In the past day or so the brake pedal has gotten progressively worse. It never been a super firm pedal but it seems im nearly to the floor on the first press. If i let off and immediately press again its much more firm. Third press is more solid as well. Master cylinder is full no recent brake work. Im leaning twards a master cylinder failing internally. Truck is a 2017 excab f250 4x4 with the 6.2. Truck has vaccum assist booster. Am I on the right track since it seems to have dramatically changed in the last few days?

 

I would start with a careful inspection of each brake and flex hose, then look for leaks in the hard lines and fittings, then move to the MC.

 

There is air in the system. When a Master goes, it goes quickly, not like you described. A failing master will go right to the floor with little pressure on it as the cups inside allow fluid to bypass them fully. On the next press it can be back to normal. What you describe is classic air in the system. You have either overheated a brake and introduced gasses from boiling fluid, or you have a leak. You need to have a full brake inspection done top to bottom to find and fix the cause. Bleeding may only be a temporary fix.

 

Follow what redford said then if under warranty take it to the dealer. If not under warranty, bleed the brakes. Get a large bottle of brake fluid do not use if previously opened. Start at the right rear and bleed until fluid is clean and there are no air bubbles, this might take a while. If the fluid being bled out is not as clean as the fluid you are pouring in the master cylinder keep bleeding.Then move on to the right rear and apply the same process. Then proceed again at the right front than left front. Eliminate the simple inexpensive issues first.

My wife's 2016 Honda pilot behaved as you describe. I checked fluid level and brake lines all looked good. What I missed was the color of the fluid in the master cylinder, it was not clear as should be. The fluid had a brownish tinge to it as soon as I started bleeding. This went on until I completely cleared out the master cylinder. When I finished bleeding all was good and has remained fine for about a year now. I have no idea how the fluid became so contaminated in three years or how the air got into the system.
Hope this helps.

 

Maybe a sticking caliper piston or two though I lean toward air/leak somewhere. I've had calipers sticking open (hard to activate resulting in spongy feeling pedal) and stuck closed (overheated and pedal was hard)

 

Update.. had some griding pad to rotor contact. Discovered it was the driver rear. Checked prices and to my shock the dealer quoted better prices that the box stores then upon me arriving further discounted the parts more. I returned to do basic pads and rotors on the rear. Once disassembled i Discovered the real issue. One of the slides was siezed. This would easily explain the spongy pedal. Fun fact. Ford sells caliper brackets separately from the rotor. Box store though sell it as all one item. On the caliper with bracket the box stores were cheaper than a caliper bracket i would have had to order. All is good now work truck stops.lime ot should and pedal feel is back to normal

 

Before you go jumping for joy, please find out exactly what they are quoting you for. First thing, dealers have accounts at the parts stores so they are going to get it cheaper.

Duralast Pads
Duralast Rotors X2
Subtotal $366.97
Package Deal price $311.92
Pads are lifetime and rotors are 2 years warranty but you probably need hardware and rubber boots and fresh grease and brake cleaner if I were to do it

Duralast Gold Pads
Duralast Gold Rotors
Subtotal $447.47
Package Deal price $380.35
Pads are lifetime and rotors are 3 year warranty and above items apply

Now depending on what I quote you, the prices can be better or worse so you need to get it straight.

Performance Kit $612.99

Now, I can beat all that pricing by getting you some cheaper junk so what brand are they giving you and how good are they?

I think you are thinking of the Irish Guy that sells a "loaded caliper" that includes pads and rotors. Is that a good set of rotors? IDK. I prefer to get my own so I know what is going in. If it were my vehicle, I would get a new caliper since I don't trust it anymore, take the other side off, get fresh boots and clean out the old grease (you don't reuse your oil year after year, do you?) and put it back with fresh grease. Do the same for the other 3 calipers. Suck the fluid out and fill it with fresh fluid and flush the entire brake system. Brake fluid should be flushed every couple of years since they pick up water and no, it isn't a sealed system by any stretch of the imagination.

 

Had the same seized pin on my 2018 F250 work truck, and pedal feel.

 

Oem rear rotor $129.90.
Oem rear pads $74.99.

I get the mentality of replacing everything but its a work truck. The caliper had nothing to do with the bracket failure. Replacing the caliper with some reman from god knows where could potentially be more disastrous then running the factory caliper with 129k. Always lool over the parts. I hate to do things over but also dont try to over spend on needless things (in my opinion)

 

I have worked on vehicles with bad master cylinders that would not immediately go to the floor. If you sat at a red light they would slowly go to the floor a repump would bring the pedal back up.

 

You are saying that the caliper slide pin is frozen? I am not sure what the fix to that is besides a new bracketed caliper. You may be able to just buy the bracket and new slide pins. Not sure. I would just buy a new caliper and be done with it. But like I said, service the other calipers and change the boots. They aren't that expensive. Clean and grease. Remember, I don't care if you ever drive it again. I would prefer that if you drive, you can stop when you want to. If you can't, it may be painful financially and/or physically. $6 at Autozone and a little brake grease. I had a brake failure at 40 before. I'm not ashamed to say I almost wet and crapped my pants. I am very particular about brakes.