Maintenance

When Bleeding Brakes Should The Car Be On? — [Answered]

No, the car should not be on while bleeding brakes. Although the engine’s vacuum brake booster can increase pedal force, if the engine is running, it can pull and introduce air into the brake lines through the bleeder screws. You don’t want that.

However, there is another case. Have you heard of ABS brakes? This type of brakes come in modern and newer cars, requiring the ignition to be on during brake bleeding. Please note: you can keep the vehicle’s engine off even in the case of ABS brakes. 

So, what have we learned so far? Let me summarize it for you! You don’t need to keep your car running or the engine on when bleeding the brakes. Even in the case of ABS brakes, you should keep the ignition on, but not necessarily the engine. 

Why Not Bleed Brakes When Car Is Running?

No car mechanic, including me, would suggest you bleed brakes while having your car running. Why? Because brakes on all the cars are designed in a way to work with the engine off. 

If you keep the car running, the power brake booster increases the force of the brake pedal. This can create a pressure imbalance in the brake system during the brake bleeding process, letting air bubbles form in the brake lines.

So, if your aim is improving the brakes’ effectiveness by bleeding them, it won’t happen in this case. Rather than removing the air bubbles, you will end up making more in the braking system.

How Is the Anti-Lock Braking System (ABS) Different? 

The ABS braking system operates electronically. It has a scanner and a pump. The pump must be running for proper bleeding, which is only possible if the car’s engine is on ignition. 

But here is the catch: even if you are bleeding ABS brakes, it doesn’t necessarily mean you have to always turn on the ignition. What? Yes, you heard right. This is what I really mean.

No need for the pump to be on so you can keep the ignitionoff — If you are bleeding base brakes and/or replacing a caliper. 

The pump MUST be activated, and ignition must be on — When replacing the ABS modulator(s). 

So, if you are simply bleeding the ABS brakes for any reason, not replacing the ABS modulator(s), you can do so without keeping the car’s engine running or putting it into ignition. 

What Does It Mean To Bleed Brakes?

bleeding-car-brakes

Bleeding brakes is removing air bubbles or trapped air from the hydraulic brake system of a vehicle or a controlled amount of brake oil along with the air bubbles or trapped air. 

Air in the brake system poses an issue as it hinders the proper compression of brake fluid. Consequently, it obstructs force transfer to the brake lines when pressure is put on the pedal, causing a spongy brake pedal and reducing braking efficiency. 

But how does this air come in there? It can enter the brake during brake component replacement or due to fluid leakage and/or improper maintenance. But remember, the same thing can happen even in brand-new cars; it is totally normal.

Can You Bleed Your Car’s Brakes On Your Own?

Yes, bleeding brakes by yourself is possible, but it is more like a two-person job. One person will need to operate the brake pedal, while the other will require to open the bleeder valves and bleed the brake fluid. So I suggest you have a partner to bleed your car’s brakes. 

The process of bleeding brakes is done by opening specific bleeder valves on the brake calipers or wheel cylinders while pressurizing or manually operating the brake pedal. 

As the bleeder valve is opened, the compressed air bubbles trapped in the brake fluid are released, allowing them to be expelled along with a small amount of brake fluid. Don’t worry! The brake fluid release from the brakes isn’t much, so it won’t affect the brakes’ performance. 

How To Bleed Your Car’s Brakes? Step-By-Step Guide

I think bleeding your car’s brakes is easy, like knowing the dirty engine oil symptoms and changing if you have the right tools and the necessary knowledge.

Note: The procedure of bleeding brakes with ABS is the same regardless of whether your vehicle is equipped with ABS or not, unless the replacement of the master cylinder is necessary.

As far as these necessities matter, I will help you know how to bleed brakes 2 people, from procuring tools to removing trapped air. 

The brake bleeding process starts with gathering the following necessary tools that you’ll need to use to do everything right.

Box-end wrench – To open and close the bleeder screws. Using an offset head design is usually best, as this will give you better access to the bleeder screws.

Brake fluid – You will need about 1 pint of brake fluid for a single bleed. If you replace the entire brake system, you will need about 3 pints.

Plastic tubing – An almost 12 inches long tube to connect the bleeder screw to the waste bottle. It must be sized to fit snugly over the bleeder screw.

Waste bottle – To catch the old brake fluid as it is bled from the system.

Brake cleaner – To clean the bleeder screws and the plastic tubing.

Another person/ Assistant – To press the brake pedal when the other person is working with opening and closing the bleeder screws.

Prepare The Vehicle.

Park your favorite car on a level surface.

Employ the parking brake.

Detach the lug nuts on all four wheels.

