POWER BRAKE BOOSTER?

[GOT_NITRO?]

ANYONE KNOW HOW TO TEST A BRAKE BOOSTER? I JUMPED ON THE BRAKES HARD AND THE LIGHT CAME ON. WHEN THE TRUCK IS RUNNING, THE PEDAL CAN BE EASILY PUSHED TO THE FLOOR AND THE TRUCK IS VERY DIFFICULT TO STOP. I CHECKED ALL THE LINES AND REPLACED THE MASTER CYLINDER....NO CHANGE. COULD IT BE A BAD BOOSTER? HOW ABOUT A VALVE OR SOMETHING GOING TO THE BOOSTER? IT IS A VACUUM SYSTEM (NOT HYDRO). THE BRAKE LIGHT IS STILL ON AND THERE IS NO RESISTANCE WHEN PUSHING ON THE BRAKE PEDAL. THANKS

[GM-Tech]

With the engine off, pump the brake pedal 4 or 5 times to deplete any vacuum in the booster. Keep your foot on the brake pedal with a slight amount of pressure and start the engine. You should feel the pedal fall as vacuum builds and boost is achieved. This should happen pretty much instantly when the engine starts.

[71GMC_3/4T]

There should be a proportioning valve down by the frame usually, sometimes it's up by the M/C. It should have a wire that comes off it (that's what makes the brake light come on). The purpose of this is to show you when you lose pressure in the front or rear (they're on separate pistons for safety). There is a little slider that moves when something fails, which turns on the light.

If your pedal is going all the way to the floor, it most likely isn't your vacuum booster. It's more likely you have a leak somewhere, or a lot of air.

Get a big can of brake fluid, a piece of clear hose to fit the nipple on the bleeder and go to town. Don't let the M/C run dry, or you'll be starting over. Bleed the farthest back brake first, then the other back brake, then the Right front, then the Left front. Put the hose you bought into a clear jar so you can see when you get the last of the bubbles out. Chances are, if you just replaced the M/C, you've got air clear up by the M/C and it will take you a long time to get it down to the wheel cylinders, and the air likes to go uphill. If you have access to a power bleeder, by all means use it! It will save you a lot of time.

[GOT_NITRO?]

There should be a proportioning valve down by the frame usually, sometimes it's up by the M/C.  It should have a wire that comes off it (that's what makes the brake light come on).  The purpose of this is to show you when you lose pressure in the front or rear (they're on separate pistons for safety).  There is a little slider that moves when something fails, which turns on the light.

If your pedal is going all the way to the floor, it most likely isn't your vacuum booster.  It's more likely you have a leak somewhere, or a lot of air.

Get a big can of brake fluid, a piece of clear hose to fit the nipple on the bleeder and go to town.  Don't let the M/C run dry, or you'll be starting over.  Bleed the farthest back brake first, then the other back brake, then the Right front, then the Left front.  Put the hose you bought into a clear jar so you can see when you get the last of the bubbles out.  Chances are, if you just replaced the M/C, you've got air clear up by the M/C and it will take you a long time to get it down to the wheel cylinders, and the air likes to go uphill.  If you have access to a power bleeder, by all means use it!  It will save you a lot of time.

 

<{POST_SNAPBACK}>

 

 

 

NO LEAKS. NO AIR ENTERED THE SYSTEM. COULD THE PROP. VALVE BE STUCK OR BROKEN AND NOT ALLOW THE FLUID TO TRAVEL TO THE CALIPERS / WHEEL CYLINDERS? WHAT DOES IT MEAN WHEN THE LIGHT IS ON? NO PRESSURE?

[71GMC_3/4T]

The light means there was a pressure differential between the front and back brakes. Simply put, it's a sliding plunger that stays in the middle if the brake pressures are near equal. If you lose a rear brake line, the front brake pressure pushes the slider over, turning on the light.

[GOT_NITRO?]

WELL, I WILL CHECK THE LINES AT THE VALVE. DO YOU HAVE ANY SUGGESTIONS ON HOW TO REMOVE RUSTED / DETERIORATED BLEEDER SCREWS? THE FRONT ONES ARE REALLY BAD. IS HEAT THE BEST OR PB BLASTER????