Thread: How do you bleed the master cylinder?

Tech 2 scanner from what I've heard.

Only a tech 2 can open all the valves in the master cylinder from what i've been lead to believe.

Or was that the ABS.... I think its the ABS now.

97 Pontiac Grand Prix GT
I removed the master cylinder / Delphi ABS VI assembly from the car in an attempt to replace the master cylinder. Upon inspection I decided not to replace the master cylinder, cleaned and reinstalled the master cylinder / Delphi ABS VI assembly and successfully bled the system without the use of a scanner. The brakes work perfectly.

On Bosch 5.3 ABS modules (like the one on my '98 GTP), you don't need to cycle the cylinders either. They have internal reservoirs that are only opened with then ABS is activated. As such, if you expose the ABS module to air (by replacing the Master Cylinder), as long as you don't activate the ABS (by slamming on the brakes and slipping the wheels or toggle them with a scanner) you can bleed per normal.

As far as bleeding the master cylinder, you need to bench bleed it. Instructions are all over the place including here. After you've bench bled it, put it back in the hydraulic circuit and bleed at each caliper going from the furthert away from the Master Cylinder to the closest.

You don't need a scanner for any brake service related to bleeding with a Bosch ABS system. Some Delphi systems can use a scanner to home the internal valves, but this can also be accomplished without a scanner.

I've done lots of brake work and I've found this to be a VERY handy tool.