Brake Pad Thickness Variation Questions
 

For the first time ever, I checked the thickness variation of my 1991 Civic's
front brake rotors (NON-abs). I used a micrometer whose calibration I trust. It
actually reads to the nearest 0.0001 inch, but I have rounded to the nearest
0.001 inch below. The minimum thickness required on these rotors is 0.75 inch.

On one of the rotors, the readings were

0.812 inch
0.814
0.811
0.809

So this rotor's maximum thickness variation is 0.005 inch.

The spec is to have a thickness variation of no more than 0.0006 inch. This is
the AllData spec for the 91 Civic. Chilton's gives a spec of 0.0028 inch(!).)

There is a groove in this rotor, too. Chilton's says some scoring is normal, as
long as it's not deeper than about 0.0152 inch. I have not yet checked the
depth, but the groove is not all that easy to feel. It's easier to see. So I'm
not too concerned.

The other rotor shows no thickness variation.

The pads are a little over 2 years old and are about 5/16 inch thick. In other
words, there is plenty of pad left.

My brakes feel and work fine; no pulsing.

I can't see a good reason for resurfacing or replacing the rotor right away. At
some point I figure in the next couple of years, I'll have to replace the pads.
Then maybe I'll revisit the rotor issue.

Can anyone point out any detriment to the operation of this car's brakes or
wheels and tires by ignoring this thickness variation on the rotor for a year or
more?

I'm figuring on keeping the car for another five years or so (when I think the
rust from northern driving may take its toll on the body and other parts), so I
buy new stuff for it with only a five-year time frame in mind.

This is, as is common for many of my posts these days, more of an academic
inquiry. Again, the car drives fine. I'm just curious about the notion of
thickness variation.

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:
> For the first time ever, I checked the thickness variation of my 1991 Civic's
> front brake rotors (NON-abs). I used a micrometer whose calibration I trust. It
> actually reads to the nearest 0.0001 inch, but I have rounded to the nearest
> 0.001 inch below. The minimum thickness required on these rotors is 0.75 inch.
>
> On one of the rotors, the readings were
>
> 0.812 inch
> 0.814
> 0.811
> 0.809
>
> So this rotor's maximum thickness variation is 0.005 inch.
>
> The spec is to have a thickness variation of no more than 0.0006 inch. This is
> the AllData spec for the 91 Civic. Chilton's gives a spec of 0.0028 inch(!).)
>
> There is a groove in this rotor, too. Chilton's says some scoring is normal, as
> long as it's not deeper than about 0.0152 inch. I have not yet checked the
> depth, but the groove is not all that easy to feel. It's easier to see. So I'm
> not too concerned.
>
> The other rotor shows no thickness variation.
>
> The pads are a little over 2 years old and are about 5/16 inch thick. In other
> words, there is plenty of pad left.
>
> My brakes feel and work fine; no pulsing.
>
> I can't see a good reason for resurfacing or replacing the rotor right away.

unless you can feel pulsing, or notice the brake to be grabbing in any
way, i'd ignore it. chances are, thickness variation of this magnitude
is going to cause less variation in braking force than any variable
elastic expansion in the brake lines, so i wouldn't bother doing any
resurfacing.

> At
> some point I figure in the next couple of years, I'll have to replace the pads.
> Then maybe I'll revisit the rotor issue.
>
> Can anyone point out any detriment to the operation of this car's brakes or
> wheels and tires by ignoring this thickness variation on the rotor for a year or
> more?
>
> I'm figuring on keeping the car for another five years or so (when I think the
> rust from northern driving may take its toll on the body and other parts), so I
> buy new stuff for it with only a five-year time frame in mind.
>
> This is, as is common for many of my posts these days, more of an academic
> inquiry. Again, the car drives fine. I'm just curious about the notion of
> thickness variation.
>
>

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:
> For the first time ever, I checked the thickness variation of my 1991 Civic's
> front brake rotors (NON-abs). I used a micrometer whose calibration I trust. It
> actually reads to the nearest 0.0001 inch, but I have rounded to the nearest
> 0.001 inch below. The minimum thickness required on these rotors is 0.75 inch.
>
> On one of the rotors, the readings were
>
> 0.812 inch
> 0.814
> 0.811
> 0.809
>
> So this rotor's maximum thickness variation is 0.005 inch.
>
> The spec is to have a thickness variation of no more than 0.0006 inch. This is
> the AllData spec for the 91 Civic. Chilton's gives a spec of 0.0028 inch(!).)
>
> There is a groove in this rotor, too. Chilton's says some scoring is normal, as
> long as it's not deeper than about 0.0152 inch. I have not yet checked the
> depth, but the groove is not all that easy to feel. It's easier to see. So I'm
> not too concerned.
>
> The other rotor shows no thickness variation.
>
> The pads are a little over 2 years old and are about 5/16 inch thick. In other
> words, there is plenty of pad left.
>
> My brakes feel and work fine; no pulsing.
>
> I can't see a good reason for resurfacing or replacing the rotor right away.

