Brake pedal goes to floor after replacing calipers

There are only two things that will cause this after what you replaced. This is air in the lines or you still have a leak either internal to the master cylinder or external.

Here is a guide that will help with this:

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

When putting the master cylinder on, did you bench bleed it? If not, there could be an internal leak causing the fluid to not build pressure.

I would block off all the ports coming out of the master cylinder and press the brake pedal. Does the pedal still go to the floor? If it does then it is the issue. If not, attach one leg of the system at a time until it drops so that we know which one is the issue.

Let me know if you have questions.

Good morning,

If you have ABS, you must do the automated bleed process to get the air out of the unit or you will have little or no pedal.

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

I posted it below for you to view. You will need an advanced scan tool to perform this.

Roy

ABS Automated Bleed Procedure

Notice; When adding fluid to the brake master cylinder reservoir, use only Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.

Important: This procedure may be performed on all vehicles EXCEPT those equipped with option code JL4, Vehicle Stability Enhancement System (VSES).

Important: The base hydraulic brake system must be bled before performing this automated bleeding procedure. If you have not yet performed the base hydraulic brake system bleeding procedure, refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure) in Hydraulic Brakes before proceeding.

1. Install a scan tool to the vehicle.
2. Start the engine and allow the engine to idle.
3. Depress the brake pedal firmly and maintain steady pressure on the pedal.
4. Using the scan tool, begin the automated bleed procedure.
5. Follow the instructions on the scan tool to complete the automated bleed procedure. Release the brake pedal between each test sequence.
6. Turn the ignition "off".
7. Remove the scan tool from the vehicle.
8. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11 GM P/N 12377967 (Canadian P/N 992667) or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.
9. Bleed the hydraulic brake system.
10. With the ignition "off", apply the brakes 3 - 5 times, or until the brake pedal becomes firm, in order to deplete the brake booster power reserve.
11. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
12. If the brake pedal feels spongy, repeat the automated bleeding procedure. If the brake pedal still feels spongy after repeating the automated bleeding procedure inspect the brake system for external leaks.
13. Turn the ignition key "on", with the engine "off"; check to see if the brake system warning lamp remains illuminated.
14. If the brake system warning lamp remains illuminated, do not allow the vehicle to be driven until it is diagnosed and repaired.
15. Drive the vehicle to exceed 13 kph (8 mph) to allow ABS initialization to occur. Observe brake pedal feel.
16. If the brake pedal feels spongy, repeat the automated bleeding procedure until a firm brake pedal is obtained.

Okay, I would get some vice grips and clamp off the brakes hoses and see if you have a pedal. If you do, then the issue is at one of the wheels.

If you do not, then back to master cylinder.

Roy

Okay, still do the test and let me know the results.

Roy

I agree with Roy. You may have a faulty master cylinder out of the box.

The way I test it is remove the hard lines from the master cylinder and find some short bolts (don’t bottom them out on the master cylinder so compare the depth to the fitting on the line) that will thread in the master cylinder. Put some o rings on them (all easily available at ACE) and then press the pedal. This eliminate everything except the master cylinder and if you have a hard pedal then start putting the lines back on one at a time and press the pedal to find out what leg has the issue.

Vice grips work also but I have seen guys not get them tight enough and get fooled so just be mindful of that.

Thanks.

Yes, do not get carried away and collapse the hoses.

Roy