my brake master is bad

Hello,

It sounds like you could have some air in the hydraulic system. I would suggest that you first try and bleed the hydraulic system as air in the lines or master cylinder can make the brake pedal feel very spongy, giving the impression of a failed master cylinder.

Below is a detailed instruction how to bleed brakes.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

If this procedure is not successful and you still would like to replace the brake master cylinder then proceed as follows:

Drain brake fluid reservoir using a syringe or other suitable tool.
Disconnect the low brake fluid warning connector.
Remove the reservoir from the master cylinder.
Loosen the brake fluid pipes at the master cylinder.
Loosen the 2 nuts holding the master cylinder to the brake booster.
Assemble in reverse.
Ensure that the rubber seal between the master cylinder and the brake booster is installed properly.

Careful to tighten the securing nuts for the master cylinder.
Brake Master Cylinder Self-Locking Nut 25 Nm (18 ft lb).

Below is a guide how to replace the brake master cylinder.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Once the master cylinder has been replaced and the brake pipes and reservoir
have been refitted, fill the reservoir with fresh brake fluid and bleed the brakes as described above.

Let us know how you get along.

Cheers, Boris