Whenever the hydraulic part of a braking system is invaded, air will be introduced and it will have to be bled out. Though at first the task seems simple, there are some basic mistakes that end up creating other issues.
It is not commonly recognized that even though a hydraulic brake system is considered closed, the fluid in the system, over time and thermal cycles, will absorb moisture, even if it was never open to atmosphere. This happens slowly, but the effects are the same. The formation of corrosion and acids will attack all of the brake parts, ending in a system failure. Every hydraulic brake system should be bled and refilled with fresh fluid to remove moisture.
A simple method to accomplish this without bleeding is to suck most of the fluid out of the master cylinder with a pump or kitchen meat basting utensil. Make sure you don’t expose the circuit to air when taking the fluid out. Then refill with fresh fluid. The only caveat to this procedure is that you will need to do it a number of times over the course of a few months to exchange all of the brake fluid. The task is so easy that it can be performed when you do another service, such as an engine oil change. After two or three times, most – if not all – of the fluid will end up being exchanged.
A brake system can also be bled a number of different ways by using the master cylinder (pumping), introducing a vacuum, through gravity, or with pressure (pressurized brake fluid). The most common way is to have a helper pump the brake pedal (thus using the master cylinder) to evacuate the air.
A vacuum pump, either handheld or otherwise, will suck fluid through the lines and components, pulling out air and creating a solid fluid mass.
A power bleeder connects to the master cylinder and feeds fresh fluid into the system, pushing out the air and old fluid.
The best method (though impractical for a farm shop) is the power bleeder. It is an expensive tool, requires many adapters for the different master cylinders, and is awkward to use.
A vacuum bleeder is the most practical approach since it is inexpensive, simple to use, and doesn’t require two people.
Pumping the brake pedal is effective, but it requires two people and also has the most chance of damaging the system.
The chemistry of brake fluid makes it very susceptible to wicking in moisture. Buy small cans of fluid, mark them with the date they are first opened, and seal the cap with electrical tape. Buying a big can of fluid is only a buy if you use it quickly. Fluid on a shelf for more than a year or with the lid not closed tightly should not be used. When moisture is introduced, it lowers the fluid’s boiling point and causes corrosion and pitting in the brake system, which leads to failure.
When using the brake pedal to bleed the system, place either a piece of wood or your other foot under the pedal to limit pedal travel. When the bleeder is opened, the pedal will sink. This allows the piston in the master cylinder to travel past the bore, injuring the plunger cup when it goes back in. Shortly afterward, the master cylinder fails due to the torn piston plunger cup.
Not cleaning the master cylinder cover or bleeder screws before opening introduces dirt into the fluid, which acts as an abrasive and destroys the seals in the master cylinder, wheel cylinders, and calipers.
When bleeding, begin with the wheel farthest from the master cylinder and work your way to the closest wheel.
Finally, always keep the master cylinder full and the lid tight while bleeding. If it runs dry, your efforts are all in vain.
FAQs
Can I change my brake fluid myself? ›
Simple to do, but dirty and time consuming
Changing your brake fluid yourself is not particularly difficult. It is, however, a fairly messy and time-consuming job. The tools to do the job can be costly, even if the fluid itself is relatively cheap.
A good rule to follow is to have your mechanic check your brakes and brake fluid during every oil change. They'll be able to give you the best feedback on how your brakes are working and if they need new fluid. Most drivers find they need to change their brake fluid every four to five years.
What to do after changing brake fluid? ›YES. You HAVE TO pump the brakes to push the fluid back through the system when you have finished. What you are doing is priming the brakes to be ready to stop the car by allowing them to pressurize. You should pump the brakes about 30 times to prime them properly.
How much does it cost to get brake fluid exchange? ›In general brake fluid ranges in price from $6 to $39 per quart, mechanics charge $150-$210 per hour, and changing the brake fluid in most vehicles will cost you an average of $100.
Can I mix old and new brake fluid? ›Unless the existing brake fluid within the system is contaminated (dirt, water etc.) you can probably safely add fluid to the old. Just ensure that the new fluid that you add is the same as what is in the system.
How long should brake fluid last you? ›Brake fluid absorbs moisture, which reduces its performance. For that reason, it's best practice to change brake fluid every two years. However, brake fluid is one of the maintenance items that drivers miss most often. People rarely change their brake fluid before it goes bad.
Can I just add brake fluid without bleeding? ›Can You Add Brake Fluid Without Bleeding? Bleeding is not a mandatory part of this process, so yes, you can do it without it. Just inspecting the amount of liquid doesn't require bleeding.
How do you bleed brakes after changing fluids? ›Release the bleed nipple at the back of each brake calliper/wheel cylinder to drain the old brake fluid. Go to each caliper/wheel cylinder in turn and open the bleed nipple to complete the brake fluid change draining out the last of the old fluid and any air bubbles until the new fluid comes through.
Do I need to flush brake fluid after changing pads? ›Answer: Yes, flushing or changing the brake fluid is legitimate preventive maintenance for your car. We typically recommend a brake fluid flush when we're already changing brake calipers, pads or rotors.
Why would I need a brake fluid exchange? ›Why you should get a brake fluid exchange. Regular brake fluid exchanges prolongs the life of anti-lock braking systems (ABS), which prevents the brakes from locking up during emergencies, allowing you to maintain steering control. This maintenance option also ensures that your brake pedal is firm.
