The master cylinder is a vital component of your vehicle’s hydraulic brake system. It is responsible for converting the force applied to the brake pedal into hydraulic pressure, which is then transmitted to the brake calipers or wheel cylinders. When the master cylinder fails, it can cause a loss of braking power, which can be extremely dangerous. Therefore, it is important to know how to change a master cylinder if it fails.
The first step in changing a master cylinder is to disconnect the brake lines from the master cylinder. Be sure to plug the brake lines to prevent brake fluid from leaking out. Next, remove the bolts that hold the master cylinder to the brake booster. Once the master cylinder is loose, you can pull it out of the brake booster. Before installing the new master cylinder, be sure to bench bleed it to remove any air from the system. Then, install the new master cylinder and tighten the bolts that hold it in place. Finally, connect the brake lines to the master cylinder and bleed the brake system to remove any air from the lines.
Changing a master cylinder can be a challenging task, but it is important to be able to do it if the master cylinder fails. By following these steps, you can safely and effectively change the master cylinder on your vehicle.
Assess the Master Cylinder Condition
The master cylinder is responsible for converting the force applied to the brake pedal into hydraulic pressure that actuates the brakes. A faulty master cylinder can lead to poor braking performance, which can be dangerous. There are a few signs that can indicate that your master cylinder need to be replaced:
- Leaking brake fluid: A leak in the master cylinder can cause brake fluid to leak out of the system, which can lead to a loss of braking power. Check for leaks around the master cylinder and brake lines.
- Spongy brake pedal: A spongy brake pedal feels soft and springy when you press on it. This can be caused by air in the brake system or a faulty master cylinder.
- Low brake fluid level: A low brake fluid level can indicate a leak in the system or a worn master cylinder. Check the brake fluid level regularly and add brake fluid as needed.
If you notice any of these signs, it’s important to have your master cylinder inspected by a qualified mechanic as soon as possible. A faulty master cylinder can be dangerous, so it’s important to address the problem quickly.
Visual Inspection
The first step in assessing the condition of the master cylinder is to visually inspect it. Look for any signs of damage, such as cracks or leaks. You should also check the brake fluid level. If the fluid level is low, it could be a sign of a leak.
Pressure Test
A pressure test can be used to check the condition of the master cylinder’s internal components. A pressure gauge is attached to the master cylinder, and the brake pedal is depressed. The pressure gauge will measure the pressure that is generated by the master cylinder. If the pressure is too low, it could be a sign of a faulty master cylinder.
Brake Pedal Feel
The feel of the brake pedal can also be an indication of the condition of the master cylinder. A spongy brake pedal can be a sign of a faulty master cylinder. The brake pedal should feel firm and responsive when it is depressed.
| Symptom | Possible Cause |
|---|---|
| Leaking brake fluid | Faulty master cylinder |
| Spongy brake pedal | Faulty master cylinder or air in the brake system |
| Low brake fluid level | Leak in the brake system or worn master cylinder |
Gather Necessary Tools and Materials
Tools
To successfully replace a master cylinder, you will need the following tools:
- Wrench set (metric): Includes various sizes for loosening and tightening bolts and nuts.
- Socket set (metric): Similar to a wrench set, sockets provide better leverage and can be used with a ratchet.
- Brake line flare tool: Used to create flares on brake lines for secure connections.
- Bleeder wrench: Designed specifically for opening and closing bleeder screws on brake calipers.
- Brake fluid: Replaces the old fluid and must meet the manufacturer’s specifications.
- Safety glasses: Protects your eyes from potential brake fluid splashes.
- Gloves: Prevents skin irritation from brake fluid.
- Brake cleaner: Cleans and removes contaminants from brake components.
- Shop towels: Used for wiping spills and cleaning up the work area.
