pitted brake discs, again

When a vehicle is not used for a lengthy period, one of the first things to suffer are the brake discs, the surface becomes rusty and pitted. The following images came from the rear of a peugeot 306 that had been left idle for 3 months.

Although the pitting in this image doesn’t look severe enough to fail on the mot, it caused no imbalance, but it did cause severe judder when the brakes were tested in the rolling road brake tester.

When inspecting the  discs after replacement the reason was immediately clear, the disc on the drivers side at the rear had patches that had corroded to a greater extent than others thus leading to fluctuation in the braking effort on that wheel.

When the brake on this wheel was tested it felt as if the the rear wheel was egg shaped.

If for some reason you are unable to use the vehicle for an extended period, it’s worth moving it a couple of yards weekly just to clean the surface of the disc of the build up of surface corrosion.




4 comments so far

  1. James on

    What do you class as too corroded to pass? I’ve a car that was sat for 4 years but had new discs before this. The discs are obviously covered in corrosion but it does not seem overly deep to me – a quick scutch with a drill and wire brush got most of it back to something similar to the top left disc in your images, the fronts look similar without work. I’ve some expectation that a quick blast before the MOT will see the majority of the corrosion removed and just mild pitting left. I don’t want to fail the MOT but a set of 4 discs will come in just shy of £350 and is an expense I’m fairly sure is not needed as the brakes are smooth, plenty strong enough and will get new pads after a few dozen miles of machining the surface rust away! Any thoughts?

    • an Mot tester on

      Hi James
      Approximately 12 months ago vosa changed the rules on pitting and scoring of brake discs, there is no longer a reason for rejection for discs excessively pitted or excessively scored.
      However if the discs look bad enough that we’re unable to complete a brake test because the brakes may fail in use when testing on the brake test then that is a reason for failure, as we’d be unable to complete a brake test, thus the test should be aborted, I haven’t seen any that bad yet.
      On the other hand, when checking the brake performance in the brake tester if excessive judder is noted then that is a reason for failure.
      If the vehicle has been sat for 4 years tho, I would perhaps be concerned with the calipers sticking and causing brake imbalance.
      If you’re experienced enough to remove the pads and check the caliper pistons slide back freely and the caliper moves freely on it’s sliding pins then a clean up and check should enable you to go to the test reasonably confident.

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