The ATC 400 and ATC 500 transfer cases are used in specific models, with the ATC 400 featuring a four-bolt front driveshaft flange and the ATC 500 utilizing a front driveshaft connection.
The ATC 500 includes an additional disc in the clutch set and a greater distance between the input and output shafts compared to the ATC 400.
driveshafts can wear over time, and rust in the spline area may indicate potential issues.
Both transfer cases use a multi-disc clutch to distribute torque variably between the front and rear axles.
When fully engaged, the axles turn at the same speed.
The input shaft is permanently connected to the rear axle, and when disengaged, all torque goes to the rear.
Electronic regulation adjusts clutch pressure, allowing stepless coupling of the front axle.
Torque distribution depends on traction.
Under acceleration, if traction is equal, the rear axle receives more torque due to weight shift.
If the front axle has better traction, more torque is directed there.
A servomotor with a worm gear rotates a disc cam, adjusting pressure on the multi-disc clutch via ball ramps.
The motor includes a Hall sensor for position and speed detection.
The plastic gear in the motor drive can be a potential failure point.
A coding resistor accounts for manufacturing tolerances in the clutch.
During production, locking torque is measured, and a resistor matching these characteristics is installed.
The control unit reads this resistor upon engine start to select the correct program map.
In case of sensor or control unit failure, a limp-home mode maintains four-wheel drive functionality using precontrol and traction/slip control.
If critical signals are lost, substitute values are calculated until four-wheel drive is no longer viable, triggering a light and alert.
Oil condition is monitored by the control module, which determines service intervals based on slip, torque, speed, mileage, and road conditions.
A fault code indicates when fluid replacement is needed.
Common fault codes include:
- Worn transfer case fluid, requiring replacement.
- Faulty servomotor or worn gear, leading to lights and clicking noises.
- Servomotor or coupling force issues, requiring motor or module checks.
- Transfer box malfunction, necessitating component inspection.
For diagnostics, the servomotor can be tested while plugged in.
If power and ground are present but the motor doesn't rotate, replacement is needed.
If no power is detected, the control module should be inspected.
If the motor functions correctly, the transfer case may require service or replacement.
Draining the fluid and inspecting its condition can help diagnose issues.
If gears were previously replaced, check for renewed wear.