Soft brake pedal/long pedal travel after new Master cylinder?

LANCE OWEN

MEMBER
2008 MERCURY MARINER
3.0L
V6
2WD
AUTOMATIC
128,000 MILES

Hello,

I am having an issue with my new to me 2008 mercury mariner. The previous owner sold me the vehicle after it was inspected by ford and found it to need new front calipers, rotors, pads, lines, and a right front speed sensor.

The right front caliper was frozen, and the ABS and TC lights were on with a code that signified a bad speed sensor.

I brought the vehicle to a local shop. They replaced all of these parts and cleared the codes. The vehicle had much better braking action, and the brake pedal wasn't totally firm but seemed reasonable for a 15-year-old SUV.

Everything was going fine and then a few days later it snowed, and I went to brake at a stop sign. The ABS kicked in for the first time and I completely lost my brakes and the pedal fell to the floor.

I could get pressure and brakes by pumping, so I limped it back to the shop and called them the next day.

They brought the vehicle in and checked it out. They told me the old master cylinder failed and wanted to put a new one in.

The next day after getting the car back I noticed the brakes felt fairly soft when first applying the pedal. Maybe the best way to visualize it is like the first 70% of pedal travel I don't feel much of anything, then the last 30% of brake pedal you have firm functional brakes. I don't think it is normal for the pedal to travel to nearly the floor before you feel good brake bite. Additionally, the ABS is functioning too. I asked them about this, and they claim that the new master could be faulty and or I just need to drive it for a bit to "let things settle". They claim they bleed everything multiple times including the ABS 4 times.

I guess I'm just feeling a bit defeated because I paid $650 to be told that I need to let the brakes settle which sounds like BS.

Thanks for your input.

1 Reply

STEVE W.

MECHANIC
13,445 POSTS

It is BS, it sounds like they replaced the front parts but never bled out the ABS system and the first time it activated it dumped the fluid into the air pocket in the ABS system. Because the pedal went all the way down I would have advised you to replace the master as well, but that would have been because of the crud and trash that settles into the cylinder over time and then you drug the pistons and seals over that when the pedal went down, but in my shop I would eat that cost as it would have been my fault for not following procedure and bleeding the system properly in the first place. Other shops won't agree with that. However, it sounds like the system still needs to be flushed and bled. Then if the ABS is triggering all the time, you still have a speed sensor issue where it thinks a tire is stopping before the others. I would find a different shop or take it to a dealer and have them do it. Around me the dealers have been getting much better on pricing but that may just be my area. Unfortunately, you need some special tools to bleed those systems and a way to look at the speed sensors and ABS system to see where that fault is. In my area of NY the common issue is rust that eats up the tone wheels in the front or rust jacks the sensors out of the knuckle. That gives the sensors a weak signal and when you slow down the signal level drops out on a single sensor, so say you are slowing down and at 20 MPH the signal is okay, then as you slow down 4 wheels show up at 15 but at 10 MPH one of them is showing a very weak signal and at 5 it drops out completely, the system won't flag it as the signal is there and the wiring is complete but it will activate the ABS because it thinks that tire has stopped rolling. The best way to see that is with a scan tool that can read the ABS signals.

You can try:

https://www.2carpros.com/articles/abs-wheel-speed-sensor-test

However, it may not show you the info you need unless you have an old-style analog meter.

As an example:

https://www.youtube.com/watch?v=oGwyrLxtaNY
https://www.youtube.com/watch?v=oXW0mqPrmPs

Images (Click to make bigger)