unless you can feel pulsing, or notice the brake to be grabbing in any
way, i'd ignore it. chances are, thickness variation of this magnitude
is going to cause less variation in braking force than any variable
elastic expansion in the brake lines, so i wouldn't bother doing any
resurfacing.

> At
> some point I figure in the next couple of years, I'll have to replace the pads.
> Then maybe I'll revisit the rotor issue.
>
> Can anyone point out any detriment to the operation of this car's brakes or
> wheels and tires by ignoring this thickness variation on the rotor for a year or
> more?
>
> I'm figuring on keeping the car for another five years or so (when I think the
> rust from northern driving may take its toll on the body and other parts), so I
> buy new stuff for it with only a five-year time frame in mind.
>
> This is, as is common for many of my posts these days, more of an academic
> inquiry. Again, the car drives fine. I'm just curious about the notion of
> thickness variation.
>
>

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:
> For the first time ever, I checked the thickness variation of my 1991 Civic's
> front brake rotors (NON-abs). I used a micrometer whose calibration I trust. It
> actually reads to the nearest 0.0001 inch, but I have rounded to the nearest
> 0.001 inch below. The minimum thickness required on these rotors is 0.75 inch.
>
> On one of the rotors, the readings were
>
> 0.812 inch
> 0.814
> 0.811
> 0.809
>
> So this rotor's maximum thickness variation is 0.005 inch.
>
> The spec is to have a thickness variation of no more than 0.0006 inch. This is
> the AllData spec for the 91 Civic. Chilton's gives a spec of 0.0028 inch(!).)
>
> There is a groove in this rotor, too. Chilton's says some scoring is normal, as
> long as it's not deeper than about 0.0152 inch. I have not yet checked the
> depth, but the groove is not all that easy to feel. It's easier to see. So I'm
> not too concerned.
>
> The other rotor shows no thickness variation.
>
> The pads are a little over 2 years old and are about 5/16 inch thick. In other
> words, there is plenty of pad left.
>
> My brakes feel and work fine; no pulsing.
>
> I can't see a good reason for resurfacing or replacing the rotor right away.

unless you can feel pulsing, or notice the brake to be grabbing in any
way, i'd ignore it. chances are, thickness variation of this magnitude
is going to cause less variation in braking force than any variable
elastic expansion in the brake lines, so i wouldn't bother doing any
resurfacing.

> At
> some point I figure in the next couple of years, I'll have to replace the pads.
> Then maybe I'll revisit the rotor issue.
>
> Can anyone point out any detriment to the operation of this car's brakes or
> wheels and tires by ignoring this thickness variation on the rotor for a year or
> more?
>
> I'm figuring on keeping the car for another five years or so (when I think the
> rust from northern driving may take its toll on the body and other parts), so I
> buy new stuff for it with only a five-year time frame in mind.
>
> This is, as is common for many of my posts these days, more of an academic
> inquiry. Again, the car drives fine. I'm just curious about the notion of
> thickness variation.
>
>

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:
> I can't see a good reason for resurfacing or replacing the rotor right away. At
> some point I figure in the next couple of years, I'll have to replace the pads.
> Then maybe I'll revisit the rotor issue.

only if the thickness is below spec. then replace. ive never turned or
replaced a rotor on any of the cars ive done brake jobs on. including a
77 accord with grooves i could feel with my fingernail.

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:
> I can't see a good reason for resurfacing or replacing the rotor right away. At
> some point I figure in the next couple of years, I'll have to replace the pads.
> Then maybe I'll revisit the rotor issue.

only if the thickness is below spec. then replace. ive never turned or
replaced a rotor on any of the cars ive done brake jobs on. including a
77 accord with grooves i could feel with my fingernail.

