Should my brake discs have failed MOT

Car is a 3 year old Clio 1.2 16v with 32k miles (pads first changed at

18k).

It failed it's MOT due to "Front brake discs corroded badly". The receptionist said it failed due to corrosion on the inboard side, which on inspection there is.

The corrosion has reduced the effective braking area (I've measured with a steel rule) from 1 7/8" to 1 5/16".

Was the inspector correct to fail it ?

Reply to
Paul S
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If it's the outside edge that's rusted then it wouldn't seem unfair,they're hardly expensive, if oit's the inside edge then it's a tad harsh, but I doubt you'd win an appeal.

Reply to
Duncan Wood

Dunno what the rules are, but in my personal opinion, yes. The disks weren't going to be able to give you 100%, personally I want my brakes to be 100%, and i wouldn't mind everyone elses being perfect too ;)

If they'd passed, when would you have replaced 'em, next MOT ?

Sorry if you think it's harsh, but come on, they're your "brakes" FFS :)

Reply to
Tony Bond

Duncan, It's the inside edge of the inboard side (that doesn't have the wheel to protect it) that's rusted.

Reply to
Paul S

If it's the bit next to the hub, then of itself it won't make much difference, but does imply your calipers need servicing, if it's the outer edge then that's what does most of the braking.

Reply to
Duncan Wood

snipped-for-privacy@anyone.plus.com(Paul S) wrote in news:465cad52$0$8757$ed2619ec@ptn- nntp-reader02.plus.net:

Wheel doesn't protect it, your calipers are not working as they should.

Reply to
Tunku

You can improve stopping power for a given pedal travel by reducing the effective braking area. It's a cheap and dirty trick that's been used for years in grass roots motorsport, you remove friction material from the pad towards the center of the disk thus moving the centre of effective area out, it's almost counter intuitive but it works at the expense of pad life.

Reply to
Depresion

I'm no expert but I would have thought that was the clear conclusion, unless the pad had begun to disintegrate. I would certainly want it sorted out.

Andy

Reply to
Andy Cap

Tunku ( snipped-for-privacy@dsl.pipex.com) gurgled happily, sounding much like they were saying :

Agreed. Never mind the symptom, address the cause.

Reply to
Adrian

Depresion (127.0.0.1) gurgled happily, sounding much like they were saying :

Not really. Given that you're exerting a certain force to the piston, there's two ways to increase the pressure at the pad.

Increase the force Decrease the surface area.

Reply to
Adrian

Which will give you the same frictional force when you multiply the two together. However if you remove the material from the inside only it will act firther away from the hub and apply more leverage.

Reply to
Duncan Wood

In news:465c8c10$0$8732$ snipped-for-privacy@ptn-nntp-reader02.plus.net, Paul S wittered on forthwith;

So he's right.

Still right, in a panic stop from 70 mph that's a lot of brake disc that isn't being used.

Yes.

If you're going to skimp and not maintain your vehicle properly, please hand your licence back to the DVLA now. You'd be upset if someone hit your car because their brakes were knackered....

Reply to
Pete M

Decreasing the surface area as such makes no difference. Moving its centre may well.

Reply to
Dave Plowman (News)

Corrosion on one side only means the caliper isn't working normally - it's either stuck on its pivot or the piston(s) on that side have seized.

Corrosion on both sides can happen when the car isn't used - but should clean up with use.

Reply to
Dave Plowman (News)

Probably. I think it's subjective to a point. Clio discs can be bought for less than a tenner each so it's hardly a big deal other than the cost of the MoT.

Reply to
adder1969

The message from adder1969 contains these words:

Clios in particular seem really prone to this.

Reply to
Guy King

My car failed on brakes too, and they suggested replacing the disks, I have normally found that brakes fail the brake test on the MOT before they reach the physical wear limits set by the MOT eg. my bike pads are in theory allowed to have only 1mm for the MOT but I was told to replace them before then because the brake was binding on.. sorted the problem nicely too. I suspect there is considerable scope for testers to use their judgment here I suspect they have a 6th sense !

Reply to
mr p

And other things (bonnet catches) which all can be prevented by decent servicing. It would appear that either Clio owners don't bother or the mftrs service schedule has some massive holes in it.

Reply to
Conor

Pretty well all other makers seem to be able to design secondary bonnet catches that will survive neglect. Seems to me a prime design objective for a secondary safety feature - like using say maintenance free pivots on it. It's not something subject to heavy continuous use, so it's hardly rocket science to make it up to this job.

Reply to
Dave Plowman (News)

I find the opposite - brakes that are wafer thin and/or rusty and look really really poor but still pass the MoT test. I guess you want it that way really.

Reply to
adder1969

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