Bad brakes

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Schurkey

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Forgot to say that my rpms move when i press the brake. Searched it up and a bad booster can cause that too.
It's a vacuum booster.

Excess brake pedal travel causes excess vacuum loss from the booster--the pssssst sound you're hearing. Excess vacuum loss from the booster acts like a vacuum leak, affecting engine operation.

FIX THE EXCESS PEDAL TRAVEL, see if the "booster problems" go away on their own. It's a total waste of time, effort, and enthusiasm to hunt down booster problems when there's excess pedal travel.

Bleed the brakes with a scan tool, which may/may not also involve bench-bleeding the master cylinder. The master may be faulty, or there may just be a bunch of air in the system including in the existing master cylinder.




Did you bleed the system with a scan tool? If not, you didn't do a thorough job.

Why suspect the booster when the problem is a low pedal?

Does the truck stop? What is the history of this? Low brake fluid level? Why were the rear cylinders changed--did they leak? Front pads worn-out? How many miles since the previous brake work?
You haven't answered any of my other questions, so I don't suppose you'll answer this one: When you replaced the wheel cylinders, did the master cylinder fluid level drop so that air got into the master cylinder from the reservoir?
 

Marcelo

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It's a vacuum booster.

Excess brake pedal travel causes excess vacuum loss from the booster--the pssssst sound you're hearing. Excess vacuum loss from the booster acts like a vacuum leak, affecting engine operation.

FIX THE EXCESS PEDAL TRAVEL, see if the "booster problems" go away on their own. It's a total waste of time, effort, and enthusiasm to hunt down booster problems when there's excess pedal travel.

Bleed the brakes with a scan tool, which may/may not also involve bench-bleeding the master cylinder. The master may be faulty, or there may just be a bunch of air in the system including in the existing master cylinder.





You haven't answered any of my other questions, so I don't suppose you'll answer this one: When you replaced the wheel cylinders, did the master cylinder fluid level drop so that air got into the master cylinder from the reservoir?
My bad i didnt get any alerts of ur replies. I replaced the rear brake cylinders. I dont remember if the fluid level dropped. When i bleed the brakes they the brake pedals hard. But when i start the engine is when they get soft and hear the pssst sound.
 

Marcelo

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My bad i didnt get any alerts of ur replies. I replaced the rear brake cylinders. I dont remember if the fluid level dropped. When i bleed the brakes they the brake pedals hard. But when i start the engine is when they get soft and hear the pssst sound.
And if bleed the system what order should i go in?
 

FrankieD61

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Marcelo, it sounds like you need to bleed the air out of the ABS system. A scan tool can actuate the usually-computer-controlled valves in the ABS system.

I ran into this with my truck; once I bled the ABS system of any air and followed up by then bleeding the wheels, I was in the clear. If the master was run dry, that will need to be bled as well. Start from the top (master) and work your way down (ABS mod/valve, connections, wheels). Work in that order and you WILL find the problem.

BTW, I'm NO expert by any means. This is just what I did and my brakes are no longer an issue. (Besides the small JB3 system; that's another issue .)
 

Schurkey

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can anyone help me figure out what js wring with my brakes on my 98 c1500?

And if bleed the system what order should i go in?

If the master need bled, that first. Then right rear wheel, left rear wheel, right front, left front, ABS as needed, repeat wheels as needed.
Just to amplify Supercharged111, and FrankieD61:

1. Make sure the rear brakes are properly adjusted. If anything, adjust them "too tight" rather than too loose. The 254mm (10") Leading/Trailing shoe drum brakes on most 1500s are INFAMOUS for being out-of-adjustment. They rely on the vehicle operator using the park brake regularly, and almost no-one does. In the rare case that your 1500 has the 11.x" Duo-Servo rear drums, they adjust when you release the brakes after stopping firmly in Reverse. Much more likely to stay in adjustment.

2. Bleed the master cylinder as needed. Most master cylinders are mounted to the vehicle so that they're tipped "up" in front, and that can trap an air bubble. Lift the rear of the vehicle, or disconnect the master from the booster (DON'T disconnect the brake tubing) and carefully push the front of the master "down". Then either "tickle" the brake pedal, (Push gently, slowly, and not very far) or lightly push the master cylinder primary piston with the front of the master tipped "down" so that air bubbles pop up into the reservoir via the little drilled passages. There should be little "geysers" of brake fluid as the pedal, or piston is pushed. If you have a helper to push the pedal, you can verify the fluid flow. Not unusual to have bubbles at first, then the lil' geysers.