Materials
In addition to the tools listed above, the following materials are essential for this task:
| Material | Description |
|---|---|
| New master cylinder: | Replacement part that matches the original specifications. |
| Brake lines: | May need replacement if they are rusted or damaged. |
| Brake fluid reservoir: | Sometimes needs replacement if it is cracked or leaking. |
| Copper washers: | Used to create a leak-proof seal between brake lines and fittings. |
Disconnect the Brake Line Fittings
The next step is to disconnect the brake line fittings from the master cylinder. To do this, you will need a flare nut wrench or a line wrench. Place the wrench on the flare nut and turn it counterclockwise to loosen it. Be careful not to overtighten the wrench, as this could damage the flare nut or the brake line. Once the flare nut is loose, you can use your fingers to unscrew it the rest of the way. Repeat this process for the other brake line fitting.
Once the brake line fittings are disconnected, you can remove the master cylinder from the vehicle. To do this, simply lift the master cylinder straight up and out of the bracket that is holding it in place. Be careful not to spill any brake fluid when you remove the master cylinder.
Here is a table summarizing the steps for disconnecting the brake line fittings:
| Step | Description |
|---|---|
| 1 | Place the flare nut wrench on the flare nut. |
| 2 | Turn the wrench counterclockwise to loosen the flare nut. |
| 3 | Unscrew the flare nut the rest of the way by hand. |
| 4 | Repeat steps 1-3 for the other brake line fitting. |
Remove the Master Cylinder Reservoir
Before removing the master cylinder, you’ll need to disconnect the reservoir. Here’s a detailed guide:
-
Gather Tools:
- Wrench or socket set
- Screwdriver
- Plastic bag
- Brake fluid
-
Cover the Work Area:
- Spread a plastic bag or cloth over the work surface to prevent brake fluid from staining.
-
Disconnect Battery:
- Locate the battery and disconnect the negative terminal. This will prevent electrical shocks.
-
Remove Reservoir Cap and Fluid:
- Locate the master cylinder reservoir, typically made of plastic.
- Remove the cap and inspect the fluid level.
- Use a turkey baster or syringe to carefully remove most of the brake fluid from the reservoir.
- Dispose of the old brake fluid in an approved hazardous waste container.
-
Disconnect Reservoir Hoses:
- Identify and disconnect any hoses connected to the reservoir. These may include vacuum hoses and brake lines.
- Use a wrench or socket set to loosen the fittings.
- Secure the hoses with zip ties or clamps to prevent any spillage.
-
Remove Reservoir Mounting Bolts:
- Locate the bolts that secure the reservoir to the master cylinder.
- Use a screwdriver or wrench to unscrew these bolts.
-
Lift Reservoir:
- Once the bolts are removed, carefully lift the reservoir straight up and away from the master cylinder.
- Avoid spilling any remaining brake fluid.
Unscrew the Master Cylinder Mounting Bolts
Before removing the master cylinder, you’ll need to disconnect it from the brake lines and unscrew the mounting bolts that hold it in place. Here’s a detailed guide to help you through this process:
1. Locate the Master Cylinder
The master cylinder is usually located in the engine compartment, either on the firewall or near the brake booster. It’s a cylindrical-shaped component with brake lines connected to it.
2. Disconnect the Brake Lines
Use a flare nut wrench to carefully disconnect the brake lines from the master cylinder. Place a rag or towel under the connections to catch any fluid that might leak out.
3. Remove the Brake Booster Pushrod (if applicable)
If your vehicle has a brake booster, you’ll need to detach the pushrod that connects it to the master cylinder. Locate the pushrod and unclip it using a pair of pliers or a screwdriver.
4. Identify the Mounting Bolts
Locate the bolts that secure the master cylinder to the firewall or the brake booster. These bolts are typically 10mm or 12mm in size.
5. Unscrew the Mounting Bolts
Using the appropriate socket wrench, carefully unscrew the mounting bolts. Be gentle and avoid overtightening or stripping the bolts. It’s important to support the master cylinder while you’re unscrewing the bolts to prevent it from falling.
| Bolt Location | Size |
|---|---|
| Firewall (top) | 12mm |
| Firewall (bottom) | 10mm |
| Brake Booster (left) | 12mm |
| Brake Booster (right) | 10mm |
Once the mounting bolts are removed, you can carefully lift the master cylinder away from its mounting surface. Proceed to the next steps to complete the master cylinder replacement process.
