Weird brake issue

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Joined
Mar 14, 2014
Messages
185
Reaction score
3
Location
Texas
My Car
1971 Mustang Convertible 351c 4v 4 speed

2013 Mustang Boss 302
I'm experiencing an odd, and scary brake issue with my new (to me) 71 429. 98% of the time the brakes are working fine. But 3 times recently I've been driving and stepped on the brakes and.... NOTHING! The brake warning light comes on, the brake pedal has its normal resistance but no brakes at all. I get off the pedal then reapply and the brakes engage normally. I have not been able to find any leaks and it has plenty of fluid. The mechanic who installed the new carb and a few other times couldn't find anything either.

Anyone experienced this before? Have any ideas? Don't really want to start replacing parts hoping to fix it but ultimately the car isn't safe to drive until I know the brakes will work 100% of the time so I might just have to.

 
I've never had this happen or heard of it happening. Because the brake warning light is coming on pressure is coming out of the master cylinder. I would suspect the proportioning valve/safety switch, maybe some rust or debri in it.

 
Happy to report that replacing the proportioning valve did the trick. The brakes work perfectly. I sure appreciate the help with diagnosis.

 
TxBoss23,

I just wanted to thank you for taking the time to come back to the thread the report what fixed it. That "closes the loop" and makes the thread so much more informative for others who may have a similar problem. Taking that step makes forums like this exponentially more valuable to the other members. Thanks!

 
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