Xantia with ABS bleeding question

[ksanturion10]

Hi to all,
as I mentioned in another thread, I'm onto the search of information about proper bleeding of an ABS system.
Please, if you need my VIN don't bother

Into the S2 Xantia.pdf file, kindly provided by the forum , there is written, that a Lexia can be used, so to make the procedure more easy, but it is not said in what respect?
I mean, does it opens all brake valves prior the bleeding, and if so, if this is necessary, can it be done without the Lexia? -> 1st question
I have Lexia, but my OBD16pin-to-PSA30pin adapter cable is not still rearranged properly, and so can't use the Lexia onto the car - I've made some cables so I can read the ECU at home (on a bench ) only - can post a pic if someone is interested.
The other, mechanical problem, which dates back some time after I've bought the car , is that the front left wheel calliper was blocking the wheel - it had mechanical damage over the piston, which I kind of smoothed out , but it turned out in the end, that the ABS ECU is playing games also, because now with the ABS fully disconnected, the calliper piston doesn't seize!
So my second question is, should I reconnect back the ABS plug for the bleeding procedure, despite I'm not going to use my Lexia? -> 2nd question
The low-high-low-high followed by the "one man show" is understood as I did this for the fronts before.

BR
Martin

[Mandrake]

I've never used a Lexia to bleed the brakes on the Xantia. I don't think it's necessary.

By default the ABS block is in bypass mode - this means the pressure from the brake pedal passes through to the brake callipers unaltered. When the ABS activates it selectively releases the brake on individual wheels, (although I think the Xantia actually only uses a 3 port system so can control the front wheels separately but rear operate together) and it does this by disconnecting the line to the brake pedal and connecting the line to the calliper to overflow return.

So there really isn't anything to bleed that won't be bled by simply bleeding the brakes at the calliper. The ABS block in a green blooded Citroen is much simpler than a conventional vaccum assisted car because no ABS pump is needed to "pump" the brakes on and off - the main hydraulic pump and accumulator takes care of quickly applying the brakes again in between each release cycle. (in vacuum servo systems there is an electric pump in the ABS block in addition to the solenoid operated hydraulic valves)

So just bleed the brakes at the calliper and you'll be fine! My favoured method (since I work on my own) is to wedge a length of 2x4 between the seat and the brake pedal, leave the engine running, then crack each bleed nipple open until it runs clear and close it again. Closing the nipple while the pedal is still depressed prevents any air being drawn back in via the bleed nipple. Suspension should be at the maximum height setting otherwise you probably won't be able to bleed the rear callipers.

Regarding your ABS block "fault" I can't see any way in which the ABS block can fail such that it blocks the return from the brake calliper - the valve can only either switch the calliper between the brake control valve (which has its own return when the pedal is not pressed) or directly returning it when the ABS solenoid is activate.

I'd be more suspicious of a damaged brake hose which is collapsing internally under partial vacuum, especially if the calliper area has suffered damage in the past. If the hose is internally damaged I'd really get that replaced if I were you - not only can it cause the calliper to stick on (and thus overheat the pads) it will also prevent the ABS from pulsing on and off properly, allowing the wheel to lock when ABS is trying to prevent it locking.

Here's a great video on diagnosing internally collapsing brake hoses:

[CitroJim]

I've never used a Lexia to bleed the brakes on the Xantia. I don't think it's necessary.

No, it's not necessary... I can happily confirm that

On the other issue, fully in agreement with Simon on all points...

Worth looking out for a squashed rigid brake pipe too where they cross the subframe... They should not be subject to damage but a bit of careless jacking or grounding in the past might have done some damage...

[ksanturion10]

Wow, hi again . Having both of you here, think it settles the matter, just one thing more to clarify.
Ok, it can be done without the Lexia, but I presume your connector to the ABS ECU was plugged in, right?

Regarding the brake hoses (the rubber type at the callipers), I've watched the video - nice one, but mine are brand new, and generally they should have two layers of reinforcing braided steel mesh, like the originals, so don't believe they have something to do with the locking. I had the same cracks over the original hoses, but this is the top weathering layer, which is just for protection of the bottom layers - of course it is always better to have them intact . The car kept locking even with the new hoses, so I'm discarding that idea.
Well, this hint for the rigid (steel) pipe is something I should check upon, but as I said in the first post, the wheels are not locking, when the ABS ECU is fully disconnected, which points towards the ABS system itself.

Unfortunately we don't have enough information of the mechanics and inner workings of that particular system, so trying to diagnose, what really makes it block only one wheel, would be futile in my view. The bad thing, with this locks, is not only the increased fuel consumption, but also hardened brake pads, which leads to premature fatigue of the brake disks combined with a lot of unnecessary heat generation, which f*cks up everything around the hub assembly, wheel rims and finally the tyres

BR
Martin

[white exec]

Hi Martin,

This is the official hydraulic bleeding procedure - from Citroen Mechanic's handbook, Xan-XM-Synergie, 2001

This also bleeds the hydraulic system, after any component (eg a sphere) has been removed.
Rear brakes are fed from rear suspension circuit, as you know.

