Component Test

Self-Engagement of Automatic Hublocks, F-150 and Bronco

A ratcheting noise from the front axle and/or a self-engagement of the automatic hublocks can occur on some vehicles. This can be caused by a combination of high axle motoring torque and hublocks that require little torque input to engage.

Reduce the axle motoring torque by replacing the differential side gear thrust washers and adjusting the pinion preload. This procedure will reduce the axle motoring torque to a level below the required hublock torque to engage.

NOTE: The front axle should be broken in for 402 km (250 miles) before proceeding with additional diagnosis or repairs. To break in the front axle, engage four-wheel drive, drive forward and then shift out of four-wheel drive without disengaging the hublocks. Driving with the hubs engaged will break in the axle. If the vehicle is backed up during this time period, the hublocks will disengage and will have to be engaged again by repeating this procedure.

NOTE: The Axle Motoring Torque Reduction Kit F6TZ-4228-BA, used in this procedure, contains the following:

• 2 Differential Side Gear Washers (0.025-inch)
• 2 Pinion Shims (0.005-inch)
• 3 Pinion Shims (0.003-inch)
• 1 Pinion Seal
• 1 Pinion Washer
• 1 Pinion Nut
• 10 Ring Gear Bolts
• 1 Keystone Boot Clamp
• 1 instruction Sheet (I.S. No. 7144)

Service Procedure

1. Remove the front driveshaft and tie a 4-pound test fish line between the front axle pinion and the frame member.

2. Tie a second line between the front output yoke of the transfer case and the vehicle frame.

3. Drive the vehicle in two-wheel drive with the hubs unlocked for a minimum of 3 km (2 miles), including some lock-to-lock figure eight turns.

   • If the string tied to the front axle pinion breaks and wraps on the pinion, the concern is generated by the front axle. It will require further diagnosis and service using Axle Motoring Torque Reduction Kit F6TZ-4228-BA. Refer to Measure the Motoring Torque of the Front Drive Axle.
   • If the string tied to the front output yoke of the transfer case breaks, the concern is generated by the transfer case. It will require further diagnosis and possible repair. Refer to Transfer Case Diagnosis and Repair.
   • If neither fish line breaks, proceed to Measure the Motoring Torque of the Front Drive Axle, and follow through all of the service procedure until the concern is resolved.

Measure the Motoring Torque of the Front Drive Axle

1. With the vehicle on a lift, remove both front wheels and the hublocks.

2. With the left axle shaft free to rotate, slowly rotate the right axle shaft in a clockwise direction using Axle Torque Metering Socket T96T-3219-A, and a dial or beam-type inch-pound torque wrench.

3. Stop at the highest reading, then restart and record the breakaway torque reading.

4. Repeat Steps 3 and 4 in a counterclockwise direction, stopping at the highest reading, then restarting and recording the breakaway torque reading.

5. Repeat Steps 2, 3 and 4 for the left axle shaft.

6. Place a screwdriver in the U-joint to prevent the axle shaft from rotating.

7. Repeat Steps 2-5.

8. If all the torque readings through the differential obtained in Steps 2-5 are 2.8 Nm (25 lb-in) or less, and if all the torque readings through the pinion obtained in Steps 6-8 are 6.8 Nm (60 lb-in) or less, return the vehicle to the customer and ask that an additional 240 km (150 miles) (with the hubs engaged) be put on the vehicle and note any additional occurrence of hub lock self-engagement.

9. After the additional 240 km (150 miles) have been driven, repeat Steps 2-7.

   1. If the torque measurements have dropped, the self-engagement should be eliminated.
   2. If the torque measurements have not dropped, and the concern continues, proceed to Front Drive Axle Diagnosis and Repair.

Front Drive Axle Diagnosis and Repair

1. If all torque readings obtained in Steps 2-4 above are 2.8 Nm (25 lb-in) or less, the differential side gear washers do not need to be replaced. Proceed to Step 2.

   If any of the torque readings through the differential obtained in Steps 2-4 above are 2.8 Nm (25 lb-in), replace the two flat differential side gear thrust washers with the 0.025-inch thick washers supplied with the Axle Motoring Torque Reduction Kit F6TZ-4228-BA. Follow the procedure in Section 05-03A for differential and carrier removal instructions.

