Front Brake Imbalance

[chis]

Just had my car mot'd, 2001 vvti." It only just met the front brake imbalance requirements".Does anybody know what the cause of this could be.

cheers

[gazza1286]

Assuming there is no air in the system there are a couple of reasons for this.

The pads themselves harden over time/usage and can develope a 'glaze' on their face which may account for an inconsistancy. On high performance cars you see groved discs. This has the effect of continually deglazing the pads under use. It also significantly shortens their service life. (However, although an imbalance is possible due to this I think it would be unlikely). Glazing on one side only could be caused by a partially siezed caliper. The pad will then be in constant contact with the disc. A journey of 5 miles or so would present you with a front wheel rim which is significantly hotter than the other. The pads on this side may be much more worn than the other.

I would suspect that the inboard face of one of your discs is rusting up. This obviously will affect/reduce the total surface contact between the pad and disc under braking. Hence a brake imbalance. If this is the case pads and discs will need replacing.

I presume that you haven't noticed a problem with your brakes? Car isn't pulling to one side or other? I'm surprised that the MOT tester didn't give you his opinion whilst the car was on the ramp?

[Ray99]

Hi Chis

Gazza is mostly right- all except the air in the system. Even with air in the system the pressure is equal at all points. Air in the system will give a long pedal travel and will feel spongy. The most likely cause is the corrosion, as the braking effort of a pad against fresh metal is much greater than that of a pad against a corroded surface. Another possibility is a pad stuck in the caliper due to corrosion. The brake still works but to a lesser degree. You can't afford to skimp on brakes, insect and repair as required. Regards Ray

[IKR]

I have a 2001 Avensis, and recently changed the front discs and pads due to severe corrosion on the inside of one disc. I had a circular ridge of rust over about 50% of the braking surface. It's very hard to see, due to the shield, but can easily be felt if you stick your finger into the gap between the disc and the shield. It wasn't spotted at the service either (franchised dealer).......

Braking performance didn't seem to be affected, with no imbalance detectable during driving or at the MOT. Worth checking though, as I'd imagine that the massively reduced pad area would be more susceptable to fade. Pads and discs were about £80 from www.brakeparts.co.uk

Ian