13+ SHO master cylinder failure?

lamrith · August 17, 2020, 12:49:43 PM

Been lurking for last few months, just enjoying the car. She just crossed 80k mi last month.

I had mentioned before that the ABS did not seem to kick in even in emergency stop situations. Braking force while extreme never made the tires loose traction to make abs engage. It had been mentioned that it could possibly be air in the system. I had the chance to get the car into a ship today to have the system flushed and bled. When sitting in the lot before going in, my son said the pedal went to the floor on him. The shop said they think maybe MC failling? I asked them to go ahead and do just the flush and bleed 1st as I have never had an issue like that with the car. Just seems odd with so low miles, is this a common issue for 13+? If so what can I have them look for, do they leak externally?

TopherSho · August 17, 2020, 01:09:12 PM

That is interesting .. My 2010 will ''sink'' to the floor over the span of 20 seconds if i apply steady pressure.. yet have never had any issues with emergency braking.

hmm

lamrith · August 17, 2020, 01:16:03 PM

Quote from: TopherSho on August 17, 2020, 01:09:12 PM
That is interesting .. My 2010 will ''sink'' to the floor over the span of 20 seconds if i apply steady pressure.. yet have never had any issues with emergency braking.

hmm

I had a pair of panic stops a while back, 40mph or so to dead stop. The car stopped and stopped hard, uncomfortably hard into seatbelt, everything in car flying forward sort of hard. I was honestly shocked and impressed the car stopped as quickly as it did.

BUT I never felt the ABS engage or the tires break loose on pavement. That seemed odd to me as I would think the brakes should be able to overpower tire to pavement grip regardless or how good tires or pavement surface are..? MY son did not clarify how fast or slow the pedal went to floor, just that it did. It has never done that before.

TopherSho · August 17, 2020, 02:44:20 PM

hmmm need to wiki it up, but ABS is supposed to pulse the brakes to prevent skidding, But on our SHOs it is a lot harder to get them to skid because they are wide heavy and 3/4 the power-train sits on top.

lamrith · August 17, 2020, 03:06:57 PM

Quote from: TopherSho on August 17, 2020, 02:44:20 PM
hmmm need to wiki it up, but ABS is supposed to pulse the brakes to prevent skidding, But on our SHOs it is a lot harder to get them to skid because they are wide heavy and 3/4 the power-train sits on top.

Yeah I have had plenty of other vehicles with abs kick in. This car has never locked up under braking for it to kickin, even with max emergency pedal stomp and hold. Now I am running nice fresh 275's, but I would think it should still be able to lock a wheel under panic stop even with all that grip, weight transfer should be unloading the tail at least..

6500rpm · August 18, 2020, 07:15:03 PM

Go for lock up on wet pavement or something with loose gravel and see if the ABS kicks in. Pedal dropping all the way to the floor, as in completely bottomed out without fluid loss is a good indication of fluid leaking past the cup seals inside the master cylinder internally. All the way to the floor will have a distinctive hard hit felt in the pedal when it hits bottom fwiw.

lamrith · August 18, 2020, 11:35:08 PM

Quote from: 6500rpm on August 18, 2020, 07:15:03 PM
Go for lock up on wet pavement or something with loose gravel and see if the ABS kicks in. Pedal dropping all the way to the floor, as in completely bottomed out without fluid loss is a good indication of fluid leaking past the cup seals inside the master cylinder internally. All the way to the floor will have a distinctive hard hit felt in the pedal when it hits bottom fwiw.

Yeah this is not that by any means. I talked with my son (17yrs old just started working for Goodyear) about it, it was not a soft pedal to floor. Pedal has nice modulation, till max stopping power, then heavy pedal for a bit farther, it never goes to floor, but the press past max braking had me scratching my head. They did a flush and bleed and the pedal feels a hair harder at max braking now. It just does not get rock hard like I thought it would. no fluid leaking anyplace at this point. I will see when we get rain next and test that though, good idea.

Macgyver · August 19, 2020, 06:23:51 PM

New pads and bed them ?

lamrith · August 19, 2020, 06:31:12 PM

Pads are good, lots of life left in them, and they grip very well, the system bites well. Best way I can put it is that hard braking is uncomfortable to say the least, in fact I can't fathom why the tires are not locking up. I have not had a car that stops so hard and not lock a tire up to make abs kick in. That is what is throwing me off if that makes sense, just that it is not kicking abs in, I have no complaint with how quickly the car stops, she stops very well imho.

Pedal is def better with the flush and bleed. Much firmer at max braking than it was before. I need to find a safe place to get the car to reasonable speed and do panic stop testing. you know, for science.

6500rpm · August 19, 2020, 08:58:08 PM

13 PP brakes are good to go. For the life of me, unless you auto x, I don't have a clue why so many go to aftermarket. The factory PP pads have a hard innitial bite and I haven't had fade issues. I think the only time I've kicked ABS in was in the snow and possibly one hard apply in the rain. Be happy, the damn things stop really well..Ford got that right!

JMR76 · August 20, 2020, 03:16:01 PM

Quote from: lamrith on August 19, 2020, 06:31:12 PM
Pads are good, lots of life left in them, and they grip very well, the system bites well. Best way I can put it is that hard braking is uncomfortable to say the least, in fact I can't fathom why the tires are not locking up. I have not had a car that stops so hard and not lock a tire up to make abs kick in. That is what is throwing me off if that makes sense, just that it is not kicking abs in, I have no complaint with how quickly the car stops, she stops very well imho.

Pedal is def better with the flush and bleed. Much firmer at max braking than it was before. I need to find a safe place to get the car to reasonable speed and do panic stop testing. you know, for science.

I know exactly what your talking about. My 13 PP feels the same. I did brake flush and bled a few months ago.

About 2 weeks ago a guy lane changed in front of me and had to slam his brakes on because of stopping traffic in front of us. I was on the pedal as hard as I could and never locked up. It did stop (about 3 inches from his rear bumper) but for a moment it felt like I wasn't going to.

I then took it to a friends garage and then again checked all my calipers and slide pins myself. Master cylinder seems fine. New Ford rotors and pads have been bedded and are about 6 months old.

I can't complain about normal or moderate braking though. Never had warped rotors. It brakes as straight and smooth as can be. I've always loved the braking compared to all my other vehicles. In fact, my other vehicles (explorer and fusion) If I panic brake just a little I almost put myself through the windshield. Not really, but it feels like that. The panic braking on the SHO did scare me it wasn't going to stop, but again it did. Doesn't matter how fast or hard I step on the brake, it usually won't lock up, even with two feet.

On a side note. If I did a hard brake 2 times (heated up the pads and rotors) I can get it to lock up somewhat and pads will stick better). I can test this by brake boosting also. On cold brakes it can't brake boost past 2,000 rpm without breaking loose. With warm pads and rotors I can go to about 2,500 rpm.

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