When I had the car tested today the mechanic said the front service brake had an imbalance of 25% which was on the legal limit. Can anyone tell me what this means, what causes it, how it affects the car and how you correct it. Thanks.
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Drivethru
What it means - one front brake is applying more braking effort than the other - I'm assuming from the comment that one brake is applying only 75% of the braking force of the other. This means that one brake will tend to lock the wheel before the other, and it may also tug at the steering. This unbalances the car under braking and is a particular risk on slippery roads. Hence a limit on unbalance.
Now, given that the foot brake is hydraulic, and therefore applies equal pressure to each caliper, this shouldn't happen.
Causes. Could be a number of things. I'd guess a sticky hydraulic piston in one caliper or brake pads siezed in the caliper and not moving freely are the most likely culprits. If it's a floating caliper system, then one caliper could be siezed on the guide pins. It could be problems with worn discs or pads, but it's quite an imbalance, and discs are visually inspected as part of the MOT.
Needs the front brakes stripped down, and checked for the above problems.
JS
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Thanks John, it passed the MOT but the mechanic said the discs were showing signs of corrosion on the inner face and the pads were quite worn so that could be the cause, I will have it looked at.
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Drivethru
Yes, wise of you to get that work done. If they are that bad the fault may lay there, and most of the other potential problems will be corrected in a disc and pad change. Given the pads have probably been in for quite a while, it's quite common to find that a combination of corrosion and brake dust makes them tight in the calipers.
JS
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