AutoBanter - View Single Post - What are some car-repair jobs you always wished you could do but have never done?

**Xeno**

On 6/11/2017 7:02 PM, wrote:
> On Mon, 6 Nov 2017 04:48:30 +0000 (UTC), RS Wood >
> wrote:
>
>> Xeno wrote:
>>
>>> Any scoring on a rotor will fail it. As you say, there might be less
>>> than 50% of the pad surface in contact with the rotor surface. No way
>>> will that bed in properly. You will get localised overheating both on
>>> the pad and on the rotor.
>>
>> I'm not gonna argue vehemently because, in practice, while I've seen those
>> "wavy" rotors too, my rotors tend to be smooth so I don't deal with
>> "scoring".
>>
>> However, anyone who says "any scoring of rotors will fail it" has NOT looke
>> up the manufacturer's spec for scoring tests.
>>
>> I have. Long ago.
>>
>> The result was shockingly huge.
>>
>> I don't remember the actual number but I remember being shocked at how huge
>> it is. Something like tens of thousanths of an inch in width huge.
>>
>> We're talking Grand Canyon in rotors.
>>
>> I may be wrong but if someone says "any" scoring, that's just preposterous.
>> Let's see a manufacturer's spec for anyone who says that.
>>
>> Sorry. It's just not logical that 'any' scoring fails a rotor.
> ANY mechanical damage fails the rotor on DOT test. Some smoth wear is
> allowed - but you NEVER install new pads on rotors that have an uneven
> friction surface because it is virtually impossible to properly bed
> the new pads to the uneven rotor withot localized overheating

Exactly. The new pads will charcoal grill on the high spots and *never*
properly bed in.
>
> At the price of rotors today even on your Bimmer, it just is not
> worth it. The pads cost more than the rotors on MOST vehicles today.
> No reputable shop will do it because comebacks are expensive - and
> real mechanics KNOW the comebacks will happen if they do something
> stupid like installing new pads on badly worn rotors.
>
Brake pulling is most likely as the most grooved disc will have less
surface contact.

--

Xeno