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Measuring brake pad/disc wear?


How do dealers decide how much wear a set of pads and discs have?

The reason I ask is because 6k miles ago the Trophy had it's 12k service. It had new front pads fitted and the rears were noted as being 30% worn.

Today it had an oil and filter change and general checkup. The fronts were at 50% which is understandable after doing 3 track days since they were fitted, but the rears were at 20%, which is obviously rubbish as they were supposidly at 30% 6k miles ago. Is there really that large a margin for error or are they having me on?


  E92 M3 Monte Carlo
i think they put whatever they feel like,i had my 12000 mile service and the week before i put new discs and pads and they recogned there was 40% wear


edde said:
They do it by looking thoguh the gap its more guesswork hence why number go up and down.

That's what I suspect.

I wanted them to actually look at them. They've been on track 3 times and come off smoking. I wanted a mechanic to have a look for me and tell me how they were. Not give me a rough guess based on the miles the car has done.

I'm going to phone and ask for an explanation.
  Lionel Richie
we've had customers with new brake kits (2 days old) told their brakes have 70% left! ok whatever! its guess work