[Shotimes] Re: Odd rotor stripes

[Jon Heese]

I know that the tolerances involved here are often beyond eyeballing, 
but I figure it's worth mentioning the edge of the pad where it contacts 
the rotor appears to be perfectly uniformly flat up against the rotor 
(i.e. no visible gap whatsoever).  I can't really make sense of this 
fact when I look at the stripe of untouched oxidation in the middle of 
the swept area.

Regards,
Jon Heese

Jon Heese wrote:
 > The weird thing is that they were fine (i.e. no stripes) on the original
 > (allegedly warped) rotor I had on the car for almost 6 months
 > (mis-estimated the date in my orininal post).  I can't see geometrically
 > how a warped (axially-deformed) rotor could cause pad cupping in a
 > radial cross-section.  The only thing I can imagine is that due to the
 > warping, the fauly rotor bulged in the middle (like a donut, with an
 > almond-shaped cross-section), causing the pads to wear concave.  I've
 > never heard of this, but it's all I can come up with.
 >
 > I honestly don't know what brand of pad they are, I bought them with the
 > "upgrade" as a package deal and didn't pay close attention to the box.
 > My 6-month-old fuzzy memory is telling me that they were OEMs, but I'm
 > only about 55% sure of that.  Either way, I suppose I'll try
 > sanding/re-bedding them tomorrow and if that doesn't fix it I'll try a
 > new set.
 >
 > Thanks for the quick replies.
 >
 > Regards,
 > Jon Heese
 >
 >
 > Donald Mallinson wrote:
 >
 >> Jon,
 >>
 >> Chances are it is the used pads.  They are almost never perfectly
 >> flat.  YOu can try a couple of things, sand the pads and clean the
 >> disks and then really go out and bed them in by doing about 10
 >> moderately hard stops from 40-45 mph.  Don't try to get the ABS on,
 >> but do a quick stop.  Do them over the course of a couple of miles,
 >> and then see if they are still doing a "stripe".  If so, then try new
 >> pads.  Even cheap disks are usually flat and straight.
 >>
 >> What type of pads are you using?
 >> Don Mallinson
 >>
 >> Jon Heese wrote:
 >>
 >>> About 3 months after doing the '96 brake upgrade on my '95 SLO (using
 >>> "barely"-used rotors and new pads), I started getting some shaking
 >>> during braking, which got worse over the course of the next month.  I
 >>> assumed that one or both of the rotors was/were warped, so I bought
 >>> one Wearever $24 rotor (xref NAPA 86334) from Advance and swapped out
 >>> the front drivers' side.  After a quick test drive, everything felt
 >>> and looked fixed, so I figured that rotor must've been warped.
 >>>
 >>> About a week later, I started feeling the shaking again, so last
 >>> Sunday, I went and bought another identical rotor and swapped the
 >>> front passenger side.  After a quick test drive, once again, the
 >>> problem seemed solved, but when I got back in the driveway and
 >>> looked, I saw that the shiny new rotor had only been swept by the
 >>> brake pad in one stripe, about 1/2" wide, on the outer boundary
 >>> (towards the rim) of the normal swept area.  My firstworn funny and I
 >>> probably needed a new set.  It was after 7pm and the sun was going
 >>> down, so I stabled the car for the past week and pulled it out today
 >>> to check it.
 >>>
 >>> When I took it around the block today, once again, everything felt
 >>> fine, but now the rotor is being swept in two stripes, the same outer
 >>> one and now a 1/4" stripe on the inner (towards the wheel hub)
 >>> extreme.  I took the caliper off and inspected the pads and they
 >>> seemed prisitinely straight with a good 1/2" of material left.  There
 >>> was no (discernible) slant to their wear patten.  I put everything
 >>> back on and took it for another test spin and saw the same
 >>> double-stripe rub pattern on the rotor.  It didn't occur to me until
 >>> today to look at the inner surface (towards the axle) of the rotor,
 >>> but when I did, I saw the same double-stripe pattern on that surface.
 >>>
 >>> Now, the question:  What is the likelihood that my brand new (cheap)
 >>> rotor is cupped so that the center stripe of the swept area is
 >>> recessed from the brake pads?  Since the pattern is present on both
 >>> the inner and outer surfaces of the rotor, I'm leaning away from my
 >>> original thought of oddly-worn brake pads due to a misshapen old
 >>> rotor.  Unfortunately, I didn't keep the receipt for the rotors, so
 >>> either way I go, I have to put down $25-30.  So I figured I'd consult
 >>> the oracle first.
 >>>
 >>> What do you all think?
 >>>
 >>> Regards,
 >>> Jon Heese