When you go to stop sometimes pedal will go to floor

1CHRIS

MEMBER
2005 CHEVROLET EQUINOX
3.4L
V6
4WD
AUTOMATIC
80,000 MILES

Vehicle has good brake pedal but when you go to stop sometimes pedal will go to floor. Has good pedal and then feels like a line blew. No leaks, front are disc, rear brakes are drum. Rear line blew, replaced line, wheel cylinders (both sides) shoes are good shape and bled lines out. Front has new calipers brakes and rotors, bled those too. Seems like the more you use the brakes the spongier it gets. Thanks for any help.

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,128 POSTS

Welcome to 2CarPros.

If the pedal goes to the floor, it sounds like the master cylinder is going bad or is already bad. Fluid can bypass the plungers in the MC allowing the pedal to fade to the floor. This can happen and you never heave a noticeable leak.

Try this. Start the engine and place an average amount of pressure on the brake pedal. Hold it and see if it slowly fades to the floor. If it does, replace the MC.

Take a look through this link:

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

Here is a link that shows in general how one is replaced:

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

Another thought, make sure none of the rubber flex brake hoses are expanding when the pedal is pressed.

If you find it is the master cylinder, here are the directions specific to your vehicle for replacement. The attached pictures correlate with the directions.

Caution: Refer to Brake Fluid Irritant Caution in Service Precautions.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.
1. Disconnect the electrical connector from the brake fluid level sensor.
2. Disconnect the brake pipes from the master cylinder.

3. Important: Install a rubber cap or plug to the exposed brake pipe fitting ends in order to prevent brake fluid loss and contamination.

Plug the open brake pipe ends.
4. Remove master cylinder mounting nuts.
5. Remove the master cylinder from the vehicle.
6. Drain the master cylinder reservoir of all brake fluid.

Installation Procedure

1. Bench bleed the master cylinder.
2. Install the master cylinder to the brake booster.

3. Notice: Refer to Fastener Notice in Service Precautions.

Install the master cylinder mounting nuts.
Tighten the master cylinder mounting nuts to 25 Nm (18 ft. lbs.).

4. Remove the plugs from the brake pipes.
5. Connect the brake pipes to the master cylinder.
Tighten the brake pipe fittings at the master cylinder to 18 Nm (13 ft. lbs.).
6. Connect the electrical connector to the brake fluid level sensor.
7. Bleed the hydraulic brake system.

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

Images (Click to make bigger)