There was a recall for that problem. I have a '93 Dynasty that was included. They both use the Bendix-10 anti-lock brake system which by now you know is REAL effective. If I really stomp on mine I'll just about tear the seat belts loose. That's not really the purpose of the system though. It's only meant to maintain steering ability when braking. GM used a similar Bendix-9 on some of their vehicles including squad cars. They modulate brake pressure to both rear wheels together when either one is about to lock up, while the Chrysler version modulates them independently. There has to be more to the story because a friend who is a county deputy says those cars need MUCH longer stopping distances than the same models without ABS. That was the Caprice Classic.
As for the recall, it involved replacing the piston assembly in the master cylinder. I never did that to my car since it only has 4,200 miles, but I have the part on hand. When I worked at the dealership, I was told that parts replaced under a safety recall had a lifetime warranty. I don't know what they mean by "lifetime" or if that only applies to the original owner. The only symptoms I can remember were the pump would run too much and / or the pedal would fade to the floor.
It's a good idea to flush the brake fluid every few years because it sucks moisture out of the air over time. That lowers the boiling point which can lead to brake fade, and it promotes corrosion of metal parts. $400.00 seems like WAY too much for that service. I'd ask for a detailed description of what they plan to do, but that isn't going to solve the problem of the intermittent sinking pedal.
You can do a partial drain and refill yourself quite easily. You must be absolutely certain to never get even a hint of petroleum product in any hydraulic brake system. That includes engine oil, transmission fluid, and power steering fluid. First you have to empty the accumulator. Check the level of the fluid in the reservoir. You'll see it's no where near full. That's normal. With the ignition switch off, pump the brake pedal at least 40 strokes. The pressurized fluid is providing the power assist. By about the 30th stroke you'll suddenly feel the pedal get harder to push. By the 40th stroke, it will be even harder. All of the fluid has now gone into the reservoir. Check the level. That's where it should end up before you turn on the ignition switch again. When you do, you'll hear the pump run for about 20 seconds. It's taking fluid from the reservoir and pumping it back into the accumulator. That's the round ball to the right of the reservoir. When the pump turns off, the level should be about the same as before you pumped the pedal 40 times.
Use a clean turkey baster to suck as much of the old brake fluid out as possible, then replace it with new fluid from a clean, sealed container. If you want to do a really thorough job you'll need to bleed at all four wheels but if you live where they use road salt to make the roads more dangerous than just driving on snow, you can expect them to be rusted tight and they might snap off. Even with just doing a partial job from on top that new fluid will work its way around eventually. If you do the same thing every year or two you'll be getting more old dirty fluid out than most people ever do.
To get back to the mechanic's comments about a dirty filter, while that is indeed possible, it's not going to cause your symptoms. If that filter is plugged the pump will run too long. The computer will turn it off to prevent overheating the motor, it will turn on the yellow warning light, and there will be a diagnostic fault code stored related to that. With low fluid pressure you won't have power assist. The pedal will push really hard but you'll still have the regular "base" brakes. The anti-lock function is turned off when the yellow light is on so the tires can be made to skid just like on older cars without ABS.
If the red warning light was also on, that is due to a different problem. It turns on of course when the parking brake is set, but also if the fluid is low in the reservoir or if there is a leak in one of the two hydraulic circuits. The low fluid and unequal pressures can be related. Those unequal pressures will result when there is internal leakage in the master cylinder, (that's what the recall addresses), or if there's some other regular leak in the system. For an intermittent leak which would cause your symptom, the rear wheel cylinders are the logical suspects. If the pedal were to sink to the floor each time the pedal was pressed, a rusted steel line would be more likely. Before long though you'd be out of fluid and wouldn't have any brakes.
Friday, July 29th, 2011 AT 4:29 AM