Foot brake problem - steering and apply the foot brake, pedal goes to the floor

[Ozvtr]

Was the power steering masking the feel of the roll bar hitting the calliper? Did you feel the contact of the roll bar and calliper through the steering or was that the funny "bush back" sensation you described?

It explains the clunk symptom most have mentioned.

In your original post you said on "full lock in any direction". Wouldn't the calliper only hit the roll bar in one direction?

It's a good find but I cant understand the reason why the brake peddle would go to the floor. Unexpected increase in pressure in that circuit causes the ABS to freak out? Why doesn't the ABS fail light come on?

I can only hope some of the other victims inspect the roll bar and comment.

[C3bri]

I couldn’t feel any resistance in the steering, only the noise I could hear, the antiroll bar would push against the calliper moving it towards the disc, moving on its slides and pushing the piston into the calliper, hence no brake on the first press after, I did say in any direction as the missus did describe it as that but it could of only been when on lock to left

[Ozvtr]

the brake Pedal hits the floor, take my foot off and press again and the brake is back to normal

This is the bit that concerns me and I don't have an answer for.

If it was the fact that the roll bar was pushing on the calliper and causing the piston to push on the disk I don't see how the brake peddle would loose pressure and go straight to the floor. If anything it would tend to push back against the peddle pressure and the peddle would get stiffer? This is all supposition. I've never tried pushing on the brake while the piston is being compressed or vice versa. Then add to that what the ABS would do when it "sees" this situation?

I still believe the ABS ECU is causing this problem and it is doing something the engineers didn't count on. Having said that, I guess it shouldn't happen in the first place (the calliper hitting the roll bar).

Oh well, I guess the best we can do is warn forum members if we see these symptoms in the future.

Thanks C3bri for telling us your findings.

[Ozvtr]

Wow, I cant let go of this one can I?

C3bri, is it possible that the peddle "went to the floor" just as you were turning the steering wheel BACK (away from full lock)? Or do you believe you lost peddle feel as you hit full lock (and the roll bar)? If it was the former, I have a theory, if not I have a headache.

[C3bri]

The pedal would go to the floor as the piston had been pushed back, just like when you have changed the discs and pads and you have to pump the pedal to get them working, same principle as the antiroll bar hitting the calliper and no the pedal dropping was whilst it’s on lock NOT coming away, the abs wouldn't see the issue as it wouldn’t see the pressure change as it sees pressure via the pedal, with the pedal Switch being activated and the slowing of the vehicle through the wheel speed sensors so as far as the vehicle is aware nothing has changed, so the abs would have no reason to trigger/activate lights or warnings

[Raceydriver]

I have investigated this issue on my wife's C3 as it is doing the same, new shape with only 25500 miles on clock. When turning left or right on full lock the drop link lower ball joint where bolted to the anti roll bar, the threaded section pushes against the back of the calliper pushing back across which forced the piston back into the calliper causing the pedal travel. Of course as the pads and disc wear the calliper will move closer to the drop link connection making the pedal travel worse. Replace the pads and it will go for a short time before the fault returns. It will be very close but not quite touch when stood still with the cars weight on the suspension, but as you move off the car will rise at the front causing the anti roll bar to move on the ends and will make the threaded section of the drop link to push against the calliper. Take vehicle to your dealer to get this sorted out as is a very serious design fault and needs to be sorted out. If we all do nothing then no issue for Citroen to sort out thus no safety recall.

[Raceydriver]

We have now had the car into Citroen and the same has happened to my wife's car as in previous post above. The anti roll bar has moved over to the right by a couple of inches causing the drop link threaded end to be pushing against the back of the caliper. This is moving the caliper over causing the brake pedal travel to reset the calliper and piston the normal braking operation resumes. The anti roll bar bushes are not worn, car has only covered 26,000 miles from new with full service history. There is no damage to anything underneath and they at present are at a loss as to why. They cannot get it to go back into its proper position without the subframe being dropped and the clamps for the bushes undone. They are awaiting for Citroen UK to get back to them as to how the dealer is to proceed forward. I will keep updating on this situation.
I believe the issue starts after the first MOT as this is usually the first time the suspension is fully extended during the test and when the anti roll bar is pushed down it is catching on something to push it over as with a bar cannot be pushed back when the suspension is fully extended as when on a 2 post lift, lets see?

