Adding fresh brake fluid to your vehicle’s hydraulic brake system is an essential part of regular maintenance. But once you top up the brake fluid reservoir, should you take the extra step of pumping the brakes? The short answer is yes – here’s why:
Why Pumping the Brakes Is Necessary
Pumping the brakes after a brake fluid top-up helps distribute the new fluid throughout the system and removes any air bubbles that may have been introduced during the filling process.
Here are the key reasons why brake pumping is a critical follow-up step:
- Distributes the new brake fluid through the lines – Brake fluid gets transferred through the brake lines when pressure is applied via the brake pedal. Pumping helps circulate the newly added fluid.
- Removes air bubbles – Air can inadvertently get introduced into the brake lines when topping up fluid. Air compressibility reduces braking power. Pumping the brakes helps purge any air pockets.
- Builds proper hydraulic pressure – The hydraulic pressure generated when you press the brake pedal is what enables your brakes to work. Pumping helps build the correct pressure with the fresh fluid.
- Restores proper brake pedal feel – The brake pedal may feel soft or spongy after a fluid top-up. Pumping until the pedal feels firm restores proper operation.
Overall, pumping the brakes creates vital hydraulic pressure with the new brake fluid, ensuring your brake system functions safely and as designed.
Step-By-Step Process to Pump Brakes
Pumping your vehicle’s brakes after adding fresh brake fluid is straightforward:
1. Start the Engine
Have the vehicle running so that the brake hydraulic system is powered on. Keep your foot off the brake pedal for now.
2. Press and Release the Pedal
Press down on the brake pedal firmly, then let it back up completely. Repeat this pressing and full releasing motion in quick succession.
3. Pump Until the Pedal Firms Up
Continue pumping the pedal around 30 times. As you pump, the pedal should start to firm up as it engages the pistons. Keep pumping until the pedal feels rigid and solid.
4. Press Hard for Several Seconds
After pumping, press down hard on the pedal and hold it there for about 5 seconds. This helps seal the pistons and gets the pads fully against the rotors.
5. Check Pedal Feel
The brake pedal should now feel firm and responsive. Repeat pumping if you still feel any softness or sponginess.
And that’s it! Pumping until the pedal is firm ensures you’ve built proper brake system pressure and purged any air with the fresh fluid.
Why Air in the Lines is a Problem
Whenever you remove part of the hydraulic system, such as when changing brake fluid, air can inadvertently get introduced into the brake lines. Air inside the lines causes major problems for brake performance and safety.
Air is highly compressible, so when you press the brake pedal, the air pockets compress rather than transmitting full hydraulic pressure. This gives a soft, spongy pedal feel and reduces overall braking force.
High temperatures can cause small air bubbles to rapidly expand forming larger air pockets. These air pockets can block the fluid flow in the lines, leading to a dangerous condition known as vapor lock. Vapor lock severely reduces braking power when it is needed most.
Moisture in the air leads to brake fluid gradually absorbing water over time. The water contamination lowers the boiling point of the brake fluid, making it more prone to boiling under hard braking. It also promotes corrosion of the brake system components.
With air trapped in the lines, you’ll never be able to achieve the designed hydraulic braking pressure when pressing the pedal. More pedal travel will be required before the brakes start to engage.
Getting all the air out of the hydraulic system is critical through proper bleeding and pumping the brakes after servicing. Air degradation of braking capability poses a dangerous safety concern for any vehicle.
Signs You Need to Bleed the Brakes
If air was introduced into the brake system, you may experience symptoms that indicate bleeding the brakes is necessary:
- Spongy brake pedal feel
- Excessive brake pedal travel before slowing happens
- Brake pedal nearly reaching the floor before braking engages
- Need to pump the brakes to achieve any braking
- Brake failure or reduced performance
- Brake pedal not firming up even after pumping repeatedly
Bleeding purges air from the hydraulic lines. Bleeding involves draining a small amount of fluid to pull air bubbles out of the system. This may be needed if pumping the brakes fails to firm up the pedal.
How Does a Hydraulic Braking System Work?
Understanding the basics of how your hydraulic brakes work helps explain why pumping the pedal is so critical after servicing the system.
The master cylinder is the core component that converts physical force from your foot on the brake pedal into hydraulic pressure. It builds this pressure in the brake fluid within the closed loop system.
This pressurized brake fluid travels through the lines and hoses to the brake calipers at each wheel. In the caliper, the hydraulic pressure acts on pistons which are pushed out.
The pistons in turn push the brake pads against the rotating brake rotor, creating friction between the pads and rotor. This friction is what actually slows the wheels and stops the vehicle.
The entire hydraulic braking system relies on incompressible brake fluid transmitting pedal force into pressure through the closed loop lines and hoses. Air degrades this hydraulic pressure delivery capability.
That’s why pumping the pedal after brake work properly pressurizes the fresh fluid, purging any problematic air pockets or bubbles from the system.
Bleeding Hydraulic Brakes – Step-by-Step
If pumping the brake pedal fails to make it firm, a full bleed of the hydraulic system may be needed. Here are the steps:
- Brake bleeder tool
- Assistant inside the car
- Brake fluid to top up the reservoir
- Clear tubing to fit bleeder valve
- Container to catch old fluid
- Wrenches to open bleeder screws
- Open bleeder screw on the wheel furthest from the master cylinder
- Have assistant press and hold pedal down
- Loosen bleeder just enough to release fluid & catch in container
- Tighten bleeder, then have assistant release pedal
- Repeat process until only clean fluid releases at bleeder screw
- Move to next closest wheel and repeat process on each wheel
- Refill reservoir with fresh fluid as needed
- Repeat bleeding procedure until pedal is firm
- Discard old fluid properly
Bleeding purges old, air-contaminated fluid and replaces it with fresh, air-free fluid. It restores the closed hydraulic system so proper pressure builds.
Frequently Asked Questions About Pumping Brakes
Should you pump brakes before or after bleeding?
Always try pumping the brakes first to attempt to build pressure in the system. Bleed the system only if pumping fails to firm up the pedal.
How many times should you pump brakes after adding fluid?
Pump the brakes up to 30 times after adding fluid until the pedal firms up. Then hold the pedal down for about 5 seconds.
How do you get air bubbles out of brake lines?
Pumping the pedal vigorously can help purge air bubbles and pockets from the hydraulic lines in many cases. If pumping doesn’t work, then a complete brake system bleed is required.
Can you drive after adding brake fluid without pumping?
You should never drive a vehicle after adding brake fluid until you successfully pump the brakes to build hydraulic pressure. Air in the lines is dangerous.
Does pumping brakes push air into the lines?
No, pumping does the opposite – it builds pressure that purges air pockets from the lines and wheel cylinders. It’s vital after any brake service.
While it may seem like an optional extra step, pumping the brakes after adding fresh brake fluid is critical. By pumping until the pedal firms up, you remove air introduced during the fluid top-up process.
Pumping circulates the new fluid through the hydraulic system, builds proper brake line pressure, and ensures your brakes will function as designed. Don’t skip this simple bu