Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.
Vacuum-Type Brake Booster Failure
If your vacuum-type brake booster has failed, most likely you'll have to replace it with a new or rebuilt unit. Depending on the particular type of booster installed on your vehicle, you may rebuild the unit yourself (a rebuild kit will contain a diaphragm, valves, some rubber parts, and other components). However, most brake boosters need to be replaced. Either way, you'll need to remove and reinstall the unit if you want to do the repair yourself.
You can install a brake booster replacement at home using a few common tools on a Saturday morning at home. It's not a difficult task, and you can save some money in the process. Depending on your particular vehicle make and model, expect to pay between $200 and $900 dollars for a rebuilt or new brake booster, and perhaps about $100 or more in extra parts in some cases. Still, you'll save around $250 dollars or more in labor costs.
This guide shows what steps you need to take to replace the unit at home. For many models, this guide is all you need; but, if you still need specific help to deal with some components, you can consult the repair manual for your particular vehicle make and model. If you don't have your own copy, you can buy an inexpensive, aftermarket repair manual at most auto parts stores or online.
First, we'll go through the steps needed to remove the brake master cylinder, so you can replace the new brake booster.
How to to Replace the Brake Master Cylinder
- Remove the old brake master cylinder.
- Remove the brake booster.
- Install the brake booster.
- Install the brake master cylinder.
Each of these steps is described fully below.
Removing the Brake Master Cylinder
Before you start, be aware that on some vehicle models, you don't need to remove the brake master cylinder from the engine compartment. All you need to do is unscrew the cylinder mounting nuts that secure it to the brake booster.
This way, you can pull the cylinder away when you are ready to remove the brake booster off the vehicle—but be careful not to bend or damage the brake lines connected to the master cylinder. However, if you need more clearance to remove the booster, you do need to remove the master cylinder from the engine. The next procedure will help you in either case.
NOTE: On some vehicle models you may need to remove the air cleaner assembly, power center (fuse, relay box), or some other components to clear space around the brake master cylinder and brake booster for repair. Consult your vehicle repair manual, if necessary.
- First, disconnect the negative battery cable and secure the cable terminal away from the battery.
- Unplug the sensor electrical connector from the brake mastery cylinder.
- Using a line wrench, loosen the brake lines from the master cylinder.
- Then, one by one, disconnect the brake lines.
- Plug the outlet ports on the brake master cylinder using a clean piece of plastic sheet, plug the brake-line ends using a clean piece of plastic sheet and secure the sheet with a rubber band. This prevents contamination of the brake lines.
- Loosen the nuts (two or four, depending on your application) that attach the master cylinder to the brake booster, and carefully remove the master cylinder from the vehicle.
- Place the master cylinder in a clean plastic bag to prevent contamination, and put it away in a safe place until you are ready to reinstall it.
Once out of the vehicle, carefully inspect the master cylinder. If the cylinder is beginning to leak or it's an old unit (eight or more years), consider rebuilding the unit or installing a new one to avoid damage to the new brake booster. You'll save money on repairs later.
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How to Remove the Brake Booster
- In some vehicles, you need to remove the panel underneath the steering wheel to reach the upper part of the brake pedal assembly and its connection to the brake-booster push rod clevis.
- You can remove this panel using a Phillips screwdriver or ratchet and socket of the appropriate size. Depending on your particular model, you may need to remove other components located under the dashboard. Consult your vehicle repair manual, if necessary.
- Get under the dashboard at the driver's side and Unplug the brake light switch electrical connector at the brake pedal.
- Then, disconnect the booster push rod from the brake pedal; in most configurations, you need to pull out a retaining clip from the push rod clevis pin using a pair of pliers. Then slide the pin off the clevis.
- Now, remove the brake light switch from the brake pedal and any mounting hardware.
- Take note of the location and mounting order of any washers, sleeves, spacers, and other parts that connect the push rod to the brake pedal.
- Keep the push rod mounting components in a box or bag, separate from other components and put the container in a safe place.
- Now, locate the four booster mounting nuts (two, on some applications) under the dashboard and begin to loosen the nuts using a wrench or ratchet and socket.
- Finish removing the booster mounting nuts and put them away in a safe place.
