It would surprise many people to learn there are several individual components that make up today's windshield wipers. In the "good old days" the windshield wipers were comprised of a blade, attached to a blade then attached to a motor that was operated by a switch. However, even back then, that windshield motor had multiple speeds that were activated by a wiper gearbox.
Even with multiple electrical and computerized additions that make up today's modern windshield wiper system, the basic elements that comprise the wiper gearbox have not changed very much. Inside the wiper motor is a gearbox that contains multiple gears for different speed settings. When a signal is sent from the switch through the module into the motor, the gearbox activates the individual gear for the setting selected and applies this to the wiper blades. Essentially the wiper gearbox is the transmission of the wiper blade system and like any other transmission, can be subject to wear and tear and may sometimes break.
It is extremely rare for the wiper gearbox to suffer mechanical failure, but there are some rare occasions when issues with the windshield wiper blades are caused by a malfunction of this device that will require the assistance of a local ASE certified mechanic to replace the wiper gearbox if needed.
Listed below are a few of the common warning signs that you should be aware of that might signify a problem with this component. If you notice any of these symptoms, contact a mechanic so they can properly diagnose the issue and repair or replace the parts that are causing trouble with your windshield wipers.
1. Wiper blades move erratically
The wiper motor is controlled by the module, which receives a signal from the switch that was activated by the driver. When a speed or delay setting is selected by the driver, the gearbox stays in that selected gear until the driver changes it manually. However, when the wiper blades move erratically, as in moving fast, then slow or staggered, this could indicate that the gearbox is slipping. This condition may also be caused by loose fitting wiper blades, worn out wiper blade linkage, or an electrical short in the wiper switch.
Either way, if this symptom occurs, it's best to contact a mechanic as soon as possible to diagnose the problem and make the appropriate repairs.
2. Only one wiper blade is working
The gearbox drives both sides of the windshield wipers, however there is a small rod that is attached to both wipers and the gearbox. If you turn the windshield wipers on and only one of them is moving, it's possible and highly likely that this rod has broken or is detached. A professional mechanic can repair this problem most of the time, however if it has been damaged, it may be required to replace the wiper motor which will include a new gearbox.
Most of the time, if this is the problem you're experiencing it is going to be the driver side windshield wiper blade that moves by itself, indicating that the broken linkage is on the passenger window.
3. Wipers stop working when selected
When you activate your wipers, they should operate until you turn the switch off. After turning the wipers off, they should move to the park position which is at the bottom of your windshield. However, if your wipers quit working in the middle of operation without you turning the switch off, then it is mostly likely a failed wiper gearbox, but it could also be a problem with the motor, or even a blown fuse.
If you experience any of the above warning signs of a failing wiper gearbox, it's very important for you to have this fixed before operating your vehicle. All 50 US States require functional wiper blades on all registered vehicles, which mean that you may be cited with a traffic infraction if your wiper blades don't work. Your safety however is more important than traffic tickets. If you notice any problems with your windshield wipers, contact a local ASE certified mechanic so they can help you diagnose the right problem and fix what's broken.