Good morning,
This sounds like air in the system and needs to be addressed immediately. The pedal should not be soft. It should be high and hard and able to stop the truck safely.
https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system
Yes, it could be the master cylinder but I would have another shop check it. For a shop to tell yo you a soft pedal is acceptable, that is wrong on so many levels.
https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder
I also attached below the procedure for bleeding the ABS unit. If air gets in there, it will give you a soft pedal.
Roy
Removal and Installation
WARNING: Use of any other than approved DOT 3 motor vehicle brake fluid will cause permanent damage to brake components and will render the brakes inoperative. Failure to follow these instructions may result in personal injury.
WARNING: Carefully read cautionary information on product label. For EMERGENCY MEDICAL INFORMATION seek medical advice. In the USA or Canada on Ford/Motorcraft products call: 1-800-959-3673. For additional information, consult the product Material Safety Data Sheet (MSDS) if available. Failure to follow these instructions may result in personal injury.
CAUTION: Brake fluid is harmful to painted and plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it with water.
1. Disconnect the battery.
2. Using a suitable suction device, drain the brake fluid reservoir.
3. Disconnect the brake fluid level switch electrical connector.
4. NOTE: Cap the brake tubes and plug the master cylinder ports.
Disconnect the 2 brake tubes from the master cylinder.
To install, tighten to 17 Nm (13 ft. lbs.).
5. Remove the 2 master cylinder nuts.
To install, tighten to 25 Nm (18 ft. lbs.).
6. To install, reverse the removal procedure.
Bleed the brake system.
Anti-Lock Brake System (ABS) Hydraulic Control Unit Bleeding
NOTE: This procedure is only required when a new hydraulic control unit (HCU) is installed.
NOTE: When any part of the hydraulic system has been disconnected for repair or new installation, air may get into the system and cause spongy brake pedal action. This requires bleeding of the hydraulic system after it has been correctly connected. The hydraulic system can be gravity bled, manually bled or bled with pressure bleeding equipment.
1. Connect the scan tool and follow the ABS system bleed instructions.
2. Use the gravity bleed or manual bleed procedure(s) to bleed the system. Begin at the RH rear caliper.
Images (Click to make bigger)
SPONSORED LINKS
Tuesday, April 6th, 2021 AT 12:21 PM