Suggest throwing 1L of extra LHM into the reservoir before bleeding.
RR bleed screw will draw off the majority of aerated fluid from the system - expect 1L (or even a bit more) from there before fluid runs clear.
Far less from the other three bleed screws.
ABS is self-bleeding, s.f.a.i.remember, so doesn't need special attention.
Length of wood between driver's seat front and brake pedal will keep it lightly pressed.
Check fluid level after it's all done.

[admiral51]

Not sure if you have seen This Info about the ABS system.

[CitroJim]

Wow, hi again . Having both of you here, think it settles the matter, just one thing more to clarify.
Ok, it can be done without the Lexia, but I presume your connector to the ABS ECU was plugged in, right?

Yes, correct, bleed with engine running and ABS ECU fully connected

No Lexia required....

[ksanturion10]

Hi again,
been busy with my bike and today tried to "ease" the rear callipers before the bleeding. Really liked how it is designed back there .

Yes, correct, bleed with engine running and ABS ECU fully connected

No Lexia required....

Ok, that is a relief, thanks

Not sure if you have seen This Info about the ABS system.

Yes, have seen it before, but haven't time to go through all the writings. Think to check on the car how really the rear breaks and spheres are connected.

This is the official hydraulic bleeding procedure - from Citroen Mechanic's handbook, Xan-XM-Synergie, 2001

Yes, this is what I'm citing also. Unfortunately more questions are arising in my mind after taking a more through all look at it.
Hope you don't mind, as the additional info you all are providing is great

1. I have two highest settings, one at the "full tyre" sign, and one slightly before that - the car stays at the same level at both. I know the "full tyre" is the position for changing tyres. Which one should be used for the bleeding, and could there be a malfunction at the level before it (this is the "offroad" setting, right?)?
2. Putting on stands and removing all the wheels is just for better access to the bleed nipples or there shouldn't be any external force at the hydraulic cylinders?
3. I guess I'm getting picky on this, but into the procedure they say, that with Lexia you can open the ABS hydraulic valve block, and if it is self bleeding, could it be, that the ABS will bleed after some time driving and applying the brakes?
4. Pressing the brake with engine running and ABS ECU connected, doesn't opens the separate hydraulic valves onto the ABS block, right?

Generally, it is not that crucial, but still I think it is important and interesting procedure, as it seems, that it has influence also onto the suspension itself.

BR
Martin

[Hell Razor5543]

One thing to be careful of is seized bleed nipples. If you find that they don't want to move DON'T FORCE THEM!!! If they shear it is a bl00dy pain! Get hold of some Plus Gas (also known as "Dismantling Fluid") and dose the nipples daily for a week or so. Then you should find they come undone easily. What you might then want to do is remove each nipple and smear a touch of copper slip grease on the thread (making sure not to go too far down the nipple, as you do not want to contaminate the LHM fluid).

When I have bled the brakes on a Xantia I have done so at the top suspension setting, with an axle stand taking the weight. I only do so one wheel at a time, in the order of Rear Right, Rear Left, Front Right, Front Left.

[ksanturion10]

Hi, and thanks for the info.
Already have them unscrewed and screwed back, so that part is done. We have different producers here, but yes, I've used something similar to the Plus Gas you are referring, it is called Penetrating oil and it makes miracles
This with the one wheel off and a stand you made for providing clearance to the calliper or didn't want to push on that particular suspension cylinder, or both?

BR
Martin

[xantia_v6]

For bleeding the rear brakes you need to have pressure in the rear suspension circuit and have the engine running to open the anti-sink valve. To ensure that there is pressure in the rear suspension circuit it is advisable to have the suspension set to the highest position before you jack the car off the ground.

[ksanturion10]

So you are creating the necessary pressure, needed at the rear callipers for the bleeding, by setting the car at the highest position ("full tyre" sign), because you have to jack the wheels off the ground? I though the pressure is created by the weight of the vehicle itself .
OK, it seems will have to try it first, before asking more questions.
Thanks all for the info!

BR
Martin

[xantia_v6]

The weight of the vehicle should be sufficient,- if the wheels are on the ground, but it is often necessary to jack the car up or remove the wheels for access to the bleed nipples.

[white exec]

Even with all the wheels off the ground (or removed, hubs hanging), putting the car on max height will create downward thrust pressure in the suspension rams, which is correct for proper/easy bleeding. The weight of the car will not be there, but the system will be pumping against the suspension-movement stops.

[CitroJim]

All the gen on brake bleeding (and other things) is here: viewtopic.php?t=24595