When to replace brake pads?

glider3560

almillar wrote: »

Using this logic, assuming you drive the same as before, they'll last another 3 years or 23,000 miles.

That's a good way of thinking about it!

I bought the car at 14,000 miles about nine months ago. They were 30% worn at that point.

9,000 miles = 20% wear at my current driving style

Therefore another 13,500 miles until I get to 20% worn.

System

I usually get around 80k out of mine. The rule of thumb that used to be the case when I was a mechanic was to advise at 3mm that they be changed before the next service. Saying "50% worn" or whatever is meaningless because you don't know how thick they are when they're new.

Nowadays, assuming they're not ones with a wire on them to connect to a low pad indicator they tend to have wear markers in them in a form of a horizontal groove in the middle and when that's gone they're usually around 2-3mm left.

debtdebt

almillar wrote: »

No. Pads are the bit that's meant to wear, discs are not.

Are you for real? Why do people sell discs if they do not wear? All manufacturers give a minimum disc thickness. Once they're passed that, you need new discs. Discs may last longer than pads but that doesn't mean that they do not wear.

A quick rule of thumb is that one set of discs will last two sets of pads.

nickcc

Don't think it's been mentioned but make sure the caliper sliders aren't sticking or seized. Rapid wear of pads is often due to the sliders being seized or sticking.

Richard53

debtdebt wrote: »

Are you for real? Why do people sell discs if they do not wear? All manufacturers give a minimum disc thickness. Once they're passed that, you need new discs. Discs may last longer than pads but that doesn't mean that they do not wear.

I think what he meant was that the pads are the bit designed to wear out, not the discs. Yes, the discs do wear, but this is an inevitable consequence of the friction. The pads are the bit that is designed to wear out, and are easily replaceable because of this. I can remember when cars were lighter and less powerful, and when pad compounds weren't so hard, when changing discs was quite rare - pads might last 20k miles and discs the life of the car. One of the reasons my Dad never had an automatic was because they were 'hard on the brakes'.

debtdebt wrote: »

A quick rule of thumb is that one set of discs will last two sets of pads.

That's pretty much what works for me.

almillar

Are you for real? Why do people sell discs if they do not wear?

Yes I am. Did you miss the two little words 'MEANT TO'? As above in this thread, some wear does occur, and apparently it happens more now than it used to with tougher braking systems, but if you're routinely changing your discs, something's wrong. You're right on the minimum thickness. A lip round the edge, and small grooves, is perfectly acceptable though. They can also become warped, another reason why people sell discs.

Discs may last longer than pads but that doesn't mean that they do not wear.

I know that. I never said they don't.

I think what he meant was that the pads are the bit designed to wear out, not the discs.

Bingo, thanks.

A quick rule of thumb is that one set of discs will last two sets of pads

I hope not, but I guess it varies car to car. I don't think I've run a car long enough to completely use a set of discs!

AdrianC

almillar wrote: »

As above in this thread, some wear does occur, and apparently it happens more now than it used to with tougher braking systems

Not "tougher". The older asbestos-based friction materials wore the discs much less. Also, replacement discs used to be HORRENDOUSLY expensive.

but if you're routinely changing your discs, something's wrong. You're right on the minimum thickness. A lip round the edge, and small grooves, is perfectly acceptable though. They can also become warped, another reason why people sell discs.

Agreed. If they're not warped, not badly grooved, and not towards minimum thickness - no point in replacing. But claiming they aren't a consumable is just ridiculous. They are.

I think what he meant was that the pads are the bit designed to wear out, not the discs.

Bingo, thanks.

They're both designed to wear out.

Bigphil1474

Just a quick aside - I've never been good at looking at the right bit of brake pads - don't know why. Anyway, had a full service and MOT on a 2009 Ford Fiesta in October 2016. I bought it in October 2015, and do about 12k miles a year. The place that does my servicing send the car out for MOT's - no mention from either of them about any issues with brakes (plus no issue when driving).
Far as I know the MOT tester wouldn't check the actual pads left (just whether they work)?, but am I safe to assume that the pads would be checked as part of a full service and either replaced if necessary, advised if nearing replacement time, or not advised if nothing to worry about?

AdrianC

Bigphil1474 wrote: »

Far as I know the MOT tester wouldn't check the actual pads left (just whether they work)?, but am I safe to assume that the pads would be checked as part of a full service and either replaced if necessary, advised if nearing replacement time, or not advised if nothing to worry about?

Yup.

Tester can't take anything off, so unless the pads are visible (through the wheel or from behind/underneath), they won't get tested unless they're on the metal and it fails on effort.

Any kind of service worth the name certainly SHOULD check the pads...