General Information
Notice: When the interaxle differential (IAD) lock is engaged on a tandem axle that has tires with varying diameters, the wheels of one axle try to rotate at a different speed than the other axle. In this event, torque builds up between the drive axles, which prevents the IAD lock from disengaging and leads to a severe increase in axle operating temperature that can cause premature oil failure and result in gear, bearing, or seal damage. Using the interaxle differential lock on a tandem axle with different size tires can cause catastrophic damage to the axle and axle components.
The interaxle lock (axle lock, interaxle differential lockout) feature causes the drive axle shafts to rotate together, and is recommended for use under adverse road conditions where greater traction is needed.
When engaged, the interaxle lock essentially makes the driveshaft a solid connection between the drive axles. Power entering the forward axle is transmitted straight through to the rearmost axle(s). Driveline torque is now delivered equally and the drive axles, and wheels, turn together at the same speed. The interaxle lock increases drivetrain and tire wear and should be used only when improved traction is required.
See the axle manufacturer's website for more information.