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:
> I can't see a good reason for resurfacing or replacing the rotor right away. At
> some point I figure in the next couple of years, I'll have to replace the pads.
> Then maybe I'll revisit the rotor issue.

only if the thickness is below spec. then replace. ive never turned or
replaced a rotor on any of the cars ive done brake jobs on. including a
77 accord with grooves i could feel with my fingernail.

Re: Brake Pad Thickness Variation Questions
 

On Sat, 09 Oct 2004 08:50:56 GMT, SoCalMike
<mikein562athotmail@hotmail.com> wrote:

>> I can't see a good reason for resurfacing or replacing the rotor right away. At
>> some point I figure in the next couple of years, I'll have to replace the pads.
>> Then maybe I'll revisit the rotor issue.
>
>only if the thickness is below spec. then replace. ive never turned or
>replaced a rotor on any of the cars ive done brake jobs on. including a
>77 accord with grooves i could feel with my fingernail.

I second the motion! NEVER turn Honda rotors!

Re: Brake Pad Thickness Variation Questions
 

On Sat, 09 Oct 2004 08:50:56 GMT, SoCalMike
<mikein562athotmail@hotmail.com> wrote:

>> I can't see a good reason for resurfacing or replacing the rotor right away. At
>> some point I figure in the next couple of years, I'll have to replace the pads.
>> Then maybe I'll revisit the rotor issue.
>
>only if the thickness is below spec. then replace. ive never turned or
>replaced a rotor on any of the cars ive done brake jobs on. including a
>77 accord with grooves i could feel with my fingernail.

I second the motion! NEVER turn Honda rotors!

Re: Brake Pad Thickness Variation Questions
 

On Sat, 09 Oct 2004 08:50:56 GMT, SoCalMike
<mikein562athotmail@hotmail.com> wrote:

>> I can't see a good reason for resurfacing or replacing the rotor right away. At
>> some point I figure in the next couple of years, I'll have to replace the pads.
>> Then maybe I'll revisit the rotor issue.
>
>only if the thickness is below spec. then replace. ive never turned or
>replaced a rotor on any of the cars ive done brake jobs on. including a
>77 accord with grooves i could feel with my fingernail.

I second the motion! NEVER turn Honda rotors!

Re: Brake Pad Thickness Variation Questions
 

"John Ings" <nodamned@spam.org> wrote
> <mikein562athotmail@hotmail.com> wrote:
>
> >> I can't see a good reason for resurfacing or replacing the rotor right
away. At
> >> some point I figure in the next couple of years, I'll have to replace the
pads.
> >> Then maybe I'll revisit the rotor issue.
> >
> >only if the thickness is below spec. then replace. ive never turned or
> >replaced a rotor on any of the cars ive done brake jobs on. including a
> >77 accord with grooves i could feel with my fingernail.
>
> I second the motion! NEVER turn Honda rotors!

Thank you, Jim, Mike, and John.

I note the original (91 Civic) rotor thickness was 0.83 inches. So it's taken 13
years to wear down about 0.02 inches. At this rate, unless I put on some non-OEM
pads that are unusually hard or have some other weird mishap (like a major
gouge), the rotors are unlikely to hit the minimum thickness spec of 0.75 inch
before the engine itself dies.

I theorize whatever caused the groove may have thrown the thicknesses out of
whack on the rotor.

Anyway, per your suggestions, I am not going to touch it again until I hear the
wear indicators or happen to be rotating the tires and see the pads are about
down to the min. specified thickness.

Re: Brake Pad Thickness Variation Questions
 

"John Ings" <nodamned@spam.org> wrote
> <mikein562athotmail@hotmail.com> wrote:
>
> >> I can't see a good reason for resurfacing or replacing the rotor right
away. At
> >> some point I figure in the next couple of years, I'll have to replace the
pads.
> >> Then maybe I'll revisit the rotor issue.
> >
> >only if the thickness is below spec. then replace. ive never turned or
> >replaced a rotor on any of the cars ive done brake jobs on. including a
> >77 accord with grooves i could feel with my fingernail.
>
> I second the motion! NEVER turn Honda rotors!

Thank you, Jim, Mike, and John.

I note the original (91 Civic) rotor thickness was 0.83 inches. So it's taken 13
years to wear down about 0.02 inches. At this rate, unless I put on some non-OEM
pads that are unusually hard or have some other weird mishap (like a major
gouge), the rotors are unlikely to hit the minimum thickness spec of 0.75 inch
before the engine itself dies.

I theorize whatever caused the groove may have thrown the thicknesses out of
whack on the rotor.

