Xantia 1.8 Dimension Petrol, 1996
Just failed MoT on poor rear brakes, about 24/20%
The pistones seemed to be free when I checked them. Any suggestions? seems like a hydraulic problem.
BTW I have noticed that the rear of the car "nods" rather excessively when braking, and this might be connected.
Xantia - poor rear brakes
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RichardW
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Put a couple of bags of sand in the boot - that should make the brakes work for the MOT[:D]
But seriously, if the back rises up during breaking this is a sign that you have gas in the circuit somewhere - try bleeding the brakes. If you find excessive gas, suspect that one of your rear spheres has burst a membrane and is leaking nitrogen into the system. Sounds like you have worked the pistons a bit, so now bleed them and see what happens. Might need to change the rear spheres if the problem comes back.
But seriously, if the back rises up during breaking this is a sign that you have gas in the circuit somewhere - try bleeding the brakes. If you find excessive gas, suspect that one of your rear spheres has burst a membrane and is leaking nitrogen into the system. Sounds like you have worked the pistons a bit, so now bleed them and see what happens. Might need to change the rear spheres if the problem comes back.
I had a problem with noticeable rising of rear end of the Xantia (almost up to rebound stops) during braking. So I presumed it was air in rear brake circuit. Went to MOT (out of schedule) and asked the guy to check the brakes for a small tip. Tried rear brakes myself. Pressed the pedal with full force, and first about two seconds device didn't show any braking force, than it progressively, within a second or so, reached maximum braking force, determined by load on rear axis, so it was clear it was air in the system. Device displayed braking force about 24 "units" for each front wheel and about 15 for rear.
Could be a problem with brake pads or worn discs also.
Could be a problem with brake pads or worn discs also.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by RichardW</i>
Put a couple of bags of sand in the boot - that should make the brakes work for the MOT[:D]<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Will my toolkit do?
(Citroen owner, so silly question really [:D] )
The roadwheel-spheres have been changed, but not the antisink or accumulator ones. I'm wondering if one of these might be the culprit.
BTW, is there a pressure-regulator (anti-lock) valve on the rear brakes, if so how does it work? (non-ABS model, BTW)
Put a couple of bags of sand in the boot - that should make the brakes work for the MOT[:D]<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Will my toolkit do?
(Citroen owner, so silly question really [:D] )
The roadwheel-spheres have been changed, but not the antisink or accumulator ones. I'm wondering if one of these might be the culprit.
BTW, is there a pressure-regulator (anti-lock) valve on the rear brakes, if so how does it work? (non-ABS model, BTW)
No brake force limiter valve is found. This function is build into the master (doseur or pedal) valve - rear brakes circuit.
With new wheelspheres - you should have more than adequate rear accumulator brakes action - despite any flat HA or antisink sphere - provided the engine is running supplying system pressure to keep valves open.
I suggest you do the Citaerobics AND then manually bleed the rear brakes.
<i>Difference</i> in available brakes force at each rear wheel is however related to mechanical problems - i.e. rusty disc surfaces and/or stuck caliper pistons.
With new wheelspheres - you should have more than adequate rear accumulator brakes action - despite any flat HA or antisink sphere - provided the engine is running supplying system pressure to keep valves open.
I suggest you do the Citaerobics AND then manually bleed the rear brakes.
<i>Difference</i> in available brakes force at each rear wheel is however related to mechanical problems - i.e. rusty disc surfaces and/or stuck caliper pistons.
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uhn113x
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1997 ZX 1.9D Dimension. - x 1
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">What is wrong whit system when hydraulics does opposite (rear end sinks) while using brakes? It usually does it when I want to brake hardly.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Hi
I assume that by 'brake hardly' you mean the opposite; 'brake hard'! You probably need a new doseur valve - rear suspension pressure is used for the rear brakes
Hi
I assume that by 'brake hardly' you mean the opposite; 'brake hard'! You probably need a new doseur valve - rear suspension pressure is used for the rear brakes
Behaviour of rear end of the car during braking depends on the braking force of rear brakes. If their braking force is too low, rear end will rise (you can verify this by applying parking brake during the drive, because on Xantia it acts on front wheels). If braking force is high enough, rear end can dive a bit.
Just had my Xantia (1997, 101k+ mls) serviced and had to replace my rear drums (among other things) as they were below minimum. I don't know how to check it, but as my car has a Full Cit Service History, this seems to be the 1st time. Not sure what mileage you have, but might be worth looking into as they rear breaks did act funny before they were replaced!
Cheers,
John
Xantia 1.8i Desire (1997, 101k mls now)
Cheers,
John
Xantia 1.8i Desire (1997, 101k mls now)
As I understand it the Xantia rear brakes and suspension are similar to those on a BX with the addition of the anti-sink mechanism (valve and sphere)
The system is unusual in that they are linked and the rear brake section of the doseur valve is actually fed from the rear suspension circuit. The reason for this is to provide compensation for loads which it does rather nicely. (heavier load, higher rear suspension pressure, higher braking force. . . )
In common with other Citroen circuits it can be considered in 2 parts for bleeding purposes. The easier bit is the common part and the difficult bit is the one way pipes to each rear brake. Gas may enter the system from the spheres as they deflate but generally this will be expelled as the car rises and falls during use. If you've got anti-sink then this won't happen so easily as it does in a BX which drops completely overnight - so it can be expelled by cit-aerobics - just raise the car fully and drop it a few times.
If the gas has got into the lines to the wheel cylinders you will have to bleed each one but do the aerobics first to get all the air out of the rest of the system.
Many a good doseur valve has been replaced in the search for elusive problems - they seem generally reliable. Sinking rear under braking can be caused by a number of things and remember that the action of the trailing arms is to rotate rearwards when the brakes are applied which will produce a slight drop. Another point is that if you observe it at a certain place - ie a particular traffic light for example - is the question of whether the suspension is just levelling itself as it should do.
jeremy
The system is unusual in that they are linked and the rear brake section of the doseur valve is actually fed from the rear suspension circuit. The reason for this is to provide compensation for loads which it does rather nicely. (heavier load, higher rear suspension pressure, higher braking force. . . )
In common with other Citroen circuits it can be considered in 2 parts for bleeding purposes. The easier bit is the common part and the difficult bit is the one way pipes to each rear brake. Gas may enter the system from the spheres as they deflate but generally this will be expelled as the car rises and falls during use. If you've got anti-sink then this won't happen so easily as it does in a BX which drops completely overnight - so it can be expelled by cit-aerobics - just raise the car fully and drop it a few times.
If the gas has got into the lines to the wheel cylinders you will have to bleed each one but do the aerobics first to get all the air out of the rest of the system.
Many a good doseur valve has been replaced in the search for elusive problems - they seem generally reliable. Sinking rear under braking can be caused by a number of things and remember that the action of the trailing arms is to rotate rearwards when the brakes are applied which will produce a slight drop. Another point is that if you observe it at a certain place - ie a particular traffic light for example - is the question of whether the suspension is just levelling itself as it should do.
jeremy