Clutch

Understanding the Clutch

The purpose of the clutch is to disconnect and connect engine power at the transmission. A vehicle at rest requires a lot of engine torque to get all that weight moving. An internal combustion engine does not develop a high starting torque (unlike steam engines) so it must be allowed to operate without any load until it builds up enough torque to move the vehicle. To a point, torque increases with engine rpm. The clutch allows the engine to build up torque by physically disconnecting the engine from the transmission, relieving the engine of any load or resistance.

The transfer of engine power to the transmission (the load) must be smooth and gradual; if it weren't, drive line components would wear out or break quickly. This gradual power transfer is made possible by gradually releasing the clutch pedal. The clutch disc and pressure plate are the connecting link between the engine and transmission. When the clutch pedal is released, the disc and plate contact each other (the clutch is engaged) physically joining the engine and transmission. When the pedal is pushed in, the disc and plate separate (the clutch is disengaged) disconnecting the engine from the transmission.

Most clutch assemblies consists of the flywheel, the clutch disc, the clutch pressure plate, the throw out bearing and fork, the actuating linkage and the pedal. The flywheel and clutch pressure plate (driving members) are connected to the engine crankshaft and rotate with it. The clutch disc is located between the flywheel and pressure plate, and is splined to the transmission shaft. A driving member is one that is attached to the engine and transfers engine power to a driven member (clutch disc) on the transmission shaft. A driving member (pressure plate) rotates (drives) a driven member (clutch disc) on contact and, in so doing, turns the transmission shaft.

There is a circular diaphragm spring within the pressure plate cover (transmission side). In a relaxed state (when the clutch pedal is fully released) this spring is convex; that is, it is dished outward toward the transmission. Pushing in the clutch pedal actuates the attached linkage. Connected to the other end of this is the throw out fork, which hold the throw out bearing. When the clutch pedal is depressed, the clutch linkage pushes the fork and bearing forward to contact the diaphragm spring of the pressure plate. The outer edges of the spring are secured to the pressure plate and are pivoted on rings so that when the center of the spring is compressed by the throw out bearing, the outer edges bow outward and, by so doing, pull the pressure plate in the same direction - away from the clutch disc. This action separates the disc from the plate, disengaging the clutch and allowing the transmission to be shifted into another gear. A coil type clutch return spring attached to the clutch pedal arm permits full release of the pedal. Releasing the pedal pulls the throw out bearing away from the diaphragm spring resulting in a reversal of spring position. As bearing pressure is gradually released from the spring center, the outer edges of the spring bow outward, pushing the pressure plate into closer contact with the clutch disc. As the disc and plate move closer together, friction between the two increases and slippage is reduced until, when full spring pressure is applied (by fully releasing the pedal) the speed of the disc and plate are the same. This stops all slipping, creating a direct connection between the plate and disc which results in the transfer of power from the engine to the transmission. The clutch disc is now rotating with the pressure plate at engine speed and, because it is splined to the transmission shaft, the shaft now turns at the same engine speed.

The clutch is operating properly if:

1. It will stall the engine when released with the vehicle held stationary.
2. The shift lever can be moved freely between 1st and reverse gears when the vehicle is stationary and the clutch disengaged.

Driven Disc and Pressure Plate

REMOVAL & INSTALLATION

Loosen and remove the clutch and pressure plate bolts evenly, a little at a time ...

... then carefully remove the clutch and pressure plate assembly from the flywheel

Check across the flywheel surface, it should be flat

If necessary, lock the flywheel in place and remove the retaining bolts ...

... then remove the flywheel from the crankshaft in order to replace it or have it machined

Upon installation, it is usually a good idea to apply a threadlocking compound to the flywheel bolts

Check the pressure plate for excessive wear

Be sure that the flywheel surface is clean, before installing the clutch

Typical clutch alignment tool, note how the splines match the transmission's input shaft

Use the clutch alignment tool to align the clutch disc during assembly

The pressure plate-to-flywheel bolt holes should align

You may want to use a threadlocking compound on the clutch assembly bolts

Be sure to use a torque wrench to tighten all bolts

1. Raise and safely support the vehicle.
2. Remove the transmission.
3. If the clutch and pressure plate are going to be reused, mark the pressure plate and cover assembly and the flywheel so that they can be reinstalled in the same relative position.
4. Loosen the pressure plate and cover attaching bolts evenly in a staggered sequence a turn at time until the pressure plate springs are relieved of their tension. Remove the attaching bolts.
5. Remove the pressure plate and cover assembly and the clutch disc from the flywheel.
6. Remove the pilot bearing in the crankshaft by removing using a suitable puller.

To install:

The self-adjusting pressure plate on the F-150, F-250 and Expedition models should always be adjusted before installation.

