Brake bleeding is one of those jobs that fill most DIYers with dread; bleeding the brakes needn’t; with a little preparation, the right tools, and know-how, you’ll be bleeding like a pro.
To bleed car brakes, begin by filling the brake fluid reservoir, then starting at the wheel furthest from the reservoir, fit the bleed kit, open the bleed valve, pump the brakes three times to purge the air, and tighten the valve. Top up the fluid level and repeat on the remaining wheels finishing with the wheel closest to the reservoir.
In this post, you’ll learn the correct brake bleed sequence, how to set up the bleed kit and how to bleed the brakes.
Tools to Bleed Brakes
There are many different brake bleed tool options out there; there’s a semi-pro type that uses a compressor to pressurize the brake system via the brake fluid reservoir, and there’s a hand-operated vacuum pump that sucks the fluid via each brake valve but the one I recommend is the humble brake hose and bottle.
I say humble because you can easily make one yourself. In fact, I did exactly that and wrote a post about it, and you can see how I did that right here.
The tools and supplies you’ll need include:
- Lug nut wrench
- Axle stand
- Box/Ring wrenches (usually 8 or 9 mm)
- New brake fluid
- Brake bleed kit
- Paper towel
- Wire brush
- Some grease or vaseline
- Torque wrench
Brake Bleed Sequence
Most hydraulic brake systems prefer bleeding in a particular sequence. That sequence isn’t hugely important unless your brake fluid system has run dry, and if that’s the case, you’ll likely need a scan tool to help bleed the ABS modulator.
Anyhow, typically, brakes are bled in pairs as brake circuits are paired from the ABS unit.
Diagonal is the more common set up meaning the front right (FR) brake is paired with the rear left (RL) and the front left (FL) is paired with the rear right (RR).
But some vehicles may pair both front brakes on one circuit and both rear brakes on another circuit.
You can easily identify how your brakes are paired by checking the ABS modulator body, the pairing is stamped into the body..see the illustration.
Pre Brake Bleed Tips
It makes sense to cover what can go wrong when brake bleeding so we can avoid them, and that’s what this section is about.
The process of bleeding the brakes is not difficult, but things can and do go wrong, and if they do, you should know you won’t be able to drive your car. As soon as brake valves are open, they allow air into the system, and the brakes are compromised.
You may be bleeding the brakes because they are compromised anyway, or you may be bleeding to replace the brake fluid.
OK, so what can go wrong when bleeding brakes?
Common problems when bleeding brakes include the following:
- Allowing the reservoir to run dry while bleeding – To avoid this top-up reservoir after each wheel is bled
- Using the wrong type of brake fluid – brake fluid is categorized by DOT, and while DOT3, 4, and 5.1 shouldn’t be mixed, they may if you are in a pinch. However, DOT5 must not be mixed with any other type of brake fluid
- Using old brake fluid – always use new foil-sealed brake fluid; even brake fluid with a lid on attracts moisture
- Stripping old bleed valve – clean the valve with a wire brush and ensure you are using the correct size wrench
- Breaking off the bleed valve – if the valve looks old and crusty, know there’s a chance it could break. Having a spare makes sense before you begin the mission
Brake fluid compatibility chart
In this guide, I’ll use a humble homemade brake bleed kit (clear bottle with clear hose). You can check out how to make a homemade bleeder here.
Prepare the bleed kit as follows:
- Ensure the bottle is clean and dry
- 1/4 fill with fresh brake fluid
- Ensure the clear hose is submerged below the surface of the fluid but off the bottom of the bottle
The bottle will need to be emptied after each brake is bled, so a waste container will be needed for the waste fluid.
The brake bleed process is as follows:
While this process may be nailed successfully solo, a helper to pump the brakes makes the job move like butter.
- Pop the hood and fill the brake reservoir with the specified DOT fluid marked on the reservoir cap and refit the cap
- Remove the rear left wheel (RL), I start at the RL because I like to finish with the wheel closest to the reservoir (FL). (always use an axle stand or similar to support the vehicle)
- Remove bleed valve rubber dust cap
- Clean the bleed valve with a wire brush and spray threads with WD40
- Add a smear of grease on the threads of the valve (helps seal threads)
- Fit the Box/Ring wrench
- Fit the bleeder kit hose to the valve
- Open the bleeder valve
- Have a helper (or you) pump the brakes three times fully to the floor
Air in the system may be seen as bubbles in the clear hose; repeat this process so long as air bubbles are present but top up fluid between each cycle of three brake pumps
- Tighten the valve before removing the hose
- Clean the valve with brake cleaner and refit the dust cap
- Refit wheel and torque to spec (100lb-ft (135Nm) in a star sequence
- Move to the paired wheel, typically the front right (FR), and repeat after first refilling the brake fluid reservoir
- Repeat on the right rear (RR) after first refilling the brake fluid reservoir
- Finally, repeat on the driver’s wheel (FL) and top up brake fluid to the full mark
With the bleed complete, the pedal should be firm. Now go around each wheel and, using a light visually check each bleed valve is dry.
No need to remove the wheel to inspect, you’ll see enough through the wheel spokes. If you find a weep, dry it and reinspect after pressing the brakes a few times.
If your pedal does not hold pressure and is sinking to the floor, you have a leak. Go back and check all brake valves.
Last job, check your brake fluid reservoir and fill it to the max mark. if overfull remove the excess.
Other common causes of a soft brake pedal generally are:
- Faulty master cylinder – leaking master cylinder chamber
- Contaminated fluid – water, air, old fluid
- Corroded hard brake lines – rusted-out steel brake lines typically under areas of trapped chassis muck
- Faulty flexi brake hose – an inner wall of the twin wall hose ruptures and bulges the outer wall under braking pressure
That’s it brake bleed is complete. Great Job!
You may find the following posts helpful:
- Brake resources page
- About the Author
- Latest Posts
John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.