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Old January 10th 18, 09:34 AM posted to alt.home.repair,rec.autos.tech
Mad Roger
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Posts: 61
Default Drum brakes - do you disconnect the parking brake cable?

On Tue, 09 Jan 2018 23:55:56 -0500,
Clare Snyder wrote:

>>It's usually *hard* to find the scoring spec; it's a lot easier to find the
>>thickness and runout specs, so I'm not saying it's an easy spec to find.

>
> not hard at all. here's one:
> https://www.cbsparts.ca/admin/bullet...nd%20Rotor.pdf


Um... you just proved my point.
There's no spec for scoring and grooving in that PDF.

And in *anything* on a car, there is no such thing as 0 tolerance. It just
doesn't exist. 0 may be 0.090 or it might be 0.001 but it's never going to
be 0 on anything.

Specifically "free of scoring" is not a spec for how thick the scoring can
be. (Yes, I know you *intimate* zero, but 0 inches is not the OEM spec, as
I've seen OEM specs when I looked. They're hard to find, but they're
nowhere near 0 inches).

I'm not chastising you for finding that PDF, as I know it's nearly
impossible to find any manufacturer's spec for how thick a groove or
scoring can be before it's rejected - but when you find the spec (as I have
in the past), you'll be shocked how deep and wide the grooves can be and
still be within manufacturers' specs.

> and another:
> https://www.cbsparts.ca/admin/bullet...20Problems.pdf


Um... this proves point also, which is that there is no spec in there for
scoring or grooving other than 0, which is a ridiculous number that isn't
the manufacturer's spec.

Again, I'm not chastising you for finding out what I already knew to be the
case, because I too looked and it's not easy to find a spec but when you
find it, you'll be amazed how wide the grooves can be and still be within
the manufacturers' specs.

> see page 402 at :
> https://books.google.ca/books?id=O01...limits&f=false


Ch 8 Drum Brakes wasn't visible to me when I looked.

> "If scoring or light grooves cannot be removed by hand (with emery
> cloth) the drum MUST be refinished or replaced"


Again, this proves my point. Unless you actually believe 0 is the spec, but
I already know, from my past searches years ago, that it's huge, so it's
not even close to zero.

> There is NO ALLOWABLE AMOUNT OF GROOVING ALLOWED ON A DRUM when
> replacing friction m,aterial- PERIOD.


I see your words and I believe it says that but it's not a manufacturer's
spec.

Now, I did look it up only for the rotors because the vehicle didn't have
drum brakes, so, maybe drums are different - but that doesn't change the
fact that none of these are Toyota specs.

> read ALL of:
> http://www.aa1car.com/library/drum_brakes.htm


Um. Again, it proves my point, saying only that "Minor pitting and scoring
are acceptable as long as the grooves are not too deep and can be removed
by resurfacing."

As in the other PDFs, that implies 0 but it's just not 0 IMHO.
I may be wrong for drums, because what I looked up was the manufacturer's
spec for scoring of rotors - but the scoring limit for rotors is *huge* so
why would drums be different?

Maybe drums *are* zero (I'm not saying they're not); all I'm saying is that
you and I both know that it's damn hard to find the *manufacturers* spec
for the depth and width of a scoring that will fail a drum.

To be clear, I'm not trying to argue with you as you found exactly what I
found, which is that it's damn hard to find the manufacturers' spec for the
size of scoring where it's *easy* to find their spec for the diameter and
other things.

That last article does say the following:
"One way to tell if the surface finish is in the recommended range
of 80 microinches or less"

Ok. That's 80 millionths of an inch, or 0.000080 inches, but that's the
overall "roughness" factor and not scoring per se. And, notice it's not 0
simply because nothing in a vehicle is at 0 tolerance.

My main comment stands which is that, at least for rotors, scoring has to
be huge to fail a rotor, according to the specs I don't have now but that I
unearthed in the past from a vehicle manufacturer.

Whether rotor scoring is similar is unknown to me but it's a good question
of what Toyota things is a scoring limit. But really this is theoretical
since I'm keeping the drums as they're in fine shape with no "visible"
scoring.
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