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My 2000 Honda Civic Aerodeck just failed its MOT (roadworthyness test) on Front Brake Imbalance (51%).

I changed the pads a few months ago, and had trouble with both calipers on the driver's side of the car sticking. I tried to free them off, but obviously not well enough at the front (the rear imbalance was only 8%)...

Any suggestions as to how to reliably free it off? I'm pretty sure the problem lies with the sliders rather than the piston - at least, that was the problem before...

Any suggestions for a reliable means of testing it would be helpful too, I don't want to try and fix it and have it fail again...

The numbers on the brake test report:

  • Measured weight (kgf) Lh 372, Rh 357
  • Drag (kgf) Lh 17, Rh 9
  • Brake Forces (kgf) Lh 287, Rh 268
  • Brake Difference (%) 51

The discs are worn, but not badly.

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  • Is there any rust in the piston housing? Can you replace the sliders or clean any rust if present?
    – FossilizedCarlos
    Jan 29, 2013 at 15:33
  • Not really an on-topic comment but wow, MOT is so thorough! Here in the US, safety inspections are largely a joke. I don't even know where one could go if one wanted to quantify brake balance--I don't know of anyone with the equipment!
    – mac
    Feb 1, 2013 at 17:32
  • @mac - It's quite worrying how little safety inspections a lot of countries have. Knowing how little attention some people pay to maintaining their cars, I'm quite glad they get checked at least once a year - the guy in front of me in the queue had three bald tyres. Plus, as you say, brakes are something it's difficult to quantify yourself.
    – Nick C ♦
    Feb 2, 2013 at 14:24

1 Answer 1

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Your brake system's balance can fall into several areas of concern:

  • The calipers in and of themselves have sliders and pistons that can cause uneven pressure.

    sliders: I always remove, clean and grease the sliders first, be mindful that some vehicles actually have rubber on the sliders that will swell over time and cause lockup/drag... just replace the sliders if this is the case.

    pistons: The seals on your pistons can become weak and your cylinder walls can become scored. If you lift the dust seal back and any fluid leaks out then you should remanufacture/replace the leaking caliper. I personally would never replace just one side but I leave that decision up to the person spending money.

  • Conventional brake fluid absorbs moisture. As the fluid becomes diluted by moisture it will become thick and dirty, eventually affecting performance. A good brake flush every 30k - 60k (I do mine every 30k) can help keep your system performance up and also prolong life of the individual components.

  • Equalization components exist in your brake system to compensate for differences in line length and line construction between the master cylinder and the calipers. On my cars this is a solid ported valve design but yours could be different. If you have any equalization through the ABS system or other more dynamic balancing systems then those could become suspect in your search for a solution.

I've just highlighted a few possibilities and they are pretty much in the order I'd address since brake caliper failure is probably the most common issue you will have aside from brake pad problems.

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  • I'm with you on the sliders as the first suspect. I've just discovered I can get new sliders, so that's an easier option than I thought it might be. I too would always replace both calipers as a pair, but I'm hoping I won't need to!
    – Nick C ♦
    Jan 29, 2013 at 16:19
  • I've had 2 single side caliper failures on my car. Both right fronts, on 2 different cars. I wouldn't be in a rush to replace both with as expensive as calipers can be. 1 car was $350, the other $650 per caliper.
    – Brian Knoblauch
    Jan 30, 2013 at 20:37
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    @BrianKnoblauch right side is the "gutter side" in the US. IMO everything seems to fail faster on the "gutter side" of the car. I wonder if the left hand side components fail faster in the UK?
    – mac
    Feb 1, 2013 at 17:35
  • Fixed - It was indeed a sticking slider.
    – Nick C ♦
    Feb 2, 2013 at 14:20
  • @mac - it was the driver's side on this occasion.
    – Nick C ♦
    Feb 2, 2013 at 14:21

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