Lost my brakes

dgr

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I think I jinxed myself. Hadn't had time to be on here for awhile. Logged in today and later on I lost my brakes. Turns out I must have a leak in the rear brake circuit.

I got the brakes bled and the brake light off but now it feels like there is a brick under the brake pedal. It is extremely stiff after a couple of inches of travel. Brake performance is very marginal. I can barely skid 1 rear tire with a lot of force on the pedal. If you pump the brakes a few times with the engine off, you can hear the vacuum booster bleeding off. If you start the engine while lightly pressing on the pedal, you can feel the pedal drop as the vacuum increases.

Brakes were bled farthest to nearest. Vacuum was measured at idle and around 1500 rpm. Vacuum max is. 16 inches. Without the soup can vacuum canister on the drivers side, the brakes bleed the vacuum down about 5 inches with each press of the pedal with the engine idling. With the canister it is about 1 inch. Vacuum holds at 16 once engine is turned off.

Any thoughts on this? Could something have been damaged when the rear circuit was ran out of fluid and I had to use what brakes were left to get the truck stopped? Is there something in the brake warning switch that needs to be reset? I thought bleeding it was how you reset that switch. It is an 86 so I am not aware of any RABS on it

Thank you for your thoughts on this.
 

icanfixall

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Your vacuum pump is shot. You need more inches of vacuum than 16 to safely operate the brakes or the truck. Hard peddle is bad vacuum. Might want to check the vacuum hoses for leaks before replacing the vac pump.
 

NO_SPRK

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Also pull the line off the booster. if it makes a noise then you know you have no leaks just a bad pump.

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dgr

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OK. Vacuum is holding with engine off So i do not believe there are any leaks. What should vacuum measure with a good pump? Looks like stepping up plans for my hydroboost
 

dizdak

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don't know if you got it figured out, when mine did similar another member told me to see if my a/c came through the vents...apparently that vaccum pump is tied into brakes and a/c.. i hard hard brake pedal and a/c only come through defrost vents.. replaced pump, brakes were good, and a/c coming back through a/c vents..
 

dgr

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I got to thinking about this. Isn't this the same brake system as a gas engine. Idle vacuum on a gas engine is 14-18 isn't it?

I don't think I'm describing it well. With engine off and vacuum bled, the pedal is hard from the top. With engine running, I can feel the vacuum assist until it gets to a certain point. Then the pedal just stops. Just checked it. Brake warning lamp just came on a couple times while I w playing with the brakes. Baffled
 

icanfixall

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Our vacuum system runs 3 things on our trucks. The cruise if you have it. The power brakes and all th vents to run ac thru the dash. If the vacuum fails the brake peddle gets hard as hell to push down and the ac fails thru the dash vents but will only come out the defroster vents on the windshield. Thats the safety effect the defroster vent has. BTW the vents used to clear a windshiled is the ca running. When the ac runs the air is dry and hot. Many years ago it was just hot. No ac compressor running. Now the ac compressor runs to dry up the air directed to the windshield.
 

laserjock

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I don't know about the vacuum numbers but I would check your linkages and the master. If it goes down normal and stops short of the floor or has a hard stop that is not "normal" force from the brakes, you may have a bad master or a linkage bound up. If the vacuum is not high enough, it should just be really hard to push.

In these trucks I think the brake warning light is wired to a vacuum switch so it could be simple vacuum. If Gary says the numbers are low, he's probably right. ;Sweet
 

dgr

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Thanks for the numbers guys. Would you say a no vacuum situation would make the brakes feel like they do before you start it. Or like a truck with oversized tires and manual brakes? This is not what they feel like. They feel like there is vacuum assist until the pedal hits that invisible brick. There is no further braking beyond that point no matter how hard you push
 

laserjock

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Check the master and the linkage. Regardless of vacuum if it hits a hard (brick) stop, I'd be checking the mechanical parts of the system. Something is wrong.
 

OLDBULL8

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The adjusting screw out of the booster is adjusted to one inch (1") to the tip, from the flat surface next to the MC mounting bolts, it has to be measured from there. It's the same whether it's a single or double diaphragm booster. Check the booster mounting nuts inside the cab.
A good vacuum pump will pull 25-26 inches and shouldn't go below 20" for C6 operation.
 

SearsMech

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Your rear shoes on one side are soaked with brake fluid or gear lube or both. It also sounds like maybe your fronts aren't quite up to par, I would check your brake hoses (rubber).
 

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