Disc Brakes

They failed my Sierra on a worn steering rack that subsequently passed MoTs obtained elsewhere for at least another 10 years.

I think all this business about changing through gears & always being in ge ar comes from the early days of the driving test when cars were a bugger to get into gear, and needing all your acceleration to avoid someone was a fr equent thing. Times have changed a lot. Once you know your vehicle one can go into the right gear in a moment, there's no hanging about - this makes b eing in gear all the time redundant.

It's quite doable. But to be honest I think doing that is the sign of not h aving learnt how to do it properly. You get a lot more braking effect by on ly braking as hard as it can take rather than repeatedly skidding & coming off the brakes. So use the candence thing when you really haven't got the h ang of the car and/or road coditions, but normally once you release to stop skidding you should be able to judge fairly well how hard to brake. Manual ABS is something you need to practice to get the hang of. Friction is less than stiction, so skidding gets you less braking not more.

Some cars use single circuit ABS. If 3 wheels have good grip & one doesn't, it lets off all 4 brakes. Such systems are a hazard.

NT

I've never ever seen a disc pad with the lining riveted. Even in the 1960s.

And likely from the days when cars had very poor brakes indeed.

Jethro_uk pretended :

That is because they are taught to actually drive. No silly racing up to a junction and banging on the brakes at the last second.

I always do and I agree - they have to make up for the discounted MOT somehow, the somehow is usually by finding some chargeable work that needs doing. If there is none, make something up that needs to be done. Halfords seems to be one of the worst culprits for doing this I have come across.

That's not true, I have paid half price for MOT for the last 12 years and have had one fail and that was a headlamp that blew while being tested. They fitted my spare for free and retested for free there and then.

Ok, well whatever was worn caused the pads to score the discs when they were applied. I assumed that rivets were revealed when the lining wore down, but evidently I'm wrong with how the scoring was caused.

He didn't say it was a police car.

Some police cars have a hard life some don't.

I have yet to have any brake pads fitted to any of my cars, but the wife has had one set of pads. The current cars are 8 years and 4 years old now.

I've seen riveted drum brake linings, can't remember what on though. Glue is better, but I don't know what sort of glue they use, must be impressive stuff.

NT

Not true. You can change gear and not do any extra wear on the clutch or gearbox if you do it properly. The engine does the braking and it will be running anyway. It won't be using any fuel while slowing so where does the extra pollution come from?

You don't have to drive like an idiot just because you are in London.

dennis@home was thinking very hard :

I had Halfords make up a spurious reason to fail and repair, yet passed it with a very obvious fault that was pointed out to them by me before the MOT.

That road must have been very slippy to take over two seconds to stop from 20mph.

A car that just about passed the MOT should take a maximum of about 1.7 seconds.

It would travel about 25 feet so it was a narrow road too.

A modern car would do it in less than a second and travel less than 15 feet.

NY expressed precisely :

Pads don't have rivets, the are glued on. Same with modern brake shoes too. I suspect when you were down to the steel backing plate that the braking effect wasn't reduced by much.

I haven't seen pads with rivets for years.

I believe it has been law for many years that cars have a warning system to show worn pads. Its used to be a copper stud set into the pad connected to a wire that shorts to the disk and lights a lamp. Mine is indicated by the computer but I expect its still a copper stud. The biggest failure mode is the wire falling off the pad.

Heat? Would the outer edge of the disk get hottest as it's rotating fastest? Therefore having extra metal beyond the pad gives a bit of a heat buffer zone to both dissipate heat as it's generated and give a grater cooling surface and more even temperature under the pad it's self, I think the reasons aren't just down to a single "because" but the entire combination of suggested reasons.

Jim GM4DHJ ... formulated the question :

Well, they maybe ought to be listed on a sheet of paper, rather than made public on the site.

Each inspector will have their own favourite faults they look for, each will have a different opinion on what is and is not worth flagging up. I don't think the get access to the list of advisories when a vehicle is presented for testing.

Think the shoes were riveted on my Mk2 Cortina, definitely seen a lot of riveted shoes in the past as the rivet holes used to accumulate a build-up of dust which we'd wilfully blow out with the air-line until such practice became frowned upon.

Could it be the copper stud embedded in the pad that causes the scoring of the disc in the same way that (in the olden days) rivets would do.

I checked the warning light when I experienced the symptom, knowing about brake pad warning wires/studs, and the light (the same one as used for handbrake-on) did not light, so it may be that the wire had fallen off since the last time the brakes have been checked and passed for another X thousand miles.

I'm intrigued that a lot of people have done large mileages without needing new discs, because on all the cars that I have had, brake discs tend to be needed roughly every three times that the pads need changing. And that's with fairly gentle progressive braking (ie not rushing up to lights at 60 and then slamming hard on at the last moment).

I presume it makes a difference if you live in hilly country: even with engine braking to take some of the braking load, you will still use your brakes more than if you live in flat terrain. Mind you, modern learners are taught not to use engine braking on a long hill, but to stay in a fairly high gear and rely entirely on brakes - that's what my nephew said he was told, anyway.

I wouldn't like to descend Porlock Hill, Rosedale Chimney or Park Rash using only my brakes, without going down into maybe third or second to give at least *some* engine braking.