I went through this recently, and didn't find any information here on doing this, so after working it out on my own, I thought I would post this.
First off: How to check that your locking hubs are working correctly.
- Put your truck in park. Make sure it is in 2WD high. Set the parking brake.
- Jack left front wheel off the ground.
- Find the front driveshaft - it's the round bar (about 1 1/2 inches in diameter) going from the transfer case (behind the transmission) to the front differential (the big round thing in the middle of the front wheels).
- Turn the front driveshaft. It should turn freely. You should see the half shaft (the shaft connecting the front differential to the wheel) of the raised wheel turn as you turn the driveshaft.
- Within one or two turns, the hub in the wheel should lock up, and the wheel should start turning, either forwards or backwards (depending on which way you are turning the shaft).
- Hold onto the driveshaft to try to prevent it from turning. Try to rotate the wheel in the same direction it was just turning. It should turn the driveshaft you are hanging onto as you turn the wheel.
- Hold onto the driveshaft to prevent it from turning. Rotate the wheel in the opposite direction. You should feel the hub unlock, and the wheel should spin freely without turning the driveshaft.
- Turn the front driveshaft in the opposite direction you did before. You should see the half shaft (the shaft connecting the front differential to the wheel) of the raised wheel turn as you turn the driveshaft.
- Within one or two turns, the hub in the wheel should lock up, and the wheel should start turning, the opposite way than it did before.
- Hold onto the driveshaft to try to prevent it from turning. Try to rotate the wheel in the same direction it was just turning. It should turn the driveshaft you are hanging onto as you turn the wheel.
- Hold onto the driveshaft to prevent it from turning. Rotate the wheel in the opposite direction. You should feel the hub unlock, and the wheel should spin freely without turning the driveshaft.
- Lower the wheel, jack up the opposite wheel, and repeat the tests.
If everything happens as described above, your hubs are operating correctly. If not, chances are your hubs are dirty and/or full of grease.
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