u/InterestingDrive4039

Just picked up a 2005 Lincoln Navigator 4x4 5.4L V8 and I actually really like the damn thing. It’s loaded as hell for a 20-year-old SUV — sunroof, rear entertainment/TV, parking sensors, 4x4, AdvanceTrac, etc. The engine and transmission seem strong and it actually has a surprising amount of power.
But I’m dealing with a pile of issues and I’m trying to figure out what I’m actually looking at before I start throwing parts at it.
The biggest issue is the brakes. When I bought it, the brakes were basically nonexistent. I flushed the entire system with fresh DOT 3 and bled all four corners. The old fluid was absolutely disgusting and visibly contaminated, and I’ve pulled a shitload of air out of the system.
The weird part is that the pedal can be rock solid with the engine off. Sitting in Park, I can stand on the pedal and it won’t go anywhere near the floor. With the engine running, it gets some booster assistance, but the weird brake problem still doesn’t consistently happen while stationary.
The problem seems to occur only when it’s in Drive/reverse/actually moving. Sometimes the pedal feels completely normal and hits a very firm stop, and other times it has excessive travel and gets dangerously soft. It’s extremely inconsistent. I cannot reproduce the same behavior reliably while sitting in Park.
I disconnected the brake booster vacuum hose as a test and the pedal became more substantial, but it was still somewhat soft and the underlying problem wasn’t eliminated. I also checked inside the booster for brake fluid and it was completely dry.
There’s some wetness around the front-left brake, although I haven’t found an obvious active leak.
The vehicle has ABS/AdvanceTrac, so I’m wondering if I’m dealing with an ABS hydraulic unit issue, wheel-speed sensor issue, pad knock-back/wheel bearing problem, trapped air in the ABS unit, or possibly a bad master cylinder.
I’m currently planning to replace the master cylinder, and completely bleed the system again. If that doesn’t fix it, I’m taking it to a shop with an ABS-capable scan tool because I’m done guessing.
Other issues:
OBD-II port isn’t communicating with my scanner at all.
A/C compressor isn’t engaging.
Check-engine light started flashing intermittently, then stopped.
I’m suspicious the catalytic converters may be partially restricted because the power sometimes feels strong and other times falls off, and the floor gets pretty hot.
I temporarily cut the muffler off so I could actually hear what the engine/exhaust is doing. It also made me considerably happier. 😂
Suspension warning keeps coming up.
Despite all this, the engine starts, runs, shifts, and drives surprisingly well.
4x4 works.
Sunroof works.
The damn TV works.
Parking sensors work.
It’s actually a really comfortable truck.
I paid $1,700 for it and I’m willing to put enough into it to get it sorted, but I’m setting myself a $3,000 absolute all-in ceiling.
So, what would you guys check first for the intermittent brake pedal that ONLY seems to happen in Drive/motion? Especially interested in anyone who’s dealt with this generation Navigator/Expedition/F-150 brake system.

Everyone on Reddit seems to either have something to prove or is just looking for someone to argue with, even when they’re blatantly wrong. I’m still pretty new to Reddit, but holy shit, some of you need to grow up.
I’m politically independent. I don’t give a shit about either political party, and I certainly don’t care about hearing someone’s political opinion when it has absolutely nothing to do with the conversation. Nobody cares about your political talking points. Not every discussion needs to be turned into some ideological pissing contest.
And yes, that includes the people who seem to think communism is some brilliant solution to everything. Communism isn’t suddenly a good idea because you put a progressive slogan next to it. The ideology has repeatedly produced authoritarian governments, economic disasters, and massive restrictions on individual freedom. You can criticize capitalism all you want without pretending that centralized economic control and one-party authoritarianism are somehow the answer. That isn’t edgy or intelligent; it’s just historically ignorant.
What’s even more ridiculous is how confidently some people will argue about things they clearly know nothing about. I spent eight years in the Army, including time as a Ranger, so maybe I have a pretty low tolerance for bullshit. But there’s a massive difference between disagreeing with someone and refusing to acknowledge reality because you don’t like being wrong.
I had a Redditor tell me that my lawyer was wrong about the legal situation involving my service dog. My lawyer has over 20 years of experience, and I had already worked through the legal side of the situation with him. So I asked this person what law school they went to and what legal authority they were basing their argument on.
Their response? They blocked me.
That is exactly the kind of shit I’m talking about. If you’re going to confidently tell someone that their lawyer is wrong, you should probably be able to explain why when someone asks you to back up your claim. You don’t get to throw out bullshit, get challenged on it, and then run away because you don’t like the answer.
And the amount of people who act like absolute fucking babies the second someone disagrees with them is honestly impressive. If someone proves your argument wrong, maybe consider the possibility that you were wrong instead of throwing a tantrum, blocking them, or changing the subject.
I’m not saying everyone on Reddit is like this, but there are enough people acting this way that I’m seriously considering deleting the app. I came here expecting to have conversations and hear different perspectives. I didn’t realize so many people would treat every disagreement like a personal attack.
Quit with the bullshit. You’re allowed to be wrong. You’re allowed to have a shitty political opinion. You’re even allowed to disagree with me. Just grow the fuck up, defend what you’re saying, and stop acting like the world is ending because somebody challenged you.