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My red Brake light just came on. What is the Culprit?

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Old 07-10-2017, 07:55 PM   #1
Alwyn678
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Default My red Brake light just came on. What is the Culprit?

I bought a new Master Cylinder since mine was from 1974. Is there anything else that I should look at fixing/repairing as well. Before the light came on the braking was very poor and you had to push the pedal almost to the floor to get it to stop. There was no real "Bite" to the brakes.

Thanks for the help......
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Old 07-10-2017, 08:29 PM   #2
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Originally Posted by Alwyn678 View Post
I bought a new Master Cylinder since mine was from 1974. Is there anything else that I should look at fixing/repairing as well. Before the light came on the braking was very poor and you had to push the pedal almost to the floor to get it to stop. There was no real "Bite" to the brakes.

Thanks for the help......
There are typically two things that result in the brake light coming on. 1st is the parking brake lever not being completely seated.

2nd is a pressure differential being detected between the front and rear brake circuits. There is an electrical switch located on the brake distribution valve next to the master cylinder. If a leak should develop in one of the calipers or a line in the front or rear circuit, pressure will be lost on that circuit and the valve in the distribution block will be forced toward the lower pressure side and activate the switch on the distribution block. This will in turn illuminate the brake light.

Considering your comments in the above post, I would be examining the brake calipers and looking for a leak somewhere.

You also didn't mention, but do you have power or non-power brakes?

Good luck... GUSTO
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Old 07-10-2017, 08:41 PM   #3
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Originally Posted by Alwyn678 View Post
I bought a new Master Cylinder since mine was from 1974. Is there anything else that I should look at fixing/repairing as well. Before the light came on the braking was very poor and you had to push the pedal almost to the floor to get it to stop. There was no real "Bite" to the brakes.

Thanks for the help......
If your saying you just changed the M/C, then stomp on the brake a few times real hard. This usually resets the valve/light.
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Old 07-10-2017, 09:34 PM   #4
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Originally Posted by Alwyn678 View Post
I bought a new Master Cylinder since mine was from 1974. Is there anything else that I should look at fixing/repairing as well. Before the light came on the braking was very poor and you had to push the pedal almost to the floor to get it to stop. There was no real "Bite" to the brakes.

Thanks for the help......
I just went through the same thing.

You have air in the Master Cylinder, once you fix this up you will need to bleed each caliper again.

Read my post
https://www.corvetteforum.com/forums...gy-brakes.html
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Old 07-10-2017, 11:45 PM   #5
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Easy way to tell the difference between the parking brake or regular brakes is to unplug the wire at the proportional valve. If your dash light stays on, its the parking brake. If the light goes out, its the regular brakes. Good luck.
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Old 07-11-2017, 08:30 AM   #6
Street Rat
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I always use this tool when bleeding the brakes on my C3. It keeps the valve centered in the prop valve when bleeding the brakes. Take the tool out after you are finished. Replace the light switch and your done. No more pesky brake lights. It costs less than $10.


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Old 07-11-2017, 10:42 AM   #7
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Quote:
Originally Posted by Alwyn678 View Post
I bought a new Master Cylinder since mine was from 1974. Is there anything else that I should look at fixing/repairing as well. Before the light came on the braking was very poor and you had to push the pedal almost to the floor to get it to stop. There was no real "Bite" to the brakes.

Thanks for the help......
When you replaced the master cylinder, did you bench bleed it first?
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Old 07-11-2017, 03:39 PM   #8
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I always use this tool when bleeding the brakes on my C3. It keeps the valve centered in the prop valve when bleeding the brakes. Take the tool out after you are finished. Replace the light switch and your done. No more pesky brake lights. It costs less than $10.


Can you tell us exactly what this thing is called or provide a link or some other information where someone could track this down?


Adam
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Old 07-11-2017, 04:39 PM   #9
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Old 07-12-2017, 05:21 AM   #10
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Quote:
Originally Posted by Street Rat View Post
I always use this tool when bleeding the brakes on my C3. It keeps the valve centered in the prop valve when bleeding the brakes. Take the tool out after you are finished. Replace the light switch and your done. No more pesky brake lights. It costs less than $10.


Will this help if the air is in the MC ?
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Old 07-12-2017, 08:20 AM   #11
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Will this help if the air is in the MC ?
No.
It simply centers the piston in the prop valve during bleeding.
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Old 07-17-2017, 01:01 PM   #12
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Thought to post this here since the thread is fairly new and this just started happening this weekend. 1979 with 26,000 miles, excellent very well kept all original car. I purchased it in March from the second owner in Grand Rapids, MI and now it's in San Antonio, TX. The (original) calipers began to leak so replaced all four back in April. Driving the car in this weekend the brake light will go on after driving a while and braking from a relatively high speed 55+. Checked everything and there are no leaks. Check MC and full fluid. After I check the MC and start the car the light goes out, and stays out for a while until sporadically it lights again when I brake. What should I be looking for? I was told by some friends with C3's that it's probably the MC starting to go (age?). Thoughts?
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Old 07-17-2017, 06:02 PM   #13
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Originally Posted by Big2Bird View Post
If your saying you just changed the M/C, then stomp on the brake a few times real hard. This usually resets the valve/light.
Follow Big2Bird's suggestion and really press on the brake pedal with your foot as hard as you can. Do it a few times, too. You might feel something give or move when you do that. And the brake light will go out. I believe this centers the proportioning valve to its original position.
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Old 07-17-2017, 11:36 PM   #14
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You also didn't mention, but do you have power or non-power brakes?

Good luck... GUSTO[/QUOTE]

They are power brakes
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Old 07-18-2017, 01:51 AM   #15
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As Long as you are not finding leaks and no fluid loss it is just a matter of resetting the valve. Jolt the brake pedal a few times with the car off and should reset the valve. Check the inside of your wheels/tires for any leaks, also at the back of the MS to see if it is damp. Sometimes it will leak into the booster. Brake Fluid Drys pretty quickly so maybe check it an hour or so after parking it. May have some air in them.

Last edited by JayRay; 07-18-2017 at 01:52 AM.
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