* Binding in the front differential: This is the most common cause. The internal components of the differential might be seized or severely worn, preventing them from rotating freely. This often happens due to lack of lubrication (low or bad gear oil), rust, or damage from driving in 4WD on dry pavement. This would cause the wheels to try to turn at different speeds, creating binding and lockup.
* Front axle u-joints or CV joints: Worn or damaged u-joints (if it's a solid front axle) or CV joints (if it has independent front suspension, less common on a '94 Silverado but possible) can bind and prevent the wheels from turning freely, especially under load.
* Binding in the front wheel hubs (on manual locking hubs): If your truck has manual locking hubs (common on older 4x4s), they may not be engaging properly or might be sticking. Ensure they are properly locked *before* engaging 4WD. If they're locking in incorrectly, they could be the source of the problem. If they are automatic locking hubs, they could be malfunctioning.
* Incorrect 4WD engagement: Engaging 4WD on dry pavement at speed can severely stress the drivetrain and cause components to bind. Always engage 4WD at low speeds on a slippery surface (snow, ice, mud).
* Transfer case problems (less likely): Though less probable given the symptom, a problem within the transfer case itself could contribute, but usually manifests in other ways before wheel lockup.
Troubleshooting Steps:
1. Check the front differential fluid: Low, dirty, or old gear oil is a major suspect. Inspect the fluid for metal particles or unusual color/consistency. Replace if needed.
2. Inspect the front axle u-joints or CV joints: Look for play, damage, or signs of wear. Replace any that are suspect.
3. Check the front wheel hubs (if applicable): Ensure they lock and unlock smoothly. Replace if necessary.
4. Try engaging 4WD on a slippery surface at low speed: See if the problem persists. If it doesn't, the issue might be related to driving style and drivetrain stress.
5. Professional diagnosis: If the issue persists after these steps, it's advisable to take your truck to a mechanic specializing in 4x4 vehicles. They have the tools and expertise to diagnose the specific problem, which could require more advanced diagnostics such as disconnecting components to isolate the binding area.
Important Safety Note: Driving with locked front wheels is extremely dangerous. Avoid driving the truck in 4WD until the issue is resolved. The locked wheels can cause loss of control, especially during turns.
