How to bleed brakes: one person, two people, and the order on a car with ABS

When a brake hose or pipe is replaced, the circuit is opened and air gets in. It is bled out at each wheel’s bleed screw until the fluid runs free of bubbles: with a helper on the pedal, or alone with a one-way valve hose, vacuum pump or pressure bleeder. The wheel order comes from the vehicle’s service information, and some cars with ABS also need a scan tool routine.

How does air get into a brake circuit?

Air gets in when the circuit is opened or the reservoir runs empty. The brake systems course module from Turkey’s Ministry of National Education (MEB) names both: after any repair, or when the fluid in the reservoir runs out.

A hose change should let in as little air as possible. FCA’s instruction for replacing brake hoses on the 2018 RAM 4500/5500 chassis cab (recall U41) props the pedal down first, which isolates the master cylinder and stops the reservoir draining while the lines are open: “This will allow you to bleed out the area of repair instead of the entire system.”

MOTOR Magazine warns against pinching a brake hose shut with pliers, which can damage its structure. When a hose is due for replacement is covered in the brake hose article.

How do you bleed brakes with two people?

One person works the pedal, the other the bleed screw. These are the steps in FCA’s service instruction for the 2018 Dodge Journey, the 2018–2019 Dodge Caravan and Jeep Compass, and the 2019 Jeep Cherokee (recall U86):

1. Reservoir. Clean the cap, open it and top up to the MAX mark.
2. Hose. Run a clear hose from the bleed screw into a jar, its end under fresh fluid.
3. Pedal. The helper pumps the pedal three or four times and holds it down.
4. Bleed screw. Open it at least one full turn and close it once the pedal has dropped. Only then is the pedal released.
5. Repeat. Until no more air comes out, usually four or five times. Keep the reservoir from running dry.

Timing is where it goes wrong. The MEB module asks the two people to confirm every stroke to each other, and gives the rule for the master cylinder outlet union:

“The union must be tightened before the foot is lifted from the brake pedal. Otherwise air enters the system again.”

Ministry of National Education (Turkey), Brake Systems course module, 2013

One objection comes from Gunson, which sells a pressure bleeder: with repeated pumping, “the piston inside the master cylinder can travel past the slight lip on the bore that has formed with normal usage, possibly damaging the seal.” FCA still uses the pedal on these vehicles, but recommends pressure bleeding where the equipment is available.

How do you bleed brakes by yourself?

MOTOR Magazine’s Brake Shop column describes three one-person methods.

• One-way valve hose. A one-way valve in the bleed hose lets the screw stay open while one technician pumps the pedal, stopping only to top up the reservoir. MOTOR mentions temporary Teflon tape on the screw threads without saying why; our reading is that it keeps air from being drawn in past the threads as the pedal returns.
• Vacuum pump. A hand, shop-air or electric pump draws the fluid out through the bleed screw. The mistake is to forget the reservoir: the pump “can very quickly suck the system dry”, which puts air straight back in.
• Pressure bleeder. An adapter cap seals the reservoir, the reservoir is pressurised and the bleed screws are opened in turn. The drawback is finding an adapter that fits.

Gunson’s sheet, for a bleeder fed from the spare tyre, limits the pressure to 20 psi, or 10 psi for older systems. The kit is first connected without fluid and checked for air leaks at the reservoir cap.

Which wheel do you start with?

There is no single correct order: the four documents we opened do not agree.

The FCA rows apply only to the model years each instruction names.

So “start at the wheel furthest from the master cylinder” is not enough on its own. Even Gunson qualifies it: “as in the sequence usually found in the handbook”. The order for a given vehicle is read from its service information.

What changes on a car with ABS?

On a car with ABS the job may not end at the wheels. FCA’s RAM instruction says so in a note (HCU: hydraulic control unit):

“ABS system bleeding requires conventional bleeding methods plus use of a scan tool. The procedure involves performing a base brake bleeding, followed by use of the scan tool to cycle and bleed the HCU pump and solenoids.”

FCA US, service instructions for recall U41 (NHTSA 18V-277), June 2018

The wheels are then bled a second time, “to remove any air released by the ABS”, as the passenger-car instruction (U86) puts it. That instruction follows the same three stages and first asks for a fully charged battery and cleared fault codes.

MOTOR notes that the pedal method, with or without a helper, does not reach fluid trapped inside ABS components. Whether another car needs the scan tool is for its own service information to say.

Which brake fluid goes in?

The grade named in the vehicle’s handbook. Both FCA instructions call for DOT 3, and Gunson warns that fluid with a lower DOT rating than the handbook’s “could boil”. Brake fluid takes up moisture, and according to the MEB module moisture lowers its boiling point.

FCA says the same of the container: “An open container will absorb moisture from the air and contaminate the fluid.” Fill from a freshly opened container, and never return fluid that has come out of a bleed screw.

What do you check when the job is finished?

1. Bleed screws. Close them and refit the dust caps. MOTOR warns that a bleed screw is hollow and may break off if overtightened.
2. Reservoir. Top up to the mark.
3. Pedal. Before the vehicle moves, it should be “firm and not mushy”. If travel is excessive or the pedal feels spongy, FCA says, air may still be trapped; bleed again.
4. Leaks. Check every joint that was opened. Sealing washers should have been renewed; banjo bolt washers have their own article.
5. Road test. Confirm the brakes and the pedal feel on the road.