Vaccum issue

so here's is probably a goofy question.i have a 1983 K10 with 383 stroker long bed with dual tanks, with less than. 100k miles. Why would I hear a significant change in My idle with my foot on the brake? I go from sitting there in neutral listening to my truck at idle, to pushing the brake pedal, and hearing the Idle pick up. Not crazy like redlining or anything but def noticeable to my ears. Is that a vacuum issue, because the master cylinder works off vacuum right?.

Applying brakes does allow vacuum to flow into the power brake unit. That's how the system assists with braking. Engine speed should only momentarily increase when the brakes are first applied. If the higher engine speed continues during brake application there is likely an internal leak. Most of the time a leak can be diagnosed by letting the vehicle sit [engine off] for a few minutes to an hour or more. Pull the vacuum check valve at the booster. Should hear a hiss as air rushes into the booster. If not, booster and or check valve is bad.

fast 99 said:

Applying brakes does allow vacuum to flow into the power brake unit. That's how the system assists with braking. Engine speed should only momentarily increase when the brakes are first applied. If the higher engine speed continues during brake application there is likely an internal leak. Most of the time a leak can be diagnosed by letting the vehicle sit [engine off] for a few minutes to an hour or more. Pull the vacuum check valve at the booster. Should hear a hiss as air rushes into the booster. If not, booster and or check valve is bad.

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Doesn't the cruise control also have a vacuum switch to kill the cruise when you hit the brakes?

Don't know if that switch is vacuum or electric but yes, cruise is killed by brake.

If you suspect a problem, temporarily plug the vacuum hose to diaphragm.

gmbellew said:

Doesn't the cruise control also have a vacuum switch to kill the cruise when you hit the brakes?

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ok thanks ALOT I'll try that. the brakes seem to work fine, I jus noticed the engine rpms higher at say a stop light,and it made me wonder, I do have another brake related question...my brake light on the dash, which is for when the parking brake is engaged,right? it constantly stays on, I've checked the cable between both rear end sides to where they meet, and I've adjusted that drastically both ways, meaning I've put almost no tension when e brake is off and I've put tension on when e brake is off, and I adjusted it back to where I'm sure its not dragging, is that some sort of a sensor on the pedal itself? and if so what causes it to change do they go bad? how doesmit work? because there is no wire ran to the rear of the brakes, so what tells that to turn brake light on the dash on? because its pretty simple at the brakes on axle, the brake drums springs and the brake cylinder that is all that is back there, there are no extra lines or wires or anything I can see, so what lets the indicator know when to engage or disengage? thanks in advance

There is a switch on top of parking brake assembly and a proportioning valve built into the brake lines. Valve should be on the front crossmember somewhere. Try disconnecting wires on one or both.

Thhank u kindly...appriciate u taking time to get back at me