Hoist Test

WARNING: IF ONLY ONE DRIVE WHEEL IS ALLOWED TO ROTATE, THE SPEED MUST BE LIMITED TO A MAXIMUM SPEEDOMETER READING OF 55 KM/H (34 MPH) SINCE THE ACTUAL WHEEL SPEED WILL BE TWICE THAT INDICATED ON THE SPEEDOMETER. EXCEEDING A SPEED OF 55 KM/H (34 MPH) OR ALLOWING THE DRIVE WHEEL TO HANG UNSUPPORTED CAN RESULT IN TIRE DISINTEGRATION/DIFFERENTIAL FAILURE, WHICH CAN CAUSE SERIOUS PERSONAL INJURY/EXTENSIVE VEHICLE DAMAGE.

After a road test, it is sometimes useful to do a similar test on a hoist. (Use an axle hoist, not a frame hoist. An axle hoist will not change the driveline angles. If only a frame hoist is available, axle stands must be used.) Make sure the 4x4 selector is in the 2WD mode on a 4x4 vehicle.


1. Elevate the rear wheels slightly. Check to make sure both wheels will turn.

WARNING
- THE ELECTRICAL POWER TO THE AIR SUSPENSION SYSTEM MUST BE SHUT OFF PRIOR TO HOISTING, JACKING OR TOWING AN AIR SUSPENSION VEHICLE. THIS CAN BE ACCOMPLISHED BY TURNING OFF THE AIR SUSPENSION SWITCH. FAILURE TO DO SO CAN RESULT IN UNEXPECTED INFLATION OR DEFLATION OF THE AIR SPRINGS, WHICH CAN RESULT IN SHIFTING OF THE VEHICLE DURING THESE OPERATIONS.
- A VEHICLE EQUIPPED WITH A TRACTION-LOCK(R) DIFFERENTIAL WILL ALWAYS HAVE BOTH WHEELS DRIVING. IF ONLY ONE WHEEL IS RAISED OFF THE FLOOR AND THE REAR AXLE IS DRIVEN BY THE ENGINE, THE WHEEL ON THE FLOOR COULD DRIVE THE VEHICLE OFF THE STAND OR JACK. BE SURE BOTH REAR WHEELS ARE OFF THE FLOOR.

2. Start the engine and place the transmission selector lever in DRIVE (D). Explore the speed range of interest using the drive/cruise/coast/float tests.
3. A coast down in NEUTRAL must also be conducted. If the vehicle is free of vibration when operating at a steady indicated speed and behaves very differently in in DRIVE and coast, an axle concern is likely.