I can feel the brake pedal fade

Hi,

Replacing a brake master cylinder takes a little time, but really isn't too hard to do. I recommend getting a lifetime replacement part so you never have to pay for a new one in the future.

First, here is a link that shows in general how it is done. Here are the master cylinder installation instruction you have requested. Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://youtu.be/WDxvEQrMkBg

and

https://youtu.be/w7gUsj2us0U

and

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

Here are the directions specific to your vehicle. The pics attached below correlate with the directions.

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With a new master cylinder, it is necessary to bleed it before use. I will start with those directions first.

2006 Mitsubishi Eclipse L4-2.4L (4G69)
Basic Brake System
Vehicle Brakes and Traction Control Hydraulic System Brake Master Cylinder Service and Repair Procedures Master Cylinder Bleeding Basic Brake System
BASIC BRAKE SYSTEM
BLEEDING

CAUTION: Use only brake fluid DOT 3 or DOT 4. Never mix the specified brake fluid with other fluid as it will influence the braking performance significantly.

MASTER CYLINDER BLEEDING
The master cylinder used has no check valve, so if bleeding is carried out by the following procedure, bleeding of air from the brake pipeline will become easier. (When brake fluid is not contained in the master cylinder).
1. Fill the reserve tank with brake fluid.
2. Keep the brake pedal depressed.

pic 1

3. Have another person cover the master cylinder outlet with a finger.
4. With the outlet still closed, release the brake pedal.
5. Repeat steps 2 - 4 three or four times to fill the inside of the master cylinder with brake fluid.

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Removal and Replacement

2006 Mitsubishi Eclipse L4-2.4L (4G69)
Basic Brake System
Vehicle Brakes and Traction Control Hydraulic System Brake Master Cylinder Service and Repair Procedures Removal and Installation Basic Brake System
BASIC BRAKE SYSTEM
MASTER CYLINDER ASSEMBLY AND BRAKE BOOSTER

REMOVAL AND INSTALLATION

Pre-removal & Post-installation Operation

pic 2

Removal Steps 1-12

pic 3

Removal Steps 1-17 & Required Special Tool

pic 4

INSTALLATION SERVICE POINTS
>>AB

You need a new master cylider beause it is bad.

Master cylinders can fail after replacing the brakes pads because they would be subjected to further than normal travel during priming up the calipers pistons and this can damage the internal seals.