Brake rotors already grooving

On Thu, 13 Jan 2005 09:16:01 -0500, Corky Scott
> wrote:

>I also wondered about machining rather than putting on new rotors.
>Doing the job properly took a certain amount of time and when you
>added that up versus simply cleaning up the hub and slapping on new
>rotors, it did not seem like there was much difference, plus, the
>customer was getting a brand new rotor.

On a bus or a big truck with massive rotors, there's enough meat to
make turning rotors practical. On light cars there's seldom enough.
50 to 60 thou is mentioned as an average figure for the metal
available. That's less than 1/16 of an inch!

How often do you think those turn-the-rotors enthusiasts check the
rotor with a micrometer after their machining to see if it's below the
'machine to' spec?

One correspondent in this newsgroup pointed out that the mechanic who
insists on machining rotors is often just seeking to protect himself
against ignorant customer callbacks about brake squeal while new pads
are seating in.

In article >, the fly wrote:

> Brake rotors (and drums) all tend to warp as the casting ages.
> They also get a lot of abuse in handling. The machining of hubs and
> mounting surfaces may be true to the friction surfaces when they're
> made at the factory, but after shipping, stocking, and even just
> months on the shelf, it's a different story. Some are worse than
> others, but they ALL need to be surfaced before installation. Anyone
> with experience on a brake lathe is aware of this, as is anyone with
> formal training in automotive technology.

Laugh. castings warp on the shelf.... I've designed cast parts
considerably more delicate than a brake rotor and they don't warp sitting
around for months. If they did, they wouldn't fit on the machine they go
on.

I've also never bought a brake rotor that showed signs of rough handling
or damage. If I did, I would exchange it.

BBA wrote:
>
> > >Did you happen to have the rotors cut or resurfaced? i.e. happens to be a
> > >requirement when replacing a rotor!
> >
> > Foo!
>
> same to you pal!
>
> > Where did you get that nonsense!
>
> I don't know what where you come from! Here in the US most NITB rotors will
> require a base cut before installation
>
> bba

As far as I know, no US vehicle manufacturer recommends this
practice. In fact both Ford and GM don't recommend routine
rotor resurfacing at all. And when it is required, they want
it donet on the car.

I try to do my own brake pads. I also try to stay away from
shops that do routing rotor resurfacing.

Ed

On Wed, 12 Jan 2005 21:29:33 -0800, "BBA"
> wrote:

>LOL >> Ever wonder why your life is so ****ed up? Most people are born with a
>little common sense! Except in your case where as you are at an all time low! >>
>Probably born in the negative margin - or possibly your lacking brain cells -
>maybe when someone figures out what to do with stem-cell technology -- someone
>may find a need to do some much needed maintenance on your cerebral cortex!

Translation: He's been shot down and he hopes creative invective will
be mistaken for devastating riposte.

On Thu, 13 Jan 2005 11:21:15 -0800, John Ings >
wrote:

>On Wed, 12 Jan 2005 21:29:33 -0800, "BBA"
> wrote:
>
>>LOL >> Ever wonder why your life is so ****ed up? Most people are born with a
>>little common sense! Except in your case where as you are at an all time low! >>
>>Probably born in the negative margin - or possibly your lacking brain cells -
>>maybe when someone figures out what to do with stem-cell technology -- someone
>>may find a need to do some much needed maintenance on your cerebral cortex!
>
>Translation: He's been shot down and he hopes creative invective will
>be mistaken for devastating riposte.

I'm only interested in The Facts here, not interested in impugning
anybody's ego/reputation, but I can't let billy's "routine base
cutting" get by without critique.

I'm not a brakemaster like some here, but when I see TSB's from GM and
Ford that say "Don't do that" and somebody comes along and says he
knows better than the manufacturer, it's time to take out the can of
bull**** spray.

No hard feelings billy, but you're not doing the DIY automotive
community any favors by passing along inaccurate information.

Listen to the brakemasters, and learn something. I know I have.

Lg

John Ings wrote:

> On a bus or a big truck with massive rotors, there's enough meat to
> make turning rotors practical. On light cars there's seldom enough.
> 50 to 60 thou is mentioned as an average figure for the metal
> available. That's less than 1/16 of an inch!

I machine rotors all the time. Typically, I can get a rotor clean with
a .005" cut on each side. That's only a total of .010"...depending
on how the customer drives....you might actually be able to get
two cuts on a set of rotors before throwing them out. I see it
all the time.

