Brake pad wear limits

There's no such thing as "cannot" here.

What you should not forget is that on many modern cars, rear discs are used as much, if not more so, than front discs - especially if you're a light user. It's to balance out the braking effort and ensure rear brake components don't seize.

I'm expecting to have to change the Accord's rear brake components before the fronts.

MOT is 1.5mm for the actual friction material if this helps.

The pads on my car were at 2.5mm, I'd bought new pads but hadn't fitted them because of snow, took it for an MOT and they failed it because the pads would have been too low by the next service interval. I said I don't go by service intervals, I replace stuff when it needs doing and look at the pads frequently but they wouldn't pass it unless the pads were changed so I had to get frozen doing the damn things in the snow.

Check that exact wording again. Does it say pad material thickness or pad thickness? The fact that they quote a different figure for a pad without the self-adhesive shim makes it seem obvious to me that the figure referred to is for the whole pad. The shim will be 0.8mm, and that gives the 0.8mm difference between the two figures. 7.2mm minus the 5mm thickness of metal gives 2.2mm, which is the 1.5mm someone else mentioned, plus a safety factor.

Only by measuring the whole pad would the thickness of that shim make any difference.

Steve

I did 80k hard miles in my two years in my 75 and in that time had one front pad and disk change only IIRC, rears didn't need changing. Bear in mind they were called upon for lots of hard braking from three figure speeds (was working a lot across Europe) and the back roads around east yorkshire were my way of relaxing.

I think I would have appealed on that one; the MOT tests the condition of the car on the day, not at the next service. Your garage was in the wrong.

Another example of garage fraud. The MOT guidelines clearly state 1.5mm being the lower limit. For all they know the car might be booked in for a service elsewhere the next day.

Yeah, it'd give you ~ 3mm material which is about right.

Correct.

I hope not.

Agreed. Apply brakes - car stands on it's nose, leaving the rears with very little to do. Basic physics, innit.

For a more extreme example, look at how small the rear brake is on a modern sportsbike compared with the fronts.

(Most sportsbike rear brakes look like they've been nicked off a passing mountain bike)

SteveB (sbrads@nildramDOTcoDOTuk) gurgled happily, sounding much like they were saying :

I wonder what they'd do with all this current stuff with 20k+ service intervals? Brake pads are very likely to need replacing within that distance on many cars.

You might want to concede the point now?

Conor missed a key point and you jumped on the bandwagon: "What you should not forget is that on many modern cars, rear discs are used as much, if not more so, than front discs - especially if you're a light user. It's to balance out the braking effort and ensure rear brake components don't seize."

That's not extreme. It's why many cars have chunky big vented discs at the front and solid discs at the back. Under light check braking, many modern all-disc braked vehicles use all four brakes. Our Ka's brake bias under check braking was something like 99% front 1% rear. The Accord is much closer to equal.

No. Off you go and provide your proof.

They have absolutely no right to do anything other than test the vehicle in the state it is presented on the day. Next service interval is completely irrelevant. It makes me wonder what the MOT tester training is like if these people can pass it and hold a certificate and still have no clue how to do a test properly.

I'm driving it...

Poppycock. One of the most dangerous braking conditions a car can have is too much effort on the rear compared to the front which can promote a rear lock up and a spin. No car, modern or otherwise, will be deliberately designed like that. On a rwd car with relatively even front/rear weight bias the rears might do 1/3 the work of the fronts. On a front heavy fwd car it will be lower still. On fwd race cars I've been involved with you actually have to more or less disable the rear brakes to stop them locking because the rear tyres will hardly be on the ground under braking. The usual trick was to hacksaw half the brake shoe material away.

Stop doing handbrake turns then. I've never come across a car where rear brakes wore at anything like the rate of the fronts. If there is such a case then it'll only be because the rear pads were made too small for the work required of them and thus wear out relatively fast. What it won't be anything to do with is the actual front v rear braking effort.

Unfortunately they know perfectly well what they're doing. And the sooner its treated as fraud which it is, the better.

Ding.

I'm not saying that there's a stronger rear bias compared to the fronts, but with electronic brake force distribution, larger vented discs up front and smaller (sometimes larger) solids on the back, some cars do have a habit of wearing out their rears just as quickly if not more so than the front.