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MOT Query


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Hi all

Just received the dreaded phone call from the garage that the faithful Octy had failed it's MOT. So, now waiting on a new NSR caliper & discs being fitted. However, one of the advisories on the MOT was for "brake imbalance", clearly only slight or it would have failed on this too but what I wondered was could brake imbalance be mistaken for a wheel imbalance problem??

It may sound a silly question but I haven't noticed any judder, shaking or wheel pulling to left or right; I have noticed that when I get up to around 70 -75 mph (allegedly!!) I get a bit of vibration through the steering wheel. There is absolutely no problem at lower speeds & brakes seem to work absolutely fine.

Any comments??

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That's what I thought too cntuning, but the caliper is being replaced due to hand brake issues. After being stripped & cleaned it improved things for a few months & then it was as if the hand brake lever was attached to nothing at all, had to pull it up about 8 or 9 notches & obviously only the osr was engaging properly.

Just wondered if you could have brake imbalance front or rear or corner to corner?? Apologies for dumb question, just trying to learn a thing or too!!

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I change my rear calipers about a month ago due to one of them sticking and the other not working, but as for the braking imbalance bleed the whole system and that should sort it

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Brake balance is usually on the front and you're allowed 20%. If it was near 20% you'd already know about it as it wouldn't brake in a straight line. AS has been said, write exactly what is on the sheet.

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Brake imbalance is measured on the steered axle only. On the roller brake tester (RBT), both front wheels are spun together, the brake is applied to a point well before the wheels lock and the readings recorded, you may get a reading of 200kg on one side and 180kg on the other. This gives a 20kg difference which is 10% of the larger reading which gives an imbalance figure of 10%. The maximum allowable imbalance is 25%.

You can't fail a non steered axle on imbalance.

When testing the rear brakes on the RBT as well as measuring the efforts from each wheel for the service and parking brake (if applicable) the rate of increase of the brake effort is checked on applying the brake and the rate of decrease when releasing the brake, both brakes should increase/decrease at roughly the same rate.

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Ok, got MOT receipt back today & the refusal slip states this "Brakes Advisories: RBT Front Brake Imbalance: 15%"

Then underneath an explanation which says"Front brakes only just et the front brake imbalance requirements. it would appear the braking system requires adjustment or repair."

The other advisories were for a deteriorated front suspension bush that didn't result in excessive movment & tyre close to the legal limit.

However on the retest it only has the advisories about the bush & the tyre & NOT the brake imbalance.

Could the work done on the rear caliper have sorted this & would they have tested the RBT on the front again.

The car drives absolutely fine, brakes in a straight line & there is no sign of pull to either side??

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