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Brake warning light on and off when pressing pedal?

flamesoldier

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Update….. i pulled the brake warningswitch and it works perfectly fine. I adjusted the rear drums that work well and without leaks. It stops well and even as well. So when brake pedal pressed down hard the brake light goes out. So my next step is what? Master cylinder probably not providing proper pressure or i have to bleed brakes.
 

Challenger RTA

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I would check parking brake switch and wire to make sure it's not hanging up or shorted. It is part of that circuit. It just might be the master cylinder residual valves not working. There is 5-7 psi on a disc -drum system.
If your not losing fluid and the system is pumping up. It's not master cylinder. At least that part.
 

flamesoldier

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I would check parking brake switch and wire to make sure it's not hanging up or shorted. It is part of that circuit. It just might be the master cylinder residual valves not working. There is 5-7 psi on a disc -drum system.
If your not losing fluid and the system is pumping up. It's not master cylinder. At least that part.
What am i looking for with the switch wire or switch am i looking to see of it is open or ground
 

sixpactogo

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What am i looking for with the switch wire or switch am i looking to see of it is open or ground
You should see an open circuit when testing the switch to ground. Your brake light is always hot looking for a ground to complete the circuit. If there is a problem with either the front or rear brakes, the piston in the valve will move to that side providing a ground that sends a ground to your brake light. If you removed the switch and it shows an open, then the piston in your proportioning valve has moved to one side or the other. Or, you could have developed a ground somewhere on that black wire between the switch and the light. Or.....it could also be a ground from the parking brake circuit as mentioned in post 22.
 
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flamesoldier

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You should see an open circuit when testing the switch to ground. Your brake light is always hot looking for a ground to complete the circuit. If there is a problem with either the front or rear brakes, the piston in the valve will move to that side providing a ground that sends a ground to your brake light. If you removed the switch and it shows an open, then the piston in your proportioning valve has moved to one side or the other. Or, you could have developed a ground somewhere on that black wire between the switch and the light.
What causes the piston to move to one side or the other causing pressure issue? Bad Master cylinder maybe or improperly bled brakes?
 

Ricks72Chlgr440

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What causes the piston to move to one side or the other causing pressure issue? Bad Master cylinder maybe or improperly bled brakes?
The piston moves to the side of lower pressure due to a hydraulic failure or leak (seals, etc). If you have a leak you should be able to see the fluid leaking, wet spot, etc. The fix is to open the bleeder on one side of the front or back and press on the pedal, then close the bleeder. If that does not do it, then do that same procedure on the other side you did not do and see if that fixes it.
 

sixpactogo

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What causes the piston to move to one side or the other causing pressure issue? Bad Master cylinder maybe or improperly bled brakes?
Usually, it is a broken line and loss of fluid and or pressure to either front or back. I can't imagine a bad master cylinder causing it because they either push fluid or not.
If the brakes have been improperly bled, I suppose that could indicate a problem and make the piston move to one side or the other.
 

sixpactogo

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Update….. i pulled the brake warningswitch and it works perfectly fine. I adjusted the rear drums that work well and without leaks. It stops well and even as well. So when brake pedal pressed down hard the brake light goes out. So my next step is what? Master cylinder probably not providing proper pressure or i have to bleed brakes.
To me, this scenario indicates that when you press hard on the pedal, the piston is trying to go back to center from which ever side it is on. Effectively opening the ground. I have heard that stomping on the pedal a few times can move the piston back but I have no proof of it. Worth a try though.
 

flamesoldier

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The piston moves to the side of lower pressure due to a hydraulic failure or leak (seals, etc). If you have a leak you should be able to see the fluid leaking, wet spot, etc. The fix is to open the bleeder on one side of the front or back and press on the pedal, then close the bleeder. If that does not do it, then do that same procedure on the other side you did not do and see if that fixes it.
Perfect will do fluid bleeding today. I inspected everything and no leaks and everything look how it should
 

flamesoldier

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To me, this scenario indicates that when you press hard on the pedal, the piston is trying to go back to center from which ever side it is on. Effectively opening the ground. I have heard that stomping on the pedal a few times can move the piston back but I have no proof of it. Worth a try though.
Thats exactly what is going on i did try the pedal trick did t work, today i will go to store and get brake fluid and bleed.
 

sixpactogo

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Thats exactly what is going on i did try the pedal trick did t work, today i will go to store and get brake fluid and bleed.
I had an issue years ago with a brass proportioning valve that the piston didn't want to move back to center after I had a rear brake cylinder fail and lost fluid to the rear brakes. I removed the switch and used a small pick to reach in and move the piston back. You may have some luck with that. It doesn't explain why it happened in the first place though.
 

Challenger RTA

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"It doesn't explain why it happened in the first place though."

Moister. That could be the problem. I use dot 5.1.
 
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Challenger RTA

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We can use dot 5.1 with our stock systems?
You have to purge the system and start over.

brake fluid 5.1.jpg
 

flamesoldier

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Ideally start with new components. Short of that make sure to get rid of ALL the old DOT 3/4 fluid as they are incompatible. The pedal feel will be different after converting to the purple stuff too!
I dont want to go through all the stuff that is good will just stick with dot 3 and get myself back to square 1
 
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