brake force imbalance Mot

[ih]

Wife's car 4 year old went for Mot which it did pass but the ATL test results under brake force of imbalance % axle 1 is showing 30% and dash (-) under axle 2 and in final test summary under service brake force imbalance the limit is 25 % resulting in final value 30%with overall result fail.
Will appreciate any help/advise on what is involved and how can I put this right and if axle 1 means front.(FYI the dealer did say front pads had 70% wear) is this related to that.also if I get pads replaced by local garage will this effect warranty with dealer.
Thanking in advance
Ih

 

[AlanE]

And wife's car is a?????

 

[ih]

Sorry! kia soul with 17k on the oddometer and petrol engine 1.6

 

[Avocet]

It means one of the front brakes isn't doing the same amount of work as the other. On a healthy braking system, pad wear (until you get to 100%) shouldn't make any difference. Have a look at the front discs and see if (on both the inside AND the outside face of each disc) they are clean over the whole of the area swept by the pads, or whether they have big rusty grooves and ridges on them. The latter would suggest a sticking brake caliper. The solution would be new pads AND discs. Once the disc is badly grooved, forget just replacing pads. If not, it's likely to be a sticking caliper. There are typically three ways n which (most) modern calipers can stick. Either the pads stick in the slots that they are supposed to slide in (easy to fix with a file); or the sliding part of the caliper can stick on its slides (harder to fix) or the piston itself is sticking in the caliper body (reconditioned caliper is the easiest fix for that).

 

[Mursal]

So it failed on the rear brake (axle 2) imbalance, yes?

If so, imbalance is usually caused by a buildup of residue on the disk (both inside and outside of both disks must be shining). The back suffers badly because the brake system is designed to only apply adequate pressure to the pads. Because if to much brake force is applied to the back axle the driver could loose control of the car.
If all surfaces of the disks are shining you may have a partially seized rear brake caliper, reducing the brake force on that wheel.
It might be worth asking the main dealer why the car at 4 years old failed the MOT? Doubtful if pads alone will cure this problem.
If you have a manual handbrake (not electric) pulling then releasing it while traveling at low speed might clean the rear pads/disks for you.

 

[ih]

The car did passMot but it f u mean failure on the imbalance then yes.my knowledge on car is very limited.you also mention failure on the rear axle but am not familiar have given facts as I know in my first post according to the paper work provided.am confused if only the front axle is involved or the rear as well?

 

[Mursal]

Sorry, from your original post I cant work out which axle failed

Axle brake imbalance =
(Max brake force - Min Brake force) divided by the Max Brake Force

Multiply your answer by 100 to give as a percentage

Max Brake force is the larger of the two regardless whether its right or left

The same rule applies whether its back or front axle, service (foot) or parking brake.

Does that make it any clearer?

Think of it like this:
As long as you have the same brake force on both sides of the axle in question, it will pass the imbalance test. Even if you had little or no brakes on that axle.

 

[ih]

Mursal the failure from what I understand is axle 1 which if I am not wrong is front axle.
In the ATL test it shows 30% axle 1 and there is just dash (-) in axle 2 no figure in axle 2 hope this clarifies. Thanks for your help.

 

[Burnerman]

With a 4 year old vehicle, when it goes in for service its only the thickness of the disc pads thats really checked, and at 17k they are unlikely to be past it and certainly not 70% worn.....however, the discs are likely to be quite badly corroded on the inside face and this will cause your imbalance.
As for Kia honouring a 7 year warranty on brakes - no chance.....they are leaders on diddling you out of claims!
The brakes should be stripped for cleaning every year - whatever anyone says.
John