Ok here is the situation. About 6 months ago I went into the garage ( i drive every day) and noticed fluid on the garage floor on the drivers side under the door hinge area. There was a hard stop the day before. I opened the master cylinder the rear rez was empty. Front res nice and full. Brake light comes on obviously no pressure rez empty. So I looked for leaks, didnt find any, looked for rusty lines, didnt find any, master cylinder fittings dry. Bled the air on back brakes far side first. Installed one way bleeders couple years ago so no helper needed. Pump brakes, nice healthy pedal again, test drive everything nice, brake light goes out, everythings normal again. check for leaks, no leaks. Life goes on. Pedal stays good no leaks, fluid stays normal no losses. 6 months goes by, brake light comes on, open master cylinder, rear rez empty. Check for wetness, none found anywhere. So i dont go far and I dont have time to fix it right away, I only put put around town, front brakes good. Note to self, need to fix back brakes, trying to figure out what it is though. Today, pedal sinking and not pumping back up. throttle emergency brake, no problem get home. Check master cylinder, front rez 1/4 full, air in lines. Where did all the fluid go? Only thing I can think of is it sloshed into the empty back rez and escaped into the empty back brake lines. Is this a separate problem or could it be related to the rear brake problem? But my question. How can the back brakes be bled, have good pedal again, light goes off but still be a leak in the back brake system? In other words how can you have an intermittent leak in a back brake system? Tomorrow I have blocked off time to deal with these brakes. Please advise. Thanks Gary
Its a sealed system, so there has to be an external leak somewhere. Sometimes the master leaks out of the back where it attaches to the booster. The fluid can actually leak out of the bottom of the booster. Which would probably dump fluid right around the door hinge area on the ground. If the pedal is now sinking, you have an internal leak in the master now.
This happened to me a while back. Rebuilt master would move all the fluid from the rear to the front reservoir and it leaked against the firewall. The leak was not obvious though. NEW master and problem solved.
Ill check it. Normally in the past when MC goes it sinks but then you can pump it back up quickly pumping it. My pedal does no such thing. It doesnt sink anymore it just goes to floor without resistance or effect. Ill check the back of the booster. The fluid got to go somewhere!
UPDATE: I found brake fluid on the bottom back of the master cylinder casting just in front of the booster. Would this explain why Im losing fluid in both rez or just the rear rez? Thanks Gary
Yes, internal seals are failing in the master. While it's most common just to lose the rear fluid, I have seen instances of a by-passing situation where it will lose fluid out of the front and rear, yet the Brakes seem to work. It's a gradual thing, over time you will lose the fluid, and will not notice it until it results in brake failure. Time for a new Master, or a rebuild. JW
There's no advantage to rebuilding your original, other than you get to keep the number/date correct appearing original. You can still do that if you don't give it to them for the core charge + rebuild it later on.
Rust and sludge and old man time! Consider this a golden opportunity to get your brake system back in order. The crap you will find in the master cylinder has compromised the seals and pitted the bore. The same conditions exist in all your wheel cylinders as well. They may already be leaking but you can't tell unless you remove the drums and roll back the rubber cups. Replace all 4 wheel cylinders and all rubber hoses in the system, flush brake lines before reconnecting and bleeding. Then you will have a safe and dependable system. If you don't, you will be fixing another leak at the wheel cylinders next month. Parts are carried at local auto stores know for these old cars, I think my wheel cylinders and rubber lines were about $12.-$13 apiece.
There is no advantage to rebuilding it yourself. More often than not, the bore is rusted or pitted. There is no way to address that situation as a DIY'er. The master will need to be overbored and sleeved. In a best case, you need to hone the bore. Stay away from rebuilt masters and spend the extra few bucks for a new Bendix master. There is a 100% probability that you will go through at least 2 rebuilt masters before you get one that actually works.
oh no. I already ordered and paid for the rebuilt one from napa. It will arrive at 2:30 today from tampa for pickup in my town. I picked the rebuilt because it was the original style not the one with plastic rez. Now what? You said 100% it will be a bad mc ? seriously?
You may get lucky. last time I went through 4 rebuilts before I got one that worked. I try and just buy new ones. The cost difference isn't much Just as an FYI, a new master would look like your old one. They don't make plastic reservoir masters for our cars- new or otherwise. If the guy was going to give you one with a plastic res, he was giving you the wrong one
he asked me on the phone if I want one with or without the rez?? so I said, the one i have basically is one piece casting, the rez is not removable so I assume he had a type that has a plastic removable rez that Ive seen on later gm cars. I did this all by phone so I didnt want to take a chance and just got rebuilt one. Is that why rebuilds are bad a lot because the bores are pitted and all they do is light hone and new piston?
Sadly, most parts countermen these days just read from a computer screen. Why I have to tell them the car has A/C and power windows to get a set of spark plugs is beyond me, but I digress....Some are just not old enough to know any better. As far as the rebuilt masters, it depends on the rebuilder and the condition of the casting. I don't believe any rebuilder sleeves them. They either rebuild them or discard the casting. For the record, if you had a rare master or wanted to keep the original master for whatever reason, a complete rebuild with a brass sleeve installed is about $250.
ok got the new master on. Bench bled it per instructions that came with. bled each bleeder starting with back brakes, closest one first . Then did front brakes, again closest one first. Car runs and drives, brakes good but light wont go out and cant lock the front brakes up, back brakes will lock up if forced. I must still have some air in the lines.
Nope, air is not an issue if the pedal is not spongy. There is a pin switch in the proportioning valve with a single wire to it. The pin slides back and forth internally if the pressure on both sides are not balanced. You will have to reset it. Try having someone hold the brakes down very hard first to see if it will reset on its own, if not, have them hold pedal down firmly while you crack open a bleeder on the front or the rear circuit, if light does not go out, switch to the other circuit. Some are manually resettable at the proportioning valve but not sure about yours. John Eddit: If braking is still not acceptable, re-bleed the front brakes till pedal is "hard".
Ok ill try it. The last time I bled the system I just took it for a drive and one good lockup and the light went out. But alas I cannot lock the front brakes only the back.
In the classic car marketplace, it's desirable to have the correct looking master cylinder typically. No problem for your 73, other than having or not having the bleeders, that is one of the most common cylinders. Until recently, we re-did all the early disc brake masters locally, with a stainless steel sleeve installed in the bore. Now that master is in reproduction, so it's much easier to get the correct one on an early disc car. Nothing I think looks worst than a 70 disc brake GS, with the 71 up master on it. Just doesn't look right at all. JW
my car is not a rare (well maybe it is now that theve all been crushed due to lack of interest) but my car is not sought after or very collectible but still I have to make an effort to keep it as original as is reasonably possible just out of respect for the vehicle.
