Abs

[Jojo919]

Hi I am new on here but I desperately need help! So I have a 2003 Ford explore 4.6 four-door XLT my brakes are giving me problems recently I started experiencing no pressure on my brake pedal it has pressure but if I press it too hard then it just vibrates a little bit and sinks to the ground my question is how do I find out if I have a bad master cylinder or if it’s my ABS system my ABS light stays on it will pop off occasionally but lately comes right back on I have no leaks that I can find I do hear a vacuum leak at least I think it’s a leak and as soon as I engage the brake pedal then that suction I hear stops. I don’t know if that’s even an issue with what’s going on can somebody please help me determine what my problem is here before I ruined something thanks

 

[J_C]

First I'd make sure your brake fluid reservoir isn't near empty, though it is normal for it to drop fluid level some over brake pad service life, as the brake pads wear and the caliper pistons are extended further. This is just to leave no stone unturned and make sure you're not risking brake failure.

The ABS light is a very strong hint, that your ABS module, or more likely your ABS speed sensors (or wiring) is failing. A scan tool capable of reading Ford-specific codes (not "just" OBD2 codes) is what to do next, or a scan tool capable of live data to see the ABS speed sensors' values when the event occurs.

Although it is premature to assume it, around the age of your vehicle, these often have the hubs wear out and a failing speed sensor can be an early indicator that the hub needs replaced, and hubs generally do come with a new ABS speed sensor, but with the warning light coming on, pulling the code is the thing to do next.

It is not likely to be the master cylinder. Are there any particular situations that make the problem more likely, for example going very slow or slowing to a stop, or slippery roads, or spirited driving (or hauling a load down long hills) causing elevated caliper temperatures?

While the scan tool is hooked up, you can look at long term fuel trims to see if you have a vac leak. If it is adding more than single-digit, the leak is significant enough to look for in addition to resolving the separate braking issue. Vac assists braking, a leak to the booster won't cause ABS to activate and pedal sinks, rather harder braking if there was a leak there.

 

[XploX]

Sounds like the brake booster diaphragm.

 

[94Eddie]

It could also be a bad rubber line(s) that connects to the calipers. They can lose their structural integrity over time and expand when the brakes are applied. This can cause the pedal to go to the floor with little or no stopping power and no leaks will show either.

 

[J_C]

... but that/those don't explain the ABS light. Put all symptoms together and it's most likely there is an intermittent loss of signal from a speed sensor, for whichever reason.

 

[94Eddie]

It likely isn't the cause but it is easy to check and eliminate as an issue.

 

[Jojo919]

Update!!
Ok so the problem was a deeper issue, I had to get it up in the air so I could do a complete inspection of the front end to see if I could diagnose the problem, with your feedback and the history of this Explorer and a little poking around I figured it out and fixed it , only after buying a few parts that I really didn’t need to buy to correct the issue. I had a clanking noise coming from the front right tire a month or so back so I changed my ball joints because inspection of them they needed changing, so I Thought I fixed the clanking but I heard the clanking again just recently with this brake issue going on.. at first I thought my booster, then maybes my master cylinder, then after the abs light I thought oh no it’s the abs control unit.. but somebody said I could read the code if the abs light is on so I did that and it came up as front right speed censor (abs) .. so I rushed in and bought a censor before really checking everything out, but after I bought the censor I started thinking what would make the censor go bad, and one thing that can trigger that censor for abs would be metal shavings and grease making the censor faulty unable to read because of debris, or vibration of some sort.
The Fix:
I lifted the front end and started all over with the ball joint test by moving the tire to see if any play with the ball joints but what I found is my tire was moving a lot but at the hub..further investigation revealed that my barings and hub has gone bad.. hence the clinking noise I thought was the ball joints turned out to be worn out hub assembly, which would cause vibration and triggered the censor for abs… so 400$ later and new hub assembly and brakes and rotors.. it’s back on th the road driving better than ever, until the next part that decides it’s not immortal and breaks, so I am grateful for all your help … and I done all the work myself with help from my buddy who knows a lot more about mechanics than me…but learned a lot about my Explorer and gave me the confidence to start changing and fixing everything that’s needed…well maybe not everything….: thanks you all….