- Working from the engine compartment, disconnect the vacuum hose from the brake booster check valve. You may need a pair of pliers to disconnect the hose from the valve.
- When ready, carefully pull the booster off the firewall until the booster mounting studs clear the firewall and then remove the booster from the engine compartment.
How to Install the Brake Booster
- Place the new or rebuilt brake booster in position on the firewall along with a new sealing gasket.
- From under the dashboard, hand-start the booster mounting nuts, but do not tighten them yet.
- Align the pedal support and booster clevis along with the spacer, brake light switch and other components as necessary (on some vehicle models you'll need to adjust the brake light switch. Consult your repair manual, if necessary).
- Install any other washers and mounting hardware and secure the brake pedal pin with the clip.
- Plug in the brake light switch electrical connector at the brake pedal.
- Tighten the booster mounting nuts gradually in a crisscross pattern. Finally, torque the mounting nuts to 13-25 ft. lbs. (18-33 Nm) using a torque wrench. NOTE: New or rebuilt units come with the push rod pre-adjusted, ready for installation. But if you think the new unit needs adjustment, consult the instructions that come with your new booster or your vehicle repair manual.
- From the engine compartment, connect the vacuum hose to the brake booster check valve. Secure the hose with the hose clamp, if necessary, using a pair of pliers.
- Next, install the brake master cylinder, then head to the next section.
Installing the Brake Master Cylinder
Before installing the brake master cylinder, top the fluid reservoir with new brake fluid, if necessary.
NOTE: If you are re-installing the same brake master cylinder, you don't need to bleed the unit before the installation if you plugged the outlet ports as you disconnected the brake lines. But make sure your brake master cylinder is not leaking, otherwise, it'll ruin your new booster.
- If you are installing a new master cylinder, follow the bleeding procedure described in the installation instructions that come with your new unit before installation.
- Place the master cylinder on the brake booster mounting studs and hand-start the mounting nuts.
- Then, tighten the nuts to 13-25 ft. lbs. (18-33Nm) using a torque wrench.
- Working on one brake line at a time, remove the plugs from the master cylinder outlet port and the corresponding brake line and hand-tight the line to the master cylinder. Tighten the line using a line wrench.
- Install the other brake line(s).
- To bleed the air from the master cylinder:
• If necessary, cover the fender with a piece of cloth or plastic, on the driver side, to avoid ruining the body paint with the brake fluid. And place rags or newspaper under the master cylinder.
• Have an assistant depress the brake pedal and hold the pedal down.
• Then crack open (about 3/4 of an inch) the line closest to the front of the vehicle using the line wrench.
• Let air and brake fluid come out and tighten the line again.
• Then, release the brake pedal and wait for five seconds.
• Repeat the previous steps until you see brake fluid flowing free of bubbles through the outlet port. Don't let the brake fluid reach below the MIN mark on the reservoir, add new fluid as necessary.
- Repeat the bleeding procedure on the other line(s), as well.
- Plug in the electrical connector to the brake master cylinder.
- Add more fluid to the master cylinder reservoir, up to the MAX mark, if necessary.
- Remove the rags or newspapers from under the master cylinder and wash away any residual brake fluid from the engine compartment, if necessary.
- Connect the battery negative cable.
- And one more thing: If you had to remove the brake master cylinder off the vehicle, bleed the air out of the brake lines to prevent brake performance problems.
OK. It's time to drive test your vehicle in a low-traffic street. Check that the brake lights are working (adjust the brake light switch, if necessary) and confirm that you have repaired the brake problem. If you need some visual clues, the following video gives you an overview of the brake booster replacement process.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: What possible internal damage can occur to vac. brake booster if there is too much side-to-side movement to the pushrod, and how much is too much movement to pushrod? I am removing the booster from the car.
Answer: The pushrod needs to be adjusted to specifications. The rod is pushing against the master cylinder. Check your repair manual for the proper adjustment for your particular model.
Question: I tried replacing my brake booster, but still can't get any peddle up. What can be the issue?
Answer: Make sure the push rod is correctly adjusted - consult your repair manual for the specs for your model.
Question: Does a brake booster need to have gaskets put back on or is it able to go without?
Answer: Put a new gasket when replacing the booster.