Mushy brake pedal + ABS light + calipers won’t bleed

Maintenance/Repairs
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1

Not my car, but I’m working on a ‘08 Lincoln MKZ with brake issues. It’s got me thoroughly confused.

The car was driving totally fine, then one day the brake pedal was suddenly quite soft compared to the day before. It stopped as per usual, but pedal travel was mostly to the floor before it would bite.

I pulled the wheels off to check for leaks & the condition of the pads/rotors. No exterior leaks anywhere, reservoir was full, and the pads were nearly new from a not-too-long-ago brake job (done at a shop).

I changed the brake fluid since the old stuff was basically black, & everything went smoothly. No issues bleeding the system. The pedal felt a bit firmer after that, but still not what is should be.

I did some online research & thought that the master cylinder might be to blame, so I put in a new one. The pedal felt almost normal immediately after that. Took it out for a drive & did some aggressive braking to test it out. It wasn’t great, but pretty darn good. It stopped when you wanted it to, so I wasn’t too mad.

Now we get to the confusing part. The next day, the pedal was back to going almost all the way to the floor. It would stop, but not safe to drive. I thought maybe I should try bleeding the calipers to make sure there wasn’t air in there from doing the master cylinder, but the damn things won’t bleed now!

Here’s how it’s going: the car is up on jacks & has ZERO brakes. When I open the bleeder valve, fluid drips out as it should. When I put the tube of my one-man-bleeder over it, it slowly starts filling with fluid. Some air bubbles come out too. When I go & push on the brake pedal, it looses pressure after say 3 pumps. This is while the car is OFF. Some fluid flows into the tube when my foot is down, but it flows right back into the caliper when I lift off. Each pump pushes less & less fluid out of the calipers.

I tried the two man procedure too, opening & closing the valve while someone else works the pedal. It keeps the fluid from flowing back in, but no fluid really comes out either.

So, I guess there’s air somewhere. Maybe quite a lot of it. I thought it could be in the ABS system, so I put the car in drive & got the rotors spinning, then slammed the brakes to activate the ABS & hopefully move things around. I’m not kidding when I say there’s no brakes, I had to put her in neutral and wait for the rotors to stop spinning before putting it back in park! The pedal went to the floor & felt like it was grinding something. It was horrible. Not a normal ABS buck-off feeling.

I did this twice, then tried bleeding again. No change. I attacked the ABS for a 3rd time, then it flipped out. Suddenly the ABS light came on. Scanned it & got two codes, C1235 (right rear wheel speed sensor) & U0415 (invalid data from ABS module).

The ABS shut itself off, there are still no brakes, and it still isn’t bleeding properly. I did try to bleed it once more before I quit today, and it was a little better than it’s been, but the fluid is still flowing up & down not really making forward progress.

I don’t know what the hell is wrong with this thing. Could I have done something horribly wrong when I put the new master on? Even if that’s what’s causing this issue, I don’t get why it went from perfectly fine to having a ton of pedal travel overnight in the first place!

Any thoughts would be appreciated. This car always seems to have some major (expensive) issue, & it’s driving me nutty.

2

Even if what you are doing would normally work, normal isn’t happening now. It’s time to go to the manual and find out the right procedure. The car may have to go where it can be done that way.

3

Sounds like you might have an ABS modulator/dump valve problem… You might have to use a proper scan tool to command the modulator while bleeding the system, or possible it is just bad and requires replacing…

Like @pleasedodgevan2 said, time to go to the service manual for the proper bleeding procedure to bleed the brakes on this vehicle… and it still may require an advanced scan tool that can command the modulator…

ASEmaster and a few others might be more familiar with this system…

4

I had one experience that was similar. I had what felt like no brake at all at the rear on a motorcycle. I bled the line many times and there was no air coming out. What it was, was a loose brake caliper. The whole caliper was shifting under braking pressure so all the force from the master cylinder was lost shifting around the caliper rather than pressing the pad against the rotor.

5

I’m guessing even if the ABS function has failed, you’d still have working brakes. I’m doubting the ABS as a cause for the no-pedal theory. One idea, the brake booster is involved. Are you able to disconnect the brake booster entirely from the MC? Temporarily, as a test. If so, see if the pedal returns then.

If not, suggest to try a gravity bleed procedure. Sometimes pumping on the pedal while attempted a bleed will move more air into system than was there before. Takes some time, be patient. Wheel by wheel, in correct order for your car’s configuration. Attach clear hose to bleeder, loop hose up a little, then back down into jar. Open bleeder. Gravity will cause fluid to move from MC to caliper and out the hose. Once all the bubbles are gone,-- might take several hours – close the valve and do the next wheel. Top off MC as required.

If problem is air in ABS, you’ll may have to use a Ford scan tool to open & close valves in ABS unit to fix that.

No calipers were recently replaced, right? Bleed screws are all at the top of the calipers?

6

https://www.justanswer.com/ford/8xkhl-lincoln-mkz-08-lincoln-mkz-brake-pedal-goes.html

Tester

7

@Tester, that link takes you to their web page where they want you to start a chat with them, it does not give the answer.

@USRPTVT you will probably need a scan tool for this, and maybe a pressure bleeder. Also, did you bench bleed the MC before you installed it?

One more thing, when doing the two man bleed, after each pump, the pedal must be SLOWLY returned to the up position. Even if you did bench bleed the MC, it may need to be done again as it sounds like air has gotten in somehow. It has to be bench bleed off the vehicle.

8

Didn’t you read what the Ford mechanic suggested?

Tester

9

I tried. I saw the question and clicked on the box, but it did not give me the answer, it just opened a chat session.