....and
[email protected] spake unto the tribes of Usenet, saying...
> On Sat, 18 Feb 2006 10:15:29 -0000, "Richard Brookman"
> <[email protected]> wrote:
>
>> ...and [email protected] spake unto the tribes of Usenet,
>> saying...
>>
>>
>>> The vehicle has 38K miles and general braking performance has never
>>> been a problem except for a squeal when braking lightly at low
>>> speed.
>>>
>>> The dealer reported that the front disc brake pads had plenty of
>>> wear remaining but the front rotors had worn too thin! The service
>>> tech thought that the wear on the rotors had caused a ridge on the
>>> rotor to develop that contacted the caliper and caused the squeal.
>>> After replacing the rotors I still have the squeal.
>>>
>>> I tend to be easy on brakes with mostly highway travel, no
>>> tailgating, and look ahead driving.
>>>
>>> Comments?
>>>
>>> TIA
>>
>> Your mechanic was partly right. The wear leaves a ridge which
>> contacts the sides of the brake pads rather than the friction area
>> and makes them rattle and squeal at low speeds. If the disc (rotor)
>> was contacting the calipers you would have a real problem. I cured
>> it on my P38 (similar axles) by replacing the discs - a very easy
>> job. If these have been replaced, were new pads fitted (I should
>> hope so)? If so, taking the pads out and applying a small amount of
>> copper grease to the backs and any areas that might contact the
>> calipers might cure it. Easy or heavy on the brakes should make no
>> difference - correctly set up, they should work and not squeal.
>
> Thanks for your reply. I may have misunderstood what the wear-created
> ridges on the rotors were contacting, maybe it was the side of the
> pads - I was picturing that contact to be to the caliper itself.
>
> The pads were not changed. On my next routine visit to the dealer
> I'll explore changing pads and ask about the use of copper grease.
>
> With my limited mechanical experience I'm still surprised that the
> pads were fine but the rotors wore out!
>
> Thanks again,
>
> LB
I'm very surprised the pads were not changed with the new rotors. The pads
contact most of the disc/rotor area, but there is a small band on the very
outside, perhaps 2mm wide, where they do not. As the disc/rotor wears, it
leaves a step on the outside of the disk which will also corrode as it is
not swept by the pads. As the pads oscillate slightly, a step is also worn
in the side of the pads. It is the interference between these two steps
that caused the pads to vibrate and sqeal. There is a similar unswept area
on the inner part of the disc, and of course the same on the other side. In
effect, the pads and discs wear a pattern into each other, and it is always
good practice to replace both if you are replacing the disc.
I doubt if the original pads lasted 38k miles, so they will have been
replaced at some point. With a heavy vehicle like a Disco, a very hard pad
compound is necessary, which does tend to wear the discs out in time. These
days I regard brake discs as consumable items, which will probably need
replacing 40-80k miles from new. 38k seems quite soon, but doesn't surprise
me.
The copper grease dodge shouldn't, strictly speaking, be necessary if all
the parts are fitted back correctly with new anti-rattle shims etc, but in
reality it is often the cure for an annoying squeal that won't respond to
anything else. Just make sure that only a smear is used, and can't get
anywhere near the friction surface.
--
Rich
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