Disconnect the Brake Pedal Pushrod
Before you can remove the master cylinder, you’ll need to disconnect the brake pedal pushrod. Here’s how to do it:
- Locate the brake pedal pushrod. It’s a metal rod that connects the brake pedal to the master cylinder.
- There’s a cotter pin or a retaining clip holding the pushrod to the brake pedal. Remove the cotter pin or clip.
- Pull the pushrod off the brake pedal.
Tips:
- If the pushrod is rusted or seized, you may need to use penetrating oil to loosen it up.
- Be careful not to damage the brake pedal or the pushrod when removing it.
Warning:
- Do not attempt to remove the master cylinder without first disconnecting the brake pedal pushrod. This could damage the master cylinder or the brake pedal.
Additional Details:
Once you’ve removed the cotter pin or clip, you may need to use a screwdriver or pry bar to gently pry the pushrod off the brake pedal. If the pushrod is particularly stubborn, you can try tapping it lightly with a hammer.
If you’re having trouble removing the pushrod, consult your vehicle’s repair manual for specific instructions.
Here’s a table summarizing the steps for disconnecting the brake pedal pushrod:
| Step | Action |
|---|---|
| 1 | Locate the brake pedal pushrod. |
| 2 | Remove the cotter pin or retaining clip. |
| 3 | Pull the pushrod off the brake pedal. |
Remove the Old Master Cylinder
Once the brake lines are disconnected, you can remove the master cylinder. There are two nuts that hold it in place. Use a wrench to loosen the nuts, then carefully lift the master cylinder up and out of the brake booster.
Be careful not to spill any brake fluid when you remove the master cylinder. If you do spill any fluid, be sure to clean it up immediately. Brake fluid can damage paint and other surfaces.
Here are some additional tips for removing the old master cylinder:
- Make sure that the brake lines are completely disconnected before you remove the master cylinder.
- Use a wrench to loosen the nuts that hold the master cylinder in place. Do not use pliers or other tools that could damage the nuts.
- Carefully lift the master cylinder up and out of the brake booster. Do not pry or force the master cylinder out of place.
- If you spill any brake fluid, be sure to clean it up immediately.
| Part | Location |
|---|---|
| Brake lines | Connected to the master cylinder |
| Nuts | Hold the master cylinder in place |
| Brake booster | The master cylinder is mounted on the brake booster |
Install the New Master Cylinder
Once you have the new master cylinder in hand, it’s time to install it. Here are the steps:
1. Clean the mounting surface.
Use a clean rag and some brake cleaner to clean the mounting surface where the master cylinder will be installed. This will help to ensure a good seal.
2. Install the new master cylinder.
Place the new master cylinder on the mounting surface and secure it with the bolts. Do not overtighten the bolts.
3. Connect the brake lines.
Connect the brake lines to the master cylinder. Be sure to tighten the fittings securely.
4. Bleed the brakes.
Bleed the brakes to remove any air from the system. This is a critical step, so be sure to follow the instructions carefully.
5. Check for leaks.
Start the engine and check for any leaks. If you see any leaks, tighten the fittings until the leak stops.
6. Pump the brake pedal.
Pump the brake pedal several times to build up pressure in the system.
7. Check the brake fluid level.
Check the brake fluid level and add fluid as needed.
8. Road test the vehicle.
Once you have installed the new master cylinder and bled the brakes, it’s important to road test the vehicle to make sure that the brakes are working properly. Drive the vehicle in a safe area and test the brakes at different speeds. If the brakes feel spongy or if the vehicle pulls to one side when braking, there may be a problem with the master cylinder or the brake system. In this case, you should have the vehicle inspected by a qualified mechanic.
Reattach the Brake Line Fittings
9. Reattach the brake line fittings to the master cylinder. This is a critical step, as any leaks in the brake lines can lead to catastrophic brake failure. Use a flare nut wrench or crows foot wrench to tighten the fittings to the specified torque. The torque specifications vary depending on the vehicle and brake line fitting, so refer to your vehicle’s service manual for the correct torque values.