> How often do you think those turn-the-rotors enthusiasts check the
> rotor with a micrometer after their machining to see if it's below the
> 'machine to' spec?

Every time. And we aren't "turn-the-rotor enthusiasts"....we are people
that see what a "new" rotor will cost the customer. It's much more
cost effective to machine rotors. Done properly, it works very well.
If I want to make a ton of money....then I'll upsell new rotors every
time. But since I'm not interested in ripping the customer off, I'll
machine the rotors. I get paid the same either way, so it's actually
a disadvantage to me, financially, to machine rotors.

> One correspondent in this newsgroup pointed out that the mechanic who
> insists on machining rotors is often just seeking to protect himself
> against ignorant customer callbacks about brake squeal while new pads
> are seating in.

If you actually know how to do a proper brake job.....and you use
a good quality brake pad....you don't have to protect yourself
against anything. Those type of complaints simply don't come
up where I work.

Ian

On Thu, 13 Jan 2005 22:44:58 GMT, "shiden_kai"
> wrote:

>> On a bus or a big truck with massive rotors, there's enough meat to
>> make turning rotors practical. On light cars there's seldom enough.
>> 50 to 60 thou is mentioned as an average figure for the metal
>> available. That's less than 1/16 of an inch!
>
>I machine rotors all the time. Typically, I can get a rotor clean with
>a .005" cut on each side.

Then it probably didn't need machining.

>> How often do you think those turn-the-rotors enthusiasts check the
>> rotor with a micrometer after their machining to see if it's below the
>> 'machine to' spec?
>
>Every time. And we aren't "turn-the-rotor enthusiasts"....we are people
>that see what a "new" rotor will cost the customer. It's much more
>cost effective to machine rotors. Done properly, it works very well.

My experience is that the turned rotors go bad within a few months and
you end up needing new ones anyway.

John Ings wrote:

>> I machine rotors all the time. Typically, I can get a rotor clean
>> with a .005" cut on each side.
>
> Then it probably didn't need machining.

Maybe you are working on a different make of vehicle. On
GM vehicles, you can easily experience a pulsation from a
rotor that can still be cleaned up with a .005" cut on both
sides. We machine all rotors anyway, as not doing it is
a guarantee that you "will" get complaints from the customer.

> My experience is that the turned rotors go bad within a few months and
> you end up needing new ones anyway.

You must be working on a different make of vehicle. I've been doing
this in the dealership environment for over 20 years...have never seen
turned rotors "go bad". What usually happens is not that the rotor
goes "bad", but the surface of the hub wasn't properly prepared, runout
measurements weren't performed after the machined rotor was installed,
and excessive runout wasn't repaired. If you don't do a brake job
properly, then even a new rotor will go belly up.

Ian

On Thu, 13 Jan 2005 15:22:02 -0800, John Ings >
wrote:
>>
>>Every time. And we aren't "turn-the-rotor enthusiasts"....we are people
>>that see what a "new" rotor will cost the customer. It's much more
>>cost effective to machine rotors. Done properly, it works very well.
>
>My experience is that the turned rotors go bad within a few months and
>you end up needing new ones anyway.

Then someone's doing something wrong. Machining brake rotors
is a fairly exacting skill, but it isn't rocket science. Get the job
done correctly, and they'll last just as well as brand new.

On Fri, 14 Jan 2005 00:26:29 GMT, "shiden_kai"
> wrote:

>>> I machine rotors all the time. Typically, I can get a rotor clean
>>> with a .005" cut on each side.
>>
>> Then it probably didn't need machining.
>
>Maybe you are working on a different make of vehicle. On
>GM vehicles, you can easily experience a pulsation from a
>rotor that can still be cleaned up with a .005" cut on both
>sides. We machine all rotors anyway, as not doing it is
>a guarantee that you "will" get complaints from the customer.

Exactly. That's just what the guy I was exchanging posts with a while
back said. It's a mechanic's CYA. I isn't necessary, but it precludes
callbacks from ignorant customers fussing over a few squeals. Costs
them thousands of miles of rotor service, but hey, that's money in the
mechanic's pocket.

>> My experience is that the turned rotors go bad within a few months and
>> you end up needing new ones anyway.
>
>You must be working on a different make of vehicle.

True enough. Not big American iron with big fat brakes.