and components wear out.

Ty Guys for the input.. I removed all the wheels yesterday and no leaks. Nothing under dash either.. And my fluid level hasn't moved.. could it be my booster? mind u, when pedal drops car stays braked..

id get a new master cylnder. its not holding the fluid where it needs to be to keep the pedal off the floor when you press it, though its not leaking. i bet its leaking internally (not losing fluid or taking in air)so the fluid maybe jus be doing laps through your master without leaking. ive never had that problem. it sounds scary. id check a junk yard for one.

"id check a junk yard for one." ...... really?

a new master is like $40. brakes are kinda important, splurge and get a new one