New brake system, car won't stop!

Booksix

New Member
Dec 8, 2003
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San Diego, CA
I just finished putting 13" Cobra brakes on the front of my Thunderbird and 11.65" Lincoln brakes on the rear. I used a 92 5.0 Mustang booster and a 94 Cobra Master Cylinder. I have a gutted prop valve from an 87 5.0 Mustang (bottom rear of the valve split with a t-fitting for the front two brakes, bottom front going to a FMS proportioning valve (by Wilwood - 1/8 27 npt) via 3/16" line and then out to the rear via the stock 1/4" brake line.

So the whole system bled out great, everything seemed all good. But when we got the car going, the pedal pushed extremely hard and wouldn't lock any brakes up (rear prop valve fully open or closed), even on gravel. So you have the push the pedal as hard as you can and the car barely slows...
 
Booster problem?

Why are you using a 92 Mustang booster? Are there problems with fitament with the larger SN95 booster? I'd try to squeeze a 94-95 booster in if you could.

Hard pedal with that MC most likely points to the booster. Either it's not getting vacuum for some reason or it's faulty.
 
Booksix said:
I just finished putting 13" Cobra brakes on the front of my Thunderbird and 11.65" Lincoln brakes on the rear. I used a 92 5.0 Mustang booster and a 94 Cobra Master Cylinder. I have a gutted prop valve from an 87 5.0 Mustang (bottom rear of the valve split with a t-fitting for the front two brakes, bottom front going to a FMS proportioning valve (by Wilwood - 1/8 27 npt) via 3/16" line and then out to the rear via the stock 1/4" brake line.

So the whole system bled out great, everything seemed all good. But when we got the car going, the pedal pushed extremely hard and wouldn't lock any brakes up (rear prop valve fully open or closed), even on gravel. So you have the push the pedal as hard as you can and the car barely slows...

Did you ever solve your issue? Did you replace the brake booster with the 93 Cobra unit? I have the same issue and I just ordered the 93 Cobra brake booster and wanted to know if I made the right choice before I install.
 
thehueypilot said:
Did you ever solve your issue? Did you replace the brake booster with the 93 Cobra unit? I have the same issue and I just ordered the 93 Cobra brake booster and wanted to know if I made the right choice before I install.

You cant go wrong with the 93 Cobra BB.