Brake Discs minimum thickness

KillerWatt

somech wrote: »

they cant fail an mot unless they are excessivley worn/pitted (they cant measure them for an mot)

If the tester can get a vernier guage on the disc without removing any parts (including the wheel) and accurately measure it, then they can fail it.
A lot of the MOT test is down to the testers "opinion", so it is quite possible that one garage will issue a pass whereas another garage will issue a fail.

somech

a vernier gauge is not part of the mot testing equipment afaik

Gloomendoom

The brake disc thickness is not specifically checked at an MoT. The MoT tester does do a visual check on the overall condition though.

If the OP does an internet search on 'brake disc minimum thickness' along with the make/model of his car, he will find the minimum thickness (it can vary slightly depending on the manufacturer of the discs). He can then check it himself using a micrometer. A vernier is not ideal because there is normally a raised ridge around the perimeter of a worn disc and the thickness can also vary across the surface of the disc.

Mankysteve

Go see a proper garage first and count your lucky stars that the disk didn't magically become scored and oil sprayed in your dampers.

KillerWatt

somech wrote: »

a vernier gauge is not part of the mot testing equipment afaik

That is correct, but if the tester is not happy with the visual inspection and he (or she) can get a measuring device in there without removing any parts and the end figure is not in line with the manufacturer specs then it will be a failure.

For me personally, I'd be changing the discs & pads without question as they are the main components responsible (along with the shocks & tyres of course) for me not ploughing in to anything.

C_Mababejive

My car has 95k on the clock and still has its original discs. They still work.
kwik fit are there to make money out of you.

steadynerve

Thanks for the replies.

Anyone have any comments on why haynes manual indicates once reach minimum thcikness they are good until brake pads wear out.? This implies some tolerance (one set of brake pads). Obviiusly if the disc shows signs of dangerous stress from heat dissapation etc it needs to be replaced immediately at mot or otherwise regardless of the thickness!! But i'm just talking about discs that look fine but only are below mininimum thickness though weren't when last set of pads put on. Obviosluy if the minimum had tolerance in them then it would be perfectly safe to change once pads worn out.

Strider590

steadynerve wrote: »

Hi I just had my brakes tested at kwik fut (free service) they show that the fromt pads are fine but the front discs are sllighly below manufacturers minimum thickmess.

Free test = opportunity to drum up business.

In just the same way as low cost MOT's always end up costing the earth in repairs.

I seriously doubt they have access to the manufacturers specs for every car.

ukmike

Ask them what the minimum thickness is & what yours measured,bet they can't answer.

Gloomendoom

steadynerve wrote: »

Thanks for the replies.

Anyone have any comments on why haynes manual indicates once reach minimum thcikness they are good until brake pads wear out.? This implies some tolerance (one set of brake pads). Obviiusly if the disc shows signs of dangerous stress from heat dissapation etc it needs to be replaced immediately at mot or otherwise regardless of the thickness!! But i'm just talking about discs that look fine but only are below mininimum thickness though weren't when last set of pads put on. Obviosluy if the minimum had tolerance in them then it would be perfectly safe to change once pads worn out.

You are barking up the wrong tree here.

It doesn't matter if the pads were changed five miles before the discs became under size. You still need to change the discs as soon as you become aware that they have worn below the set limit.

The manufacturers are not required to ensure that the brake discs last the life of the last set of pads that were fitted, nor do they.

It is not just a matter of heat dissipation, the discs can fail mechanically too. See below..



If you don't believe KwikFit (I can understand why), thne measure them yourself, or get someone else to do it for you. If it turns out that KwikFit were correct, then for goodness sake, change the discs!