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Old 12-09-2009, 12:20 AM   #1
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brake warning light..

Lost all brakes on the car a while ago turned out it was master cylinder...anyway brake warning light came on when thay failed,changed master/bleed brakes /new fluid,but still unable to get light to go out,i no what the problem is but no idea how to re set the shuttle piston ,have tried differant things but no joy...brakes work fine but some people say as its stuck it will restrict fluid to one side of brakes and others say it wont....anyone had this problem before ? 67 289 vert thanx steve
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Old 12-09-2009, 08:19 AM   #2
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Re: brake warning light..

does the brake fluid have a sensor that comes on when the fluid is low? If so check it, it may be bad and causing a bad fault... especially if the brake system was bleed correctly and the brakes feel normal. Other issue might be vacuum, you can check your vac system under idle/load etc and drop off (from rpm high to idle) to ensure its with in spec and doesnt jump... depending on the cam setup you might have an issue here that can cause brakes to not work nearly as good.
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Old 12-09-2009, 11:53 AM   #3
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Re: brake warning light..

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does the brake fluid have a sensor that comes on when the fluid is low? If so check it, it may be bad and causing a bad fault... especially if the brake system was bleed correctly and the brakes feel normal. Other issue might be vacuum, you can check your vac system under idle/load etc and drop off (from rpm high to idle) to ensure its with in spec and doesnt jump... depending on the cam setup you might have an issue here that can cause brakes to not work nearly as good.
no such thing it is 40 odd years old/let me explain....as an added safety feature ,an instrument pannel warning light will go on if a pressure loss occurs in either half of the system.The light is conected to a shuttle piston between the front and rear brake lines. Normally ,the shuttle piston does not move.But ,should a pressure loss occur in either brake system ,a significant differential in pressure results and the shuttle piston activates a switch that turns on the warning light when brakes are applied.67 mustangs are equipped with dual hydraulic brake system.system has dual master cylinder ,separate hydraulic lines connect one master cylinder to front brakes and one to the rear.so any loss of hydraulic pressure in one half of the system would not leave the other half of the system inoperative.so the shuttle has moved to one side ,what i need to no is,how to re centre it.....
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Old 12-12-2009, 08:31 AM   #4
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Re: brake warning light..

Your explanation says that if one side of the brakes fail, then the shuttle valve will kick over and throw the light. Your original post said that ALL of the brakes failed on the car. Did you replace both master cylinders and fill/bleed fronts and rears? It sounds to me like a pressure balance problem; you have more pressure in one loop than the other, which prevents the shuttle from resetting. If you only replaced one master, you might have some leakby in the other which is causing the pressure disparity. Do you have a Chilton's or other DIY manual? Might find the solution in there.
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Old 12-12-2009, 02:53 PM   #5
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Re: brake warning light..

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Your explanation says that if one side of the brakes fail, then the shuttle valve will kick over and throw the light. Your original post said that ALL of the brakes failed on the car. Did you replace both master cylinders and fill/bleed fronts and rears? It sounds to me like a pressure balance problem; you have more pressure in one loop than the other, which prevents the shuttle from resetting. If you only replaced one master, you might have some leakby in the other which is causing the pressure disparity. Do you have a Chilton's or other DIY manual? Might find the solution in there.
master cylinder seals had gone hence no brakes....not pushing fluid to brakes ,changed m/c and job done,its one m/c with two ports each side does front and rear brakes,all been bled ok....
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Old 12-12-2009, 03:49 PM   #6
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Re: brake warning light..

I would try to re bleed the system starting from the wheel farthest away from the master cylinder. I had the same problem with my 67 and that cured it. Good luck...
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Old 12-13-2009, 02:25 AM   #7
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Re: brake warning light..

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I would try to re bleed the system starting from the wheel farthest away from the master cylinder. I had the same problem with my 67 and that cured it. Good luck...
Done that and no joy,when this happend to yours did it effect your brakes?mine seem fine but some people say it effects the brakes !!!thanx for your help dude.
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Old 12-13-2009, 10:25 AM   #8
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Re: brake warning light..

They felt OK for 4 wheel manual drum brakes lol...
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Old 12-13-2009, 11:45 AM   #9
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Re: brake warning light..

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They felt OK for 4 wheel manual drum brakes lol...
Yeh good pointlol...
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Old 01-19-2010, 02:00 AM   #10
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Re: brake warning light..

First try to lift the emergency brake pedal and see if the light goes off. You may have a bad switch. All dual circuit brake systems use a pressure differential warning switch to alert the driver of a pressure loss in one of the hydraulic circuits. You may have a leak in your hydraulic system. Inspect all four wheels for brake fluid leaks. You may also have air in the master cylinder. If you do have air in the master cylinder it is usually caused by a leak in the hydraulic system.
Hope I helped!!
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Old 01-19-2010, 07:07 AM   #11
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Re: brake warning light..

man i have no idea i went as far as to ask around for you and nothing! good luck bro the only answer i could get was check the fluid and you already have! Good luck bro
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Old 01-19-2010, 12:54 PM   #12
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Re: brake warning light..

Cheers to you all for your help...tried just about everything and still the light stays on....!!!
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