Brake booster shot?

[88sclb350]

88 k1500 5.7 and had this truck for a year never had a vehicle with vacuum boosted brakes so I don’t know.

Basically my brakes have half of the pedals travel applying no brakes until the pedal is halfway down then I can feel the pedal actually applying the brakes.

The brakes work ****** to okay at best I’ve replaced nearly everything in the system to try to fix it and they’re better but still bad.

With a proper working vacuum booster should I have brakes as soon as I press the pedal? If so I’m ordering a new booster.

 

[GrimsterGMC]

88 k1500 5.7 and had this truck for a year never had a vehicle with vacuum boosted brakes so I don’t know.

Basically my brakes have half of the pedals travel applying no brakes until the pedal is halfway down then I can feel the pedal actually applying the brakes.

The brakes work ****** to okay at best I’ve replaced nearly everything in the system to try to fix it and they’re better but still bad.

With a proper working vacuum booster should I have brakes as soon as I press the pedal? If so I’m ordering a new booster.

You just described the standard 88 K1500 brakes. Make sure the rear brake shoes are adjusted and the handbrake is too, then get any air out of the system especially the master cylinder and RWAL unit. I recently replaced the front discs and pads and had the back of the truck jacked up higher than the front. When the fluid got pushed back into the master cylinder it took all of the air that was trapped in the master cylinder back into the reservoir since the cylinder was tilted forward. Now the brake pedal starts working right from the top.

 

[Erik the Awful]

Adjust, adjust, adjust the rear brakes. Use your parking brake religiously to help keep them adjusted.

 

[88sclb350]

Adjust, adjust, adjust the rear brakes. Use your parking brake religiously to help keep them adjusted.

Okay my drums are adjusted well because I just did cylinders shoes and hardware. My parking brake cable needs to be replaced. But you’re saying the booster isn’t the culprit

 

[Schurkey]

Almost certainly NOT the booster.

As already said--rear brake adjustment, get the park brake working--and USE IT. The 1500 pickups nearly always have 254mm (10") leading-trailing shoe drum brakes that are an abomination. They're always out of adjustment because nobody uses the park brake.

The RWAL should have a bleeder screw on it.

As said--if you can get the ass-end of the truck high enough, the master cylinder will tip "down" in front, which can dramatically help remove air from the master.

If this is a regular-cab 1500, you've probably got JN3 brakes--the weakest, crappiest power brakes ever installed on a GMT400. Thin rotors, small pistons in the calipers, small-diameter master cylinder, thin, weak power booster, and those hateful leading-trailing shoe rear drums. GM quit using the "3" brakes in the early '90s.
The JN5 got you thicker rotors, bigger pistons in the calipers, larger-diameter master and bigger booster--but kept the crappy rear drums. Often found on extended-cab trucks, and most 1500s after they dropped the JN3 brakes. My '88 K1500 had JN3 brakes until I grabbed all the JN5 stuff from the Treasure Yard and converted. I also replaced the rear axle and in the process got the much-better 11.x Duo-Servo rear drum brakes, making my truck the equivalent to JN6 brakes.

Perhaps a moderator will move this thread out of "Engines" and into "Axles + Brakes".