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Re: Front Brake question

To: MG List <>
Subject: Re: Front Brake question
From: Max Heim <>
Date: Wed, 04 Jun 2003 10:38:07 -0700
Not at all. What I was complaining about is that you had to calculate that
number for yourself -- they didn't spell it out. Why the H*** not? Just

For example, say I have an old rotor. I DON'T KNOW whether the original
thickness was .35 or .34 -- how could I? Therefore, I don't know if the
minimum thickness allowable FOR THIS ROTOR is .31 or .30 (according to the
spec as written). Not that it probably makes any difference, but this
ambiguity is inherent in the way they wrote the spec, as a "maximum amount
that can be removed" as opposed to the simpler, more logical, unambiguous
"minimum amount required to be left" (which is how everyone else does it,

That is just a poorly-written spec, no matter how you look at it...


Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires

on 6/4/03 10:08 AM, Dave Wood at wrote:

> Max,
> I think you missed the point of the spec.  Up to .040 inch can be ground off
> the original .350 to .340 inch.  So when the disc needs to be ground to
> below .300 or .310 its time to replace the disc.
> Dave 72 B
> ----- Original Message -----
> From: "Max Heim" <>
> To: "MG List" <>
> Sent: Wednesday, June 04, 2003 9:25 AM
> Subject: Re: Front Brake question
> That is just about the stupidest spec I've ever read. After it has been
> ground once, how would you know what the original thickness was? Why don't
> they just spec it as a minimum total thickness, rather than a maximum cut
> off an indeterminate original thickness? Written by lawyers, apparently, or
> a particularly bloody-minded engineer -- not by a mechanic, that's for sure.
> [end of rant]
> What it boils down to, of course, is a minimum thickness of .30... but why
> didn't they just come out and say that in the first place? (oops, slipped
> back into rant mode)
> on 6/4/03 9:11 AM, Telewest (PH) at wrote:
>> "Run-out must not exceed .003 in.  If it is found necessary to regrind the
>> disc faces they can be ground up to a maximum of only .040 in off the
>> original thickness of .350 to .340 in.  This may be ground off equally
> both
>> sides, or one more than the other, provided that the total does not exceed
>> .040 in.  The reground surface must not exceed 63 micro-in.  After
> grinding
>> the faces must run true to within a total clock reading of .002 in and the
>> thickness must be parallel to within .001 clock reading."
>> Leyland Workshop Manual.
>> ----- Original Message -----
>> From: "Dodd, Kelvin" <>
>> To: "'Bob Howard'" <>; <james.feyrer@Dartmouth.EDU>
>> Cc: <>
>> Sent: Wednesday, June 04, 2003 4:36 PM
>> Subject: RE: Front Brake question
>>>> Jim,
>>>>   In the workshop manual somewhere is minimum thickness
>>>> allowed for the
>>>> rotors.
>>> I have been looking for this spec. and have not found it in any workshop
>>> manuals.  If anyone has, please let me know.  New rotors supplied by
>> Brembo
>>> are imprinted with   "Min thickness 7.6mm or .30 inchs" so I would think
>>> that is a good spec. to go with.
> --
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the primer red one with chrome wires

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