Will that make the pedal sink when you press it hard (with the engine running)?
Depends on how far it sinks. If a long way, then as you suspect there could be air in the system. If in any doubt get back onto the garage that did the work and ask them to bleed the system. How old is the car? Might be worth geting them to change the brake fluid if more than 2 yrs old.
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Car is 3 years and 2 months old, brake fluid changed at 2 years on the dot.
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Will that make the pedal sink when you press it hard (with the engine running)?
If the pedal sinks wqhen you press hard and continues to sink then it indicates a leak in the system.
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I read often, only post occasionally
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I cant believe that your garage didnt bleed the front brakes when the pads were changed.
If they havent been done - get your garage to bleed them - and then get a new garage.
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I cant believe that your garage didnt bleed the front brakes when the pads were changed. If they havent been done - get your garage to bleed them - and then get a new garage.
I don't see any reason why the garage should have bled the brakes if they didn't open the brake hydraulic circuit.
Number_Cruncher
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Exactly-if a garage has to bleed brakes to change pads they're doing something wrong.
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On one or two cars I have had the brake pedal does sink down if you press the pedal hard when stationary. If you then turn the engine off and exhaust the vacuum it hardens up.
I dont know the reason for it but only a couple of weeks ago was talking to my local independant garageman about this after he had replaced the rear wheel cylinders on my wifes car.
He said most cars do this and isnt a fault.
He did explain why but can't remember his explanation.
Try it on you own car with the engine running and press very hard.
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And also...If you start the engine with your foot pressed hard on the brake pedal it sinks down immediately.
Something in one of my handbooks about this saying its not a fault.
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Alvin,
What you describe is normal operation of the servo unit.
On most cars, the servo is a direct acting suspended vacuum servo. It is the large pancake shaped object inbetween the brake master cylinder/fluid reservoir and the bulkhead.
Inside the pancake shaped chamber are two sealed volumes, seperated by a diaphragm. The pushrod from the brake pedal is connected to a valving system at the central boss of the diaphragm, the boss is, in turn connected to the first piston of the tandem master cyclinder.
Under normal operation, both volumes are held at low absolute pressure (or under high vacuum if you prefer). When you push the brake pedal, the valving does the following, in order,
1) Closes the connection between the two volumes
2) Begins to admit air, usually from the car's interior into the rearmost sealed volume.
3) The extra force given by the pressure difference in the two chambers is added to the force the driver exerts, thus giving assistance.
4) The rate at which air is admitted into the rearmost chamber as a function of pedal load is governed by a compliant part of the valve, usually a rubber reaction disc.
When you release the pedal, the connection to atmosphere is closed
Then, the connection between the two volumes is re-established, the air in the rearmost volume being passed via the valve and the piping, which usually incorporates a one-way valve, into the intake manifold.
It is quite easy to estimate an upper limit for how much assistance the servo may provide. If you have a 10" diameter servo, you can easily calculate the area of the diaphragm. Taking an extreme case of having atmospheric pressure on one side of the diaphragm, and zero pressure on the other, you can estimate the force - for a 10" diaphragm, this is about 5kN.
Sometimes, for packaging reasons, more than one diaphragm can be put in series. Then the canister begins to look much more like a cylinder than a pancake!
Also, the same type of device can be constructed using hydraulics - some older BMWs certainly used this. I suspect some Citroens did too, but I know nowt about them!
Number_Cruncher
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If the C5 arrangement is the same as the Xantia/BX, then the piston is "screwed" back into the caliper to reset the automatic adjuster for the handbrake mechanism. I have found that sometimes, after fitting new pads the handbrake feels ok but the pedal does feel a little soft. I have found that doing the following improves the pedal feel:-
1 Start engine and allow the hydraulics to "settle down".
2 Apply the footbrake hard.
3 With the footbrake applied, pull the handbrake on harder.
4 Release footbrake.
5 Repeat above 2/3 times.
6 Release hand and footbrake.
7 re-apply handbrake.
This has worked for me on several occaisions. I don't know why, but I would guess that it is to do with "settling" the adjuster mechanism.
The "wet" Citroens do not have a conventional servo. All (power steering, brakes, suspension and abs) are driven by the same system. I would guess that the complexity of it is no more so than a non Citroen with separate power steering pumps, servos, abs booster pumps etc.
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The C5, oddly enough, has a 'conventional' braking system - it has nothing at all to do with the suspension hydraulics! The Xantia was fed by the same system, but for some reason Citroen opted out of this for C5 and went 'ordinary'.
How they let a Citroen out of the factory with such a thing beats me. Maybe Monsieur Quirk had a day off.......
Graeme
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C5 Owner, I'm totally amazed. In that case my comments are well wide of the mark. You've almost put me off looking for one when the Xantia expires.
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I know, it's a bit of a shock to the system! Mind you the C5 has very good brakes. I always thought the Xantia had super duper anchors, but I had a run in my sister's Xantia at the weekend and realised that C5 is much better - much more feel but equally powerful.(The Xantia takes a bit of getting used to - little pedal travel but fierce bite!)
C5 also has assisted braking in emergencies (extra oomph on the pedal, accompanied by automatic hazard warners) I've only had mine come on once - a young deer jumped out in front of me a couple of weeks after I bought the car. It stoppppppppped!!!! Deer totally unscathed. I reckon the old Xantia would have mashed it.
Graeme
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Re: opening the hydraulic circuit. They sometimes open a bleed valve on the caliper to prevent fluid in the master cylinder reservoir overflowing, when they push/screw back the piston, or to prevent damage to the master cylinder seals in some cases.
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Indeed, this is true.
However, in doing so, you are expelling fluid rather than admitting air.
However, when I use this method, I also tend to pump the pedal a couple of times to get rid of the nastiest fluid that has been lurking in the caliper and flexi - so perhaps that counts as a partial bleeding operation?
Number_Cruncher
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I think I will have to check the number of days off I have before new year and book the car into the garage where the mechanics are craftsmen (a long drive away) and get the combined brake/clutch fluid changed.
Ben
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Forgot to say, the brakes pull up well and stop the car fantastically. Just the pedal feel isnt the best and the clutch probs mentioned elsewhere on here.
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