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Discussion Starter #1
Hey everyone,

After installing new SS lines front and rear and new seals on calipers the pedal firms up and very slowly drops to floor, any ideas what this could be?

I followed all instructions for rebuild and double checked all connections after installing lines. Followed the brake flush procedures and flushed with RBF600. After putting the wheels on I pumped up the pedal and drove around the block to make sure I can stop and everything feels normal, but on harder stops or me holing the pedal down it ever so slowly goes to the floor. Reservoir is at max level and hasn't dropped, car stops as expected (the pedal feels a little mushier but not too noticable), and I bled the brakes one more time before going on a longer drive with no air coming out and fluid coming out clean.

Maybe air got into ABS system without me realizing? I will admit I didn't pay attention to the fluid levels during rebuild and line swap but I'm not sure if this was a problem because when I got ready to flush brakes there was a but of residual fluid in the reservoir I used a turkey baster to get out to pour in fresh fluid. Maybe there was less in there than I thought.

Any help is appreciated, thanks!
 

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System pressure bled with motive power bleeder
Ok. All I can suggest is to re bleed the whole system again. Logic tells us it's an introduced fault and if everything else checks out then it has to be air in the system.
Did you bleed the inner AND outer bleed nipples on the front callipers?

Ciao
 

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Discussion Starter #5
Yea everything definitely checks out. Just went out for another drive and am able to slam on brakes repeatedly, no fade and consistent pedal feel, ABS is activated, and still cannot see any leaks from any fittings or brake lines or fluid on ground or wheels.

Good idea, can't hurt. Just bought two more liters of RBF600 for another complete flush, should be here Sunday. Will see how it goes. I also called around some brake shops for possibly flushing ABS module but was told repeatedly to just try a flush if car stops normally. Will see if how the flush on Sunday goes!
 

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I will say that it is normal for the pedal to slowly drop to the floor with strong constant pressure while the motor is running.

I did the same thing you did: first brake flush job, I swore the pedal felt mushier and I was worried about the drooping pedal. I re-bled it but no change.

Finally I drove it back-to-back with my friend’s stock RS and it felt exactly the same! I think I just never paid close enough attention to pedal behavior before I worked on the brakes.

I can’t say for sure this is the same for you - it is probably worth re-bleeding. But if that doesn’t change it and it stops fine, it may all be in your head!
 
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Discussion Starter #7
Alright, another 1000ml of RBF600 came in and I bled the entire system sans clutch again. RR, RL, pump e-brake 10x, RR, RL, FR inner, FR outer, FL inner, FL outer, and used about 700ml. In combination with my original flush I've probably put 1750ml of RBF600 through the braking system and have not gotten any bubbles, not even getting the tiny bubbles on rear calipers some are getting.

Pedal drops even faster now. Before it was much less noticeable but now it's concerning sitting at a stop light and feeling my pedal drop all the way. No change in brake performance, car stops just as hard, ABS kicks on, I can "feel" ABS "pulse" through the brakes when it kicks on, I can modulate brakes without pedal sinking, havent noticed fluid disappearing, can't see any leaks on brake lines or feel any leaks on banjo bolts, everything is normal sans a slightly mushier pedal. Pedal is hard when car is off, as soon as the car starts the pedal sinks all the way in, not too slow but not fast.

Anyone got any ideas? Will be taking it to a brake shop as I ain't comfortable with this.
 

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Alright, another 1000ml of RBF600 came in and I bled the entire system sans clutch again. RR, RL, pump e-brake 10x, RR, RL, FR inner, FR outer, FL inner, FL outer, and used about 700ml. In combination with my original flush I've probably put 1750ml of RBF600 through the braking system and have not gotten any bubbles, not even getting the tiny bubbles on rear calipers some are getting.

Pedal drops even faster now. Before it was much less noticeable but now it's concerning sitting at a stop light and feeling my pedal drop all the way. No change in brake performance, car stops just as hard, ABS kicks on, I can "feel" ABS "pulse" through the brakes when it kicks on, I can modulate brakes without pedal sinking, havent noticed fluid disappearing, can't see any leaks on brake lines or feel any leaks on banjo bolts, everything is normal sans a slightly mushier pedal. Pedal is hard when car is off, as soon as the car starts the pedal sinks all the way in, not too slow but not fast.

Anyone got any ideas? Will be taking it to a brake shop as I ain't comfortable with this.
I would do an old fashioned pump the pedal brake bleed first. You may have actually had an issue before you tor into the system but didn't realise. Maybe previously you just rested your foot on the brake at a stop and there wasn't enough pressure to cause the pedal drop. Now you use more pressure and are looking for an issue you find one?
It does sound like a bypassing master cylinder but with no previous issues it's strange it would give an issue after bleeding.
For anyone else attempting this sort of task I would normally do 1 calliper/line at a time bleed it and confirm its ok and then move onto the next wheel. It limits the variables if something go's wrong as in this case. Pulling the whole system apart at the same time creates confusion and complexity if you need to troubleshoot. I rarely modify or break into more than one component/system at a time. This approach has served me well over the years.

