DougW wrote:
>
> There are several.
>
> 1) heat soak
> When you use the brakes a lot then sit there at the light with your foot
> on the brake. The pads hold heat in the rotor and that difference affects
> the material and can lead to warping.
> 2) drenching
> When you get the brakes real hot then stick them in water (like a stream
> crossing).
> 3) Worn caliper mounting bolts
> As these things age the brake pads don't always back off and sometimes one
> side of the pad will ride against the rotor. Always check pad thickness.
> If one pad is thinner than the other you have this problem.
> 4) Worn piston
> If the piston doesn't retract properly the brakes will rub and get hot
> 5) Defective rotors
> DC stock rotors/two piece/ el-cheapo
> 6) Improper turning of rotors/surfacing of rotors
> Midas (for example) and some other chains use the old milling machines
> with one blade, not the multiblade rotary milling machines. What was good
> for gramp's vehicle isn't good for modern rotors.
> 7) Probably should be up higher.... Impropper break-in of new rotors/pads
> If you don't break in rotors properly they will not wear well.
> The procedure is fairly easy.. stillen has it on the website last I checked.
>
> That's just a few.
>
> --
> rbg
A coupla more ideas:
1) When you torque (re-torque) the lug nuts, it is best to have the
weight off the wheel thru the entire torqueing process (have someone
apply the brakes if necessary for the last stage of torqueing - probably
won't be necessary - parking pawl is generally sufficient - at least for
the fronts). If you let the weight down on the wheel during the
torqueing, not only a vertical force, but a tremendous side force is put
on the tire and wheel as the geometry of the suspension changes as the
springs settle from the vehicle weight and can result in residual
stresses in the installed wheel/hub assembly (one more factor that can
be eliminated).
2) For extra insurance against warping, especially on a problem vehicle,
you can have a new set of rotors cryogenically treated - will cost $75
plus shipping for treatment of a pair of rotors (based on: $1.50/pound
with min. job charge of $75 - a typical rotor would weigh in the
neighborhood of 15 to 21 pounds - rears are almost certainly not the
problem - only necessary to do the fronts). I recommend
www.300below.com. I had new rotors (fronts only) done on my '99
Concorde (LH cars are also plaqued by rotor warping) several months ago,
and the brakes are as smooth today as when I first put them on - and I
just spent a week vacation in the mountians of West Virginia with 3-mile
8 to 10% downhill grades braking from 55 mph to 15 mph for hairpin turns
- I think I just proved (to myself anyway) that there is something to
this cryo-treating). Side benefits: Rotor wear is decreased to 1/2 to
1/3 of non-treated rotors, pad wear decreased to 80% of normal; friction
coefficient somewhere between unchanged to slight increase.
Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")
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