Of course, leaks will also cause a drop in fluid level.Ĭheck the brake fluid level in the reservoir. As brake pads wear and caliper pistons more out of the calipers, fluid level can drop slowly over time even if there are no leaks in the system. Solution: The most likely cause here is low brake fluid level in the plastic reservoir. Problem: Red BRAKE or possibly red BRAKE and yellow ABS lights momentarily come on during hard cornering, acceleration, or braking, but brakes work normally, OR one or both lights on constantly and brakes may or may not seem to work normally. The master cylinder can not be rebuilt on your workbench, as it requires specialized tools and knowledge, and class 100 clean room conditions. If there are no leaks, and you are sure the system is bled properly, and all the calipers and flex lines are fine (not internally plugged, etc.), then the master cylinder assembly is bad and must be replaced. Either there is air in the hydraulic system that will require bleeding the system, or there is a brake fluid leak (leaking caliper, split brake line), or the master cylinder assembly is bad (leaking internal seals, etc). Solution: If the brake pedal is soft and spongy or goes all the way to the floor, the problem has nothing to do with the electro-hydraulic system (pump motor, pump, PWS, motor relay, wiring). Problem: The brake pedal is spongy or the brake pedal goes all the way to the floor, and stopping power is poor. The figure below shows the various parts of the master cylinder.īelow is a circuit diagram for the pump motor, relay, and the part of the PWS that controls the pump motor. To avoid throwing parts at the system in hope of fixing it, a relatively simple diagnosis will determine what part has failed. This relay (which Ford refers to as an “anti skid relay” even though it isn’t directly related to the ABS system) is the most common part to fail and cause a loss of power braking and the BRAKE and ABS lights to turn on, but there are other possibilities as well. Running this much current through the PWS directly would kill the switch almost instantly, so a relay is used to indirectly power the pump motor. The pump motor draws around 20 Amps in normal operation. The system is designed so the pump runs quite often for brief periods of time the keep the pressure as constant as possible. A pressure switch (called a Pressure Warning Switch, or PWS in some Ford manuals) measures the pressure in the accumulator and turns on the pump if pressure gets too low, and turns off the pump when pressure reaches the desired level. An electric pump is used to pressurize the brake fluid. The power brake system uses brake fluid stored in a hydraulic accumulator (basically a pressurized reservoir) at pressures around 2500 psi to provide pressurized brake fluid for power braking. These, and a few other related problems will be discussed below. Another not as common problem is the BRAKE and ABS lights illuminating briefly under hard or repeated braking. One relatively common problem with the braking system is a loss of power braking (often referred to as a “hard pedal”), accompanied by the red BRAKE and yellow ABS dash lights illuminating. The ABS part of the system is much more difficult to troubleshoot, and will not be discussed here. This article will discuss troubleshooting the power brake part of the braking system only. This means that a loss of power braking has nothing to do with the ABS computer, wheel speed sensors, etc. If the ABS part of the system is disabled, power braking will not be affected in any way. If there is a failure of the ABS part of the system due to a failed wheel speed sensor, open or shorted solenoid valve, etc, the ABS computer will disable the antilock part of the system, and turn on the yellow ABS light on the dash. None the less, the power braking part of the system and the ABS part of the system are nearly 100% independent of each other. Unlike modern ABS systems that use a standard vacuum brake booster and a separate hydraulic control unit (HCU) to provide the ABS, the Teves II system incorporates both the power brakes and ABS integrated into the master cylinder. The 1987-88 Turbo Coupe, as well as the early Thunderbird Super Coupes and some Lincolns from the era, use a Teves II electro-hydraulic system to proving both power braking and antilock braking. Troubleshooting the teves II electro-hydraulic braking system used on the 87-88 turbo coupes
0 Comments
Leave a Reply. |