Place the vehicle on jack stands.

Remove all four wheels.

Install a backward lug nut on each corner, tightening against the rotor surface to limit caliper flex.

Check The Brake Fluid Level (Fill It If Required). 

Open the hood and see the level of brake fluid in the reservoir.

Add brake fluid as necessary to reach the MAX marking.

Ensure the reservoir never runs dry during the bleeding process.

Start Bleeding The Car’s Brakes.

Start at the corner farthest from the driver (right rear) and work towards the closest (left front). The sequence is right rear, left rear, right front, and left front.

Find the bleeder screw at the back of the drum brake wheel cylinder or caliper body.

Set a box-end wrench on top of the bleeder screw, preferably an offset wrench, for better movement.

Attach a clear plastic hose over the bleeder screw nipple, with the other end placed in a disposable bottle.

Position the waste fluid bottle on top of the drum assembly or caliper body.

Have an assistant press/pump the brake pedal 3 times, keep it pumped firmly, and answer with “applied”. They should not let go of the brakes’ pedal until instructed.

Briefly loosen the bleeder screw with a 1/4-turn to allow fluid to flow into the waste line.

Note: When opening the bleeder screw, keep it open for a brief duration of one second or less. You will notice the brake pedal is dropped to the floor as you do this. Tell your assistant not to let go of the brakes as far as instructed to do so.

Gently tighten the bleeder screw to close it, avoiding excessive force.

Call your assistant with “release” to let go of the brakes and ensure they do not release the pedal while the bleeder screw is still in the open state.

Continue the bleeding process until all air bubbles are removed, checking the waste line for air bubbles after each wheel bleeding.

Refill the brake fluid reservoir to the MAX marking after bleeding each wheel, adding fluid as necessary.

Repeat the bleeding procedure for each corner, moving systematically towards the driver (right rear, left rear, right front, left front).

Keep an eye on the brake fluid reservoir, ensuring it remains filled up.

Finish Up Everything; Don’t Forget To Clean.

After bleeding all four corners, spray brake cleaner on the bleeder screw and wipe it dry with a clean rag (avoid spraying directly on rubber and plastic parts).

Check bleeder screws and fittings for any leaks and make necessary corrections.

Properly get rid of the used brake fluid, avoiding refilling the master cylinder reservoir with used fluid.

How Often Do I Need To Bleed My Brakes?

Like many industry experts, I recommend bleeding and replacing brake fluid every 3-5 years. However, the exact time frame can vary as per the manufacturer’s recommendations. 

While some manufacturers suggest having new brake fluid every 20,000 miles, some recommend a bleed when a car reaches 150,000 miles. Consult your vehicle’s manual for the most accurate information.

7 Precautions You Can Take for a Brake Bleed

car-brakes

Ensure the vehicle has cooled down before bleeding the brakes to avoid the risk of burns from hot brake lines and fluid.

Wear latex gloves when handling brake fluid to shield your skin from potentially abrasive/harmful substances.

Prevent contact between brake fluid and brake pads or rotors, as brake fluid’s lubricating properties can reduce brake efficiency.

Keep the work area clean to reduce the risk of accidental contamination.

If you discover a brake line leak, consult an experienced auto repair mechanic for prompt repair to maintain braking performance and safety.

Always use fresh brake fluid and avoid reusing old fluid to prevent impurities from affecting critical brake system components.

Quickly clean up any brake fluid spills to prevent potential damage to your car’s paint, as brake fluid is corrosive.

FAQs

Why Do You Bleed Brakes With The Engine Off?

The engine is turned off during brake bleeding to prevent air from being pulled into the brake lines through the bleeder screws. So, keeping the engine off ensures a more effective and air-free bleeding process.

Do You Bleed Brakes With Cap On Or Off?

I bleed and recommend bleeding the brake fluid while keeping the brake fluid reservoir cap on. This helps maintain proper fluid levels and prevents contaminants from invading the system. 

However, I recommend periodically checking and refilling the reservoir to ensure it doesn’t run dry during the bleeding process.

What Is The Correct Way To Bleed Brakes?

Start at the corner farthest from the driver (usually the right rear) and work towards the closest corner (left front). 

Open the bleeder screw on the brake caliper or wheel cylinder, have an assistant pump the brake pedal several times, hold it down, and then tighten the bleeder screw while the pedal is still held down. 

Repeat this procedure for each wheel until all air bubbles are taken out of the system.

Do You Have To Take Tires Off To Bleed Brakes?

Yes, in most cases, you must remove the tires to access the brake calipers or wheel cylinders where the bleeder screws are located. This permits safer and easier access to perform the bleeding process effectively.