Xantia brakes spongy

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Dre85
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Xantia brakes spongy

Post by Dre85 »

Hi,
I recently took my xantia for an mot and it failed due to spongy brake pedal and on the brake efficiency. Before the mot I had recently changed the front pads and discs, and have not really bedded then in yet. Since the mot I have bled the brakes but the pedal sill feels spongy. So I was wondering if anyone could point me in the right direction on what to do now? Could the Doseur valve cause the spongy brake pedal and low brake efficiency?
Any ideas would be helpful.
addo
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Post by addo »

I'd suggest a very thorough bleed of the brakes, might be in order.
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Re: Xantia brakes spongy

Post by citronut »

maybe you have the XANT/C5 rear brake syndrom,
did you get the brake reading's from the rolling road test, if not these could point you in the right direction,

regards malcolm
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Re: Xantia brakes spongy

Post by Dre85 »

I took it to an mot station so I'm guessing they did the brake test on the rolling road. Withe regards to bleeding the brakes, I have already given them a good bleed on all the callipers, but just don't know what to check now regarding the spongy brake pedal?
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Re: Xantia brakes spongy

Post by Xaccers »

Front flexi pipes getting weak and flexing too much?
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Re: Xantia brakes spongy

Post by Xantidote »

Did you get any air out when you bled at the calipers, particularly the rears? If you did remove some air, then maybe the spongey feel is not as bad as it was prior to fitting the new front pads & discs.
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Re: Xantia brakes spongy

Post by citronut »

i spoz you do know how to bleed hydraulic citroen brake's,
not the same up down up down up down up down up down as conventional brake's,

regards malcolm
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Re: Xantia brakes spongy

Post by Dre85 »

Hi malcolm
Yes I bled the brakes with the engine running, and wedged the brake pedal. I bled them one at a time with pipe going straight back to the hyd tank. There seemed to be a bit of air from the rear left caliper but didn't really make a difference to the brake pedal. Regarding the flexi pipe going to the front calipers, they look fine but can't really tell if they have gone week.
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Re: Xantia brakes spongy

Post by RichardW »

You can't have a spongy brake pedal in a Xantia - if there's air in the system, then the pump just keeps pushing fluid in to compress the gas - and then the brakes come in with a bang, as by then you've stamped on the pedal as it appears it is not going to stop :o If you got plenty of fluid out of the calipers, then that is not the problem. What was the actual failure? If it's just efficieny, then chances are it just needs the pads stripped out the front and cleaned / greased up.
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Re: Xantia brakes spongy

Post by Dre85 »

The failure that was put on the mot slip was brake efficiency below requirements and brake pedal feels spongy. The pads and discs are new so shouldn't need cleaning.
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Re: Xantia brakes spongy

Post by Mandrake »

Regarding braking efficiency, you said originally that you had new pads and discs that had not been bedded in shortly before the MOT - both front and back ?

Perhaps they need a bit of proper bedding in. Normal casual driving will take a long time to bed in a new set of discs and pads, (possibly weeks with slow city driving, and may in fact never bed in properly) whenever I've fitted new pads I usually go for a test drive on a safe quiet stretch of country road where I can perform moderately hard repeated braking from speed. (50mph or so) Starting off moderate and then increasing towards (but not reaching) an emergency stop.

It's important not to overheat the pads while bedding in otherwise they can get glazed due to the small contact area between the pads and disc until they bed into each other. So I'll generally do three progressively harder stops in a row over a period of a couple of minutes then leave it for a few minutes to cool before repeating. Also NEVER brake to a dead stop when bedding in, just slow rapidly to about 20mph then release.

For bedding in rear brakes its helpful to put a fairly decent load in the boot, because otherwise the maximum braking force of the rear brakes is limited by the hydraulic system, and may not be sufficient to properly bed them in.

Either lack of bedding in or excessive very hard braking (causing hot spots) before they are properly bedded in can result in brakes that are insensitive. In the latter case it can sometimes be necessary to pop the pads out and if they look very smooth and shiny with a slight burnt look to them in places, rub the surface slightly to rough it up again. (I just gently rub them on some smooth flat concrete for a few seconds, NOT file or sand them) Then you can go through the bedding in process again.

If the back brakes are not working efficiently, I presume the callipers have been checked to not be out of alignment due to rust ? And also that the pistons have been freed up by repeatedly pushing them back in with a screwdriver then out again with brake pressure ? Normally just doing this several times for each piston is enough, in very bad cases you might want to put a drop or two of LHM at the edge between the piston and calliper before pushing it in and out. (I would exercise the front pistons if the front reading is low too)

As for the spongy brake pedal, i'm surprised nobody has mentioned the "silly spring" unit fitted on the brake pedal arm of all Xantia's. Most of the way up the back of the brake pedal arm there is a plastic tube that contains a spring, the whole plastic tube can be removed by hand by lifting the brake pedal as high as you can, grasping the black plastic cylinder and wiggling it from side to side until it comes out from the back of the arm.

The black capsule can be easily disassembled and inside you'll find a spring and a rubber buffer. It's possible that the spring has snapped and lost a few coils of length (not common but I've heard of it happening) the purpose of the spring is to "ruin" the normal Citroen brakes feel of hard very sensitive short travel pedal and make the brake pedal feel soft and mushy with lots of movement like a normal car for people used to normal brake pedals. Seriously. :lol:

Among the Citroen purists there is a lot of debate about whether to remove this spring entirely and replace it with a section of equal length metal tube. If you do this the "spongy" feel of the pedal will go away for sure, and the feel of the brake pedal will be the same as older model Hydropneumatic Citroens like the BX, CX, GS and so on, eg stiff, with very little travel but very sensitive, responsive, and progressive.

On my previous Mk1 Xantia (and coming from older Citroens so being used to their brake pedals) I found the Xantia brake pedal very mushy and imprecise, so I performed the spring removal mod and was very happy with the results - if you have a suitable length of tube it can be done in minutes.

Interestingly on the Mk2 Xantia V6 I have now I have not found it necessary to remove the spring yet - the pedal is a bit softer and mushier than I'd like but the brakes work fairly well. I do notice its still a little bit difficult to precisely control the applied level of braking though - this is a result of the friction of the two sliding halves of the plastic capsule as the spring compresses. I may yet perform the spring mod on this Xantia I think :)

If you search the forum for "silly spring" you should find a mega thread discussing how to modify it and debating whether it should be modified...in any case, its dead easy to revert it back to original, as long as you keep the original spring.
Simon

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Re: Xantia brakes spongy

Post by Dre85 »

Thanks for the advice Simon. I'll take a look at the spring on the brake pedal and see if I can bed the pads in before the re-test.
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Re: Xantia brakes spongy

Post by Dre85 »

Thanks for all the replies. I took the xantia for the re-test today and it passed :-D
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Re: Xantia brakes spongy

Post by Mandrake »

So what did you do ?
Simon

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Re: Xantia brakes spongy

Post by CitroJim »

Mandrake wrote:So what did you do ?
Whatever you did it worked =D> Congrats on a new MOT!
Jim

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