Ford equipped the 1991 F-150 trucks with a hydraulic clutch actuation system on the 4.9-, 5.0- or 5.8-liter, naturally aspirated gasoline engines. The hydraulic clutch generates pressure at the master cylinder when the driver presses on the clutch pedal. A nylon hydraulic clutch line carries pressurized fluid to the slave cylinder on the transmission. The line is subject to damage from road debris and proximity to hot engine parts. Replace damaged hydraulic lines to prevent fluid loss and restore clutch function.
Park the F-150 on level ground and set the parking brake. Place wheel chocks behind the rear wheels. Jack up the front of the truck and support it on jack stands.
Locate the hydraulic slave cylinder coupling port on the driver side of the transmission near the bell housing. Place a catch pan under the coupling port. Push the white plastic collar on the fitting toward the transmission, using special tool T88T-70522-A to disengage the quick-connect fitting and then pull the hydraulic line from the transmission.
Remove the hydraulic line retaining clip from the bottom of the passenger compartment near the quick-connect fitting. Observe the hydraulic line routing from the master cylinder to the slave cylinder.
Locate the clutch master cylinder on the engine firewall next to the brake booster. Remove the 3/32-inch roll pin from the master cylinder near the hydraulic line connector, using a punch. Support the master cylinder while pushing the roll-pin out to prevent stressing and breaking the master cylinder body. Pull the hydraulic line from the master cylinder. Pull the old hydraulic line rubber seal out of the master cylinder using a dental pick. Discard the old roll pin and rubber seal.
Install the new rubber seal on the new hydraulic line master cylinder fitting. Route the line down to the transmission. Insert the fitting and rubber seal into the master cylinder. Install the new 3/32-inch roll pin in the master cylinder.
Push the quick-connect fitting into the slave cylinder coupling until the coupling snaps in place. Wipe spilled brake fluid from the transmission case with a clean rag. Install the hydraulic line retaining clip.
Wipe the clutch master cylinder reservoir cap with a clean rag to remove dirt or other contaminates. Remove the reservoir cap and diaphragm from the reservoir. Install a short length of clear, nylon hose to the bleeder valve on the transmission near the slave cylinder coupling. Lead the loose end of the hose into the catch pan. Open the bleeder valve, using a wrench. Have a helper monitor the fluid level in the reservoir and add DOT 3 heavy-duty brake fluid as necessary to prevent the reservoir from running dry. Observe the fluid stream in the hose and tighten the bleeder valve, using a wrench, once the fluid stream is free of air bubbles.
Fill the reservoir up to the “Full” mark and install the reservoir diaphragm. Push the clutch pedal to the floor. Hold it for a few seconds then completely release the pedal as rapidly as possible. Repeat this action 10 times. Remove the diaphragm and top off the fluid in the reservoir. Repeat this step five times.
Install the reservoir diaphragm and cap. Have your helper apply moderate pressure to the clutch pedal and loosen the bleeder valve slightly to release any residual air. Tighten the bleeder valve and remove the clear vinyl hose. Wipe up spilled brake fluid with a rag.
Raise the front of the F-150, using the jack. Remove the jack stands, and then lower the truck to the ground.
Remove the reservoir cap and diaphragm. Add fluid as necessary to bring the fluid level up to the “Full” mark. Install the diaphragm and cap.
Test the clutch for proper operation in a safe area. Inspect the hydraulic line fittings for leaks. Ensure that the clutch is operating properly before using the vehicle in traffic or other public areas.
