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NCT fail - insufficient contact between brake pad and disc

  • 10-11-2020 4:32pm
    #1
    Registered Users Posts: 1,102 ✭✭✭ WestWicklow1


    My wife's Octavia failed it's nct the other day because of insufficient contact between brake pad and disc on the nearside front inner.

    The brakes are working fine, no pull to either side under heavy braking.

    Typically, what's the cause of this?


Comments

  • Moderators, Regional Midwest Moderators Posts: 10,847 Mod ✭✭✭✭ MarkR


    I presume the pad is either not sitting properly, or has some uneven wear, so the pads face is not flush with the disk?


  • Registered Users Posts: 7,746 ✭✭✭ BrianD3


    This fail item seems have been introduced recently, one of my cars failed on it in 2019. Know several others who also failed on it. Issue generally seems to be rusted, badly scored or worn disks. My disks were 19 years old but not badly worn (low mileage car)

    Change your disks and pads.


  • Registered Users Posts: 927 ✭✭✭ nanook5


    I failed on this and got my brake disc ground down at a machinery shop. Only costed €10


  • Registered Users Posts: 12,943 ✭✭✭✭ Toyotafanboi


    The usual fail criteria for this in my experience is over 30% of the brake disc friction surface is corroded, meaning the contact surface is reduced, the cause is usually a worn/ misaligned/ distorted brake pad.

    Sometimes it's the inner face of the disc that is bad and they can look ok when inspecting through the wheel.

    It used to be the case, as you say that once brake force was even, you would pass, regardless of the visual condition of the equipment. Now you can be failed for visual issues with the system like corroded discs or brake pads excessively worn etc.

    You might find a disc looking like this.

    8b904367e5b19a9fa27e15fc62b74db1.jpg


  • Moderators, Motoring & Transport Moderators Posts: 6,374 Mod ✭✭✭✭ Irish Steve


    nanook5 wrote: »
    I failed on this and got my brake disc ground down at a machinery shop. Only costed €10

    You were very lucky, the majority of modern discs will be below minimum size (thickness) after being ground to get a good braking surface, many modern discs are not made to have a very long life, my local garage is resigned to the scenario of having to replace discs every other set of pads on some makes, as the discs are so thin, and the pads are so abrasive, and it seems to make little difference what price discs and pads are fitted, the life is still very much the same.

    It will come down to how closely the mechanic doing the inspection looks. If he sees a smooth clean disc with no lip on the outer edge, he may not check to see if the disc is still above the minimum thickness, and it will be passed, but if there is any doubt, there are specific published minimum thickness dimensions for some makes, and if they are below that figure, then regardless of how well they are working, they will be failed.

    There are some makes (citroen being one) where there are wear indicators in the outer edge of the disc, and it's very evident if the disc has worn beyond limits on them.

    Shore, if it was easy, everybody would be doin it.😁



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  • Registered Users Posts: 927 ✭✭✭ nanook5


    You were very lucky, the majority of modern discs will be below minimum size (thickness) after being ground to get a good braking surface, many modern discs are not made to have a very long life, my local garage is resigned to the scenario of having to replace discs every other set of pads on some makes, as the discs are so thin, and the pads are so abrasive, and it seems to make little difference what price discs and pads are fitted, the life is still very much the same.

    It will come down to how closely the mechanic doing the inspection looks. If he sees a smooth clean disc with no lip on the outer edge, he may not check to see if the disc is still above the minimum thickness, and it will be passed, but if there is any doubt, there are specific published minimum thickness dimensions for some makes, and if they are below that figure, then regardless of how well they are working, they will be failed.

    There are some makes (citroen being one) where there are wear indicators in the outer edge of the disc, and it's very evident if the disc has worn beyond limits on them.

    It was the rear disc on a Toyota Starlet Glanza V. The disc was not in bad shape, almost new actually. It was just pitted from lack of use. It was pitted purely due to it being a weekend car and not being used often. I believe there was 9.5mm on the disc before grinding and it was ground to 7.5mm ish. What's stupid about it is I had rebuilt the calipers myself and the imbalance and braking force on the rear was perfect but after I had the disc reground, obviously it created an imbalance and the braking force was reduced on that side. So I made the brakes worse and it passed. Doesn't make sense :confused:


  • Registered Users Posts: 1,102 ✭✭✭ WestWicklow1


    nanook5 wrote: »
    It was the rear disc on a Toyota Starlet Glanza V. The disc was not in bad shape, almost new actually. It was just pitted from lack of use. It was pitted purely due to it being a weekend car and not being used often. I believe there was 9.5mm on the disc before grinding and it was ground to 7.5mm ish. What's stupid about it is I had rebuilt the calipers myself and the imbalance and braking force on the rear was perfect but after I had the disc reground, obviously it created an imbalance and the braking force was reduced on that side. So I made the brakes worse and it passed. Doesn't make sense :confused:

    Did you replace the pads?

