406oc.co.uk

Few weeks ago going to work the brake pedal went rock hard and it was difficult to stop. Then it drove fine and it did it again a few days after. Straight away thought servo was on it way out. Drove ot for few more days and it seemed all okay So i did the servo test by pumping the pedal till it goes rock hard before i start the car, hold the pedal and start the car and the pedal should sink a little. Tried that, but, the pedal wouldnt go hard, but moves as should as soon as you start it. So again thinking is servo on it way out. Also when waiting at the light the pedal seem to travel down. There is a delay in braking. Took it to usual mechanic he said could be servo, could be caliper etc etc basically he had no idea and then took citroen/Peugeot specialist and they werent too sure, saying it could be the vaccum pump and that he has never had to replace a servo. He pulled the pipe off the vaccum pump and there was suction, there was also suction as the one way valve. He then showed me showed me the one off a picasso on the 2litre hdi engine but the vacuum pump on there had a lot more suction. So he said he would start at changing the vaccum pump first. So i sourced a 2nd hand one and changed it over in the freezing cold and it made no difference So i checked all the vaccum pipes and i have no vaccum going to turbo solenoid or egr solenoid, none going to the swirl diaphram either. I've read online of similair 406 owners who have had same issues and some have lost vacuum and replaced the servo and all is good again. I've inspected the front hoses and changed the disks and pads over as they needed doing and currently in process of changing rear shoes discs and pads.

It brakes okay but there is a delay and the pedal sinks in traffic n pedal goes hard and then also if you press the pedal you can hear a slight hiss when engine is running. Any ideas?

Sounds as though you have a vacuum leak somewhere, if the pedal goes soft eventually and then the brakes work there must be vacuum there - eventually. The non return valve on the servo may be faulty.

The vacuum to the other accessories will only be there when they are in operation.

Peter

How would you tell if the non return valve is faulty?

Disconnect the pipe after the engine has been running and the servo is working and see if there is a hiss. If it is leaking the servo will fade after the engine has stopped and brake pedal will go hard.

Peter

I've checked the non return valve by taking it off and blowing air through both sides it's working as it should and the rubber part in the servo seems okay too

How long after you switch the engine off does the pedal go hard?

Peter

Once you disconnect the pipe to the non return valve the pedal won't go rock hard.

Once you reconnect it it feels the same. You can put your put on the pedal gently and pedal will travel about 3/4 or more down.

Strange one that. It could possibly the master cylinder, that will allow the pedal to drop if its leaking internally but it shouldn't make any difference to the pressure required to stop, it sounds like intermittent failure of vacuum but I think you have already replaced the pump and there is nothing much in the servo to go wrong. Ideally what you need to do is to check for vacuum when its in fault mode i.e difficult to stop, the only way I can think of doing that is to connect a vacuum gauge to the servo supply and put it some where that you can see it when you are driving.

It could of course be a leak somewhere else in the vacuum system that is causing you to loose it to the servo.

Peter

Parm wrote:Once you disconnect the pipe to the non return valve the pedal won't go rock hard.

Once you reconnect it it feels the same. You can put your put on the pedal gently and pedal will travel about 3/4 or more down.

Hey Parm, you're right. I did that and the pedal goes down more now. thanks!