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.
1 We’re going to give you...
1 We’re going to give you an intimate look at the ’65-’66 Mustang one-speed wiper motor to understand how they function. The optional two-speed ’65-’66 wiper motor was decidedly different. We will take a closer look at the two-speed motor in a future issue.
2 This exploded view of the...
2 This exploded view of the ’65-’66 one-speed wiper motor shows a simple high-torque 12-volt electric motor with a jackscrew reduction gearbox that slows down motor drive speed to an output arm. The output arm, tied to the wiper linkage, takes rotary motion and turns it into linear motion (back and forth). The wiper linkage, in a twist of interesting events behind your dashboard, runs the wiper shafts back and forth.
3 This barber pole-like jackscrew...
3 This barber pole-like jackscrew drives a compound reduction gear transmission, which gears down and turns the output shaft arm at a slower pace. The nylon idler gear is for noise reduction.
4 Disassembly begins with...
4 Disassembly begins with the cover and removal of this C-clip, which frees up the nylon idler gear.
5a Two long screws, removed...
5a Two long screws, removed with a 5⁄16-inch socket...
5b ...Release the motor...
5b ...Release the motor case.
6 With the motor case removed,...
6 With the motor case removed, the armature is exposed. Once the nylon idler gear is removed, the armature comes right out.
7 With the armature removed,...
7 With the armature removed, you can see the brush holder and park switch. If your Mustang has been in a rainy climate, chances are the brushes are worn out and must be replaced. Brushes can be sourced at any electric motor supply store along with new springs. Armature slipper contacts should also be dressed and cleaned with fine-grain sandpaper, then thoroughly cleaned of debris. If slippers are excessively worn, you will need to replace or rebuild the armature. Just about any electric motor overhaul shop can rebuild your armature.
8 This is the park switch,...
8 This is the park switch, which terminates the motor’s ground when the wipers park. When wipers are turned on, your switch grounds the wiper motor, which starts wiper operation. As long as the wiper switch is on, the motor has a ground and continues to operate. When you turn the switch off, this breaks the switch ground, which leaves the park switch as the sole ground. When wipers reach park position, the parking cam and link open the park switch, which terminates that ground and stops the wipers.
9 This is the armature shaft...
9 This is the armature shaft endplay set screw, which adjusts shaft endplay for both smoothness and quiet operation. Armature shaft endplay is 0.003-inch for the one-speed wiper motor and 0.0000-0.005-inch for the two-speed wiper motor (’65-’66 only).
10 Nylon idler gear removal...
10 Nylon idler gear removal can be challenging. Ray uses a special tool to slide this gear out.
11 What makes these motors...
11 What makes these motors non-serviceable for the average enthusiast is these armature shaft bushings, which are spot-welded in place. If you are serious about rebuilding your wiper motor, be prepared to drill out these spot welds and search for motor bushings. Then be prepared to weld them back into place dead center. Electric motor supply and bearing supply houses can get these bushings. The trick is replacement.
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.
13 With the wiper motor parts...
13 With the wiper motor parts cleaned and inspected, they are now ready for assembly. Ray has dressed the armature slippers and checked the armature for good continuity. Gears and shafts have been cleaned, dressed, and inspected.
14 Ray has dressed the wiper...
14 Ray has dressed the wiper motor output shaft and gear with windshield wiper gear drive lubricant. This lubricant is free flowing, yet sticks to everything to ensure adequate lubrication.
15 Park switch link and nylon...
15 Park switch link and nylon shaft are installed. The park switch cam moves this link and opens the park switch, halting wiper operation at the base of your Mustang’s windshield.
16 After installing the output...
16 After installing the output shaft gear, the nylon idler gear can be installed. It consists of a large nylon gear mated to a smaller steel gear, which is how motor speed is reduced and torque multiplied at the same time.
17 New brushes and springs...
17 New brushes and springs have been installed and are held in position with a special tool that Ray fabricated for this process. One brush is positive, getting its power from the plug, while the other is negative ground to the case.
18 Ray installs the armature...
18 Ray installs the armature after applying wiper motor grease to the shaft and bushings. Once the armature is in place, Ray removes the brush-retaining tool. Brush and slipper surfaces must be hospital clean.
19 Ray assembles the motor...
19 Ray assembles the motor and gear cases. The trick here is those permanent magnets, which want to grab the armature.
20 The reduction gearbox...
20 The reduction gearbox is packed with plenty of wiper motor lube for smooth operation. If you can’t get the wiper motor lube, opt for wheel bearing grease and make sure it touches everything.
21 Our completed one-speed...
21 Our completed one-speed wiper motor has been tested and is ready for service. All this one needed was new brushes and armature service.