Anyway, per your suggestions, I am not going to touch it again until I hear the
wear indicators or happen to be rotating the tires and see the pads are about
down to the min. specified thickness.

Re: Brake Pad Thickness Variation Questions
 

"John Ings" <nodamned@spam.org> wrote
> <mikein562athotmail@hotmail.com> wrote:
>
> >> I can't see a good reason for resurfacing or replacing the rotor right
away. At
> >> some point I figure in the next couple of years, I'll have to replace the
pads.
> >> Then maybe I'll revisit the rotor issue.
> >
> >only if the thickness is below spec. then replace. ive never turned or
> >replaced a rotor on any of the cars ive done brake jobs on. including a
> >77 accord with grooves i could feel with my fingernail.
>
> I second the motion! NEVER turn Honda rotors!

Thank you, Jim, Mike, and John.

I note the original (91 Civic) rotor thickness was 0.83 inches. So it's taken 13
years to wear down about 0.02 inches. At this rate, unless I put on some non-OEM
pads that are unusually hard or have some other weird mishap (like a major
gouge), the rotors are unlikely to hit the minimum thickness spec of 0.75 inch
before the engine itself dies.

I theorize whatever caused the groove may have thrown the thicknesses out of
whack on the rotor.

Anyway, per your suggestions, I am not going to touch it again until I hear the
wear indicators or happen to be rotating the tires and see the pads are about
down to the min. specified thickness.

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:

> I theorize whatever caused the groove may have thrown the thicknesses out of
> whack on the rotor.

thats called "runout", right? ive never checked for it, or measured disc
thickness. youre definately detail-oriented, and love learning! much
props for that :)
>
> Anyway, per your suggestions, I am not going to touch it again until I hear the
> wear indicators or happen to be rotating the tires and see the pads are about
> down to the min. specified thickness.

weird thing about the indicators... sometimes, if youre on the bleeding
edge of them making noise, and have to do a panic stop, or just brake
hard? theyll break off. or they break off some other way-im just
surmising how it happened on the couple cars ive done brakes on its
happened to.

by the time i did thebrake jobs on those, it was definately making a
grinding sound, and the indicators were broken off. i wont rule out
stupidity or neglect, either :) none were my cars.

anyhoo... on the 3 that were metal on metal of the 20 or so ive done, i
just slapped new pads on em and let em bed in. no pulsing, no warping,
nothing weird happened. i imagine they "self-turned".

the last one i did a few months ago was a 92 GMC 1500 pickup of my
brothers. the passenger side rotor looked pretty chewed. slapped new
pads on, told him to drive it a while and let me know if there was any
pulsing or anything. he says it brakes normally.

of course, the friggin brake fluid is coffee colored, but if i stressed
out about everyones vehicle i ever worked on and did them to my personal
standards, id have no free time to post to usenet. besides, hes pretty
broke (student), so even getting him to spring for the raybestos
"lifetime" pads took convincing.

Re: Brake Pad Thickness Variation Questions
 

Caroline wrote:

> I theorize whatever caused the groove may have thrown the thicknesses out of
> whack on the rotor.

thats called "runout", right? ive never checked for it, or measured disc
thickness. youre definately detail-oriented, and love learning! much
props for that :)
>
> Anyway, per your suggestions, I am not going to touch it again until I hear the
> wear indicators or happen to be rotating the tires and see the pads are about
> down to the min. specified thickness.

weird thing about the indicators... sometimes, if youre on the bleeding
edge of them making noise, and have to do a panic stop, or just brake
hard? theyll break off. or they break off some other way-im just
surmising how it happened on the couple cars ive done brakes on its
happened to.

by the time i did thebrake jobs on those, it was definately making a
grinding sound, and the indicators were broken off. i wont rule out
stupidity or neglect, either :) none were my cars.

anyhoo... on the 3 that were metal on metal of the 20 or so ive done, i
just slapped new pads on em and let em bed in. no pulsing, no warping,
nothing weird happened. i imagine they "self-turned".

the last one i did a few months ago was a 92 GMC 1500 pickup of my
brothers. the passenger side rotor looked pretty chewed. slapped new
pads on, told him to drive it a while and let me know if there was any
pulsing or anything. he says it brakes normally.

of course, the friggin brake fluid is coffee colored, but if i stressed
out about everyones vehicle i ever worked on and did them to my personal
standards, id have no free time to post to usenet. besides, hes pretty
broke (student), so even getting him to spring for the raybestos
"lifetime" pads took convincing.