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NCT Failure: Brake Test

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  • 02-12-2009 2:03am
    #1
    Nomad81
    Closed Accounts Posts: 90 ✭✭


    Did my NCT last week and failed the brake test. I've read somewhere here that changing the brake drum and shoes should fix the imbalance, however, there are a few factors to consider:
    • Mechanic checked the car two saturdays ago as part of a service, he mentioned that the rear brakes are in good nick. Having said that, he doesn't have much credibility, as he said he's tightened the handbrake and it still failed.
    • NCT tester mentioned advanced corrosion on nearside rear brake line/hose. I had a look at this last week and saw that the nearside rear brake line is made of metal while the offside rear one is made of rubber. Could this be the cause of imbalance? Doesn't explain the handbrake failure though.

    Brake test detail:

    |Brake Effort|||Ovality|||Imbalance
    |Nearside | Offside || Nearside| Offside ||
    Front Axle | 2.19 kN | 2.45 kN || 63% | 65% || 11%
    Rear Axle |0.75 kN |1.14 kN || 7% |11% || 34% (fail if >30%)
    Parking brake |0.38 kN |0.78 kN || | ||51% (fail if > 50%)



    Brake Performance (Car Weight 1083 kg)
    Brake Effort ||61%
    Parking || 11% (fail if < 16%)

    Any thoughts on the details above would be much appreciated. :)


Comments

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    #2
    deceit
    Registered Users Posts: 2,315 ✭✭✭deceit


    Sounds like changing the brake drums and shoes could help with that, if its a problem with them even if the mechanic tightened the handbrake would still fail as they wouldnt be strong enough to brake properly.


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    #3
    daveharnett
    Registered Users Posts: 2,567 ✭✭✭daveharnett


    Nomad81 wrote: »
    • Mechanic checked the car two saturdays ago as part of a service, he mentioned that the rear brakes are in good nick. Having said that, he doesn't have much credibility, as he said he's tightened the handbrake and it still failed.
    • NCT tester mentioned advanced corrosion on nearside rear brake line/hose. I had a look at this last week and saw that the nearside rear brake line is made of metal while the offside rear one is made of rubber. Could this be the cause of imbalance? Doesn't explain the handbrake failure though.
    Wouldn't really blame the mechanic - the brakes may physically be in perfect nick, and just need adjustment/bleeding, which wouldn't be apparent in a routine service.

    The metal brake line shouldn't be a problem as such - if it was leaking, the effects would be much more dramatic. That said, I would swap it out before the retest - another tester might fail it outright on the visual inspection.

    If it was my car, I would
    - change out the rusted brake line.
    - change the brake fluid (should be done every 2 years), and bleed (probably the cause of the footbrake imbalance, if the shoes and drums are ok).
    - tighten the handbrake cable some more, particularly on the nearside.

    Does the car pass with 65% ovality on the front? Seems quite high.


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    #4
    anon11
    Closed Accounts Posts: 131 ✭✭anon11


    fit a set of shoes and cylinders, bleed and adjust:)


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    #5
    Nomad81
    Closed Accounts Posts: 90 ✭✭Nomad81


    Thanks for all the replies.

    The brake line was actually failed by the tester as well.

    He didnt mention anything about the ovality, so it seems alright. The NCT handbook also mentions that failure due to ovality only if it causes the car to veer to the left or right during braking or if it is felt through the brake pedal (something to that effect, i'm not 100% sure on this).

    Any idea how much the shoes, drums, brake bleeding, brake line, etc would cost at an independent garage?


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    #6
    AzureAuto
    Banned (with Prison Access) Posts: 233 ✭✭AzureAuto


    Hi,
    What car is it, year and whether it has ABS, info needed and we can then quote you...


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    #7
    -Chris-
    Closed Accounts Posts: 12,035 ✭✭✭✭-Chris-


    Boards is not for pimping your wares - take it to PM or don't do it at all.

    No wheeling & dealing on-thread.


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    #8
    martinr5232
    Registered Users Posts: 2,298 ✭✭✭martinr5232


    What make of car is it.

    Sounds like adjustment is all that is needed on the rear brakes.


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    #9
    Darragh29
    Closed Accounts Posts: 7,097 ✭✭✭Darragh29


    Nice one on posting up the data OP. I can read that for you and tell you exactly what the problem is...

    First thing to look at here is whether or not the braking imbalance is confined to the pedal braking system or the handbrake system...

