MOT Brake failure
Discussion
Afternoon chaps - bit of an odd question possibly, but my car failed its MOT recently on the grounds of 2 brake discs (1 front 1 rear) being seriously weakened on the inner side.
This is on a 5 year old Fiesta ST, to my eye the brakes look fine - some corrosion on the top hat and the outer edge where the vents are between the 2 faces of the disc. No corrosion on the friction areas - places i would expect to see some rust. Theres a very slight lip where the face has worn down, but i would suggest less than 0.5mm.
My main question is, how much of the inner disc face can you see considering it has a dust shield up against it for starters, and surely a failure on that would mean there must be a split or something critically wrong with the structure of the disc, otherwise it's an advisory at most (which i would accept, as i say, there's some corrosion but it's definitely not excessive).
I have the feeling I'm having my pants pulled down - having a second opinion at my usual garage tomorrow, and if they need replacing it will be done, but understandably a bit miffed at having an MOT fail on something that doesn't look to be a failure in my eyes.
This is on a 5 year old Fiesta ST, to my eye the brakes look fine - some corrosion on the top hat and the outer edge where the vents are between the 2 faces of the disc. No corrosion on the friction areas - places i would expect to see some rust. Theres a very slight lip where the face has worn down, but i would suggest less than 0.5mm.
My main question is, how much of the inner disc face can you see considering it has a dust shield up against it for starters, and surely a failure on that would mean there must be a split or something critically wrong with the structure of the disc, otherwise it's an advisory at most (which i would accept, as i say, there's some corrosion but it's definitely not excessive).
I have the feeling I'm having my pants pulled down - having a second opinion at my usual garage tomorrow, and if they need replacing it will be done, but understandably a bit miffed at having an MOT fail on something that doesn't look to be a failure in my eyes.
What did the tester say to you when you asked?
Bear in mind that much of the test is the opinion of the tester.
www.gov.uk/guidance/mot-inspection-manual-for-priv...
1.1.14. Brake discs and drums
"A brake disc or drum must be significantly worn before you should reject it. Being worn below the manufacturer’s recommended limits is not a reason in itself.
Defect Category
(a) Brake disc or drum:
(i) significantly and obviously worn. Major
(ii) insecure, fractured or otherwise likely to fail. Dangerous
(b) Contaminated with oil, grease etc. Major
(c) Missing Dangerous
(d) Brake drum back plate insecure Major"
Bear in mind that much of the test is the opinion of the tester.
www.gov.uk/guidance/mot-inspection-manual-for-priv...
1.1.14. Brake discs and drums
"A brake disc or drum must be significantly worn before you should reject it. Being worn below the manufacturer’s recommended limits is not a reason in itself.
Defect Category
(a) Brake disc or drum:
(i) significantly and obviously worn. Major
(ii) insecure, fractured or otherwise likely to fail. Dangerous
(b) Contaminated with oil, grease etc. Major
(c) Missing Dangerous
(d) Brake drum back plate insecure Major"
Fury556 said:
Afternoon chaps - bit of an odd question possibly, but my car failed its MOT recently on the grounds of 2 brake discs (1 front 1 rear) being seriously weakened on the inner side.
This is on a 5 year old Fiesta ST, to my eye the brakes look fine - some corrosion on the top hat and the outer edge where the vents are between the 2 faces of the disc. No corrosion on the friction areas - places i would expect to see some rust. Theres a very slight lip where the face has worn down, but i would suggest less than 0.5mm.
My main question is, how much of the inner disc face can you see considering it has a dust shield up against it for starters, and surely a failure on that would mean there must be a split or something critically wrong with the structure of the disc, otherwise it's an advisory at most (which i would accept, as i say, there's some corrosion but it's definitely not excessive).
I have the feeling I'm having my pants pulled down - having a second opinion at my usual garage tomorrow, and if they need replacing it will be done, but understandably a bit miffed at having an MOT fail on something that doesn't look to be a failure in my eyes.
Presumably you did not have anyone competent inspect it before the MOT then ? otherwise this would have been picked up and sorted so it would be roadworthy before the test ?This is on a 5 year old Fiesta ST, to my eye the brakes look fine - some corrosion on the top hat and the outer edge where the vents are between the 2 faces of the disc. No corrosion on the friction areas - places i would expect to see some rust. Theres a very slight lip where the face has worn down, but i would suggest less than 0.5mm.
My main question is, how much of the inner disc face can you see considering it has a dust shield up against it for starters, and surely a failure on that would mean there must be a split or something critically wrong with the structure of the disc, otherwise it's an advisory at most (which i would accept, as i say, there's some corrosion but it's definitely not excessive).
I have the feeling I'm having my pants pulled down - having a second opinion at my usual garage tomorrow, and if they need replacing it will be done, but understandably a bit miffed at having an MOT fail on something that doesn't look to be a failure in my eyes.
Why make a drama about it ? if it needs the brakes remedied, just do it.
