Xantia - air in brake line

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Dom_81
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Xantia - air in brake line

Post by Dom_81 »

Hello, I replaced all 4 corner spheres on my non hydractive xantia. The rear nearside was a struggle to get on, I had to put the suspension in high to stiffen the strut mount, just to turn the sphere the remaining few millimeters and to get it to seal. Whilst car was in the high position a trickle of LHM was flowing out which I caught in a container. Now I'm finding that I need to keep bleeding the caliper on that one corner.. it'll be ok for an hour, then I can feel there's a delay on the rear brakes again.
I'm wondering if I may have damaged something when wrestling with the sphere.. but I'd expect to see LHM leaking, as opposed to the system sucking air in. I discovered id knocked a return hose off that strut and reconnected it. Is it most likely that there is just a bunch of air trapped in pockets and it'll just take a while for it to all finds its way out?
I've bled them 3 times already so would like to get to the bottom of this! Many thanks.
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white exec
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Re: Xantia - air in brake line

Post by white exec »

Apart from initial slackening of spheres (where they will be tight for maybe ¼ of a turn), spheres should unscrew all the way easily, by hand, unless they have some residual hydraulic pressure behind them - which will make them stiff all the way out. When re-fitting, there should be no stiffness at all, except for the final nip-up against the sealing O-ring.

I'd check that the O-ring is sitting in its groove (in the aluminium cylinder) properly, and hasn't got damaged, or slipped out of place, which could cause problems and leaks at the final tighten. The O-ring must go on first, in place, then the sphere gently inserted through it. Hold the O-ring in place with a smear of vaseline or silicone grease, if necessary. Also check that the ring is the proper square-section one; has been known for some after-market sphere sellers to supply simple O-rings!

You are right to hold the cylinder firmly in place to prevent swivel and damage to pipework. You can also do this with a strap, if absolutely necessary, although I've never had to do that. It's the steel pipework that can get damaged by twisting the cylinder; the plastic return pipework is usually ok.
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Re: Xantia - air in brake line

Post by Dom_81 »

Thanks Chris,

I made the mistake of using some spare GSF spheres previously which had some surface corrosion on the thread.. I cleaned them up and the thread looked OK by eye, ignoring the voice of reason in the back of my mind i used them and must have damaged the thread.. but it was a good seal (I fitted Lizarte spheres last week) and I'm 99.9% sure the o ring was in place and not damaged.. I dont dare unscrew the sphere to check and id assume that we would be expecting to see LHM leaking if the o ring was damaged right?
The car is running close to 100% perfect, new height correctors set at correct height, everything flushed and clean fluids, no leaks anywhere.. the issue is just air in the brake lines and I'm hoping this is just residual air making its way out of the system as opposed to some mechanical issue.
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Re: Xantia - air in brake line

Post by Dom_81 »

On a few occasions since changing the spheres, I noticed a hard or sudden knock sound when pressing the brake pedal, felt very much like id imagine an airlock in the brake control valve would feel
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Re: Xantia - air in brake line

Post by white exec »

Have had that too. Any dismantling of parts of the system (spheres included) introduces air into the system.
The brake calipers are "dead legs", so any air trapped there tends to stay there.
The rear brakes are fed from the rear suspension, so air there can get passed towards the brakes.
Air trapped elsewhere tends to work its way out.

Rear right bleed screw will bleed most of the entire system, but it might be worth bleeding both back brakes again.
Do it with engine running, wheels (hubs) hanging, and suspension set to Highest.

Check that the reservoir is running without significantly aerated fluid.
Do a good few Highest-Lowest-Highest... citrobics before doing the bleeding.
Dom_81
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Re: Xantia - air in brake line

Post by Dom_81 »

Thanks again.
Yes the front brakes are sharp as ever, just the rear which has the problem, so ill continue to bleed until hopefully she's burped and no more gas.. ill do both sides and hope that does it, otherwise there's no good reason for it to continue, ill do as you say with the citroebics..
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Re: Xantia - air in brake line

Post by Gibbo2286 »

This is a C5 but I wonder if you have the same corrosion problem.


Armidillo
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Re: Xantia - air in brake line

Post by Armidillo »

As Chris says, check for bubbles in the reservoir.

I believe that one cause of air getting into your rear brake lines could be a rear sphere which has developed a slow leak. This would also give you bubbles in the reservoir. Not sure how long it could go on bubbling - my experience has been more with the ones that go 'BANG' - but you might find one corner is getting progressively stiffer, although if it's the so-called 'anti-sink' sphere it could be very hard to diagnose without removing it.
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Re: Xantia - air in brake line

Post by Dom_81 »

Ok thats one idea to consider.. I wondered if maybe I damaged the sphere when wrestling with it but can't think how that would occur.. also the ride is good so im hoping its just residual air in the system still making its way out... I will aim to update the thread with an outcome once the problem is fixed or fixes itself.
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Re: Xantia - air in brake line

Post by Dom_81 »

So it appears to be a faulty sphere. I was happy to find no more air bubbles in the brakes today but then the rear corner was hard as a rock, replacement sphere being sent and hopefully will recieve and fit tomorrow.
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Re: Xantia - air in brake line

Post by Dom_81 »

Armidillo wrote:
01 Oct 2021, 14:53
As Chris says, check for bubbles in the reservoir.

I believe that one cause of air getting into your rear brake lines could be a rear sphere which has developed a slow leak. This would also give you bubbles in the reservoir. Not sure how long it could go on bubbling - my experience has been more with the ones that go 'BANG' - but you might find one corner is getting progressively stiffer, although if it's the so-called 'anti-sink' sphere it could be very hard to diagnose without removing it.
I thought this the less likely option but it does appear one of the spheres was faulty! I'll update when the replacement sphere arrives.
Thanks for your input