7. Before installing the self-adjusting pressure plate, adjust as follows:
   1. Place the flywheel and pressure plate in a suitable press.
   2. Using a suitable adapter, press down on the clutch diaphragm fingers until the adjusting ring moves freely.
   3. Rotate the adjusting ring counterclockwise until the tension springs are compressed.
   4. Hold the adjusting ring while releasing the pressure on the clutch fingers.
8. Inspect the flywheel for wear, damage and flatness. Replace or resurface as necessary.
9. Install a new pilot bearing into the crankshaft using a suitable pilot bearing installer.
10. Position the clutch disc on the flywheel so that an aligning tool or spare transmission mainshaft can enter the clutch pilot bearing and align the disc.
11. When reinstalling the original pressure plate and cover assembly, align the assembly and flywheel according to the marks made during removal. Position the pressure plate and cover assembly on the flywheel, align the pressure plate and disc, and install the retaining bolts. Tighten the bolts in an alternating sequence a few turns at a time until the proper torque is reached:

• 35-46 ft. lbs. (47-63 Nm) on the 4.2L, 4.6L and 5.4L engines (except Super Duty models)
• 30-36 ft. lbs. (41-49 Nm) on the 5.4L and 6.8L engines on Super Duty models
• 22-30 ft. lbs. (30-40 Nm) on the 5.8L engine
• 19-26 ft. lbs. (26-35 Nm) on the 7.3L diesel engine
• 14-19 ft. lbs. (19-26 Nm) on the 7.5L engine

12. Remove the tool used to align the clutch disc.
13. Install the transmission.
14. Install the slave cylinder and bleed the system.

ADJUSTMENTS

Because the clutch system is hydraulic, the clutch pedal free-play is self-adjusting and requires no additional maintenance.

Master Cylinder

REMOVAL & INSTALLATION

1997-98 F-250HD, F-350 and F-Super Duty

Clutch master cylinder assembly—1997-98 F-250HD, F-350 and F-Super Duty models

Click to enlarge

1. Disconnect the negative battery cable.
2. Disconnect the clutch master cylinder pushrod from the clutch pedal by prying the retainer bushing and pushrod off the pedal pin.
3. Detach the connector for the Clutch Pedal Position (CPP) switch.
4. Remove the retaining nuts and the support bracket retaining the clutch master cylinder reservoir and reservoir to the bulkhead.
5. Thoroughly clean the area around the hydraulic tube and disconnect it from the master cylinder.
6. Remove the clutch master cylinder from the firewall carefully. It will be necessary to rotate the master cylinder 105 degrees counterclockwise to allow the CPP switch to clear the dash panel.

To install:

7. Install the pushrod through the hole in the engine compartment. Make sure it is located on the correct side of the clutch pedal. Install the master cylinder and tighten the nuts.
8. Install the hydraulic tube to the master cylinder.
9. Attach the CPP switch connector.
10. Replace the retainer bushing in the clutch master cylinder pushrod if worn or damaged. Install the retainer and pushrod on the clutch pedal pin. Make sure the flange of the bushing is against the pedal blade. Install the switch.
11. Connect the negative battery cable and bleed the clutch hydraulic system, if necessary.

F-150, F-250, Expedition and 1999-00 F-250SD, F-350 and F-Super Duty

Remove the pushpins from the clutch master cylinder assembly

Click to enlarge

1. Disconnect the negative battery cable.
2. Disconnect the clutch master cylinder pushrod from the clutch pedal by prying the retainer bushing and pushrod off the clutch pedal pin.
3. On the F-150, F-250 and Expedition, detach the Clutch Pedal Position (CPP) switch electrical harness connector.
4. On the F-250SD, F-350 and F-Super Duty models, remove the CPP switch from the clutch master cylinder pushrod.
5. Remove 2 push pins retaining the clutch master cylinder reservoir to the cowl panel.
6. Raise and safely support the vehicle.
7. On the F-150, F-250 and Expedition, disconnect the clutch hydraulic line from the transmission using Clutch Coupling Tool T88T-70552-A, or equivalent.
8. On the F-250SD, F-350 and F-Super Duty models, twist and unlock the slave cylinder from the transmission.
9. Lower the vehicle.
10. Rotate the clutch master cylinder 45 degrees clockwise and remove the clutch master cylinder and reservoir.

To install:

11. If replacing the clutch master cylinder, it must be bench bled before it is installed.
12. Install the pushrod through the hole in the engine compartment. Place the clutch master cylinder in position and rotate the body 45 degrees counterclockwise while pushing inward.
13. Place the clutch master cylinder reservoir on the cowl panel and secure with 2 push pins.
14. On the F-150, F-250 and Expedition, connect the clutch hydraulic line to the transmission.
15. On the F-250SD, F-350 and F-Super Duty models, install the slave cylinder onto the transmission.
16. Lower the vehicle.
17. On the F-250SD, F-350 and F-Super Duty models, install the CPP switch to the clutch pedal pushrod. Ensure that the CPP switch is properly positioned on the pushrod.
18. On the F-150, F-250 and Expedition, attach the CPP switch electrical harness connector.
19. Install the retainer and pushrod on the clutch pedal pin with the flange portion of the bushing facing away from the pedal blade of the clutch pedal.
20. Connect the negative battery cable.
21. Verify the starter motor will only crank the engine when the clutch pedal is fully depressed.
22. Bleed the hydraulic clutch system and check for leaks.
23. Road test the vehicle and check the clutch system for proper operation.

BENCH BLEEDING PROCEDURE

It is recommended to bench bleed a dry clutch master cylinder before installation.

