Hey everyone, new to the Forum.

I have a 2017 F150 XLT that I bought new in October 2017. Recently the brake pedal has been slowly creeping toward the floor as I sit at a stoplight. It's not fast I have to sit at a light for several minutes. When I release the pedal and reapply it always comes back and does so quickly. I've had a master cylinder go bad on previous vehicles with the same symptoms but never at 36800 miles.

I've checked the reservoir and it is full. There are no leaks detected by a visual inspection anywhere. Brake fluid tends to make a noticeable mess. I have no check engine lights or fault codes. However, the brake fluid is not clear and looks like it might be contaminated.

I'm guessing I have an internal seal that has failed and I'm getting some sort of blow-by.

Has anyone experienced a master cylinder fail at such low mileage before and might there be something else causing the problem that I'm not aware of?

Fluid level at Max Line

Brake fluid looks contaminated

 

I suppose it could be a faulty power booster. However, a master cylinder is a lot less expensive.

 

Probably a bad master cylinder. But first, I would suck out the old fluid from the mc, refill it and do a brake line bleed and fill until all the fluid was fresh if it were me. the lines will need flushing if you installed a new MC anyway. And if you do it yourself, make sure you do a bench bleed on the mc before installing it.

 

Good tip. Will do.

 

You will also need to bleed the ABS. A scan tool makes it fairly easy, if you don't have access to one it's a bit more difficult.

https://carfromjapan.com/article/car...out-scan-tool/

 

Having the truck scanned for ABS codes may be a good idea too. The normal or cheap code readers don't usually read ABS codes. ABS can do some weird things to the brake system is it isn't working properly.

 

Yes, I have several scanners and access to Forscan. I've seen the "ABS service bleed" option in the program. Shouldn't be a problem.

 

I have a scanner that reads ABS codes. The truck isn't throwing any of those either. That was actually one of the first things I scanned for coincidentally.

 

That article makes it seem like you need to disconnect the lines from the MC to drain it which is NOT the way to do it. You suck it out using a turkey baster or a hand held mity-vac or similar and those instructions are not mentioned in the article. It also seems to say you just bleed all four wheels like we've always done. If there is any directions to bleeding the ABS directly, I missed that part. On my car and truck with ABS, all I've ever done is bleed the calipers except for my truck. On the truck I replaced the master cylinder and bench bled it before installing it and then bled all four new calipers. I've never touched the ABS. So, I'm confused as to what bleeding the ABS means?

 

I know this wasn't directed at me but I assumed he meant bleeding the ABS module. Some scan tools have the ability to actuate the valves in the module. I thought it was a way of electronically bleeding the system as a whole by computer assistance and not a step in addition to bleeding at the calipers. The Forscan app has a brake bleed procedure that activates the module thus bleeding the brakes with no pumping of the pedal. You just have to make sure the reservoir doesn't run dry.

So you can do it manually or via a scan tool. Either or. That is just my understanding of it but I could be wrong.

 

For easy bleeding of brakes, I have an electric vacuum pump with a solenoid. I just hook it up and press the button. Just need to make sure there is enough fluid in the reservoir.

I replaced hoses and calipers on a friend's F150 two weeks ago and no issues. I let the system run empty, I filled the master cylinder reservoir and bleed the brakes like normal. Didn't even bother with the ABS module.

I even replaced the master cylinder, hoses, calipers, and rotors on my Harley yesterday... lol

Been doing a LOT of brake jobs lately.