Turning Rotors: a case study...

The only Taurus experience I've had was on one my #2 son owned for a couple
years. I didn't get into the brakes, but when he was in Montana the clutch
went out. Turns out the clutch on the 2.4L 4 cyl is only 6 inches diameter!
It seems to me the Ford strategy for cars (but not for trucks) is to make
something that gives three years good service, and anything goes after that.

Mike

 

yes indeed! it's all about the first owner; all the others can go hang.

buddy of mine used to work at one of their r&d facilities. all their
time & money was going into cost control [which is ok] and life
limitation [which is not, since the price differential between say ford
& honda is minimal]. if a ford was 1/3 the price of a honda, i'd have
no problem with it, but i'm wierd like that.

 

Realistically, there isn't much that can be done. The customer can't be
forced to pay for repairs he doesn't want, and restraining either the
customer or his property isn't allowed - those are crimes. If a peace
officer shows up in time he can take the car off the road but a citizen
legally can't (at least not in the US - in any state I know if.)

When I was in aviation we would occasionally see planes in obviously
unairworthy condition come through and all we could do was inform our FAA
safety inspector.

Mike

 

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Some states yes, not this one (we wish there was!)

It has to do with the quality of the OEM part. Sometimes they are better,
other times (as in the Taurus) there worse.
BMW, VW Volvo and now even Ford Focus have a extremely soft metal for the
rotors. Replace them with the pads they wear that quick.



--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/

 

Well said.



--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/

 

That's what I suspected, i.e., a lack of parallelism. Thanks for
confirming it.

Eric

 

I replaced the front rotors on our '85 Volvo with aftermarket rotors from
NAPA and pads from Volvo when money was tight (the Volvo pads don't rattle
like aftermarket pads do). Now the pads are about half worn and the rotors
are severely worn.

Mike

 

A rotor that is "warped", not simply scored, is a very poor candidate for
resurfacing. The metal's properties have been changed by the level of heat
it has been exposed to, causing a permanent change in its structure. After
machining, once heat is applied, it will revert to its prior condition.

I went through this issue with my wife's Malibu, arguing with the Chevrolet
service manager every step of the way. They resurfaced the rotors 3 times to
cure pedal shudder, but it never worked because the rotors were warped. In
this case. it was a design flaw by GM - they made them too thin in the first
place, and paired them up with lousy pads. When I finally gave up dealing
with them and did the job myself, the rotors were ~0.003" thicker than the
bare minimum, suggesting that they were able to shave off a minimal amount
of metal each time they turned them. But so what? The rotors were junk the
first time they warped.

OTOH, a rotor that is merely scored can be effectively resurfaced and
returned to service, providing that not too much metal is removed. I've done
this on cars when the pad wore too far and "kissed" ther rotor. A competent
technician can do this.

Doug

 

sorry - unless this disk has been operated well into red heat, you're
not going to get much change in microstructure. you can however have
problems with a bad disk if it was not heat treated properly after
casting. when operated hot, /that/ disk will distort. more likely is
that there are simply different cooling rates on different parts of the
disk leading to local temporary distortion. that shouldn't happen on a
disk of sufficient thickness and whose internal vanes have not lost too
much material through rust.

my experience is that the disk cutting process is far from perfect -
those cutting machines see heavy usage, and you can mount the same disk
up a dozen times and get 13 different centers.

 

if you do a basic surface scratch test for these disks vs. others of
"harder" metal, you'll not find much difference. what i know for sure
is that some oem pads have a high silica content [with some aftermarket
pad producers copying their lead]. silica is an aggressive abrasive.
this is specified by the manufacturers you cite allegedly to eliminate
disk glazing and cope with surface rust on salted roads, and it does
have some benefit for those purposes. reality however is that it's all
about life limitation.

 

i used to work in a shop and had access - that's how i know these things
can be difficult to center, giving inconsistent results.

 

Your opinion and a dollar will get you a cup of coffee. That's all it's
worth . Repeated heating and cooling cycles will definitely change the
distribution of carbon atoms in an iron matrix - and it doesn't have to be
"red" hot. The temperatures created by the crappy pads used by GM did the
job in less than 15,000 miles.

If that's your experience, that's too bad. You need to find a better
technician, or learn to do it yourself.

 

Ahhh, New equipment.... Some are sweet!


--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/

 

== 1 of 6 ==

Thanks for "confirming" suspicion of lack of parallelism
are superfluous - Stephen H had told us of it:

 

== 4 of 6 ==

Why bring up coaxiality, or lack thereof? It is
irrelevant as long as the contact surface with the pad
gets machined.

Relevant is that the machined surface and the mounting
surface are perpendicular to the axis, and it is therefor
important that the mounting surfaces are clean. This is
the area you have to concentrate on, not centering. No
wonder why you got "inconsistent results."

 

Date: Sat, Dec 17 2005 6:21 pm

Actually, he is talking about himself. He does not
understand the physical relationship between runout (I
believe this is the name - I am no mechanic) and
perpendicularity of axis and contact surfaces - he
concentrated on irrelevant coaxiality!:

 

Date: Sat, Dec 17 2005 9:20 pm

In a number of messages (maybe in all of his "cutting
rotor" messages) jim beam emphasized the importance of
centering the disks when their surfaces are being
machined. This is what I was replying to - centering,
within limits, is irrelevant, but I used the wrong term
"coaxiality." Once again, important is the
"perpendicularity of axes and contact surfaces," and
anything that throws this off will cause problems.

In fact, there is the possibility that jim beam, too, is
talking about this when he writes about the importance of
centering: in a message at another list he wrote of the
importance of cleaning the mounting surfaces of the lathe
and of the disk.

 

Date: Sat, Dec 17 2005 10:15 pm

In a number of messages (maybe in all of his "cutting
rotor" messages) jim beam emphasized the importance of
centering the disks when their surfaces are being
machined. This is what I was replying to - centering,
within limits, is irrelevant, but I used the wrong term
"coaxiality." Once again, important is the
"perpendicularity of axes and contact surfaces," and
anything that throws this off will cause problems.

In fact, there is the possibility that jim beam, too, is
talking about this when he writes about the importance of
centering: in a message at another list he wrote of the
importance of cleaning the mounting surfaces of the lathe
and of the disk.

 

Another factor is also how the disk is actually cut. Not only is each axis
perpendicular to each other, but the surfaces for the pads to be parallel.
A poor cutting bit, taking off too much at a time, or a crossfeed that is
too high can cause these kinds of problems.

I just went through all of this with Chrysler, as the Jeep Cherokee's from
2000-2003 are notorious for premature warping of the front rotors (TSB
issued). They (Chrysler) went through the trouble of changing the calipers
and pads to another design in accordance with the TSB recommendations, but
only cut the rotors (which I argued against), and they were warped again
within 4K miles. I gave up arguing with them and purchased and installed a
set of high performance rotors and pads.

 

you need to read around a bit more. if the disk plane is not
exactly perpendicular to the rotation axis, on a floating [single
piston] caliper, you have pulsing in the hydraulics because of momentum
differences due to the mass of the caliper vs. the piston. with a
fixed caliper and 2 [or 4 or 6] pistons, the mass on each side is the
same and there's little net effect.