Hoping never pans out for me, but you might hope there was air that worked its way out. I'm not sure what the ramifications are related to having the ABS hydraulic controller in the circuit, but I can share my experience with my '72 Challenger. Every spring when I dug it out, the master cylinder was empty. There was no sign where the fluid went over the winter although I never pulled the master cylinder lose to look in the booster. This happened every spring for at least five years.
By now I knew to just refill the reservoir and drive it. By the time I got out of my driveway and onto the highway I had a low pedal but at least a hint of brakes. By the time I made the five-mile drive to town and stroked the pedal a few times along the way, I had enough brake power to lock up the wheels. By the time I got home, the pedal was high and solid and stayed that way for the rest of the driving season. As I was sitting at stop lights with the brakes applied lightly, air bubbles vibrated their way back up the steel lines. They flowed into the reservoir when I released the pedal.
After running the pedal down too far for all those years, the seals in the master cylinder finally ripped. First I lost one circuit, ... So of course I kept driving! A week later the second one ripped. Luckily I was going home after midnight and there wasn't much traffic. Car was headed to a restoration shop so I wasn't interested in buying a new master cylinder. I good used one from my rusted out '78 LeBaron wagon worked perfectly.
In your case, I could see air in the system yet. It would contract in the cold weather and have reduced effect. You might try bleeding the two rear wheel cylinders. If a little spurt of air comes out as soon as you open the bleeder screw, the air might have come in past the lip seals. There's an expander spring in there to prevent that and to prevent the seals from falling over. There has always been a residual check valve in the drum port of the master cylinder. It's purpose was to maintain about 10 psi on the fluid to prevent air from entering past the wheel cylinder lip seals when barometric pressure goes up, but it just occurred to me that they can't put that valve in a master cylinder for a split-diagonal hydraulic system because you must not hold any pressure on a disc brake caliper. I don't know what or if they still incorporate a residual check valve.
If you repeatedly get air out of a wheel cylinder, I would replace that one. The clue would be that the air is there as soon as you open the bleeder screw. Air that sneaks in past the lip seal will collect at the top of the cylinder and won't go into the steel line, so it will be the first thing to come out when you bleed it. If you get a lot of bubble-free fluid long before any air comes out, the air got in somewhere else.
It wouldn't hurt to double-check the rear shoe adjustment. Don't try to separate the drums from the hubs. Pull the wheel bearing out to pop the drums off. They make gauges, but I have better luck pulling the drum off about an inch, then moving it left and right, (as you're facing the spindle), to see how much play there is. I adjust the shoes manually until there is no sideways movement but the drum will still slide on and turn freely. Also, shove the shoes up and down and sideways to be sure they're centered in the drum.
If adjusting them helps, look for the obvious broken adjuster cable and stuck star wheel adjuster, but also check the teeth of the star wheel to see if any are worn off. An often overlooked cause of failure to adjust is the adjuster lever is hanging down too low. That is caused by the cable's guide shoe not fully seated on the brake shoe. The only way to seat it properly is to remove the shoe return spring, then check that the lip under the hole of the guide drops all the way into the hole in the shoe. You gotta hold the guide in place until the return spring is installed. I don't want to belabor the obvious, but the return spring must be hooked properly for it to hold the cable guide in place. Some people just try to hang it in the hole by the hook, but that hook must be wound into the hole so it catches on the back of the shoe. That's what keeps the cable guide from popping out.
While you're in there, there are two important observations to make. Before you disturb anything, look at the large anchor pin on top. Both shoes must be resting against it. If one is not, either the return springs are weak or the parking brake is sticking. The second, related observation has to do with the parking brake strut rod right over the spindle, between the two shoes. Use your thumb to push it toward the front of the van, against the anti-rattle spring. There must be some free play. If it doesn't move at least 1/16", flex the two parking brake cables to see if one is sticking. The parking brake lever behind the rear shoe should not move forward when flexing the cable. If it does, a cable is sticking or the main cable is over-adjusted. If the parking brake lever moves backwards when flexing the cable, and the strut rod develops free play, that cable is sticking. In severe cases, you might have to use a pry bar to force the parking brake lever back to its normal resting position. Once the lever is fully released, the only thing that would prevent there being any free play in the strut rod is if the star wheel adjuster isn't extended to its proper adjustment.
Under normal operation, the front brake shoe does very little stopping. Its job is to grab the drum and try to rotate with it. As it does, it pushes on the lower link, (the star wheel adjuster), and pushes the bottom of the rear shoe into the drum. The wedging action gives the rear shoe the greatest braking power, that's why it has a longer lining. It does most of the work so it has the most wear.
When you back up, the roles are reversed. The rear shoe moves out, catches the drum, and helps apply the front shoe. When the rear shoe moves away from the anchor, it moves the cable guide shoe which tugs on the cable and adjuster lever. If anything holds pressure on the parking brake strut rod, it is already holding the shoes away from the anchor pin so the rear shoe can't move far enough to tug on the adjuster cable. That's how a sticking parking brake cable will prevent the shoes from adjusting automatically. A clue would be one of your original symptoms where the brake pedal got higher and harder when you pumped it a few times.
Friday, February 12th, 2010 AT 3:36 PM