i have being trying to resolve the problem brought up in my other post
http://www.frenchcarforum.co.uk/forum/v ... hp?t=20582
during which i have managed to cause the front brakes to become extremly sharp. i cant stop the car with out it trying to throw me through the wind screen, is this due to the system being over filled?
harsh front brakes on xantia
Moderator: RichardW
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dan_the_v8man
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Over filling will have no effect apart from making a mess when the surplus fluid leaks from the reservoir.. This is a fully powered system and all the braking force is provided by the hydraulic pump and the accumulator, and none at all by the foot pedal - which merely operates a valve.
The valve is designed to allow a progressive application and normally gives no trouble. It is I suppose possible that air in the system could cause a delay and then rapid application - as initial application would produce no reaction but fluid begins to flow, compressing the gas and suddenly appliying the brakes - - if this is the case a second application immediately after might be more normal. Air in the system can produce rushing noises from the pedal area.
Air (or gas) can come from collapsed spheres. All spheres leak into the system eventually and on non-anti-sink cars it is purged as the car sinks. Citroebics may cleaqr some of it (raising and lowering the car several times) but air in the calipers and the limbs of the circuit running to them will have to be bled in the conventional way.
The valve is designed to allow a progressive application and normally gives no trouble. It is I suppose possible that air in the system could cause a delay and then rapid application - as initial application would produce no reaction but fluid begins to flow, compressing the gas and suddenly appliying the brakes - - if this is the case a second application immediately after might be more normal. Air in the system can produce rushing noises from the pedal area.
Air (or gas) can come from collapsed spheres. All spheres leak into the system eventually and on non-anti-sink cars it is purged as the car sinks. Citroebics may cleaqr some of it (raising and lowering the car several times) but air in the calipers and the limbs of the circuit running to them will have to be bled in the conventional way.
jeremy
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dan_the_v8man
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Sounds like air or gas - could be a leaky accumulator - after all there's loads of gas in them when its released.
Is there any possibility of a leak between the reservoir and the pump? - they let air in rather than leak LHM out. Usual culprit is the join to the reservoir - which needs to be sound and tightly clipped.
Is there any possibility of a leak between the reservoir and the pump? - they let air in rather than leak LHM out. Usual culprit is the join to the reservoir - which needs to be sound and tightly clipped.
jeremy
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dan_the_v8man
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Believe it or not, if the rear brakes are not working properly (air in the rear brake lines, pads etc) then it can make the brakes quite abrupt in their action.
This is for two reasons - one is because the initial very light application of braking with fine control comes mostly from the rear brakes and then as you press harder the front brakes come in and do most of the work.
The other reason is that most of the backforce from the pedal is derived from the rear brake pressure (try pressing the brake pedal with the suspension right up and down and you'll see the difference) so if the rear brakes have a lot of air in the lines, the pedal becomes too easy to press, and therefore the front brakes seem over sensitive.
Have you tried thoroughly bleeding the rear brake lines ? (And the front ones too for good measure, but its most likely the rear ones)
Edit: just reading your other thread - did you resolve the rear suspension problem or are you driving around with the rear end of the car sitting on the bump stops?? If the rear suspension is right down there will be no rear brake pressure and the front brakes will become oversensitive due to the pedal becoming too light as described above...
In that case you need to get the suspension sorted out FIRST and then come back to the brakes...
Regards,
Simon
This is for two reasons - one is because the initial very light application of braking with fine control comes mostly from the rear brakes and then as you press harder the front brakes come in and do most of the work.
The other reason is that most of the backforce from the pedal is derived from the rear brake pressure (try pressing the brake pedal with the suspension right up and down and you'll see the difference) so if the rear brakes have a lot of air in the lines, the pedal becomes too easy to press, and therefore the front brakes seem over sensitive.
Have you tried thoroughly bleeding the rear brake lines ? (And the front ones too for good measure, but its most likely the rear ones)
Edit: just reading your other thread - did you resolve the rear suspension problem or are you driving around with the rear end of the car sitting on the bump stops?? If the rear suspension is right down there will be no rear brake pressure and the front brakes will become oversensitive due to the pedal becoming too light as described above...
In that case you need to get the suspension sorted out FIRST and then come back to the brakes...
Regards,
Simon
Simon
1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White
2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White
2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
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dan_the_v8man
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yes it was running on the bump stops
just what has left me puzzled is that it was fine before i started investigating the rear suspension. fair enough the back end was down on the stops and it appears i had no rear brakes either but the front brakes were fine though it may explain why i locked the front wheels up rather easily. all i can assume is i've disturbed a trapped pocket of air in the system during jacking it up
would letting the car go up and down the full range of suspension travel (albeit front end only) solve it so i could be in a posistion to drive it to a garage as i really dont know where to look with this now.
if i depress the pedal very slowly there is no progessiveness in the brakes they just suddenly slam on. the worrying thing is, the previous owner is not aware of this problem and it recently had the front spheres and struts done to get it through an MOT
just what has left me puzzled is that it was fine before i started investigating the rear suspension. fair enough the back end was down on the stops and it appears i had no rear brakes either but the front brakes were fine though it may explain why i locked the front wheels up rather easily. all i can assume is i've disturbed a trapped pocket of air in the system during jacking it up
would letting the car go up and down the full range of suspension travel (albeit front end only) solve it so i could be in a posistion to drive it to a garage as i really dont know where to look with this now.
if i depress the pedal very slowly there is no progessiveness in the brakes they just suddenly slam on. the worrying thing is, the previous owner is not aware of this problem and it recently had the front spheres and struts done to get it through an MOT
thourghly bleed the brakes,when ever the pedel only functions at the second presure wich is when it locks the braks on,it is due to air in the brake system,this can not circulate back to the tank like the rest of the system dose,as the brake circuit has four dead end one at each caliper,as the spheres have not long been replaced this will im sure be the braking fault,the rear susp fault will be down to either the plastic link poped of or siezed hight corector linkage,bear in mind the brake pedel unit basicly operates at two satages fist stage is normal braking presure ans second is locking the brake up,so normaly you only use the first presure and when that is not avalibale you only have loking out presure left
regards malcolm
regards malcolm
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dan_the_v8man
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tried i letting it go up and down the full travel of the suspension a few times this morning and its sorted the front brakes
has any one got any diagrams of this plastic linkage, i've traced the linkage back and its free and lubricated
the rod that travels back from the front (connected to the control next to the hand brake) operates a lever which then moves a roller along a slot in an arm which is connected to the height corrector unit, also there is the connection from the anti roll bar above.
this all apears to be intact though manually operating the linkage doesnt seem to move much apart from the first lever at the rear end of the rod. the roller travels about 8 to 10mm along the slot in the arm connected to height corrector unit but doesnt appear to move much else
has any one got any diagrams of this plastic linkage, i've traced the linkage back and its free and lubricated
the rod that travels back from the front (connected to the control next to the hand brake) operates a lever which then moves a roller along a slot in an arm which is connected to the height corrector unit, also there is the connection from the anti roll bar above.
this all apears to be intact though manually operating the linkage doesnt seem to move much apart from the first lever at the rear end of the rod. the roller travels about 8 to 10mm along the slot in the arm connected to height corrector unit but doesnt appear to move much else
