Air is the bane of hydraulic systems. Since it is compressible, it makes them feel spongy and lacks efficient transmission capabilities. That is why bleeding brakes has always been an important part of any brake job.
Your vehicle’s braking system is a typical hydraulic system that uses brake fluid to transmit pressure from the master cylinder to the slave cylinders in different brake calipers.
Any air bubbles in the system, be it in the master cylinder or somewhere in the brake lines, will soak the hydraulic pressure until it is fully compressed. This could be a bit of pressure if it is a few bubbles or all the brake pedal travel if you have a lot of air.
ProTip: Bigger trucks use air brakes. However, the air is already pressurized and compressed to the maximum; hence it doesn’t compress further when you apply brakes. Normal atmospheric pressure in a hydraulic brake system will compress.
Bleeding Brakes Gets Rid of the Air
The brake bleeding process uses gravity and sometimes external pressure to populate every part of the brake system with fluid and flush out any air bubbles.
It involves opening a bleeding nipple and having someone work the brake pedal to circulate the brake fluid by introducing pressure into the system.
During the process, you should expect:
- Some bit of brake fluid accompanied by air bubbles and pockets
- Some portions of no fluid a big air pocket is working its way out of the tubes
- A final clean flow of fluid with no bubbles at all
Why is No Brake Fluid Flowing When I Bleed My Brakes?
A normal bleeding process will have a bubbly brake fluid flow or intermittent flow. Either way, you shouldn’t be bleeding for even five seconds without seeing any fluid flow out of the bleeding nipple.
If this happens, something is wrong, and you have to troubleshoot your braking system further. Some of the reasons that could have you see no fluid at all for a while include:
The Brake System Was Totally Dry (Or is Still Totally Dry)
A totally dry brake system will need some brake pedal working or a few hours for gravity to fill up all the components of the braking system.
However, this shouldn’t concern you if you didn’t do a braking system overhaul. Regardless of how low your brake fluid levels were, there should always be some fluid in the brake lines.
A dry system should only apply to someone who did a brake overhaul that entailed:
- Changing an entire brake caliper and its flex hose. A few seconds of pumping should bring the fluid through
- Changing an entire brake line. It will take a while for the brake fluid to fill the new brake line to the affected wheel. Rear wheels need more time, but it shouldn’t be more than a minute of bleeding.
- Replacing the master cylinder
A good way to avoid stutters after overhauling such parts of the brake system is filling it up and working on something else for around half an hour before coming back to bleed the system.
ProTip: Using incompatible, dirty or blocked parts during an overhaul could block brake fluid flow leaving you with nothing when you try to bleed
The Master Cylinder Takes Longer to Bleed
If you changed the master cylinder or found that it had air, be prepared for thorough bleeding. The master cylinder is big. It will take some time and patience to remove any big air pockets stuck in it.
You can avoid all this trouble by bench bleeding your new master cylinder before installing it. Bench bleeding ensures that the master cylinder is ready to go as soon as you plug it into the system.
It will also allow you to identify a faulty replacement before you put it in your car. This spares you the pain of extra assembly and disassembly.
You Are Using the Wrong Bleeding Procedure
While bleeding brakes is simple, it can be frustrating and futile if you skip even one step. The result is little or no fluid coming from the braking system. The basic process needs two people. One in the driver’s seat and another at the wheel to access the brake caliper.
Before settling on what brake to bleed, consult your user manual to see the correct bleeding procedure. While the traditional approach is starting with the brake caliper furthers from the master cylinder, some vehicles might have a different bleed procedure.
If your car has the master cylinder on the driver’s side under the hood, the traditional bleeding procedure should be:
- The rear brake on the opposite side of the driver
- The rear brake on the driver’s side
- The front brake on the passenger side
- The front break on the driver’s side
Once you have identified the correct bleeding procedure, follow these steps to bleed your brakes.
- The person in the car should pump the brake pedal five to six times and then hold it down to provide pressure to the braking system.
- The person at the wheel should then open the bleeding screw slowly and wait for brake fluid and air bubbles to flow out for up to 10 seconds before tightening it again.
- Repeat the process until the flow is steady with no bubbles or air at all
Most cars will bleed after repeating this three to four times. If you are not getting any fluid after trying this three times, something is wrong.
Is the Brake Pedal too Light?
There should be some finesse and control on your brake pedal even when you are getting a boost from the power brake booster with the engine running.
However, a floppy brake pedal that sinks all the way to the ground without any resistance hints at serious problems in the brake system. It could be issues like:
- No brake fluid in the system
- A disconnected or faulty brake pedal
- A major leak somewhere in the brake system
Find out why the brake pedal drops away so fast before you start worrying about bleeding the brake system.
You could cut it some slack for a few pumps, perhaps three bleeding sessions if you previously overhauled the system, changed the master cylinder or the brake lines, and peg this to a lot of air in the braking system. The problem shouldn’t persist after the third bleeding cycle.
The Brake Lines to the Brake You are Bleeding are Damaged
If you are following the right bleeding procedure and you’ve confirmed there is fluid in the brake reservoir, you could be dealing with blocked or raptured brake line or lines.
A raptured brake line will leak all the fluid to the ground. Go through the entire length of the brake line, looking for leakage.
If you don’t find any leaks, you could still be dealing with a blocked line. A good way to localize the problem is trying to bleed the brakes on the opposite axle. If those brakes work, you will have localized the problem to the specific brake you were working on.
Apart from blockages or raptures on the brake lines, damaged bleeding screws or a bad flex hose can keep brake fluid off your bleed nipple.
The Bleed Screw is Damaged
The bleed screw sits on the highest spot of the brake caliper. This valve lets off some brake fluid when open.
Since it is out in the open, it is constantly washed with dirty water, mud, and salt. This could corrode it shut, making it hard to open it. You won’t get any brake fluid if you don’t open it sufficiently.
Confirm that the screw opens and even consider opening it fully to confirm that it isn’t the problem.
A Blocked Brake Flex Hose
The flex hose is the ‘final mile’ logistics for your brake fluid on its way to the caliper. It is the black hose connecting the rigid metal brake lines to your caliper’s intake. If it is kicked in the wrong way, raptured, blocked, or its inlet and outlet are blocked, you will get no brake fluid on the bleeding screw.
A Damaged Brake Caliper
The final fail point that could keep brake fluid from getting to the bleed screw is a damaged or clogged brake caliper.
The fluid must flow through the caliper before getting to the bleeding nipple. Any blockage or damage that doesn’t let the fluid run freely will give you dry bleeding.
You can confirm if the calipers are fine by unlatching the flexible brake hose from the brake caliper to check if there is the fluid flow when you pump the brakes. If you can get some fluid, consider changing or servicing the caliper.
Bottom Line
Bleeding your brakes properly is not optional. It is mandatory. Don’t quit before you get a steady flow of brake fluid from the bleed nipple with no air bubbles.
If you still can’t get brake fluid even after the above suggestions, consider getting a friend or a mechanic to help you inspect the system again and identify the problem.
After successfully bleeding and closing the bleed screw, remember to pump the brake pedal up to five times to pressurize the system before taking your car for a spin.