3. Follow the second page instructions in the attached .pdf for proper bleeding of the rest of the hydraulic system. You WILL need a scan tool, you probably will not need the "special tool" to hold the metering valve. The metering-valve tool is ONLY needed if there's no fluid flow to the FRONT brakes.
 

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Marcelo

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Marcelo, it sounds like you need to bleed the air out of the ABS system. A scan tool can actuate the usually-computer-controlled valves in the ABS system.

I ran into this with my truck; once I bled the ABS system of any air and followed up by then bleeding the wheels, I was in the clear. If the master was run dry, that will need to be bled as well. Start from the top (master) and work your way down (ABS mod/valve, connections, wheels). Work in that order and you WILL find the problem.

BTW, I'm NO expert by any means. This is just what I did and my brakes are no longer an issue. (Besides the small JB3 system; that's another issue .)
Ok bro thanks will try it out tommorow
 

Marcelo

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Just to amplify Supercharged111, and FrankieD61:

1. Make sure the rear brakes are properly adjusted. If anything, adjust them "too tight" rather than too loose. The 254mm (10") Leading/Trailing shoe drum brakes on most 1500s are INFAMOUS for being out-of-adjustment. They rely on the vehicle operator using the park brake regularly, and almost no-one does. In the rare case that your 1500 has the 11.x" Duo-Servo rear drums, they adjust when you release the brakes after stopping firmly in Reverse. Much more likely to stay in adjustment.

2. Bleed the master cylinder as needed. Most master cylinders are mounted to the vehicle so that they're tipped "up" in front, and that can trap an air bubble. Lift the rear of the vehicle, or disconnect the master from the booster (DON'T disconnect the brake tubing) and carefully push the front of the master "down". Then either "tickle" the brake pedal, (Push gently, slowly, and not very far) or lightly push the master cylinder primary piston with the front of the master tipped "down" so that air bubbles pop up into the reservoir via the little drilled passages. There should be little "geysers" of brake fluid as the pedal, or piston is pushed. If you have a helper to push the pedal, you can verify the fluid flow. Not unusual to have bubbles at first, then the lil' geysers.

3. Follow the second page instructions in the attached .pdf for proper bleeding of the rest of the hydraulic system. You WILL need a scan tool, you probably will not need the "special tool" to hold the metering valve. The metering-valve tool is ONLY needed if there's no fluid flow to the FRONT brakes.

will try this out thanks for the help
 

Marcelo

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Just to amplify Supercharged111, and FrankieD61:

1. Make sure the rear brakes are properly adjusted. If anything, adjust them "too tight" rather than too loose. The 254mm (10") Leading/Trailing shoe drum brakes on most 1500s are INFAMOUS for being out-of-adjustment. They rely on the vehicle operator using the park brake regularly, and almost no-one does. In the rare case that your 1500 has the 11.x" Duo-Servo rear drums, they adjust when you release the brakes after stopping firmly in Reverse. Much more likely to stay in adjustment.

2. Bleed the master cylinder as needed. Most master cylinders are mounted to the vehicle so that they're tipped "up" in front, and that can trap an air bubble. Lift the rear of the vehicle, or disconnect the master from the booster (DON'T disconnect the brake tubing) and carefully push the front of the master "down". Then either "tickle" the brake pedal, (Push gently, slowly, and not very far) or lightly push the master cylinder primary piston with the front of the master tipped "down" so that air bubbles pop up into the reservoir via the little drilled passages. There should be little "geysers" of brake fluid as the pedal, or piston is pushed. If you have a helper to push the pedal, you can verify the fluid flow. Not unusual to have bubbles at first, then the lil' geysers.

3. Follow the second page instructions in the attached .pdf for proper bleeding of the rest of the hydraulic system. You WILL need a scan tool, you probably will not need the "special tool" to hold the metering valve. The metering-valve tool is ONLY needed if there's no fluid flow to the FRONT brakes.

Looks like there leaks. Is the master cylinder bad ?
 

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