If you hear a grinding noise or have trouble switching between two-wheel drive (2WD) and four-wheel drive (4WD) with a switch that works intermittently, you may have a defective automatic hub. These easy diagnostic tips from our mechanics can help you get your 4×4 auto-locking hubs working smoothly again.
How to Fix a Truck with 4WD Grinding or Working Intermittently
What Does an Automatic Hub Do?
Automatic hubs are used in many 4×4 trucks to help switch from two-wheel-drive to four-wheel-drive and vice versa. They disengage or engage the front wheels whenever need be. When four-wheel-drive is engaged, the driveshaft applies torque and forces the hubs to slide in and lock. As long as the transfer case stays in four-wheel-drive, the hubs will stay locked in. This allows the wheels to rotate in conjunction with the axle shaft.
When the driver switches the vehicle back to two-wheel-drive, the same mechanism slides out to release the hubs. This leaves the wheels to rotate independently of the axle shaft. Without an automatic hub on both front wheels, the driver would have to stop the vehicle, get out and turn a dial to engage or disengage the front wheels.
Signs of Problems with the Automatic Locking Hubs
- 2WD and 4WD works intermittently
- Grinding noise when shifting to Neutral
Causes of Problems with the Automatic Hubs
Sometimes, the mechanism may work intermittently. You may find that you’re not able to get four-wheel drive when you need it. This is mostly caused by a bad vacuum actuator or a four-wheel-drive motor that is not working at the transfer case. Another problem could be a loose nut that interferes with how the wheel hubs slide in and out.
If you normally have your four-wheel-drive working irregularly, the wheel hubs could have a problem that makes them not go in and out when the automatic locking hub mechanism engages. If it’s not the vacuum actuator or four-wheel-drive motor, you’ll need to find out what stops the system from working sometimes.
Where the vacuum hub actuator connects to the CV shaft, there is a nut that holds the wheel hub in place. Even when torqued to the manufacturer’s specifications, these nuts are notorious for loosening up. They even cause a grinding noise when you change to Neutral. The noise sounds like two gears that are not copacetic anymore.
How to Diagnose an Automatic Hub That Is Not Working
How to Test Automatic Locking Hubs
- Raise the Vehicle and Enlist Help
To diagnose these problems, you’ll need to first raise the vehicle. Have someone inside the car to help you run it while you’re underneath. The most important thing here is to ensure that you’re completely safe. If you’re using jack stands, ensure they are sturdy enough to handle the weight of the car.
- Look Underneath and Have an Assistant Start the Car and Engage the Four-Wheel Drive
As you take a look underneath, have the person inside the car start it and engage the four-wheel drive. They should let go of the brake and let the wheels spin.
- Observe the Wheels for Spinning/Movement
If your front wheels don’t spin, you have a bad vacuum actuator or a bad four-wheel-drive motor. The latter can be found inside the transfer case.
How to Fix an Automatic Hub That’s Grinding
1. Raise and Secure the Vehicle and Remove the Tire
Getting your automatic locking hubs to work as required is relatively easy when you have a loose nut. To fix the problem, you’ll need to slightly lower the vehicle and take out the front wheel from where the grinding noise is coming from.
2. Remove the Cap from the Hub
You should find a cap in the middle of the hub. Pull it out using a pair of open pliers to reveal the loose nut. Avoid putting any holes on the cap. This may cause moisture to penetrate and cause corrosion.
3. Remove and Clean the Hub Nut
Unscrew the loose nut from the hub using a socket. You’ll want to check the threads to ensure they are not damaged. Use some parts cleaner to clean off any dirt or debris. Before putting the screw back in place, you’ll need to apply some thread lock on it.
4. Torque the Hub Nut
Look up the torque spec for the nut and torque it to the manufacturer’s specification. Ensure the automatic locking hub doesn’t move while you do this. Once done, put the cap back on. Double-check to ensure it’s not damaged or in bad shape. If all is well, you can put your wheel back on and lower the vehicle.
Replace Parts on Your Own Vehicle
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