[routemaster1]

We have now had the car into Citroen and the same has happened to my wife's car as in previous post above. The anti roll bar has moved over to the right by a couple of inches causing the drop link threaded end to be pushing against the back of the caliper. This is moving the caliper over causing the brake pedal travel to reset the calliper and piston the normal braking operation resumes. The anti roll bar bushes are not worn, car has only covered 26,000 miles from new with full service history. There is no damage to anything underneath and they at present are at a loss as to why. They cannot get it to go back into its proper position without the subframe being dropped and the clamps for the bushes undone. They are awaiting for Citroen UK to get back to them as to how the dealer is to proceed forward. I will keep updating on this situation.
I believe the issue starts after the first MOT as this is usually the first time the suspension is fully extended during the test and when the anti roll bar is pushed down it is catching on something to push it over as with a bar cannot be pushed back when the suspension is fully extended as when on a 2 post lift, lets see?

There is something I don't understand about this. I appreciate if the caliper has moved due to the moved droplink, but I don't understand why that alone should allow the pedal to go to the floor. That caliper will be served by one of the two circuits. The second circuit should still be functioning, and as such should prevent the pedal going to the floor. If that half of the circuit had failed as well, braking would be poor enough to be noticed.

I have only had one experience of brake failure. I had a 1963 Mini, single circuit brakes with the early trailing/leading shoe drums on the front. I had a few minor issues with the brakes which I had coped with. One day travelling home, the traffic lights changed. The Mercedes in front of me stopped, so I put my foot on the brake, which went right to the floor. Luckily on release and reapplication they worked and it stopped ok. Needless to say, the master cylinder was changed and all was ok. From my experience at the time, new seals were a waste of time.

[Ar53n1c]

Sorry for bringing up an older thread but, I had this same issue start last week.

Strangely enough mine initially would only do it in a shop parking lot that has a banked exit to the parking lot where you turn left to get out, after pumping the brakes to build pressure there was no issue with the car or brakes after that on both counts.

I booked the car in at the local garage to be checked and while on the call to the owner I explained I had come across this thread and the theory of the anti-roll bar moving, he promised to check it out but was almost certain it wouldn't be the case and was more worried about the servo possibly been bad or a leak in the system.

When I dropped off the car they also have a incline on there parking space and I went full lock left and then right to park and the pedal hit the floor so was a perfect place for them to recreate the problem.

He called me later in the day to say my rear pads wear low and need to be replaced and he found no other issues on the brake system, also bleed all the brakes after replacing the pads as a preventative measure, they had also tried as I explained full lock left and right into the inclined parking space and vice versa and could not reproduce the issue so was happy it was fixed.

I collected the car the next day and before I could even leave the workshop parking (Keep in mind the inclined parking space) , I had to do a full lock right and then full lock left to get out between the cars that were parked there and the brake pedal hit the floor again.

I left the car with them, explaining again what had just happened.

He called me totally surprised this morning to tell me I was correct that the Anti-Roll bar was indeed causing the issue and as previously mentioned seems to have moved to the right of the sub-frame by a couple of inches, he took the time to call Citroen to find out if this was a normal issue which they supposedly said they have seen it a few times but there was no recall on the car or revised Anti-Roll bars to be fitted they also couldn't explain what has caused this or why the anti-roll bar has the ability to press against the braking system pushing the piston back in if it moves.

He said in his numerous years on the job he has not encountered this problem or even this setup for the anti-roll bar and was a little at loss for words on it.

The bushes seem to be the main cause as they are moulded to the anti-roll bar and have now become degraded enough to allow the bar to slide slightly and in his own words you wouldn't notice this during any normal inspection of this setup, you would have to have an idea of what you were looking for. (Thanks to this forum!)

I now wait for a new anti-roll bar setup to be delivered and installed which includes dropping the sub-frame unfortunately it seems there is no way around this.

I will update once I have the car back and hopefully have brakes once again that can be used at low speeds no matter the wheel position in inclined parking spaces.

[Poecile]

Did this get fixed for you? If so was it the the Anti roll bar causing the problem?