On 08/05/2017 14:44, NY wrote:
"dennis@home" wrote in message
web.com...
On 07/05/2017 21:43, Steve Walker wrote:
On 07/05/2017 13:41, Andy Burns wrote:
Dave Plowman wrote:

Generally, discs need replacing every second set of pads.

That seems to be the way, though the garage generally tells me I've
been "lucky" as modern discs and pads are intended to need replacing
at the same time.

I do my own maintenance and only use a garage for a few things
(welding a sill, replacing a cambelt and replacing a dual-mass
flywheel) that would have cost me more in time off work to do it
myself than for them to do it.

In 30-odd years I have only replaced discs on two cars, both due to
slight warping - I have never worn a disc to the minimum even on cars
that have had numerous replacements of pads and mileages of 160,000+.

Are garages pushing unneccessary changes for profit?

Some will.
My MOT advisory said pads were close to limit but the service guy said
they were not and didn't need doing.

discs wear more than they did before asbestos was removed from the pads.
The pads are harder and need servos to work these days.

As the pads wear the disc, you tend to get a lip on the edge of the disc
which is outside the area rubbed by the pads. My local garage removes
the discs and skims off that lip, as part of the normal car service
every 12,000 miles. I'm not sure when I last had new discs, but I'm sure
I've had at least one set of replacement discs (maybe front only) in the
160,000 that the car has done so far.

The biggest problem is if the pads wear down to the rivets that fasten
them to the backing plates, because the rivets can there score the
discs,


I haven't seen pads with rivets for years.


Every time I have my car serviced they warn me that new pads and/or
discs will be required, but (almost) every time I get the car back an
they say "worn, will need replacing next time" so they haven't worn down
yet. I don't know whether pads have a non-destructive wear-indicator
which shows when it is time to replace them without (at that amount of
wear) scoring the discs.

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.