The clutch master cylinder transfers hydraulic fluid pressure from the clutch pedal to the slave cylinder on the transmission. This system must remain absent from air and leaks. If a leak is present, the clutch pedal will quickly lose pressure and the clutch cannot be disengaged.By Weston Chadwick – November 13, 2015
Contributors: Mark Doiron, Stooge
This article applies to the Jeep Wrangler JK (2007-Present).
When you depress the clutch pedal, fluid from the brake fluid reservoir is forced into the hydraulic slave cylinder line. The clutch master cylinders piston creates a low pressure area where the fluid is drawn to. Fluid is not compressible, so the clutch pedals movement is transferred through the fluid. The slave cylinders piston then expands, disengaging the clutch inside the transmission.
- Clip removal tool
- 10mm, 8mm, and 12mm sockets
- 1/4″ or 3/8″ ratchet
- Flat head screwdriver
- Rubber cap
- Rubber gloves
- Safety glasses
- DOT 3 brake fluid
- Clutch master cylinder
- Bungee cord
- Needle nose pliers
- Channel locks
Figure 1. The clutch master cylinder.
Step 1 – Remove part of driver’s side fender liner
Remove the two body plugs and 10mm bolt. Pry the body plugs out using a clip removal tool. Pull the liner back to expose the bottom side of the clutch master cylinder. You can wrap a bungee cord to the outside of the fender and inside the engine bay to keep the fender liner held back.
Step 2 – Remove wiring harness and ground wire from body
To create more room around the clutch master cylinder, these two components will need to be moved. This will also prevent you from loosening the brake booster. Pull against the wiring harness where the black clips slide over the firewall studs.
Figure 4. The wiring harness clips and ground wire.
Step 3 – Disconnect brake fluid reservoir line
This line will leak brake fluid once it’s disconnected. Plug the line with a bolt or rubber cap. Squeeze the clamps with needle nose pliers to move them.
Figure 5. The brake fluid reservoir to clutch master cylinder line.
Step 4 – Remove slave cylinder line from master cylinder
This line is installed very tightly into the clutch master cylinder. A metal clip locks the line to the master cylinder. Use a flat head screwdriver or pick to unlock the line by pulling against the exposed portion until it moves to the unlocked position. Pull/twist the line to remove it. There is a rubber O-ring seal on the line. Try not to lose it as you’re removing the line. It’s not a common part.
Step 5 – Disconnect clutch master cylinder from clutch pedal
The clutch master cylinder rod snaps onto the pedal using a stud. Locate the connection inside the vehicle and use a pry bar, screwdriver, or your hands to separate the two components.
This step can be done from inside or outside the cabin, depending on choice of work space. The master cylinder is keyed to the firewall. It must be rotated to line up the tabs on the cylinder with the slots on the firewall. Once it becomes unlocked from the firewall, disconnect the clutch pedal position sensor. Press down on the flexible tab while pulling the connector away from the master cylinder.
If your inside the cabin, rotate the cylinder counterclockwise and clockwise if your outside. Channel locks or similar pliers will give you a good gripping force for rotation.
Step 6 – Install new clutch master cylinder and bleed system
Install is the reverse of the removal steps. Reattach the master to the clutch lever. Reconnect the line feeding clutch fluid from the master to the slave cylinder. Reconnect the line to the brake fluid reservoir. Reattach the wiring harness and reinstall the fender liners.
Locate the slave cylinder. It’s located near the front of the transmission on the driver’s side. Make sure the brake fluid reservoir is filled to capacity with DOT 3 brake fluid. Remove the rubber dust cap from the bleed screw. Turn the bleed screw half a turn while another person has the clutch pedal depressed. Make sure your wearing rubber gloves and safety glasses. Brake fluid will come out of the screw at a high velocity. Once the pressure is gone (a couple seconds), close the screw and have the other person pump the clutch pedal about ten times. Repeat the bleeding process several times to achieve a responsive clutch pedal.