how to read brake pad wear?

[peter]

I looked at my brakes and I see this:

http://www.smugmug.com/gallery/2300127/ (front passenger side)

How do I read the wear status of the pad? Or, how do I know when to replace
the pad?
Do I have to take the wheel off and make a measurement?

This is a 2002 impreza wrx with 37K gently driven miles on original brake
pads.

 

[Rick Courtright]

How do I read the wear status of the pad? Or, how do I know when to > replace the pad?

Hi,

I can't see anything in your pic that tells me whether you can see the
pads from the "rear", but many, if not most, modern calipers are set up
such that you can remove the wheel and look thru a "window" in the
caliper where you should be able to see both pads pressed against the
rotor. With this design you can easily check any time you have the wheel
off, like at every tire rotation (hint.) If your caliper doesn't have
this window, you'll probably have to loosen a bolt to swing the caliper
up and pull the pads to measure them, though some allow enough "visual
access" from the front to see the pads. Getting a repair manual is a
good investment if you're not sure.

Your owners' manual may spec a minimum pad thickness. It's usually in
the range of 1/16" to 1/8" (~1.5-3mm.) That's from the pad side face of
the backing plate to the surface of the pad. Many pads have a groove in
them to use as a visual guide so you don't have to measure. When the pad
wears to the bottom of the groove, that's the minimum.

Personally, I like the 1/8" point as a "do it now" replacement guide,
even if the mfr specs a thinner wear limit. It keeps me from letting
things go too long, which can get to be a pricey mistake, FAST!

Rick

 

[Carl 1 Lucky Texan]

peter wrote:




Hi,

I can't see anything in your pic that tells me whether you can see the
pads from the "rear", but many, if not most, modern calipers are set up
such that you can remove the wheel and look thru a "window" in the
caliper where you should be able to see both pads pressed against the
rotor. With this design you can easily check any time you have the wheel
off, like at every tire rotation (hint.) If your caliper doesn't have
this window, you'll probably have to loosen a bolt to swing the caliper
up and pull the pads to measure them, though some allow enough "visual
access" from the front to see the pads. Getting a repair manual is a
good investment if you're not sure.

Your owners' manual may spec a minimum pad thickness. It's usually in
the range of 1/16" to 1/8" (~1.5-3mm.) That's from the pad side face of
the backing plate to the surface of the pad. Many pads have a groove in
them to use as a visual guide so you don't have to measure. When the pad
wears to the bottom of the groove, that's the minimum.

Personally, I like the 1/8" point as a "do it now" replacement guide,
even if the mfr specs a thinner wear limit. It keeps me from letting
things go too long, which can get to be a pricey mistake, FAST!

Rick

OEM should also have an 'indicator'(a tab that will make a sound when it
contacts the rotor) right? He could just wait till it starts squealing.

Carl

 

[Rick Courtright]

OEM should also have an 'indicator'(a tab that will make a sound when it
contacts the rotor) right? He could just wait till it starts squealing.

Hi,

Could do that, but I don't like those things. Here's part of the reason
why:

I have 'em on a couple of vehicles (same make--not Subie--different
models, same basic brake design) Both were purchased used. One was
dealer maintained by the previous owner, and either the pads were
changed before the noise makers kicked in, or else new noise makers were
installed w/ each pad change. No problem.

The other was maintained by a combo of a local mechanic and the local
quickie lube place by the previous owner. Omigosh... the stuff I've
found! Previous owner was an elderly gentleman who must have been hard
of hearing. The noise makers had to have been really squealing by the
time the pads were replaced. The local mechanic simply installed the old
worn noise makers on the new pads (which, sadly, IS "by the book"--even
new OEM pads from that mfr. come w/o new noise makers.) The wear on the
noise makers is such the pads will be worn below "MIN" before the next
time anyone hears any noise!

Call me a dinosaur, but for brake inspections I prefer the visual
approach!

Rick C

 

[dr.benway]

A general rule of thumb is that the pads should be thicker than the
backing plate that hold them. It's worked for decades for me..

 

[Stephen H]

On Subies take off the left ft wheel and right rear. Look at the Bottom of
each; these are the points that subies like to wear at.


--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist
Currently working at a Subaru Dealership

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