Does AutoZone do brake fluid? ›
AutoZone stocks the best in fluids for both home repairs and professional shops, so you know you're getting a quality product. Choose from a wide variety of brake fluids both online and in-store.
Is a brake fluid exchange the same as a flush? ›Although they're sometimes treated as different procedures, a brake flush is the same as a fluid exchange. This process involves removing the old fluid and replacing it with new fluid.
What problems can old brake fluid cause? ›What Happens to Brake Fluid over Time? Like oil, brake fluid loses its effectiveness over time. The fluid can absorb moisture, which can lead to corrosion in your hydraulics system and other problems that make your brakes less effective, decreasing your ability to stop in critical driving situations.
Is it OK to mix DOT 3 and dot4 brake fluid? ›Yes. DOT 3 brake fluid is compatible with DOT 4 brake fluid.
Is it OK to use different brake fluid? ›Match the brake fluid you need with the fluid type mentioned on the brake fluid reservoir cap. Always use a new, unopened container of brake fluid to fill the reservoir. Note: Modern cars primarily use either DOT 3 or DOT 4 fluid and the two should never be mixed in applications.
Does changing brake fluid improve braking? ›Changing the brake fluid will improve braking providing there are no underlying issues with your braking system. Aging brake fluid will become contaminated with water and metal particles from the parts that make up the braking system, changing the fluid will prevent corrosion and the components eventually failing.
How do you know if you need a brake fluid flush? ›- The brake fluid is dark and discolored.
- The brake pedal feels spongy.
- Your vehicle is hard to stop.
- The brake fluid is low.
- The check engine light comes on.
All you have to do is fill up the master cylinder reservoir with fresh fluid. Then starting at the wheel farthest from it (typically the right rear), loosen the bleed screw on that brake caliper/cylinder. Go inside and play on your phone for at least an hour. Close the bleed screw and top up the master cylinder.
Why is my brake pedal soft after bleeding? ›Air in the brake line(s) is the most common cause of a soft/spongy brake pedal. If air gets into the brake lines, it can prevent brake fluid from flowing properly, causing the brake pedal to feel spongy or soft. If the brakes are soft or spongy, this is a good time to change or flush the brake fluid.
Why does my brake pedal go to the floor after bleeding? ›A worn or malfunctioning master cylinder. If the master cylinder isn't performing as designed, it may need to be replaced. Defective replacement cylinder. If, after the master cylinder has been replaced and the system has been bled, and still your brake pedal goes to the floor, the new master cylinder may be defective.
Does dirty brake fluid affect braking? ›
If your brake fluid has become dirty or contaminated, it can change how your brake system operates — brake pedal feel can be affected, as can heat dissipation in repeated stops.
Should I change brake fluid before or after pads? ›Don't bother topping off that brake fluid reservoir until after you've monkeyed those new pads into place. The new and thicker pads will displace some of that fluid back into the system's lines and reservoir.
What does a brake fluid exchange consist of? ›Brake fluid service involves the testing and exchange of the liquid contained within the closed hydraulic brake system on a vehicle. The basic purpose of brake fluid is to transfer the movement of the brake pedal through various components or systems to actuate the brake pads at the wheels hence stopping the vehicle.
How much does a brake flush cost at Jiffy Lube? ›This includes internal corrosion on rust on your brake lines, brake calipers, and other brake parts that can cost several hundred dollars to replace. Thankfully, you can simply replace brake fluid and likely avoid these issues. And replacing brake fluid (also called a “brake fluid flush”) usually costs $100 or less.
What does low brake fluid feel like? ›If you are low on your brake fluid, you may notice one or more of the following signs: Brake warning light illuminated on your dash. Brake fluid appears low, discolored, or dirty. Brake pedal feels spongy or mushy.
Does Walmart change brake fluid? ›No. Walmart Auto Care Center does not perform any brake-related services.
How much is a brake fluid change vs flush? ›The average car will use about a quart of brake fluid to flush the system, so the cost will be between $10 and $20 for the brake fluid. If you decide to take your car to the mechanic instead, the labor can range from about $50 to $100 in addition to the fluid.
What happens if you don't do a brake fluid exchange? ›When you don't change your brake fluid, your car's braking capabilities suffer greatly for it, leading to poor braking performance. In most cases, you can tell simply by pressing the brake pedal: if it feels incredibly spongy, then there's a good chance your brake fluid has nearly given up.
How often should you do brake fluid exchange? ›On average, you will need a brake fluid flush every 2 years or 30,000 miles. Routine maintenance also heavily depends on your driving patterns. For example, if you tend to drive shorter routes with frequent braking, you may need more frequent brake fluid flushes.
How often does a car need a brake fluid change? ›Over time, your car's brake fluid absorbs water content which can lead to brake failure. Vehicle manufacturers recommend that you change your brake fluid every two years so that your brakes work to their optimum performance.
Why change brake fluid every 3 years? ›
What Happens to Brake Fluid over Time? Like oil, brake fluid loses its effectiveness over time. The fluid can absorb moisture, which can lead to corrosion in your hydraulics system and other problems that make your brakes less effective, decreasing your ability to stop in critical driving situations.
What color should brake fluid be? ›So, what does brake fluid look like? It's typically light yellow in color, but will brown as it ages. Now that you know what color brake fluid is, if you see it under your car around your wheel wells, you have a leak.