1. Start with the tube and reservoir attached to the clutch master cylinder, but the system removed from the vehicle. Lightly clamp the reservoir in a vise.
2. Hold the clutch master cylinder vertically with the reservoir feed hose in the highest position on the body.
3. Fill the reservoir and extend above the clutch master cylinder and make sure the quick connect on the clutch line is below the clutch master cylinder.
4. Using a small screwdriver, depress the internal mechanism of the male quick connect coupling to open the valve.
5. Stroke and fully depress and hold the push rod.
6. Release the internal mechanism of the quick end connector and release the push rod.
7. Fill the reservoir and repeat the above steps 4 more times.
8. With the clutch master cylinder still being held with the outlet tube and reservoir feed tube ends high, quick connect closed and the reservoir full, push the push rod into the body several times quickly to expel any remaining air.

Slave Cylinder

REMOVAL & INSTALLATION

Internally Mounted Slave Cylinder

Clutch hydraulic line removal

Click to enlarge

Concentric slave cylinder removal

Click to enlarge

Clutch release bearing removal with the concentric slave cylinder

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1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle.
3. Disconnect the coupling at the transmission, using Clutch Coupling Remover T88T-70522-A, or equivalent. Slide the white plastic sleeve toward the slave cylinder while applying a slight tug on the tube.
4. Remove the transmission assembly.
5. Remove 2 slave cylinder-to-transmission retaining bolts.
6. Remove the slave cylinder from the transmission.

To install:

7. Install the slave cylinder over the transmission input shaft with the bleed screw and coupling facing the left-hand side of the transmission.
8. Install 2 slave cylinder retaining bolts. Tighten the bolts to 13-19 ft. lbs. (18-26 Nm).
9. Install the transmission assembly.
10. Connect the clutch tube to the slave cylinder.
11. Lower the vehicle.
12. Bleed the hydraulic clutch system.
13. Connect the negative battery cable.
14. Road test the vehicle and check for proper transmission operation.

Externally Mounted Slave Cylinder

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle securely on jackstands.
3. Thoroughly clean the area around the hydraulic tube before disconnecting the tube.
4. Remove the retaining pin from the slave cylinder hydraulic line.
5. Remove the retaining clip from the slave cylinder.
6. Remove the slave cylinder from the transmission.

To install:

7. The installation is the reverse of the removal.
8. Replace the hydraulic line retaining pin.
9. Bleed the system.

HYDRAULIC SYSTEM BLEEDING

Externally Mounted Slave Cylinder

Bleeding the external slave cylinder

Click to enlarge

1. Clean the reservoir cap and the slave cylinder connection.
2. Remove the slave cylinder from the housing.
3. Using a ³/₃₂ in. punch, drive out the pin that holds the tube in place.
4. Remove the tube from the slave cylinder and place the end of the tube in a container.
5. Hold the slave cylinder so the connector port is at the highest point, by tipping it about 30 degrees from horizontal. Fill the cylinder with DOT 3 brake fluid through the port. It may be necessary to rock the cylinder or slightly depress the pushrod to expel all the air.

6. When all air is expelled—no more bubble are seen—install the slave cylinder.

Some fluid will be expelled during installation as the pushrod is depressed.

7. Remove the reservoir cap. Some fluid will run out of the tube end into the container. Pour fluid into the reservoir until a steady stream of fluid runs out of the tube and the reservoir is filled. Quickly install the diaphragm and cap. The flow should stop.
8. Connect the tube and install the pin. Check the fluid level.
9. Check the clutch operation.

Internally Mounted Slave Cylinder

Bleeding the concentric slave cylinder

Click to enlarge

1. Disconnect the clutch pipe from the transmission using Coupling Tool T88T-70522-A or equivalent, by sliding the clutch white plastic sleeve toward the clutch release cylinder while applying a slight tug on the clutch pipe.
2. Clean dirt and grease from around the reservoir cap.
3. Remove the cap and diaphragm and fill the reservoir to the step with clean DOT 3 or equivalent brake fluid from a closed container.
4. Using a small flat bladed tool, depress the internal mechanism of the male coupling to open the valve. While continuing to hold the valve open, slowly depress the clutch pedal to the floor and hold.
5. Remove the flat bladed tool from the coupling, closing the valve.
6. Release the clutch pedal.
7. Refill the reservoir to the step.

The reservoir must be kept full at all times to ensure that there will be no additional introduction of air into the system.

8. Repeat the above steps.
9. Install the reservoir cap. Reconnect the clutch pipe to the clutch release cylinder. Check that the connection is secure by applying a slight tug to the clutch tube.
10. Stroke the clutch pedal as rapidly as possible for 5 to 10 strokes.
11. Wait 1 to 3 minutes.
12. Repeat the stroking procedure at least 3 more times.
13. Loosen the bleed screw (located in the clutch slave cylinder body next to the inlet connection).
14. Depress and hold the clutch pedal while tightening the bleed screw.
15. Refill the reservoir to the step.
16. Check the operation of the clutch system.

Chilton® Automotive Information Systems. © 2004 Thomson Delmar Learning.