Pinpoint Test N: Grinding / Clicking / Ratcheting Noise From Front Axle In 2H Mode Under Acceleration Or Heavy Loads: Notes

Grinding / clicking / ratcheting noise from front axle in 2H mode under acceleration or heavy loads 

Courtesy of FORD MOTOR COMPANY

Normal Operation and Fault Conditions 

Locator views for the vacuum lines and vacuum reservoir are located in Description and Operation. REFER to: DESCRIPTION AND OPERATION .

In 2H mode, the TCCM provides a ground path to the IWE solenoid to supply vacuum to each IWE (disengaging the front hubs from the front axle). During certain conditions such as WOT maneuvers, manifold vacuum is lower than desired. To maintain uninterrupted IWE function in 2H, stored engine vacuum is sourced from the vacuum reservoir. A one-way check valve is implemented between the vacuum reservoir and the IWE solenoid to prevent the stored vacuum from escaping into the manifold during low engine vacuum conditions. For noise-free IWE operation under all conditions, the check valve must be operating correctly.

When following this diagnostic procedure please note the following since these system interactions may influence the results: 

When shifting to 2H mode in order for the IWE to completely disengage the vehicle steering wheel must be less than 90 degrees and 5 seconds have elapsed since the shift to 2H has been initiated.

The TCCM has two startup strategies that affect IWE operation after initial key cycle: 

• When ambient temperature is below 32 F (0° C), the IWE engage after initial key cycle and a driven gear is selected. The hubs stay engaged regardless of 4WD mode until 2 miles (3km) have been traveled above 6 mph (10 km/h). Once the set distance has been achieved, the IWE disengage (if the vehicle is in 2WD (2H)). Distance traveled resets only if the temperature is below calibrated threshold and another key cycle occurs or if customer shifts to Park (P) and back to a driven gear within the same key cycle. The TCCM uses this strategy to warm up the front axle in cold temperatures to improve driveline synchronization.
• When ambient temperature is above 32 F (0° C), the IWE engage after the initial key cycle and a driven gear is selected. The hubs stay engaged regardless of 4WD mode until 0.5 miles (0.8km) have been traveled above 6 mph (10 km/h). Engagement only occurs once per key cycle and is not reset when shifting between Park (P) and Drive (D). The TCCM uses this strategy to delay vacuum use until vacuum-intensive engine startup has completed and sufficient vacuum is available to fully disengage the IWE.

Possible Sources 

• Vacuum check valve
• Vacuum reservoir
• Vacuum supply line
• IWE solenoid
• Vacuum lines between IWE solenoid and IWE
• IWE
• IWE Cutch ring