Hi,
I have a 1994 XM Onyx estate with a serious problem - the rear brakes dont work. I only noticed the fault after 2 hydraulic pipes were replaced. The garage spent hours flushing out the brake pipes but found nothing.
Could there be air or dirt in the brake control valve ? Can the valve be bled ?
Any suggestions appreciated.
Jim
XM brakes
Moderator: RichardW
Hi Jim -
How did you found out the rear brakes wont work ?
- reason I ask is, that the rear brakes pressure is feeded off the <i>rear wheel suspension pressure</i>.
With rear wheels hanging down off ground, you then need to set the height control to <i>highest position</i>, to force pressure out in the rear suspension, thus getting pressure to the rear brakes circuit.
Often you need to lift up the hanging wheels, to make the height controller open for pressure, which then presses down hard the hanging wheels, and <font color="red"><i>then</i></font id="red"> pressurises the rear brakes circuit.
Only 2 other possibilities as I see it :
1) the replaced pipes has been mixed up
2) the brake doseur (pedal) valve is at gross fault (unlikely though)
Please find info on the XM hyd pipe connections here :
http://citroeny.cz/servis/xmser/xm.html
How did you found out the rear brakes wont work ?
- reason I ask is, that the rear brakes pressure is feeded off the <i>rear wheel suspension pressure</i>.
With rear wheels hanging down off ground, you then need to set the height control to <i>highest position</i>, to force pressure out in the rear suspension, thus getting pressure to the rear brakes circuit.
Often you need to lift up the hanging wheels, to make the height controller open for pressure, which then presses down hard the hanging wheels, and <font color="red"><i>then</i></font id="red"> pressurises the rear brakes circuit.
Only 2 other possibilities as I see it :
1) the replaced pipes has been mixed up
2) the brake doseur (pedal) valve is at gross fault (unlikely though)
Please find info on the XM hyd pipe connections here :
http://citroeny.cz/servis/xmser/xm.html
OK Jim -
- then you might find this document handy :
http://www.rwbsmith.plus.com/citroen2/Brakes/doseur.pdf
Although aimed at the BX, it's still the same brake valve.
I'm still puzzled that the brake valve would completely fail to put out pressure to the rear brakes. It does in fact points to a piping mix-up problem, as the valvewould always put out <i>some</i> pressure.
Another problem may be wrong assembly techniques with new pipes. The pipe seal <i>must</i> be fitted to the pipe end, <i>before</i> the pipe and seal is homed in the component pipe port.
The seal should <i>never</i> be fitted in the port, then fitting the pipe, because the pipe end is razor sharp, thus shearing the seal while fitting the pipe.
This may lead to either pressure leaks or blockage of the pipe.
Hope you find the problem - best of luck.
- then you might find this document handy :
http://www.rwbsmith.plus.com/citroen2/Brakes/doseur.pdf
Although aimed at the BX, it's still the same brake valve.
I'm still puzzled that the brake valve would completely fail to put out pressure to the rear brakes. It does in fact points to a piping mix-up problem, as the valvewould always put out <i>some</i> pressure.
Another problem may be wrong assembly techniques with new pipes. The pipe seal <i>must</i> be fitted to the pipe end, <i>before</i> the pipe and seal is homed in the component pipe port.
The seal should <i>never</i> be fitted in the port, then fitting the pipe, because the pipe end is razor sharp, thus shearing the seal while fitting the pipe.
This may lead to either pressure leaks or blockage of the pipe.
Hope you find the problem - best of luck.
-
Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
No doubt the car has anti sink fitted, does the suspension rise to self level when weight is added to the rear, or the control lever raised to increase height, just thinking that the anti sink valve may be siezed, locking out the suspension and depriving the rear brakes of supply pressure.
Is ABS fitted, if so do you get supply pressure up to the valve block when the brake pedal is depressed.
Like Anders, I can't imagine the doseur valve can lock out the rear brakes, unless the piston is siezed by dirt ingress, a bit unlikely.
Dave
Is ABS fitted, if so do you get supply pressure up to the valve block when the brake pedal is depressed.
Like Anders, I can't imagine the doseur valve can lock out the rear brakes, unless the piston is siezed by dirt ingress, a bit unlikely.