2. If any of the torque readings through the pinion (opposite axle held) obtained in Steps 6 and 7 are over 6.8 Nm (60 lb-in), measure the pinion bearing pre-load to determine if the pinion should be re-shimmed using the Axle Motoring Torque Reduction Kit F6TZ-4228-BA.

   Follow the procedure in Section 05-03A for differential and carrier removal instructions.

3. While the differential assembly is out of the axle housing, check the pinion for smooth, pulse-free rotation.

4. Slowly rotate the pinion in the carrier using a dial or beam-type inch-pound torque wrench. Stop at the highest reading, then restart and record the breakaway torque reading. Measure and record the torque required to rotate the pinion.

5. If the breakaway torque is more than 0.7 Nm (6 lb-in) greater than the torque to rotate or the pinion rotation is not smooth and pulse-free, inspect the pinion bearings for cage deformation or irregular roller or cup wear patterns. Replace the bearing (4621-outer, 4630-inner) if either condition is found.

6. NOTE: Use old pinion nut and washer to establish the shim pack required for reduced pinion torque to rotate. Only use new pinion nut and washer after required shim pack has been established.

   If the pinion torque to turn is greater than 2.3 Nm (20 lb-in), adjust the shim pack (using the shims provided in the kit) so that pinion torque to turn is 1.7 Nm (15 lb-in). For each thousandth of an inch added to the shim pack, the torque to rotate the pinion will decrease by approximately 0.9 Nm (8 lb-in).

7.  WARNING: DO NOT ALLOW ANY PINION END PLAY IN THE PINION BEARING ADJUSTMENT.

   While the axle shafts are out of the axle assembly, inspect the U-joints for freedom of movement and replace if seized.

8.  CAUTION: Do not use 80W90 or 90W gear lube.

   Reassemble the front drive axle following the procedure in Section 05-03A for differential and carrier installation instructions. Replace the pinion nut and washer with those supplied in the kit. If the ring gear was removed from the differential, replace the ring gear bolts with those supplied in the kit. Fill the axle assembly with 4x4 Gear Oil F1TZ-19580-A or equivalent meeting Ford specification WSL-M2C191-A.

9. Recheck torque reading to verify that axle modifications have been performed properly.

10. Return the vehicle to the customer and ask the customer to drive the vehicle for 80 km (50 miles) with the hubs locked to break in the modified axle. To break in the axle, engage four-wheel drive, drive forward, and then shift out of four-wheel drive without disengaging the hublocks. If the vehicle is backed up during this time period, the hublocks will disengage and will have to be engaged again by repeating this procedure.

Transfer Case Diagnosis and Repair

1. Check the transfer case for proper amount of automatic transmission fluid (ATF).

2. Measure the end play of the rear output shaft using a dial indicator. If the end play is over 1.27 mm (0.050 inch), there is a possibility that one of the two rear output snap rings is missing or out of position. Note end play for reassembly purposes.

3. Disassemble the transfer case following the procedure in Section 07-07, and inspect for missing or out of place rear output shaft snap rings. Repair or replace as necessary.

4. Check for a minimum of 0.25 mm (0.010 inch) clearance between sprocket and lockup hub on the rear output shaft using a shim gauge. If insufficient clearance exists, replace rear output shaft (7061), drive sprocket (7177), and hub shift collar (7100 for manual shift and 7G362 for electric shift).

5. Inspect the disassembled transfer case for galling in the following locations.

   • Between the drive sprocket bore and the rear output shaft journal. If galling exists, replace both components.
   • Between the sprocket thrust faces, the rear output shaft shoulder and hub shift collar. If galling exists, replace the rear output shaft, sprocket and lockup hub.

6. Assemble the replacement sprocket and lockup hub on the rear output shaft with snap ring.

7. Clean pump screen and magnet.

8. After reassembly, refill the transfer case with Motorcraft MERCON® Automatic Transmission Fluid (ATF) XT-2-QDX or MERCON® equivalent to just below the fill plug hole.

9. If this procedure has not resolved the concern, call the Self-Engagement Hotline at (503) 786-5486 (Monday-Friday, 10:00 AM-6:30 PM Eastern Time).