Howdy all, seeking input on a funky brake issue. It's def a safety issue I want to take care of this winter.
First the car is a 67 bird I completely redid the brakes except the pedal in 2005, it may have 10k on it. SSBC front disc conv, SSBC lines, rear rebuilt, new booster, mast cyl and Classic Industries preset brake proportioning valve, everything went smooth and it has been flawless and awesome since.
This summer I had 2 instances where some clown pulled out of a driveway and I had to hammer the brakes and come to a stop from @40mph, manual trans, clutch depressed, when I went to resume travel it was like the brakes didn't release or release completely, I had to hammer the pedal and then things returned to normal.
My guess is the proportioning valve or master cyl??
Any thoughts, I don't to just change parts hoping, thanks.
Back when I was a Mechanic your situation would not be one, I looked forward to diagnosing with all non-factory style re-engineered aftermarket parts as it always puts more question marks into the equation. That said I completely understand why you did it and this is how I would tackle your situation. First, I would get the car off the ground with the wheels in the air and statically try and reproduce the situation, that means if you have power brakes to also have the engine running and stand on the brakes with the same force you used when it happened. then without shutting off the car (if power brakes) get out and turn each wheel to see if any have drag. If you find drag in one or a pair of wheels crack the bleeder or bleeders and see if this frees them up If they won't free up and are still tight then you are looking for a mechanical and not hydraulic problem. A mechanical problem could range from a stuck pad in its holder to a rear drum brake shoe hanging up because it exceeded its travel limit. I have seen the latter when a self-adjusting brake is not working correctly and over time with shoe wear goes way out of adjustment and causes the edge of the shoe to go past the flats or mounting tabs on the backing plate and then get hung up and only jamming rotational forces can return it. If only one drum is way out of adjustment you wouldn't even notice much in the way of a low pedal.By the way, nice looking car.
The car is a 67 400 RA conv tribute. 400 4sp 3:42 rear, the motor and tranny are 68, it's a WZ, which I lucked out because the WZ has the 16 heads, neither are correct for the 67 RA but the WZ comes with 067 cam, but they did use the 068 cam with the 16 heads and it's awesome, big jump in HP
Very nice setup. Another thing I forgot to mention is if you can reproduce the problem and it's in the rear and opening a bleeder does nothing. When you pull the drum look closely at the wheel cylinder pistons. If one is sticky when you hit the brakes normally the pressure will just move the non-sticky side but when you up the pressure by standing on them unless it's completely seized it will apply the shoe. then the problem is that the return spring doesn't have enough umph to return it. This is a very common problem on old cars because they use aluminum pistons with a cast iron cylinder. It can also be exasperated by lack of maintenance Because the dot 3 and 4 used in our cars is hygroscopic and absorbs moisture from the air and all the heating and cooling cycles. Brake systems should be flushed at least every 5 to 7 years to help keep internal hydraulic corrosion at bay.