Auto Brake question

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Take a look at the thickness of that rotor on a 3/4 ton (or 1 ton) and compare it to a rotor on todays cars. No comparison.
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wrote:

If it is not grooved , pitted, or discoloured just scuffing with "40 grit abbrasive will allow them to seat just fine. HOWEVER, in at least half of North America finding rotors in that condition while requiring pad replacement is getting to be a rare occurrence. (Particularly on the inner surface of the rotor)
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wrote:

Most car makers do NOT recommend routine turning of the rotors when pads are replaced. And the worst that would happen if you don't turn them is that the pads last longer, hardly a reason not to honor the warranty on the pads. It's just another excuse the shops use to avoid doing inexpensive work.
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wrote:

Obviously spoken by a non-mechanic.
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On Mon, 18 Jan 2010 18:37:08 -0500, snipped-for-privacy@snyder.on.ca wrote:

Nope. Years of experience on my own cars. Apparently you don't bother reading the genuine repair manuals put out by the automakers.
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wrote:

Did it for a living for over 20 years. Have bought the manual for every vehicle I've owned in the last 30.
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wrote:

Group 06- Section 00, pages 17 to 19 of the Ford PG2040 manual for the 1996 Mystique /Contour states "each time the brakes are serviced, the front and rear disk rotors should be checked for scoring, runout, parallelism and thickness" Runout of over 0.006" is unacceptable, and parallelism (variation in thickness) must not excede 0.0006" and there is half a page dedicated to how to refinish a rotor. They also stipululate that you NEVER machine to miinimum thickness spec. Front rotor discard thickness is 22.2mm, or 0.87". Original spec is 25MM (0.984"). That leaves 0.114" MAXIMUM cut/wear to scrap - aprox 0.040" per side to the service limit - and .057" to scrap. So it is OBVIOUS they intend/expect that the rotors will often require refinishing or replacement.
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snipped-for-privacy@snyder.on.ca wrote in wrote:

.057 is a lot of material. 1/16" is .0625".

"often"?? that's just your assumption.It's not so obvious to me.
I doubt many brake techs actually measure runout,parallelism,or rotor thickness;they just quote new rotors,and add the cost to your bill.
How much rotor material wears off if the car's brought in before the pads reach minimum thickness? How much does a ordinary refinishing job remove? (On a rotor that is not grooved.)
Any idea? (I don't know.)
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wrote:

Brake techs, mabee - but mechanics DO.

That depends on the pads, to a large extent - and also on the rotor material I've seen rotors worn to below the limit, with NO grooves, without ever being machined. I've seen rotors that were not machinable any more with half the frictionnmaterial still left on the pads - after having pads and rotors replaced at the same time less than a year before.

That depends, but you won't get away with ten thou per side - almost guaranteed. This is assuming there is a requirement to machine them in the first place.

If the rotor is dead smooth, but badly glazed, an abrasive disk will do the job at about one thou per side. If a cut is required, (shop doesn't have the "grinder pucks" generally closer to five thou per side. Any less leaves a bad finish because the cutter needs to get UNDER the glaze to remove it. It's too hard to cut the glaze itself. Kinda like being case hardened.
Prep discs on a die grinder can take off the glaze without removing much metal - spin the rotor up (car running in gear) and run the prep disk on the grinder untill the glaze is gone - generally 80 grit does the job, but 120 could also be used

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Ashton Crusher wrote:

If you never want to replace your calipers again, flush your brake fluid every two years. I have a Motive PRoducts pressure bleeder and it's inexpensive and works great. Whenever you change pads, make sure to lube up all the caliper sliders and replace any corroded hardware. If you do this, your calipers should last at least as long as your hoses.
nate
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wrote:

With some shops that is a definite truth - they will replace anything if you let them. However, a shop makes MORE money machining a set of rotors than they do replacing that same set of rotors, all things considered. Assuming nothing goes wrong with the job and they don't end up having to do the job over on their dime a month or two down the road.
In some parts of North America 125,000 miles on the original calipers is no stretch at all. Perhaps even on the original rotors - and with strictly highway miles?? Even a chance on the first set of pads if the driver is conservative in his driving habits.
In other parts of North America, in urban driving conditions, 30,000 miles on a set of pads and rotors would be almost miraculous, and 50,000 on the calipers would be uncommon, particularly without that "un-neccesary" bi-annual brake service that all the "crooked, unscrupuolous" mechanics try to stuff down your throat.
Like the manufacturer of that orange oil filter used to say back in the sixties and seventies "you can pay me now, or you can pay me later"
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Where are these brake rotors used on the home?
Gordon Shumway
Our Constitution needs to be used less as a shield for the guilty and more as a sword for the victim.
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To help transport supplies for remodeling:):):)
GEEZ its a very valid question!
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Hmm, a bit off topic, are we?
If the shop routinely replaces the rotors, ask them why. I personally would avoid a shop that routinely replaces rotors without first checking to see if the old ones can be machined. The exception might be newer cars that come with pretty thin rotors, and they often can't be machined. Some rotors can be machined, but will warp easily afterwards because they are too thing. With a bit of experience, you know which cars will probalby need new rotors and you learn not to waste time machining them.
Most older cars come with nice fat rotors that can be machined many times. There are good reasons to routinely replace rotors on some models, but it is unnecessary and wastefull with other models.
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On Sat, 16 Jan 2010 14:25:08 -0600, Zootal

The limit on even the "old fat" ones was usually 2, or at the very best, 3 times.
As for machining vs replacing? On today's cars, with rotors often available for less than $40 and machining costing 30+, why would you EVER machine the rotor??
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snipped-for-privacy@snyder.on.ca wrote in

It cost me $25 to machine my rotors, $90 to replace them. If it really was $40 versus $30, phht, ten bucks more gets me new rotors? Replace them!
In the end I replaced them anyhow because within six months the had warped. Next time I pay $90 to replace them instead of $25 to machine them.
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snipped-for-privacy@snyder.on.ca wrote in

why would you replace rotors if they don't need replacing? Why turn them if they don't need turning?
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Because they develop a glaze on them. The new pads need a fresh surface to seat properly.
Would you install new piston rings without honing the cylinders?"
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TELL THEM IN ADVANCE YOU MUST HAVE ALL WORN OUT PARTS!
I giot into a 6 month hassle with Midas Muffler, they found a bad CV joint boot, and inssted the joint was bad too. So I said OK give me the joint:)
It was fine, but before it was thru i had talked to the president of midas muffler he assured me the local franchissee was honest as the day was long. talked to a former employee wo left cause he got tired of ripping off customers, talked to a bunch of victims err customers in their waiting room and warned them they are going to pick your pocket.
less than a month later a inverstigative report came out, midas lost their state inspection license, many stores closed, would of loved to see the people i warned say that guy was right when he nearly got thrown out of the store warning us.
a small local mechanic is often a better choice.
but in this case i support replacing the rotors.
if they dont and you leave and have a accident they run the risk of being sued
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Another way to look at it. the absolute worst thing that can happen is that you pay a bit more money. Your brakes will work like new, guaranteed. At least in this case, if you are getting ripped off, you are getting new brake parts in return so the money isn't being wasted.
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