    I suspect the same applies to my wife's Octavia. Short runs and only 5k miles per year. I'm going to take the disc off over the weekend and measure it (there's no lip) and clean it up on the lathe. When it's done I'll measure it again and if well within the minimum thickness it'll go back on.


  • Registered Users Posts: 927 ✭✭✭ nanook5


    Did you replace the pads?

    I suspect the same applies to my wife's Octavia. Short runs and only 5k miles per year. I'm going to take the disc off over the weekend and measure it (there's no lip) and clean it up on the lathe. When it's done I'll measure it again and if well within the minimum thickness it'll go back on.

    The pads were brand new!

    It turned out that the disc was warped though, the machining fixed it.


  • Registered Users Posts: 1,102 ✭✭✭ WestWicklow1


    I took the disc off today and sure enough it was like Toyotafanboi's picture only worse.

    The thickness when new of my disk is 22mm with a recommended minimum thickness of 19mm.

    I measured it before putting it in the lathe and it was 21.5mm. Finished it is 20.8mm.

    NCT retest booked for 21/11.


  • Registered Users Posts: 37 Mooretaxi


    Son in laws Seat failed nct for the same reason, he also never felt there was a problem with the brakes, new discs and pads and retest nct, all good
    Pics show how bad things were, pad material fell of the metal when removed, shows there is some value in the nct after all


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  • Registered Users Posts: 1,102 ✭✭✭ WestWicklow1


    I took the disc off today and sure enough it was like Toyotafanboi's picture only worse.

    The thickness when new of my disk is 22mm with a recommended minimum thickness of 19mm.

    I measured it before putting it in the lathe and it was 21.5mm. Finished it is 20.8mm.

    NCT retest booked for 21/11.

    Passed.


  • Registered Users Posts: 3,966 ✭✭✭ Goose81


    Mooretaxi wrote: »
    Son in laws Seat failed nct for the same reason, he also never felt there was a problem with the brakes, new discs and pads and retest nct, all good
    Pics show how bad things were, pad material fell of the metal when removed, shows there is some value in the nct after all

    Was that car ever serviced? This discs and pads are in absolute taters, how that even passed the previous nct before the one it failed it is insane.


  • Registered Users Posts: 2,864 ✭✭✭ Dr_Colossus


    Mooretaxi wrote: »
    Son in laws Seat failed nct for the same reason, he also never felt there was a problem with the brakes, new discs and pads and retest nct, all good
    Pics show how bad things were, pad material fell of the metal when removed, shows there is some value in the nct after all
    Goose81 wrote: »
    Was that car ever serviced? This discs and pads are in absolute taters, how that even passed the previous nct before the one it failed it is insane.

    Serious amount of old engine oil under the bench so poster services their own car at least. Looks like the son in law needs to pay more attention.


  • Registered Users Posts: 12,943 ✭✭✭✭ Toyotafanboi


    Yes, just goes to show there's so much more to servicing a car than changing fluids.


  • Registered Users Posts: 224 ✭✭ teediddlyeye


    Yes, just goes to show there's so much more to servicing a car than changing fluids.

    Ah but sure if someone can do it in 20 min then its a scam if a garage charges more labour :rolleyes:


  • Registered Users Posts: 2 murch11




  • Registered Users Posts: 2 murch11


    Hi i recently failed nct for this. The discs were thick not worn thin but there was that rim of rust around the outside of the disc. My question is how can this be avoided when the pad doesn't cover the full disc. Seems ridiculous to me.



  • Registered Users Posts: 12,966 ✭✭✭✭ wotzgoingon


    New discs needed or just get a shop to skim them.



  • Registered Users Posts: 14 SherryG


    Just had a 2017 superb fail it's first NCT on the same, rear discs corroded both sides and the obligatory front light alignment left side. I usually turn the lights down but thought this times I'd not mess with them, and the new auto setting beams would be ok. Pissed off as no doubt will all cost me 300. Motoring in Ireland is becoming a joke cost wise.



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