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How To Rebuild Wiper Motors On A Classic Mustang
What to do when your wipers stop working.
Windshield wipers are something we never think about until they stop working in a rainstorm. Classic Mustang wiper motor operation is through a simple high-torque electric motor that runs a jackscrew reduction gear drive tied to a linkage that cycles your Mustang's wiper blades back and forth across the windshield.
It is the motor's reduction gearbox that both slows motor speed and multiplies torque in order to overcome just about anything on your windshield, including snow and ice. When it's time to turn the wipers off, a parking cam, link, and switch enable the wipers to park at the base of your Mustang's windshield by opening the motor's negative ground. When the wipers are turned on, a circuit is completed to negative ground to get the wipers going again.
When vintage Mustangs were new, Ford dealers approached wiper problems with minor adjustments, switch replacement, or complete replacement of the motor assembly. Only savvy dealer technicians tackled wiper motor repair. Today, we need to understand how to get failed wiper motors working again by knowing how they work. That's a job best left to the professional, although you can learn how to do this yourself. We visited with Ray Sanchez at Mustangs Etc. in Southern California's San Fernando Valley to help us understand how wiper motors work and how to service them.
Classic '65-'78 Mustangs were equipped with three basic types of wiper motors. For '65-'66, Mustangs came with one- and two-speed wipers. From '67-'78, there was a new two-speed wiper motor used across the board in a variety of applications, including intermittent wipers. Regardless of configuration and model, they were all fitted with the same two-speed wiper motor.
Like most electrical accessories in your Mustang, the windshield wipers are activated by a switch that completes the electrical path to negative ground. One-speed wipers employ a straight path to negative ground. Two-speed wipers use a three-position switch along with a resistor at the motor to get low-speed operation. The resistor impedes the flow of current to ground to slow the motor down.
The '65-'66 one-speed motor is a permanent magnet type, which doesn't have a field winding around its perimeter. Instead, it has two permanent magnets to help provide the magnetic field necessary to produce torque. The '65-'66 two-speed wiper motor is shunt wound, consisting of field windings around a rotating armature.
For safety, Mustang windshield wipers are protected by a circuit breaker in the switch. Circuit breakers briefly interrupt power to protect you from a motor overheat or fire, yet keeps the wipers going long enough to clear the windshield for visibility. The Mustang headlight circuit protection works the same way to keep the road ahead lighted for safety.
Like most electrical accessories in your Mustang, the windshield wipers are activated by a switch that completes the electrical path to negative ground.
Parking Switch Contact Point Adjustment
This illustration is typical of most wiper motor park switch adjustments. Although your Ford Shop Manual gets into an involved dissertation about how to properly adjust the park switch, it is a simple process. You want this switch open with the wiper motor at park. The adjustment screw moves the lower contact closer or further from the bridge (upper) contact. Clockwise adjustment moves the lower contact closer to the bridge. Counterclockwise moves it away from the bridge.
When the wiper motor is in operation, these contacts open and close as the gear reduction package rotates. Because the wiper switch is in the on position, contact to ground is maintained and the motor continues to run. When the wiper switch is turned off, we lose our primary ground, which leaves the park switch ground intact. The motor continues to run until the park switch ground is broken. Your goal is to have the contacts open when the wiper motor is in the parked position.