Sliding single piston brake calipers when stuck on the slide pins will only press against the outer side of the disc, the inside unseen will just get rusty. But if so the brakes won’t work properly and judder. Also when tested for efficiency in the mot test it will clearly show something is amiss. Without a test drive I would say the brake calipers are seized on the slide pins hence rusty corroded inner disc face. Once the calipers are repaired, it would take a fair few miles to get the disc free of rust and giving a good efficiency reading on a mot test. To test perfect straight away new discs and pads need to be fitted.
They would have to be very worn to fail, even badly corroded on the inside face is just an advisory. Pads being less than 1.5mm is an instant fail and dangerous defect. I've only seen one car fail on discs being dangerous and they were really really bad.
However I would say that if they are bad then just get them replaced. You always have the right to contest the MOT but it does mean you pay for another test and shouldn't use the car until DVSA have been out and MOT'd it themselves, they may agree, disagree or find more things wrong.
However I would say that if they are bad then just get them replaced. You always have the right to contest the MOT but it does mean you pay for another test and shouldn't use the car until DVSA have been out and MOT'd it themselves, they may agree, disagree or find more things wrong.
saladdays said:
Hammer67 said:
Yup, recently changed the fronts on my X Type, the outer face looked fine, the inside less so.
Why is the braking surface on the inner face a different size to the outer face? Was the inner pad damaged or misaligned?Not much wrong with the pads.
Thanks for the replies - I'd like to clarify I'm not trying to cheap out on brakes, just trying to understand it all a bit better. The car's been dropped off with my usual place and will find out tomorrow what the verdict there is, and they'll get done if needs be at about half the cost the original place has quoted me (!). If not needed right away, I'll be getting the parts and swapping them myself soon anyway.
But yes, I have seen that the rear sliders on these like to seize sometimes, apparently partly to do with the hill start assist system. Just seems odd that the discs that have failed are OSF and NSR, again I'd expect it to be both rears. I stuck my head under the back and had a look, but couldn't see any of the inner face, and it didn't feel corroded to my fingers, but I can't feel around the hub area where the pics of the Jag brakes look crusty.
No mention of pad issues, feel fine to me under moderate braking, and no mention of issues on the MOT just gone for braking efficiency so they all seem to be working fine.
But yes, I have seen that the rear sliders on these like to seize sometimes, apparently partly to do with the hill start assist system. Just seems odd that the discs that have failed are OSF and NSR, again I'd expect it to be both rears. I stuck my head under the back and had a look, but couldn't see any of the inner face, and it didn't feel corroded to my fingers, but I can't feel around the hub area where the pics of the Jag brakes look crusty.
No mention of pad issues, feel fine to me under moderate braking, and no mention of issues on the MOT just gone for braking efficiency so they all seem to be working fine.
saladdays said:
Why is the braking surface on the inner face a different size to the outer face? Was the inner pad damaged or misaligned?
it always is.I'd guess it largely relates to that inner dust shield, or whatever the shield is for. Less airflow around the inner face or whatever...the inner pretty much always wears much worse than the outer.
RobXjcoupe said:
Sliding single piston brake calipers when stuck on the slide pins will only press against the outer side of the disc, the inside unseen will just get rusty.
....
I might be missing something here but I dont get that - surely the inside has the piston pressing directly onto the pad then onto the disc?....
If the sliders etc stuck, then the outside would get messed up?
Sheepshanks said:
I might be missing something here but I dont get that - surely the inside has the piston pressing directly onto the pad then onto the disc?
If the sliders etc stuck, then the outside would get messed up?
Sometimes do, sometimes don't. But get what you're saying. Although with stuck sliders often the piston will no longer press evenly on the pad on the inside as the caliper is now twisting etc.If the sliders etc stuck, then the outside would get messed up?
All just a mess really, and why things need maintained and inspected at suitable times.
Not just rocking up to MOT and hoping for the best
I think it's probably more related to the dust shield as your other answer - once rust sets in at the edges it rubs away the pad where the rust it so the pad is never fully cleaning the disc. Then the rust spreads across the disc face and you end up braking on a narrow shiny band. Outside face can look fine.
It's common on our cars that aren't used much and even when they are, they're driven gently and not in stop / start traffic.
It doesn't help that garages don't strip and clean brakes these days - it's the kind of thing you need to do yourself a couple of times a year ideally.
It's common on our cars that aren't used much and even when they are, they're driven gently and not in stop / start traffic.
It doesn't help that garages don't strip and clean brakes these days - it's the kind of thing you need to do yourself a couple of times a year ideally.
The slide pins on single piston calipers do corrode quickly if the rubber bellow seals have split. If you have a routine to get the wheels off in the summer and give everything a clean, fresh grease on the slide pins, push the pistons in and out a few times then back together they won’t ever fail you. Very simple bits of kit.
Rear calipers very similar except the piston has to be pushed and wound simultaneously. Don’t know why electronic hand brakes are fitted, old skool cable operated I think is a better fail safe.
Rear calipers very similar except the piston has to be pushed and wound simultaneously. Don’t know why electronic hand brakes are fitted, old skool cable operated I think is a better fail safe.
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