On Wed, 10 Jan 2018 16:05:28 -0500,
Clare Snyder wrote:

> the spec you talk of is how deep the scoring can be and still
> be correctable, not acceptable - you can machine uot deep scoring as
> long as you don't excede the machining limit, which is generally
> about 30 thou less than the discard limit - but on the heavy drums of
> a 4-runner or land cruiser, is equal to the discard limit.

You bring up a good point which is the "discard limit", where I never
delved into whether the number given is the number that you start with or
the number that you expect to end with.

I always assumed it's the start limit (but it might not be).

For example, these rotors say 297mm maximum diameter.

Even if a drum passed all other tests...
- If the drum measured 297.1mm in diameter, it would be discarded.
- But what if the drums measured 296.9mm in diameter?

> Give me proof

I'll have to dig that up separately as it's on a car I don't even own
anymore so I have to dig up the spec for the rotor grooves.

But even if I have trouble finding it, may whole point is that it's almost
impossible to find a MANUFACTURER's SPEC for groove thickness failure.

(I understand your point that it's assumed it's zero.)

> . Because there IS no spec.

That may very well be the case, so let's table this until I can dig up the
spec I found on an older vehicle.

> It IS different. There is NO spec for drums. There IS a spec for
> rotors, but even there, the spec is for "in service" rotors - not for
> pad replacement.

I'm not sure what you mean by "in service" rotors.
Is that just an inspection of the rotors without a pad replacement?

> Because drums are not rotors and you are reading the rotor spec weong.

Both may be true.

> And seldom is a tolerance plus or minus 50% - so that leaves you, at
> the outside, with 120 mict=roinches with a "50%/-0 TOLERANCE.

Good observation!

> With rotors directly exposed to road grit, stones, ets it is obvious
> they WILL suffer some scoring in use, wheras drums, being enclosed
> should not. WHAT is going to cause scoring in drums?????

Another good observation.

> And the spec for rotors is for in-service failure - NOT for tolerance
> for replacing friction material.

Yet another good observation.

> Your drums did look OK in the pictures. Now just buy the OEM SPEC
> linings and get it done!!!! -

Thanks for that advice. I am honing in on the friction rating for OEM being
FF, but that's not definitive yet.

> and before you install the drums on the
> new shoes DEGLAZE THEM WITH 80 GRIT ABRASIVE PAPER tocondition the
> surface to properly break in the new friction material.

That's interesting. Thanks for the advice.
I never deglazed a rotor before.
I do the standard multiple-60-to-10mph stop that everyone does to bed them.

Thanks for the advice!
You pointed out things, as did Tekkie, that I hadn't thought of.
Much appreciated.