[Fot] squaring pads

[DAVE HOGYE]

The more clearance between the slot in the caliper and the pad backing plate the quicker this becomes a problem.   I've measured .010-.012" total clearance on an NOS street pad and as much as .070" on a set of Carbotech pads.  The edges of the Carbotech backing plates looked to have been, (were definitely), ground off on and belt sander or grinder from the factory, right down to the edge of the friction pad and they were out of square by .035".  The side of the pad was making contact with the caliper slot.  This immediately caused problems with the caliper pistons cocking severely.  The pistons even left a witness mark in the bore of the calipers.  Not good.  The Carbotech pads had .070" wear diagonally across the friction surface in a couple of weekends of racing.  Unfortunately, Carbotech made many excuses and denials when I brought this to their attention.  

If the pad backing plate is held close in the slot, the piston cannot get cocked as severely under hard braking.  Squaring of pad surface may still be desirable at some point, but pay close attention between of the width of the backing plate and the caliper slot.  

I have found Hawk pads to be made with as close a clearance as factory pads and the same dimension on every order.  No variations.  The Hawk pads also have the same shape as factory pads, more like a pie cut.  Wider at the outer edge.  This helps compensates for rotor surface speed and reduces uneven wear. 

I do like the feel of the Carbotechs, but I cannot rely on their quality control.

As you apply the brakes, the piston extends.  If the pad can move greatly within the caliper slot, the piston with take the side load, not the backing plate of the pad as it should.  If the backing plate is not square, the pad will also rotate a little.  Definitely not good.

Beware,

Dave H.


> On July 21, 2019 at 12:27 PM Phil Gott via Fot <fot at autox.team.net> wrote:
> 
>     The pads wear unevenly both radially and a bit circumferentially due to different surface speeds and friction forces. As the pads wear unevenly they “cock” in the caliper and bind up. The more wear, the greater the binding. 
>     Using some sort of a device (surface grinder, drill press etc with a good dust collector and mask for the operator) to make the face of the friction material parallel to the backing plate solves this issue.
>     Yes, this does change the surface of the pad presented to the rotor. I do not change rotors as they are in good shape. Any small to microscopic irregularities between the two quickly get dealt with during the first session out after squaring the pads. This would be the same as putting new pads on the car with the old rotors. Just treat the first few laps as if you are bedding in new brakes, which to some extent you are (except for temperature effects).
>     Different from a street machine where rust and grit take their toll in the rotor surface.
>     Phil Gott
>     114 TR4A
> 
>     Sent from my iPhone
> 
>     On Jul 21, 2019, at 10:33 AM, ralph hansen via Fot < fot at autox.team.net mailto:fot at autox.team.net > wrote:
> 
> 
>         > >          
> >          
> >         not to rain on the parade but, are you turning the rotors each time to make sure they are square also? if not, you now have unmatched surfaces - in the old days with good metal rotors I could see a slight advantage, these days with the good pads we get, and soft rotors they wear together, you might actually get a very slight increase in surface contact due to the angles and dangles - and, as you machine the rotors you lose mass, the all important heat sink that makes brakes work....
> > 
> >          
> >         On Saturday, July 20, 2019, 07:19:46 PM CDT, Mathieu W. Huovinen via Fot < fot at autox.team.net mailto:fot at autox.team.net > wrote:
> > 
> > 
> > 
> >          
> > 
> >         Squaring up the pads? Please tell me more, I'm still learning. Thanks!
> > 
> >         -Marhieu
> > 
> >          
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