strange brakes

shabbir · Post by **shabbir** » 30 May 2005, 21:26

Hi all,
I recently bought a citroen xantia. It's a 93 model. I found the brakes quite scary, when the brakes are applied, the car automatically removes pressure, then takes some time to apply pressure again. All this time I have my foot on the brake. I have to tell people to brace themselves as it usually ends up to be a very sharp brake at the end - good use of the grab rail! Recently my ABS light has been coming on, and with the ABS switched off, the brakes are considerably better. Anyone know if this is how the brakes are supposed to be, and if not, how to fix it.
Regards,

Post by **RichardW** » 30 May 2005, 21:32

No they are not supposed to be like that!
1. Bleed the brakes - especially the rears. Do this with the engine running, and the suspension in high. Wedge the pedal down, and then just open the bleed screws in turn.
2. Change the accumulator sphere - the one down the front of the engine. Do a search on here, loads of posts about how to do it.

samtronic · Post by **samtronic** » 30 May 2005, 21:46

It sounds like your ABS is misbehaving, probably due to a defective ABS sensor.
Until you get the ABS fixed you should disable it (remove the fuse(s)) as it sounds rater dangerous to drive as it is.
Søren

oilyspanner · Post by **oilyspanner** » 30 May 2005, 22:16

It sounds more like air in the system to me, I eventually got mine right by bleeding a LOT of LHM through the rear brakes, something like a litre came through before the bubbles came past me (I use a long piece of clear pipe and run it back to the reservoir) the ABS is probably feeling strange because of the air, it is probably momentarily locking the wheels when the pressure catches up.
Stewart

shabbir · Post by **shabbir** » 30 May 2005, 22:30

thanks for the advice guys. I will look into the bleeding of the brakes, if that dont fix it then I will change the acc spheres. Btw, I am a newbie, what is LHM?
with regards to the abs, sometimes the light goes off, and the brakes go into their crazy mode, would this really be due to air. as with the abs off, the brakes are quite good.

oilyspanner · Post by **oilyspanner** » 31 May 2005, 00:28

LHM is the fluid used in your suspension and braking system. You should not know ABS is there unless wheels are locking, I think the crazy braking you are having is air in the system which will get compressed when you brake and make the brakes come on with a bang, locking a wheel which in turn makes the ABS go on and release pressure to the locked wheel, the wheel will then start to turn, ABS comes off, system pressurises the air again, brakes come on with a bang and around we go again.
Stewart

samtronic · Post by **samtronic** » 31 May 2005, 00:37

I am still pretty sure that one of the ABS sensors are defective. And that you get more usable brakes by disabling the ABS supports that conclusion.
Others have (on this forum) described pretty much the same symptoms:
- ABS light intermittent
- Brakes doesn't seem to work at first and the suddenly brake full force.
The idea is that the ABS ECU is confused by a sensor sending incorrect readings for a wheel and disables brakes on the wheels it thinks are blocking until it sees that it is not helping and disables the ABS function again.
Upon power on the ABS ECU checks the sensors for continuity and if ok turns off the ABS light.
If during driving the signal disappears from a sensor for some time, the ABS light is turned on again and the ABS disabled.
If the signal re-appears for some time, the ABS light is turned off again and the ABS enabled.
You can check the sensors if you have a multimeter:
- Locate the ABS ECU (between the battery and the LHM reservoir)
- Disconnet the plug on top and measure the resistance between the following pins (Some of the pin numbers are moulded into the plug):
1 and 6: Right Front
15 and 30: Left Front
29 and 31: Right Rear
19 and 28: Left Rear
The resistance should be apx. 1050 Ohms (1.05 kOhms).
You can see some pictures here:
http://medlem.spray.se/xm94/XANTIA/fels_abs.html
(Translation tool here: http://www.systransoft.com/index.html)
You should also be able to find quite a bit of info regarding ABS on this forum if you search it.
Søren

jeremy · Post by **jeremy** » 31 May 2005, 03:02

You can check the accumulator easily by getting the car to normal height, turning off the engine and sitting in the boot. The car should sink, and after about 20 seconds rise to its original height powered by the accumulator. Ideally it will do it twice but once is probably enough. If it doesn't the accumulator sphere must be changed. (about £18 from GSF.)
I doubt if the problem is ABS - its intended to be a fail safe device. The ECU fitted to the earlier Xantia's is known to be troublesome but can be repaired by a specialist. However most problems are due to sensors and often it is the lead which is at fault and can be repaired - details elsewhere on this board.
http://www.carelect.demon.co.uk/
jeremy