Thought I'd like to hear some feedback from the community. When I pump my brakes repeatedly, the RPM starts dropping until it eventually stalls. I'm already assuming the brake booster is the culprit since I had it sitting on my '86 for the past 5+ years... so there might be a good chance the diaphragm inside is bad. I've checked all vacuum connections and there aren't any leaks coming from any the lines. Already have a new booster on the way but what do you guys think?

Kudos,
Jay

Unplug the booster, seal the intake side off and take it for a drive.

Siding with the gent above me. Disconnect the booster from the intake and plug it up so theres no vac leaks on the intake.

WARNING

I know this goes without saying (hopefully, but JUST in case!) Doing so WILL disable the power-assist of your braking system. The pedal WILL be harder to push/modulate. Doable, so dont fret- but it will require a bit of "leg strength" vs the weight of just your foot.

Thanks for the tips guys. Disconnected the booster vacuum lines and plugged the port on the intake. Took it around the block a few times and no stalling issues what-so-ever. But of course, that's because the booster was running off of straight foot power.

UPDATE - I changed the booster a while ago and the brake feels much much better, I can finally feel pressure/feedback from the system. However, if I keep pumping the brakes, the rpm does continue to drop.. although it isn't as bad as before I changed the booster.. but stalling can happen if I pump it repeatedly for like 15-20 times. I'm stumped.. all my vacuum lines are good too. =/

There are two ways that the brakes are connected with the running of the engine.
The first way is by the vacuum hose. Pumping the brakes "uses up" vacuum, and
some air gets sucked out of the booster and into the intake manifold. If this tiny
amount of air did anythng at all, it would slightly raise the idle speed.

The second way is by the brake lights. Pumping the brakes switches the lights on
and off. When the brake lights switch on the diode box should open the electric
engine idle-up valve to raise the engine speed 100 rpm or so. If this does not
happen, then the stop lights will be drawing power and loading up the alternator.

Maybe that's enough to drag the engine rpm down ? You could try hooking your
multimeter up to the battery, and seeing what happens when someone pumps the
brakes... best I can come up with

Cheers... jondee86

Jondee! Awesome diagnostic! I haven't thought about the possibility of the problem being caused by electrical issues! Gonna' have it checked out once I have the time. Will update once again later on. Thanks!