Brake Master Cylinder Rear Gasket Failed - Leaks Fluid Into Booster
 

Howdy folks,

The backstory: I have a 2012 F-150 SuperCrew 5.0L 2wd with about 128k miles, and one morning I started the truck and found the brake pedal went to the floor. Checked the brake fluid reservoir - empty. Checked thoroughly for leaks at every corner and under the hood - no leaks, drips, puddles, nothing. Did some reading and I have concluded that the seal between the master cylinder and booster has failed, and vacuum has sucked all the brake fluid into the booster. I do not think any brake fluid made its way into the vacuum line, as there was no white smoke and the engine was idling normally. Also, the truck was manufactured before the dates covered by the 20S31 and 16S24 recalls, and I do not have an EcoBoost.

Of course, ideally I replace the master cylinder and the booster, but I am considering replacing the seal (costs $15) and the booster (costs $170), and leaving the existing master cylinder (costs $180).

My question: Has anyone had this problem and only replaced the faulty seal (part number 7L1Z2152A)? What was your experience? Do I really need to replace the entire master cylinder?

The Motorcraft master cylinder is $130 from RockAuto.

If you replace the seal, put everything back together, and find that it didn't fix your issue, how annoyed will you be redoing the job? If you have the space and time, save the money. If you want to only do it once without a chance of having to redo it, get a new MC.

You're absolutely right, and I ended up purchasing both the booster and MC. No reason to risk a brake failure to save just $130.