Failed MOT

[superloopy]

'Rear brake imbalance', patch weld needed to nsr sill and a dodgy suspension bush ...

The suspension's not an issue, i've a spare arm in the shed but what's the possible cause of the 'rear brake imbalance'?

I was under the impression that this couldn't be a fail due to the design of the xantia which directs more pedal pressure to the front brakes than the rear or maybe i'm imagining reading this somewhere?

Car's with the garage for the time being, i'll take a run down tomorrow to check on the sill weld that's needed but has anyone any ideas?

Not a problem to strip and rebuild the rear brakes but i doubt that this is what the tester is getting at, any knowledgeable testers about?

[chinkostu]

Means one side is working more than the other. Maybe a siezed piston or the pads stuck to the pin?

[DickieG]

Chances are that one or more likely both rear calipers are sitting at an angle to the disc due to different metal corrosion between the aluminium caliper and steel suspension arm causing the caliper to twist on it's mounting thus causing the pads wear at an angle, the remedy is to remove the caliper, scrape away the corrosion on the mounting face then fit new pads. Do the rear brakes squeal when applied?

[superloopy]

Chances are that one or more likely both rear calipers are sitting at an angle to the disc due to different metal corrosion between the aluminium caliper and steel suspension arm causing the caliper to twist on it's mounting thus causing the pads wear at an angle, the remedy is to remove the caliper, scrape away the corrosion on the mounting face then fit new pads. Do the rear brakes squeal when applied?

No ... there's no squeal and tbh i was surprised to see this failure. The rear brakes have had the 'mod' you mention not so long ago and i'd weighted the boot to ensure that the brakes did kick in

Garage just say 'a good clean up' as they do but i think there's more to this fail than that.

Just wondering if anyone else had been hit with it ...

[KennyW]

Yes, I've had similar problems in the past with the current car. I gave the pistons a check,clean and bled some green blood and she past just.

This year I'm going to run the green blood through and back to reservoir to make sure all air is removed.Will make a fliter prior to entering reservoir to remove the crud which will inevitably come through.

I never had this problem with my 1.9TD estate.

Kenny

[chinkostu]

Run it to the res after all the horrible lhm has run into a bottle or similar. That way you're only getting lhm from the res running back!

[citronut]

what Richard suggested is not a mod but a repair,

it is possible air is in the rear brake circuit as Kenny says, even if the system has not been opened gas depleting from the spheres can and will enter the brake circuit,

imbalance to front or rear is not uncommon on hydraulic citroens,

hydraulic citroen's brake system only differentiates between front and rear brakes, not side to side on one axle, although if the car has ABS it will if one wheel on either axle spins at a higher rate than another

if on the MOT stations brake rollers there is more than a certain percentage of difference between both wheels on one axle, this will incur a fail on imbalance,

ask the garage for the roller readings as this will tell you which wheel is low on performance and by how much

[superloopy]

what Richard suggested is not a mod but a repair,

it is possible air is in the rear brake circuit as Kenny says, even if the system has not been opened gas depleting from the spheres can and will enter the brake circuit,

imbalance to front or rear is not uncommon on hydraulic Citroëns,

hydraulic citroen's brake system only differentiates between front and rear brakes, not side toside on one axle, although if the car has ABS it will if one wheel on either axle spins at a higher rate than another

if on the MOT stations brake rollers there is more than a certain percentage of difference between both wheels on one axle, this will incur a fail on imbalance,

ask the garage for the roller readings as this will tell you which wheel is low on performance and by how much

Been down to the garage today ...

Rusted sills ... yep, OSF holed (by the examiner, but hey ...) near to front jacking point, likewise NSR. Both ringed in yellow so's the welder can take a look. Look fixable but will make a mess of the painted lower sills.

Rear brake imbalance ... no fail sheet reading supplied so i'll just go for a general cleanup of pads/pistons and see what happens. I don't understand what is meant by '
hydraulic citroen's brake system only differentiates between front and rear brakes, not side to side on one axle' ?

The car has abs, being an SX trim and i tend to agree that a recent flat rear accumulator *could* have leaked its air into the system although the garage dont agree that this is a possibility.

I've told them to clean everything up AND bleed the rear brakes.

Then there's the front arm to do ... which i've supplied.

A couple of advisories ... NSF suspension bush ... to be expected i suppose, the car's not had any new arms since new, she's now 20yrs young!!

Front to rear brake pipe corrosion ??? Can't see what he was looking at here as everything is under covers, including the good old engine undertray which i deliberately replaced this time around

Suppose i just need her fixed up and good for another year.

[citronut]

I don't understand what is meant by '
hydraulic citroen's brake system only differentiates between front and rear brakes, not side to side on one axle' ?

this was in response to you saying

I was under the impression that this couldn't be a fail due to the design of the xantia which directs more pedal pressure to the front brakes than the rear or maybe i'm imagining reading this somewhere?

although the garage dont agree that this is a possibility.

I've told them to clean everything up AND bleed the rear brakes.

is this garage familiar with the working of hydraulic citroens??

[superloopy]

It's the garage i've used for a good few years now but the problem these days is that no-one ever sees a 'hydraulic' citroen, they're thin on the ground.

Is there any sort of balancing valve in the system which may explain the fail?

Guess i'll give it one more go and see what happens after a cleanup but i'm more inclined towards the 'air in system' theory given that the air from the flat sphere must've gone somewhere!

If it fails after being fixed up i'll take it ack and DIY ... weather might have warmed up by then ... still no leaves on our trees yet

[citronut]

firstly what day/date was it failed as you get 10 working days to get the re/test, this is not including weekends and bank holidays,

if the garage try a clean up first, ask them if they could put it back on the brake rollers/tester before logging it back onto VOSA's computer/system,

because once its been logged on you loose your free retest,

then if it still fails the brake teast, and you still have some of the ten days left, you could take it away and look at it yourself,

you also really need to ask them for the readings of the fail, these will not be on the failure, but they will have a record of them, all be it just hand writen on the sheet they scribble the items they find as they check the car over,

wuith the results of the brake rollers you can see which wheel is low on effort