Brake pedal travels little less than halfway before it seems like it engages?

Hey Aoneal10515,

Has the brake pedal only been like this since you replaced the master cylinder?

Or did you replace the master cylinder because of this fault and it did not make any improvement?

Are you sure the car does not have ABS? From what i can see from the year model you should have ABS. There is a specific bleed procedure to carry out when replacing parts on these systems.

There is a TSB applicable for your vehicle that i have attached below.

Your vehicle may be affected by this and may require a replacement brake pressure modulator valve.I would suspect there is air in the lines. These guides can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down these guides and report back.

I would advise if you go to a Chevrolet dealer and ask them if this TSB is applicable. They can then identify what you may need and quote you on the work.

You can then decide whether or not to have them do the work, get quotes elsewhere or do the work yourself.

Hope that helps. Let us know how you get on.

Check out the diagrams (Below). Please let us know what happens.

Hey Aoneal10515,

Can you please get the TSB check done from my previous message with the brake pressure modulator valve and let me know if that helps.

It looks like this is a known issue that a dealer will be able to carry out for you relatively cheaply and will hopefully fix the issue.

Regards, Joe

Hey Aoneal10515,

Did you have any parts replaced before this issue started happening?

Like you said if the issue did not use do be there can you trace any brake repairs before this fault started?

Some bad brake linings could cause problems, aftermarket brake pads/shoes are a cause of many issues.

If it seems to get worse the more you use the brakes then I would say it is potentially to do with the fluid or will be an issue at one/more of the wheels where the brakes get hot.

You have carried out a full brake fluid flush? Old fluid can hold moisture and cause a spongy pedal that gets worse as the moisture boils.

You have drum brakes on the rear of this vehicle?

Regards, Joe

According to your vehicle specs you do have ABS. If you have a brake pedal position sensor then definitely you have ABS. Here is what is listed for your brake system unless you want to provide a VIN number to cross reference. Here is what your braking system has.

Collision

Search vehicle information
46
2009 Chevrolet Cobalt L4-2.2L
Components
Vehicle Brakes and Traction Control Antilock Brakes / Traction Control Systems Description and Operation Components
COMPONENTS
ABS Description and Operation

This vehicle is equipped with the MK 25 E Continental Teves antilock braking system.

The vehicle is equipped with the following braking systems:

* Antilock Brake System (ABS)
* Engine Drag Control (EDC)
* Electronic Brake Distribution (EBC)
* Hydraulic Brake Booster
* Traction Control System (TCS)
* Vehicle Stability Enhancement System (VSES) (w/JL4)

The following components are involved in the operation of the above systems:

* Electronic Brake Control Module (EBCM)-The EBCM controls the system functions and detects failures.
The EBCM contains the following components:
* Brake Pressure Modulator Valve (BPMV)-The BPMV contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The BPMV uses a 4 circuit configuration with a diagonal split. The BPMV directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.
Important: There is a rubber isolator located under the BPMV and on the mounting studs. The rubber isolators protect the BPMV and the EBCM from vehicle vibrations.

The BPMV contains the following components:

- Pump Motor
- Inlet Valves (one per wheel)
- Outlet Valves (one per wheel)
- Master Cylinder Isolation Valves (one per drive wheel)

* The wheel speed sensor receives a 12-volt power supply voltage from the electronic brake control module (EBCM) and provides an output signal to the EBCM. As the wheel spins, the wheel speed sensor sends the EBCM a DC square wave signal. The EBCM uses the frequency of the square wave signal to calculate the wheel speed.
* Traction Control Switch-The TCS is manually disabled or enabled using the traction control switch.
* Brake Pedal Position-The EBCM uses the BPP sensor as an indication that the brake pedal is applied.
* Lateral Accelerometer Sensor (w/JL4)-The EBCM uses the lateral accelerometer sensor as an indication of the lateral acceleration of the vehicle.
* Yaw Rate Sensor (w/JL4)-The EBCM uses the yaw rate sensor as an indication of the yaw rate of the vehicle.
* Steering Wheel Position Sensor (SWPS) (w/JL4)-The EBCM uses the SWPS as an indication of the position and rotation of the steering wheel.

I have seen where after a pad replacement the actuator go bad. You may want to try a bleed but you would need an advance scan tool to bleed the ABS unit. And again, if you do not think you have ABS, we need the VIN number to cross reference and see why you do not have ABS?

I would like to see a video of that master cylinder move erratically when you press the brake pedal.

If I can jump in here, it looks like the rear shoes are worn out causing the low pedal. here is a video of the job being done on a similar car which shows how to adjust the new shoes once you have replaced them:

https://youtu.be/1j7qDoi1LP0

Please run down this guide and report back.

Lets use three sets of vise grips and gently close off the rubber flex hoses. this should tell us if the problem is at the master or the wheels. Did you bench bleed the master if not this will be the problem? here is a guided that tells you how to bleed it correctly:

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

Please run down this guide and report back.

Sounds good.

Good to hear you got it fixed. I would check the adjustment of the brake rod going into the brake booster check that for play.