How to Replace a Brake Master Cylinder on a 90-97 Honda Accord

If you have noticed the brake pedal slowly bleeding down to the floor when you are stopped and holding the pedal, or if you see brake fluid leaking behind the master cylinder in the engine compartment, or onto the firewall behind the brake pedal, then it is time to replace your brake master cylinder. This is a fairly easy repair that you can do yourself instead of taking your 1990-1997 Honda Accord to the repair shop for service.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• 12mm socket, extension, ratchet, and a 10mm wrench (preferably a line wrench).
• Someone to help you bleed the master cylinder.
• New brake master cylinder.
• New Brake Fluid.

1. 
   Master Cylinder

   First, remove the brake fluid cap, and disconnect the two wires from the connector. You don't have to mark them, the will only fit one way. Now remove as much brake fluid from the master cylinder reservoir as you can. You can use a syringe for this, or even a turkey baster. This will help keep brake fluid off of the car's paint. Now you will need to remove the two metal brake lines that run from the master cylinder to the front and rear brakes. These lines go into the side of the master cylinder and are best removed with a flare nut or "line" wrench. This is a special wrench designed just for this purpose. A line wrench helps prevent rounding off the corners of the 10mm flare nut. Simply slide the line wrench onto the brake line, and then push it down onto the flare nut. Loosen the flare nut by turning it counterclockwise. It might take a little effort to break it loose. To speed the process, once you have broken the flare nut loose you can use a regular wrench to loosen it the rest of the way. Now loosen and remove the other brake line. Take care not to bend the brake lines too much. If you do it will make it more difficult to reinstall them in the new master cylinder.

2. 
   New Master Cylinder

   Once you have the brake lines removed you will need to remove the two 12mm nuts that secure the brake master cylinder to the brake booster. It is easiest to use a 12mm socket on an extension to remove these two nuts. Once you have the two nuts removed you will need to gently hold the two brake lines out of the way while you pull the master cylinder off of the studs.

3. 
   Flare Nut (Line) Wrench

   If the new master cylinder does not have a brake fluid reservoir then you will need to swap the old reservoir to the new master cylinder. You can do this by loosening the clamp with the 10mm bolt. You do not need to take the clamp all the way off. Simply pull the reservoir off and install it on the new master cylinder. While gently holding the brake lines out of the way slide the new master cylinder onto the studs on the brake booster. Start the two 12mm nuts by hand to insure that you do not cross-thread them, then tighten them with the ratchet. Insert one brake line into the new master cylinder and start the flare nut by hand. It is very easy to cross-thread this flare nut while trying to install the line. Be careful while reinstalling the brake lines. If the flare nut seems to get tight too soon, or if it stops turning before it is fully seated take the line off and start over. This will take some time and patience, but it is better to go slow than to ruin a new master cylinder. Tighten the flare nut with the line wrench. Repeat this procedure for the other brake line.

4. Once both brake lines are tight you need to fill the reservoir with new brake fluid to the "full" or "max" line. Since you have replaced the master cylinder and added new fluid there will be air in the system that you will need to bleed out. To do this have someone pump the brake pedal several times, making sure that they push the pedal all the way to the floor and then fully release it each time. Place shop rags or an old T-shirt under the master cylinder to help soak up the brake fluid. After several pumps have them hold the brake pedal all the way to the floor. While they are holding the pedal, take the 10mm wrench and loosen the front brake line a little, and then the rear brake line. You will notice that a good bit of air comes out of the lines, and possibly some brake fluid. Re-tighten the brake lines and have your helper start pumping again. Repeat this process until you only get brake fluid coming out of the lines, and you no longer see any bubbles in the reservoir. Plug the reservoir cap wires back in and re-install the cap. Wash any brake fluid off that might have gotten on the paint.

Tips & Warnings

• Take your time when removing and installing the brake lines. If you rush you can cross thread the flare nuts which can result in leaks.
• Be sure to communicate with your helper. If they release the brake pedal before you have re-tightened the brake lines it will suck air back into the system and you will have to start over.
• Do not let the brake fluid level get too low in the reservoir while you are bleeding the master cylinder. If you do, you will get air in the system and have to start the bleeding process again.
• Be careful where you touch when you have brake fluid on your hands. Do not touch the vehicle's paint!
• Wear safety glasses. When bleeding the master cylinder, the brake fluid will come out under pressure, and you do not want to get it in your eyes. Trust me, it hurts.
• Wash brake fluid off of paint immediately! Brake fluid will remove the paint from your vehicle.

[imquick2]

on 7/19/2009 Great instructions, clear and simple, especially for a first timer - thanks for posting!

[georgelarson]

on 5/12/2009 Good instructions for replacing a master brake cylinder.