MOT failure - Brake imbalance - your tips please?

[jonny a]

I'd like some advice on a few of the bit my truck failed the MOT on. Heres what it says on the failure sheet; 'The front brakes are imbalanced: RBT Front brake imbalance 34%' What does RBT stand for? What is a good process for ensuring the brakes are balanced and is there a way I can ensure they are working/balanced before the retest?

Another failure point is; 'Rear brake application uneven' Can anyone expand on this? I forgot to speak to the tester about this one. I assume its different to imbalance (Between sides of the car?) Nearside rear wheel bearing is knackered too, would this have any effect on 'Rear brake application uneven'? Any tips on dealing with this problem?

Many thanks in advance for your replies and ace tips!

[Lofty79]

any time i have got these failures it seems changing discs and pads, drums and shoes always is the solution.......for me anyway

[fordfan]

RBT - Roller Brake Tester. As above pads sticking in their slides, also on the Felicia pistons can stick in the caliper, piston & seal kits are quite cheap, though sticking pistons may show up as a drag on the wheel.

The tester will run both rollers on the RBT together and check that each brake on an axle increases and decreases at roughly the same rate, for a balance reading he will apply the brake at a constant pressure and record the efforts of each brake. Balance applies only to a steered axle.

Basically you need to ensure that things move freely, are not worn out, are adjusted correctly and it may be a good idea to change the fluid.

[rwbaldwin]

RBT stands for Roller Brake Test.

[Lofty79]

Or lower it Mine wont go in the RBT it grounded, so they had to do a decelerometer test, out on the road and unit on passenger seat. Dont know if they were able to test brake balance? Maybe fordfan you would know?

[jonny a]

What about 'Rear brake application uneven' Can anyone expand on this?

[jonny a]

One other thing; what significance do the bracketed numbers/letters after each failure have? For example (3.7.A.5c)

[Ben Cordy]

Mine failed on an imbalance just before i got rid of it. As suggested new discs and pads should do it, although check the slider bolts as they have a habit of seasing up, come to think of it both mine and my dad's have failed on imbalance and on both occasions it was the slider bolts although we changed the pads and discs just to be sure.

[fordfan]

The MOT testing manuals are here: (cars are class IV)

http://www.transport...lsandguides.htm

The bracketed numbers/letters references the information, inspection procedure and reasons for rejection in the testers manual, 3.7 A 5c is:

3.7 - The section in the manual - 3.7 Brake Performance (Roller Brake Test)

A - The method of inspection

5c - The reason for rejection - c. the braking efforts at the road wheels do not increase at about the same rate when the service brake is applied gradually.

Your rear brakes are not increasing/decreasing at about the same rate, so the offside one may be showing simultaneously 90Kg and the nearside only 40Kg during application, but they may still lock the wheels at identical efforts such as 110Kg.

Decelerometer tests are usually carried out at 20mph, which will give a total percentage efficiency for the service (foot) and parking (hand) brakes. Imbalance on the steered axle is assessed by noting whether the car pulls to one side, the eveness of the rear brake application can't really be assessed, though from experience the car will tend to pull to one side whilst the steering wheels remains straight.