    As you can see in your case, the two systems are failing for imbalance. If the handbrake was passing imbalance but the pedal brake was failing, then you can see that the braking surfaces are fine, but there is something causing a low braking force on the pedal brake which is usually a partially seized wheel cylinder.

    If the opposite is the case and your pedal brake is fine but your handbrake is failing imbalance, then you usually have a handbrake cable seizure problem.

    In your case above, there is a problem with braking force on both systems on the passenger side of the car, which is throwing up the 0.75kN and 0.38kN braking forces on the passenger side, (both values are way too low).

    What you have to do now is look at what component do both these systems have in common. Components like the wheel cylinder and handbrake cable are system specific, but components like the brake shoe, brake drum and brake shoe lining and common to both systems.

    What is most likely the problem here in your case is the brake shoe lining is completely worn down on the passenger (near) side and on this brake shoe, the linings are extremely low to the point where you have metal on metal (brake shoe lining is gone or partically gone and metal underneath it is now the braking force with the metal brake drum).

    What could also be the problem is that the wheel cylinder could be leaking fluid on the effected passenger side and the hydraulic oil could have contaminated the brake shoe lining. This causes the force on this shoe to be diminished as the drum is basically slipping on the brake shoe lining which is covered in brake fluid. The lining being common to both systems, would also cause the kind of fail results that you are seeing...

    Either way, the way to resolve this is to replace brake shoes AND wheen cylinders on both sides.

    Also note that your handbrake braking force (0.38kN), being a fair bit lower than the already low pedal braking force (0.75 kN), would suggest also checking the handbrake cables when the job is being done just to make sure that you don't have excess mechanical resistance on the passenger side handbrake cable that could be contributing to the handbrake imbalance problem...

    If it does turn out to be the case that the lining has worn off (fully or partially), the brake shoe assembly, drum damage can occur so I'd advise refurfacing or replacing the brake drums for completeness...

    Also, price guide for this job, around the 160-180 mark from a good independent, add around 40-60 Euro for drum resurfacing if necessary, double that if they are being replaced...


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    #10
    Nomad81
    Closed Accounts Posts: 90 ✭✭Nomad81


    Fantastic post Darragh, you've corroborated exactly what my mechanic has told me. At least I know I'm not being ripped off. :) He quoted me EUR 168 for the entire job.

    Time to re-sched that NCT now.

    It's a 2000 Ford Fiesta 1.25 LX by the way, without ABS.


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    #11
    kona
    Registered Users Posts: 7,525 ✭✭✭kona


    Is there not a mechanical adjuster on the drum? if there is you just need to adjust this.


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    #12
    Darragh29
    Closed Accounts Posts: 7,097 ✭✭✭Darragh29


    kona wrote: »
    Is there not a mechanical adjuster on the drum? if there is you just need to adjust this.

    You can adjust all you want but if you have a brake fluid leak that has caused shoe lining contamination or you have a shoe lining that is worn down partically to the metal shoe material, then these defects need to be resolved before you will get a positive outcome...


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    #13
    kona
    Registered Users Posts: 7,525 ✭✭✭kona


    Darragh29 wrote: »
    You can adjust all you want but if you have a brake fluid leak that has caused shoe lining contamination or you have a shoe lining that is worn down partically to the metal shoe material, then these defects need to be resolved before you will get a positive outcome...

    but would contaminated pads/ fluid all over the drum, not cause a higher imbalance?


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    #14
    Darragh29
    Closed Accounts Posts: 7,097 ✭✭✭Darragh29


    Nomad81 wrote: »
    Fantastic post Darragh, you've corroborated exactly what my mechanic has told me. At least I know I'm not being ripped off. :) He quoted me EUR 168 for the entire job.

    Time to re-sched that NCT now.

    It's a 2000 Ford Fiesta 1.25 LX by the way, without ABS.

    Another thing I'd advise OP is when you run into these kind of issues, if at all possible, ensure that the mechanic has a test lane in his business. This allows the job to be fully checked before the car is returned to you. There is nothing worse than paying 200 Euro to have something like this sorted and then ending up failing again, and your then pushed into a full NCT again if you are near the end of your 28 day re-test window.

    I always think a good independent garage that takes on any degree of NCT rectification work, should have a test lane to clear work 100% before releasing the car, along with emissions equipment, headlamp alignment equipment, etc.


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