Ciao
 

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Discussion Starter #12
I would do an old fashioned pump the pedal brake bleed first. You may have actually had an issue before you tor into the system but didn't realise. Maybe previously you just rested your foot on the brake at a stop and there wasn't enough pressure to cause the pedal drop. Now you use more pressure and are looking for an issue you find one?
It does sound like a bypassing master cylinder but with no previous issues it's strange it would give an issue after bleeding.
For anyone else attempting this sort of task I would normally do 1 calliper/line at a time bleed it and confirm its ok and then move onto the next wheel. It limits the variables if something go's wrong as in this case. Pulling the whole system apart at the same time creates confusion and complexity if you need to troubleshoot. I rarely modify or break into more than one component/system at a time. This approach has served me well over the years.

Ciao
Will try this today, got enough brake fluid leftover. I think this is what's happening - maybe I was expecting some drastic change after SS lines and RBF600 and when this didn't occur I freaked out. Will see what happens after the pump bleed.
Great tip, will always keep this in mind with the coming mods / work I perform.

Take it to a dealership now before you hurt or kill someone. Driving with a braking system that is so obviously defective is reckless.
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Yes, you are absolutely correct. I stated at the very end of my previous message that I'll be taking it to a brake specialist soon as I'm not comfortable with how the brakes are functioning. Came here for help while I set up an appointment and get everything sorted out. I don't know what you're hoping to achieve by restating what I already know.

Thanks.

Silly question, but are you using the correct grade of brake fluid?

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Yes, I believe many on here have used RBF600 without issue. Both the Ford recommended Motorcraft and RBF600 are Dot 4 so I imagine the change to RBF wouldn't cause what I'm experiencing?


After I learned that the pedal is holding pressure while the engine is off but sinks when started I also thought that there's some brake master cylinder issue. Perhaps I didn't have as much fluid in the reservoir as I thought when I started work and some air got around the seals or the seals went bad and started passing fluid and now I have this issue. Will see what a pump bleed does. If all else fails replacing a master cylinder and having my master, ABS, and brake system professionally flushed is next, which I imagine will solve the issue. Will see how it goes. I really appreciate everyone's help!
 

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Ok, just to clarify, it is not normal for the pedal to actually go to the floor. But it is normal for it to firm up with a couple pumps when the motor is off, then sink a little when the motor creates vacuum for the booster.

And it will feel like it hits a stop of sorts: especially if you pump it repeatedly, it will be softish with a hiss, and then hit a firm stop. That is not really the bottom (floor). That is normal.

Don’t take chances with your brakes, but also don’t freak yourself out. See if you can find a stock RS to compare to. I felt the things I describe above and was ready to go to a brake shop too. Gradually I realized it was the same as before, but I had never paid attention. That was 30k miles and 8 track days ago, and never an issue with the brakes.
 
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Discussion Starter #14
Ok, just to clarify, it is not normal for the pedal to actually go to the floor. But it is normal for it to firm up with a couple pumps when the motor is off, then sink a little when the motor creates vacuum for the booster.

And it will feel like it hits a stop of sorts: especially if you pump it repeatedly, it will be softish with a hiss, and then hit a firm stop. That is not really the bottom (floor). That is normal.

Don’t take chances with your brakes, but also don’t freak yourself out. See if you can find a stock RS to compare to. I felt the things I describe above and was ready to go to a brake shop too. Gradually I realized it was the same as before, but I had never paid attention. That was 30k miles and 8 track days ago, and never an issue with the brakes.

Thanks! Yea, I think I've set my expectations with a caliper rebuild and SS lines too high and may be way in my head now. No leaks, brake performance is fine, pedal is firm on shut down, etc. But with all this said the car is at home while this gets sorted. Pump bleeding brakes tonight and hopefully all goes well.
 

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Sounds like a leak at the servo, have all vacuum pipes been reconnected properly
 

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Sounds like a leak at the servo, have all vacuum pipes been reconnected properly
I didn't disconnect any vacuum pipes? Only brake lines. However I'll double check everything when I do my pump flush for brakes in the next few days.

Is it possible my master cylinder has gone?
 

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I didn't disconnect any vacuum pipes? Only brake lines. However I'll double check everything when I do my pump flush for brakes in the next few days.

Is it possible my master cylinder has gone?
It's a possibility. The first three areas from the Shop manual t/shooting are "in order" leaking lines/air in the brake system, the master cylinder or the HCU.
HCU test.

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I didn't disconnect any vacuum pipes? Only brake lines. However I'll double check everything when I do my pump flush for brakes in the next few days.

Is it possible my master cylinder has gone?
Maybe you didn’t but what you describe has all the classic signs of a vacuum leak on the servo. Could be a worn rubber seal, check all the servo pipe connections to be sure
 

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Maybe you didn’t but what you describe has all the classic signs of a vacuum leak on the servo. Could be a worn rubber seal, check all the servo pipe connections to be sure
I don't think so. If you completely disconnect the vacuum line what you get is a very hard pedal. The whole reason for the vacuum assist is to provide assistance to the pedal, take it away or have a leak and the pedal gets hard.
To back this statement up even the Ford shop manual troubleshooting guide lists only one troubleshooting thread under "excessive brake pedal effort" and it's all about Vacuum leaks or low vacuum from the pump or failed check valve. Yet for his specific issue, zero about the vacuum system only what I have already pointed out in a previous post.

Ciao
 

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