Section 05-03A: Wheel Hubs and Bearings, Front Wheels, 4-Wheel Drive 1995 Ranger and Explorer 4x4 Vehicles Equipped with Dana IFS Axle Workshop Manual
DESCRIPTION AND OPERATION
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Locking Hubs, Automatic
Electric Shift Transfer Case
The "Touch Drive" 4x4 system allows the driver to engage four-wheel drive at the touch of a button instead of pulling a shift lever. This button is connected to an electronic control module which controls the functions necessary to engage the transfer case (7A195) .
The hubs are the M350C-type. Inside the hublock housing are three legs with tangs. The legs are spaced 120° apart and rotate with the front axle shafts. The legs are part of a spring-loaded assembly that is internally splined. The front axle shaft splines are always mated with these internal splines. The legs are not connected to the spring assembly during 4x2 mode so that only the hub and spring assembly rotate with the rotor.
Threaded onto the spindle is a wheel bearing adjusting nut. The nut has a round mating surface on it and a cam assembly is mounted on this mating surface and held snug by spring pressure. The outer collar of the cam can still rotate around the mating surface of the wheel bearing adjusting nut. The cam assembly has pockets that the tangs of the hub legs rest in during 4x2 mode and are held in by the pressure of the hub preload spring. The cam assembly also has a raised set of tangs.
When the 4x4 button is depressed, the electronic control module energizes the electronic clutch coil in the transfer case, which causes the front driveshaft to rotate at the same speed as the rear driveshaft. The front driveshaft causes the front axle shafts to rotate by transferring its torque through the front differential. The axle shafts will then come up to speed and rotate at the same rate as the front wheels.
As the front axle shafts come up to speed during 4x4 operation, the hub legs (which always rotate with the front axle shafts) are rotated out of the pockets of the cam assembly and overcome the preload of the hub spring assembly forcing it back. This causes the entire spring assembly to mate with the legs and turn with them. The tangs on the legs ride up from the cam assembly pockets and butt up against the cam assembly tangs. At this point, the hubs are locked and everything rotates with the front axle shafts except the wheel bearing adjusting nut and the inner collar of the cam assembly. After approximately five seconds, the transfer case clutch coil turns off. A stepper motor located on the back of the transfer case then locks up the transfer case via a camming mechanism and a locking collar. A light on instrument panel illuminates to let the driver know that the shift has been completed. The entire sequence takes only a few seconds.
To disengage the transfer case, again depress the 4x4 button. This will unlock the transfer case , but the automatic hubs will remain locked. To unlock the hubs, drive the vehicle in reverse for at least 3 meters (10 feet). Since the hublocks and front axle shafts are still locked together, the front axle shafts will rotate backwards, pulling the tangs of the legs and cam assembly apart. The hub preload spring then forces the legs into the cam assembly pockets, which disengages the legs from the hub preload spring. This unlocks the hub and allows the rotor to freewheel on the spindle. The driver can then continue in the original direction. Because the front driveshaft has been disengaged from the transfer case and no longer causes the front axle shafts to rotate, the hubs will remain unlocked.
Buzzing and ratcheting noises were a constant concern with the older 4x4 vehicles. These noises occurred usually when shifting into four-wheel drive after starting the vehicle sitting cold for several hours. The noises would also occur just after shifting from four-wheel drive to two-wheel drive. Cold weather was another factor that produced the noise concerns. Colder temperatures increased the viscosity of the axle lubricant resulting in a much higher torque requirement for the transfer case clutch which could only rotate the pinion gears just enough to cause the hubs to partially lock which resulted in a ratcheting noise.
The newer vehicles, however, utilize a synthetic axle lubricant with low viscosity and a transfer case clutch with a higher output. Both innovations allow for 4x4 operation in extreme temperature conditions.
Noise concerns in two-wheel drive just after shifting from four-wheel drive can occur if one of the hublocks fails to disengage. As the vehicle moves forward, the one hublock that has failed to disengage will rotate its axle shaft through the differential and attempt to rotate the other axle shaft in the opposite direction. This is called differential motoring torque. As this torque attempts to turn the other axle shaft through the differential gears, that shaft's hublock will attempt to engage which will result in a ratcheting or buzzing noise. Unfortunately, many Ford customers do not know about differential motoring torque or how to deal with it and assume that the ratcheting hublock is damaged and will attempt to replace it. Usually, the hublocks are not damaged but only need to be broken in. Moreover, the ratcheting hublock, in this case, is not the hublock that is causing the problem. The other hublock is the problem for it has failed to disengage and is causing the other hublock to ratchet as a result. Hence, replacing the ratcheting hublock will not eliminate the problem.
This type of noise concern is usually found on axles that have very few 4x4 kilometers (miles) on them. As the front axle accumulates 161-322 kilometers (100 to 200 miles) of locked hub operation, the axle will break in, which reduces the amount of differential motoring torque significantly. To accomplish this, engage four-wheel drive and then shift out of it without disengaging the hubs. This will break in the axle. Should the vehicle be driven in reverse during this time period, the hubs will disengage and will have to be locked again by repeating the engagement procedure.
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