probably a vacume leak if possible let it run listen close under the hood for a whistling sound and maybe you can find it.
DOT 3 brake fluid.
in the engine
The 1981 Chevy Cheyenne brake fluid tank can be found attached to the firewall in the engine compartment. The brake fluid tank will be on the drivers side of the firewall.
It's in the left engine compartment.
Have you checked the brake fluid level in your brake master cylinder in your engine compartment ? a low level will turn on your brake light in the dash
in the engine area directly in front of the steering wheel
IT COULD BE A WORN ENGINE MOUNT. TO BE SURE, PUT YOU CAR IN GEAR PRESS THE BRAKE APPLY THE E-BRAKE AND ACCELERATE THE CAR IF YOU FEEL THE SAME SHAKING IS YOUR ENGINE MOUNTS. (BE Careful)
With engine off--pump brake until all vacuum is exhausted With foot on brake start vehicle--brake pedal should drop
use your parking brake this answer is in the owners manual
take off the E-brake dumb@$$
do I need brake pads or brake shoes for 1998 Chevy tracker
The power brake booster is leaking vacuum and that makes the engine die when the brakes are applied. Replace brake booster.