Watch your lip - You've been warned

gk5000

Just had a brake pad disintegrate - loss of braking etc - no warning, but lucky as it happened just on the driveway at 5mph so no accident.

Think it was caused by the lip or edge on a worn brake disk catching the pad, bending it and destroying the braking surface.

I'm not sure who changed the pads last time, myself or mechanic but know I shall be paying attention to this in future and shall stay within guidlines.
(Suppose 160k miles is a bit excessive on 1 set of disks)

I was aware of the lip but did not think it mattered so much. Course the previous NCT did not notice either... concentrating on silly stuff.

visual

NCT test is no substitute for regular maintance and up keep. Luckly you discovered this in driveway.

Obviously you'll be replacing discs and pads.
Double check calipers and any retaining clips / springs.

mickdw

Could be a pad failure.
I dont quite see how a lip would cause this. I have experienced the back of a pad catching the lip of a disk. That resulted in that brake briefly snatching then the lip being ripped off the disc. Dangerous no doubt but i dont see how it relates to a pad disintegrating.

mullingar

Imo, very very poor maintenance

All brake discs have a minimum thickness that MUST be adhered to.

CJhaughey

I can't see how a lip on a disc would do this either? Maybe if the disc was vented and the ribs inside the disc were exposed due to wear then it might cause this kind of damage? The lip on the outside of the disc runs radially and shouldn't contact the pad surface at all.

joujoujou

mullingar wrote: »

[...]

All brake discs have a minimum thickness that MUST be adhered to.

^^ This!

mickdw

joujoujou wrote: »

^^ This!

Manufacturer recommendations can be a touch on the safe side. On my car for example, the manufacturer recommendation for disc wear would result in discs being required with every set of pads. I found that the actual disc manufacturer specified a disc wear limit far in excess of what audi specified. Now i know there is an argument That the wear recommendation would change depending on car they are fitted to etc so that would result in car manufacturer specifying reduced allowable wear but i was happy enough to run the discs past the 1mm wear audi specify.
No doubt 160k is taking it into deathtrap teritory though.

slimjimmc

CJhaughey wrote: »

I can't see how a lip on a disc would do this either? Maybe if the disc was vented and the ribs inside the disc were exposed due to wear then it might cause this kind of damage? The lip on the outside of the disc runs radially and shouldn't contact the pad surface at all.

Agreed and even if it (metal pad backing) did touch the lip it wouldn't have been the first time and the OP should have noticed a grinding noise as the metal touched the lip even with thin friction material still on the pad.

OP it sounds like nothing to do with the disk and everything to do with the friction material separating from it's backing. How thick is the friction material on the other pads?

gk5000

slimjimmc wrote: »

Agreed and even if it (metal pad backing) did touch the lip it wouldn't have been the first time and the OP should have noticed a grinding noise as the metal touched the lip even with thin friction material still on the pad.

OP it sounds like nothing to do with the disk and everything to do with the friction material separating from it's backing. How thick is the friction material on the other pads?

It was the inside pad which disintigrated but the metal backing was bent.
The was at least 5mm of pad though the lip may have been nearly this as well. I think the lip may have only glansed off the backing causing the pad to crumble a bit - and then bending, causing the rest of of the pad to fall apart.

Yes, then there was a grinding noise, together with the loss of braking (on the driveway) but no warning prior to that.

I thought that disks could wear and become too thin, but did not realise that the lip itself could cause problems.