Soft brake pedal?

[AKghandi]

My 14 RS has an incredibly soft brake pedal, I can easily put it all the way to the floor.

I replaced the master cyl a month ago and it stopped like new, but the issue is back again.

I'm not really sure what would cause this. aside from the master cyl going bad again.

what should I check first?

 

[2014 Blue RS]

Hmm no issue on mine but I'd start with checking fluid level. And look for any hint of a leak. Engine should be dry and dusty. Anything went is a potential leak.

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[Papasonic]

Some causes of a soft brake pedal:
1 Air in system, bleed brakes
2 Master cylinder, internal leakage
3 Brake line rubber hoses, deteriorated/expanding under pressure
4 Calipers not sliding on mounts
5 Leak in system

You probably will find that one or more of the above issues causing your problem.

 

[MaD]

Ya lookin inside the master is easy, check for fluid in there.. basically eveything Papasonic said... [emoji106]

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[AKghandi]

No leaks anywhere. Fluid level is the same as it was.


It also has very strange braking feel. Like the pass rear corner locks up first

 

[Maddmatts]

Have you been doing any heavy braking before the symptoms occurred? Boiled brake fluid can cause a soft feel and long pedal travel. Bleeding the brakes is the only fix for this condition.

 

[AKghandi]

Have you been doing any heavy braking before the symptoms occurred? Boiled brake fluid can cause a soft feel and long pedal travel. Bleeding the brakes is the only fix for this condition.

not anything that would have boiled fluid. I flushed the system with dot4 when I put the new master cyl in.

I'm almost wondering if I lost a pad. I did hear something hit the bottom of the car before all this started.


Today I noticed that the pedal will hold higher if I pump the pedal quickly, but will go to the floor if I press it slowly.


I also took it to 2 dealers after the original issue and before I replaced the master cyl.

One told me everything was ok and that pumping the pedal was normal. Told them to go screw their hats. Second dealer told me it was a "brake booster check valve." Told them to also go and fornicate headwear.

I'm going to pull all the wheels and do a full inspection in a couple days.

 

[ChicksHateMe]

I had major brake issues. Mine turned out to be a bad check valve allowing fluid into the boost.

I could check it by ---- When I'd press the gas (or cruise was accelerating) , and I'd try to brake, brake pedal would not go down at all. But if I was off the gas, they actually felt spongy.

Was a bitch for them to get it right. First they changed master cylinder and a pump. 2nd time they got it with changing the check valve and the tainted boost.

Good luck!

 

[ChicksHateMe]

AKghandi, You ever figure it out? Just wondering...

 

[Blue Moon Sonic]

Try greasing your caliper guide pins. I've noticed the pedal feels nicer after doing so and will prevent uneven pad wear (more wear on the inside pad vs the outside pad). This is one of those missed maintenance items no one thinks about that should be done.

 

[AKghandi]

I had major brake issues. Mine turned out to be a bad check valve allowing fluid into the boost.

I could check it by ---- When I'd press the gas (or cruise was accelerating) , and I'd try to brake, brake pedal would not go down at all. But if I was off the gas, they actually felt spongy.

Was a bitch for them to get it right. First they changed master cylinder and a pump. 2nd time they got it with changing the check valve and the tainted boost.

Good luck!

Could you elaborate on this a bit more? i dont see how the booster check valve could cause these issues.

 

[Blue Moon Sonic]

Could you elaborate on this a bit more? i dont see how the booster check valve could cause these issues.

The brake booster check valve is a one way valve that, is designed only to allow air to be sucked out of the vacuum booster. When you hit the brake pedal, theres a rod that cracks open a valve, allowing air to enter the booster on one side of the diaphragm while sealing off the vacuum. This increases pressure on that side of the diaphragm so that it helps to push the rod, which in turn pushes the piston in the master cylinder. When that check valve fails, it will essentially cause that mushy pedal feel cause air is no longer being sucked into the booster when you hit the brakes. The other thing to mention for turbocharged cars, It the booster check valve prevents pressure from entering into the brake booster, you won't be able to brake while accelerating. So much for being able to brake boost at that point.

Feel free to correct me on this one.

 

[ChicksHateMe]

Sounds like a perfect short answer by Blue Moon Sonic.

My thread on the experience is here if you want to know more.

My Brakes are scaring me

 

[AKghandi]

my brakes work while accelerating, and maybe my understanding of how brake booster works is wrong but that doesn't make any sense, a bad booster would cause a hard pedal, unless the engine was making extreme amounts of vacuum, the pedal wouldn't be soft. and if that was the case the brakes would be very touchy.

To my knowledge the check valve holds vacuum in and prevents boost from entering the booster. thats it.

 

[Blue Moon Sonic]

my brakes work while accelerating, and maybe my understanding of how brake booster works is wrong but that doesn't make any sense, a bad booster would cause a hard pedal, unless the engine was making extreme amounts of vacuum, the pedal wouldn't be soft. and if that was the case the brakes would be very touchy.

To my knowledge the check valve holds vacuum in and prevents boost from entering the booster. thats it.

If you are not using the brakes, you do not want air in the brake booster, otherwise it will cause the brake pedal to be too hard. Which is correct. That's why the check valve is there even in N/A cars. It's to make it so a air does't enter the booster until you hit the brake pedal. Air will only enter the booster when you apply the brakes and as a result will help assist in braking. That's why the pedal feels firm after you push the pedal in after a certain point. Now When the pedal goes all mushy, that means there is no air entering into the brake booster when applying pressure to the brake pedal. If it's stuck where only air is getting sucked out when you hit the pedal, the pedal becomes mushy. The opposite happens if the valve becomes stuck in the other position where air enters the chamber regardless of pedal position. Now here's the kicker. If the check valve is just freely moving as though it's broken and flapping around, you'll still have braking power, until you accelerate and are under boost from the turbo. Air will still get sucked out, but air will also enter under pressure from the turbo causing the booster to pressurize which will make pushing the pedal next to impossible. The check valve is to prevent the pressure from the turbo from entering the booster but also allows it to suck air out of the booster when in a state of vacuum.

I may have a few redundant sentences in there, but this is my general understanding. It's not perfect by any means.

 

[AKghandi]

today i got the chance to pull all the wheels off and inspect everything.

It all looked good so i bled the brakes again, and that seems to have fixed it. We shall see though.

 

[Walleyeye]

I have a brand new '17 RS and while I can't push the brake pedal to the floor I am quite surprised at how soft the pedal is. To be fair it will stop on a dime and I have been quite impressed with the braking ability.

I've never had any vehicle that had such a soft brake pedal. Then again I've always driven Ford up until now.


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[ChicksHateMe]

I have a brand new '17 RS and while I can't push the brake pedal to the floor I am quite surprised at how soft the pedal is. To be fair it will stop on a dime and I have been quite impressed with the braking ability.

I've never had any vehicle that had such a soft brake pedal. Then again I've always driven Ford up until now.

I remember when I was deciding on cars, I looked at the Fiesta. I thought they had HORRIBLE Brakes. Really Mushy. I did some research and I guess it was common for them. Had to do with them not being bled right, right from factory. Only solution was bleeding both front or back at same time, and not doing one at a time. At least that's what I read. That, and the Fiesta feeling too cramped made me pick the sonic.

Then of course, my Sonic brakes failed. You might have read the issues I had, took a few times for service dept to get it corrected, but once it was solved, they were/are great. Feeling perfect to me.

Good luck solving it. Let us know what solve it if you can....