onebadsc

Unfortunately I hardly get to drive my 72, but I took it out for the first time in a few months and drove around for a few miles. I kind of take it easy usually, and didn't notice any brake issues. Took it out the following day, and I started to notice the pedal traveling a lot more and after few stops, it now goes all the way to the floor with almost no resistance and only get some braking power, albeit small, right as it hits the floor. The MC is full and could not see any leaks on the ground (haven't taken any wheels off yet) I have done some reading about very spongy brakes after some sort of brake service, but nothing brake related has been touched on this car for a few years (previous owner). I know he changed the MC, not sure what else, but the brakes have been fine. I did notice that the fluid in one of the MC chambers was quite clear, while the other was very cloudy, almost black. Do you think I should start by flushing the cloudy fluid and see if it gets better, or do you think I am looking at bad calipers?

It's a 72 4-speed with power brakes and a 350, if any of that matters.

Thanks

MelWff

you have to remove the wheels and look at the seals on all four pistons on all four calipers. Check for small amounts of fluid. If absolutely no fluid is found try bleeding the brakes. if that fails to restore the pedal you probably have a master cylinder that is failing.

theandies

I vote MC but you could have popped a brake piston out of one caliper and not noticed or found the leak yet. If a break job was done in the past and the mechanic who did it didn't check the brake rotor run-out and it is excessive then the caliper pistons can pop out of the bore causing a leak and no pedal.

EDIT - Also what brake fluid are you using? DOT3? That is hydroscopic which means it likes moisture. If you life in a humid climate and don't drive your car much as you stated you may have water in the system. If that's the case I suggest flushing the system to all four corners and changing out your fluid. I use DOT5 which is hydrophobic to keep this from happening.

onebadsc

I'm not sure what was done to the brakes prior to me owning it, but the previous owner did give me a box with the old MC and a motive brake bleeder. Also, it has been pretty humid here in chicago lately and the car sits in an uninsulated stand alone garage.

DUB

I have never encountered a piston 'popping out' of the caliper bore. If the car still has brake pads in it the piston physically can not pop out...it just can't happen....especially if the caliper is still correctly mounted and the rotor is in place.

BUT..the seal can leak if the car sits and not used..and when you press the brakes...the seals get damaged.

It is odd that only half of your master cylinder has clear fluid while the other is muddy looking.

My vote is a caliper/master cylinder is leaking and you just have not found it yet.

I would bleed the system and see what you ahve....then take it from there if it does it again if no leaks are found. But from what you described...you should find a leak...but if the run-out is not right...the system can also draw in air.

DUB

onebadsc

So, do you think a good first step would be trying to bleed the brakes, or should I suck out the cloudy fluid and replace with dot 5 (not sure what is in there now) and start bleeding with fresh fluid in the reservoir?

DUB

I would STAY with DOT 3 if that is what you have in the system. You CAN NOT put DOT 5 in a system that has DOT 3....unless you do a lot of flushing and cleaning.

Yes...you can pull out that cloudy fluid and there is a test you can do to make sure that it is DOT 3...and it will also let you know it is DOT 5 in the same test. I would bet it is DOT 3.

DUB

63split63

If there is fluid in the MC reservoir and the pedal is going to the floor I would bet that you would need a new MC .
Bill

theandies

You are correct and I guess I should rephrase that. The piston probably won't pop out but if the rotor run out is excessive the seal can pop out of the piston bore and cause a leak. It can also cause a pumping action that can introduce air (or water) into the system.

Rescue Rogers

Check the fire wall inside the car as well for leaks. If the master cylinder is leaking into the booster it can leak inside the car. Its probably the master cylinder though.

You described a gradual problem that gets worse. A leaking caliper would have fluid all over the inside of the tire its near. If nothing else was done and nothing removed its a pressure problem. A leaking master cylinder can introduce air into the system and an old caliper can pump air into the system ,but I've haven't had that problem, just read about it when my system was doing exactly what yours is.

If you can get more pedal by pumping it you're compressing the air that is in the system. If the previous owner gave you a motive pressure bleeder ,he may have had a problem and neglected to mention it. When I bought mine it was sitting for most of the summer and had a lot of water in the system and got worse as I drove it.

If you've never bleed your system before, you start farthest from the master cylinder and work your way closer. The rear calipers have 2 bleed screws each, outside and inside. You do the inside first.

Buy a big bottle of fluid and dont reuse the old fluid you bleed out. If you can bleed it into a jar you can see if its full of crap or water. If you leave the cap loose it will attract water so water can be in your system and when it gets hot it will boil and create steam which will act like air in your system.
if its been cold, start it and let us know if the pedal goes to the floor right away. If it does, Pump the pedal and let us know if it comes up off the floor. That would be air in the system. If its hard then its water in the system.