Here’s a table summarizing important information for reattaching brake line fittings:
|
Brake Line Type |
Torque Setting (ft-lbs) |
Flare Nut Wrench Size |
|---|---|---|
|
Steel |
11-15 |
10mm |
|
Copper |
7-9 |
11mm |
|
Stainless Steel |
12-18 |
12mm |
|
Aluminum |
8-12 |
10mm |
Bleed the Brake System
Once the new master cylinder is installed, it’s crucial to bleed the brake system to remove any air that may have gotten into the lines. Follow these steps meticulously:
1. Gather Necessary Tools
You’ll need a clear tube, a wrench, a funnel, and some fresh brake fluid.
2. Safety First
Put on safety glasses and gloves to protect yourself from brake fluid spills.
3. Fill Master Cylinder
Remove the cap from the master cylinder and fill it with fresh brake fluid up to the specified level.
4. Connect Clear Tube
Attach one end of the clear tube to the bleeder screw on the caliper or wheel cylinder and place the other end into a container.
5. Have an Assistant Pump
Ask an assistant to pump the brake pedal several times and hold it down.
6. Open Bleeder Screw
Slowly open the bleeder screw with the wrench while your assistant holds the pedal.
7. Close Bleeder Screw
Once you see a steady stream of brake fluid without any air bubbles, close the bleeder screw.
8. Repeat for Other Wheels
Repeat steps 5-7 for each wheel, starting with the wheel furthest from the master cylinder and working your way inward.
9. Check Brake Fluid Level
Throughout the bleeding process, keep an eye on the brake fluid level in the master cylinder and top it up as needed.
10. Drive and Re-Check
Once all wheels have been bled, take a short drive to build up pressure in the lines. Return to the work area and re-check the brake fluid level, ensuring it’s at the proper level. If necessary, top up the fluid and repeat the bleeding process until you’re confident there’s no air in the system.
How To Change A Master Cylinder
A master cylinder is a key component of a hydraulic brake system. It is responsible for converting the force applied to the brake pedal into hydraulic pressure, which is then used to actuate the brake calipers and pads. A faulty master cylinder can lead to a loss of braking power, which can be dangerous.
Replacing a master cylinder is not a difficult task, but it does require some mechanical knowledge and skill. If you are not comfortable working on your own vehicle, it is best to leave this job to a qualified mechanic.
Here are the steps on how to change a master cylinder:
1. Disconnect the negative battery terminal.
2. Remove the brake fluid reservoir cap.
3. Use a turkey baster or syringe to remove the brake fluid from the reservoir.
4. Disconnect the brake lines from the master cylinder.
5. Remove the nuts that hold the master cylinder to the firewall.
6. Remove the master cylinder from the vehicle.
7. Install the new master cylinder.
8. Tighten the nuts that hold the master cylinder to the firewall.
9. Connect the brake lines to the master cylinder.
10. Fill the brake fluid reservoir with new brake fluid.
11. Connect the negative battery terminal.
12. Pump the brake pedal several times to bleed the air from the system.
13. Check for leaks and top off the brake fluid reservoir as needed.
People Also Ask About How To Change A Master Cylinder
What are the symptoms of a bad master cylinder?
The symptoms of a bad master cylinder can include:
- A spongy brake pedal
- A brake pedal that goes to the floor
- Leaking brake fluid
- A loss of braking power
How long does it take to change a master cylinder?
It typically takes about 1-2 hours to change a master cylinder.
How much does it cost to change a master cylinder?
The cost to change a master cylinder varies depending on the make and model of your vehicle, as well as the cost of labor in your area. However, you can expect to pay between $100 and $300 for the parts and labor.
Can I change a master cylinder myself?
Yes, it is possible to change a master cylinder yourself. However, it is important to have some mechanical knowledge and skill before attempting this repair. If you are not comfortable working on your own vehicle, it is best to leave this job to a qualified mechanic.
