MOT failure Xantia

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

Post Reply
inthemicz
Posts: 18
Joined: 15 Apr 2005, 03:46
Location:
My Cars:

MOT failure Xantia

Post by inthemicz »

My xantia has failed the MOT with the note rear foot brakes not responding fast enough, could this be the accumulator sphere? If not any ideas? Its a 93 model
Cheers
Michael
johnlyn
Posts: 64
Joined: 16 May 2004, 14:22
Location: United Kingdom
My Cars:

Post by johnlyn »

I always thought that the rear brakes were load dependant on Xantias etc, in which case does this MOTer know?
John
inthemicz
Posts: 18
Joined: 15 Apr 2005, 03:46
Location:
My Cars:

Post by inthemicz »

he said it was strong enough but there was a delay after pushing the pedal
edit:spelling
User avatar
Kowalski
Posts: 2557
Joined: 15 Oct 2003, 17:41
Location: North East, United Kingdom
My Cars: Ex 05 C5 2.0 HDI Exclusive 145k
Ex 97 Xantia 1.9TD SX 144k
Ex 94 Xantia Dimension 1.9TD 199k

Post by Kowalski »

Is the rear of the car at the correct height?
If it's too low you can end up with no pressure in the rear brake circuit and no rear brakes.
Peter.N.
Moderating Team
Posts: 11563
Joined: 02 Apr 2005, 16:11
Location: Charmouth,Dorset
My Cars: Currently:

C5 X7 VTR + Satnav Hdi estate Silver
C5 X7 VTR + Hdi Estate 2008 Red

In the past: 3, CX td Safaris and about 7, XM td estates. Lovely cars.
x 1199

Post by Peter.N. »

Or if its slow reacting you could have air in the brake system.
User avatar
Mandrake
Posts: 8615
Joined: 10 Apr 2005, 17:23
Location: North Lanarkshire, UK
My Cars:
x 664

Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by inthemicz</i>

he said it was strong enough but there was a delay after pushing the pedal
edit:spelling
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Bleed the rear brakes. The supply goes from the rear suspension all the way to the front of the car, through the brake valve (and ABS block if you have ABS) and then back to the brakes again so there is a long length of pipe that could potentially have air in it.
So don't just bleed a little bit of oil and call it a job done, you want to bleed a decent amount of oil to ensure you get all the air.
Another little trick to remember passing MOT's - years ago over here before testers were Citroen savvy, my Dad always had to put some weight in the boot of his GS to pass the rear brake test - with no weight the rear brakes only work fairly lightly and were actually below the "acceptable" level of a standard car at the time due to the automatic brake equalization.
No amount of explaining to them in those days (70's) about the load equalization would get a pass so he just learnt to put a load in the boot before going in for the test [:D]
On the other hand the front brakes of the GS could easily STALL the brake testing machine much to the chagrin of the tester [:D]
Regards,
Simon
jeremy
Posts: 3959
Joined: 20 Oct 2002, 16:00
Location: Hampshire, UK
My Cars:
x 2

Post by jeremy »

The easy bit - its not the accumulator as it is not in this circuit once the car has achieved normal height. The rear brakes are powered from the rear suspenion circuit which provides a very nice way of achieving load compensation. So the car pumps the suspension up, the height corrector shuts and the weight of the car provised the rear brake pressure - increase the load, higher pressure - more power available fro the brakes. While the height corrector is closed the system is isolated from the pump, accumulator etc.
Nice but can lead to problems especially if the car is run without much fuel and no load as in effect the back brakes never work. Vauxhall recommended that some of their cars with disc back brakes were driven with the handbrake on for 100 yards per week just to keep the discs clean!
The simple answer for your car is probably to re-submit it with a load in the back. The only problem with this approach is that the callipers may have siezed and the brakes won't release properly so they should be checked for hot running afterwards. Incidentally raising the car fully will subject the rear brakes to increased pressure as the height corrector will be open and so they get full system pressure.
jeremy
User avatar
fastandfurryous
Posts: 1388
Joined: 07 Jul 2004, 17:57
Location: On the road, travelling at high speed. Meep Meep.
My Cars:
x 4

Post by fastandfurryous »

Air in the lines sounds to be the most likely reason for this to me. The best way to be sure that there is no air in them whatsoever is to get a monsterously long length of clear washer hose, and pipe from the rear caliper, back to the LHM tank. Open the bleed nipple, and just stand on the brake. Let the fluid flow for a very long time, so that you have flushed through the brake circuit, and cleared any air that may have been there.
Works best if the car is in high, as there is full system pressure available for bleeding.
I've heard that it's good to do this when you have hydraflush in the system too, as it cleans out all manner of yuck.
JohnT
Posts: 344
Joined: 27 Dec 2003, 21:29
Location: United Kingdom
My Cars:

Post by JohnT »

Perhaps a simple approach..... are the pads thick enough?
User avatar
fastandfurryous
Posts: 1388
Joined: 07 Jul 2004, 17:57
Location: On the road, travelling at high speed. Meep Meep.
My Cars:
x 4

Post by fastandfurryous »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by JohnT</i>

Perhaps a simple approach..... are the pads thick enough?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
How would that make any difference whatsoever?
User avatar
Kowalski
Posts: 2557
Joined: 15 Oct 2003, 17:41
Location: North East, United Kingdom
My Cars: Ex 05 C5 2.0 HDI Exclusive 145k
Ex 97 Xantia 1.9TD SX 144k
Ex 94 Xantia Dimension 1.9TD 199k

Post by Kowalski »

I can't see pad thickness being an issue, perhaps if the rear discs were very badly warped they would push the caliper pistons in a way, but I think the most probable suggestion is probably air in the rear brakes somewhere.
JohnT
Posts: 344
Joined: 27 Dec 2003, 21:29
Location: United Kingdom
My Cars:

Post by JohnT »

This comment in reply is not specific to this Citroen problem but referring to the point I made, is the pad thick enough? If fluid is displaced by the foot brake and all things are correct, no problem. If the rear pads/linings are worn excessively then the displacement will need more time to do the job (in preference to the front OK brakes) as more fluid is required to take up the space....hence the delay? Hence the MOT testers point. I suggest you check the pads on the rear and any air in the rear end! If you have air in the rear brakes then look to renewing the rear cylinders.
jeremy
Posts: 3959
Joined: 20 Oct 2002, 16:00
Location: Hampshire, UK
My Cars:
x 2

Post by jeremy »

John
Modern disc brakes have no retraction mechanism and are therefore self adjusting. The movement involved in appliction is exactly the same with new or old pads.
Dunlop type (later made by Girling) in the late 50's and 60's are the only ones I've come across with any form of retraction mechanism and that only realy took the pressure off rather than actually making the pad move away from the disc. These were fitted to Mk 11 Jaguars and the like. This system would operate but hit a stop when the pads wore out so needed careful maintenance.
jeremy
inthemicz
Posts: 18
Joined: 15 Apr 2005, 03:46
Location:
My Cars:

Post by inthemicz »

Ok I bled the brakes and also put the sand in and it passed!!
User avatar
Mandrake
Posts: 8615
Joined: 10 Apr 2005, 17:23
Location: North Lanarkshire, UK
My Cars:
x 664

Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by inthemicz</i>

Ok I bled the brakes and also put the sand in and it passed!!
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Maybe its time to change your sig then ? [:D]
Regards,
Simon
Post Reply