Dave
I first noticed the problem when I got the car back from the garage, I had a bad leak at the rear and lost most of the LHM. They replaced 2 pipes CIT064B and CIT324. I noticed immediately the breakes were slightly heavier but didnt give it much thought. A week later I took the wheel off to check a faulty ABS sensor and I noticed the discs were starting to rust.
I took it back to the garage and they removed several pipes and checked for blockages but found none. He said there could be a blockage somewhere else in the system or possibly a faulty valve, but I would have to leave it with him for several days. I was worried that the bill might be more than the car is worth.
Is there much chance of mixing up the pipes if only 2 were replaced ?
The car doesn't have anti-sink.
Jim
I took it back to the garage and they removed several pipes and checked for blockages but found none. He said there could be a blockage somewhere else in the system or possibly a faulty valve, but I would have to leave it with him for several days. I was worried that the bill might be more than the car is worth.
Is there much chance of mixing up the pipes if only 2 were replaced ?
The car doesn't have anti-sink.
Jim
-
Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
Can you check for supply pressure at the doseur valve from the rear suspension circuit, by loosening the pipe nut on the valve, if there is nothing there I would think there was a serious mix up of the pipework, or at a long shot a blocked pipe.
Whatever, you need to do some examination of the system to find out where pressure is getting to so that those areas can be eliminated as being at fault, you can then point a repairer at the likely areas and not have to pay them to find out what you can find out for yourself.
If it was all working ok before the pipes were replaced then this must have something to do with it.
Dave
Whatever, you need to do some examination of the system to find out where pressure is getting to so that those areas can be eliminated as being at fault, you can then point a repairer at the likely areas and not have to pay them to find out what you can find out for yourself.
If it was all working ok before the pipes were replaced then this must have something to do with it.
Dave
I did what Dave suggested and loosend the supply pipe from the rear suspension. I unscrewed it about 10mm with no sign of LHM. I kept unscrewing but it didn't come up any further, which I thought odd.
Anyway, I now have to check the other end at the height corrector. Is there a good schematics of Hydractive 2 anywhere ? The one on the cz website has the rear brake circuit missing.
Jim
Anyway, I now have to check the other end at the height corrector. Is there a good schematics of Hydractive 2 anywhere ? The one on the cz website has the rear brake circuit missing.
Jim
Jimn -
You may find a wee bit more info in Gabor's Citroen techref :
http://www.tramontana.co.hu/citroen/citroen%20guide.pdf
The pipe MUST come up from valve no big problem, just pull hard. If NOT, then you have some kind of a problem.
Also make sure it's the correct pipe you check for pressure with suspension in normal - <i>and engine idle !</i>
It's the pipe designated AR with arrow pointing into the valve.
If the pipe designated AR (arrow out from valve) is under pressure, then the pipes has been mixed up.
Note the valve is shown upside down, with pedal contact (or on UK RHD models : the pedal linkage) on LHS.
You may find a wee bit more info in Gabor's Citroen techref :
http://www.tramontana.co.hu/citroen/citroen%20guide.pdf
The pipe MUST come up from valve no big problem, just pull hard. If NOT, then you have some kind of a problem.
Also make sure it's the correct pipe you check for pressure with suspension in normal - <i>and engine idle !</i>
It's the pipe designated AR with arrow pointing into the valve.
If the pipe designated AR (arrow out from valve) is under pressure, then the pipes has been mixed up.
Note the valve is shown upside down, with pedal contact (or on UK RHD models : the pedal linkage) on LHS.
Jim - I've never seen a RHD XM brake valve fitting, but the Citroen brake valves have the front brakes lines closest to the pedal bulb, and the rear lines at far end. Each front circuit's lines will be on top & bottom of valve, but both rear circuit's lines would be approx on same side, shifted some 90deg apart over the valve body.
Thus it should in fact pretty much look like the schematic above. Note that for rear circuits, it's the line farthest away from bulb that is OUPUT (TO brakes), meaning the other nearby line would be the one under pressure (from rear suspension).
Thus it should in fact pretty much look like the schematic above. Note that for rear circuits, it's the line farthest away from bulb that is OUPUT (TO brakes), meaning the other nearby line would be the one under pressure (from rear suspension).