Brake issues. brake pedal got stuck

OK. so i finally got to go for a longer test drive yesterday after getting an alignment done after the new front end parts. All went well , until…

Brake pedal was stuck down, could not force it up, could not force it down, all four wheels had their brakes applied and car wouldn’t go anywhere.

Car is a MANUAL DRUM brake car, all four wheels. I have replaced the master cylinder with one from NPD, came with the pushrod. Replaced the brake lamp switch, bushings, and clip.

When I went back about an hour later (after i had to chill and step away from it), I was prepared to start taking things apart and it worked fine. I have had 3 instances of the brake lights staying on but playing with it enough would make it work correctly.

It felt like it was a mechanical issue- as the pedal would not budge one bit. I even took a deadblow hammer and whacked it down or up to see if i could jolt something loose… nada. would not budge one bit. But it fixed itself later on its own.

I can see how a wheel cylinder could get stuck , or perhaps more than one, if I had moisture in the fluid or something and it got hot… some have suggested the proportioning valve… but with any of those, wouldnt I be able to move the pedal back up by forcing it? My thoughts are something in that pivot area got jammed up, so that’s what i was going to start disassembling but why or how would it go back to normal on its own? I understand classics are fun and all that, but when it comes to an actual safety thing like brakes and doing this, i’m afraid to even try to drive it. If it gets stuck down, whats to say its not going to get stuck up and not be able to stop?

I am thinking to just get yet another new master cylinder, new pushrod, new bushings, new brake switch, all over again and just replace it all, which is a waste but I don’t know what else to do. For now, the car is back in the garage and i’ve stepped away from it. Hopefully not forever, but I’ve done so much to it to get it where it is now, and now be able to not drive it… its ridiculous.

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Hello, I have had the exact same problem. You got that master cylender from Napa right? I got mine for a manual brakes, all drum car, same problem. My brake lights would stay on, and the brakes would apply. Their rod is slightly too long. I shimmed mine and brought it further from the firewall about 5mm, and later on the master cylender began going all the way to the floor. I would throw that thing in the trash as soon as possible. I hope this helped!

so whats the solution? who has a MC and pushrod that will actually work ?

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I shimmed mine about 5mm. I also have a manual drum truck in which I kept my original pushrod and used that. I am not sure if the problem is with manufacturing tolerances of the master/pushrod or simply the manufacturing tolerances of the car it’s self. Keep me updates on solutions you might find aswell. :smiley_cat:

what did you use to shim it? i do remember the pivot point being a bitch to get the bushings and pin all lined up and in… i think its just to long and put everything in a bind perhaps?

(edit: Sorry, I misread your comment because I’m a little dyslexic. Yeah it sounds like the rod is too long and the fluid is pushing backwards on the pedal, building pressure in the system, though check that the lightswitch is aligned too.)
That’s possible too, the brake lights come on because when you push on the pedal, the rearward, flat part of the pushrod pushes on the plate that is in the brake light switch. If the brake light switch is misaligned and the corner of the pushrod is up against the plate, it will push on the switch. I shimmed mine with 5mm mag lug nut washers.

It’s very important to know the year of your Cougar to answer this.

oh sorry. 68

The linkage for the 70 is different. Some companies sell a one fits all that seems to fit nothing. WCCC did a nice video on the different versions.

Given all that the push rod from booster to MC is adjustable. It should extend about .98”. The shop manual shows how to make a tool to verify. If it’s too long the brakes will lock up

again, reading my info above, there is no booster. This is a manual brake car. the pushrod is fixed length, not an adjustable one.

Is there an acorn nut on the end of the push rod where it touches the piston in the master cylinder? The issue is that if the piston isn’t returning far enough to let fluid back into the master it will lock up like this. If it locks up again loosen the two mounting bolts and see if it almost instantly releases.

nope. its not adjustable. no acord nut. its just a rounded end then has the retaining clip… i will be using shims as suggested above to see if that takes care of the issue. After some research online, these manual brake pushrods in the mustang and our cars seem to have a one size fits some approach and several people have had the same issue.

Seems to have fixed it. Pedal operation feels better too- doesn’t feel jammed like it was before. Thanks for the suggestion and help. Should be good to go now

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Awesome! Glad I could help!