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Why machine brake rotors? 5
- Thread starter BobM3
- Start date
From my experiance what would cause the pads not to last as long is the fact that after 30k miles or so of use the rotors are grooved and possibly rust pitted. If they are still smooth and in good condition there shouldnt be any premature pad wear, however the rotors should be machined to get rid of the glazing and provide a fresh, clean, smooth surface for the new pads to bed against. Slapping new pads on a set of used rotors will probably give you a much greater stopping distance than installing new pads with new or freshly machined rotors. Machined rotors should have a smooth, non-directional surface finish, i don't think there is a specification or RA number for how rough or smooth they should be.
Most premature pad wear is caused by corroded or improperly lubricated pad sliders and brake hardware.
-Jon
Most premature pad wear is caused by corroded or improperly lubricated pad sliders and brake hardware.
-Jon
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1
- #3
patprimmer
New member
BobM3
In my opinion, the main reason for machining rotors is mainly to increase the cash flow for the person replacing the pads. It is a quick and easy job for which they can charge a fairly high price as it "sounds like a major job". It also greatly increases the probability of also being able to stick the customer for a set of new rotors.
I never machine rotors unless there is a noticeable uneven wear on the rotor or deep score marks.
The work hardened surface of the rotor resists wear, and removing it reduces the strength and the life of the rotor.
Rotors quickly work harden or glaze with use, so removing that finish only has a very temporary effect on brake performance. One downside is that the brakes take a little time to bed in, normally like 5 or 10 hard stops from about 80 kilometres per hour. Knowing that, you can take a short and careful drive, and repeatedly left foot brake until the brakes get a bit hot and bed in. You will know when the pedal feels right.
I also never use OEM pads (purely for cost reasons), but I do use premium quality pads from big name aftermarket vendors who are also OEM supplier, like Bendix or Hardie Ferrado. These suppliers might be different in your part of the world. They can normally provide an equal or better compound at a substantially lower cost to OEM.
I do not use semi metallic like "Metal King" as I think they are to abrasive on rotors.
Things to consider when choosing a compound to suite you are:-
Noise.
Pad life.
Rotor wear.
Braking power (friction properties).
Fade resistance.
Dust colour and appearance.
Corrosive nature of dust build up on wheels.
It also always pays to ensure the callipers are free to float easily on the pins, the pads move freely on their mounting blocks, that they have sufficient clearance in the blocks to allow them to move freely even when very hot, and that the calliper pistons move freely and retract properly, so that the brakes do not drag. This is important for avoiding steering pull to one side as the brakes are applied and to get maximum pad life and fuel economy.
Regards
eng-tips, by professional engineers for professional engineers
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In my opinion, the main reason for machining rotors is mainly to increase the cash flow for the person replacing the pads. It is a quick and easy job for which they can charge a fairly high price as it "sounds like a major job". It also greatly increases the probability of also being able to stick the customer for a set of new rotors.
I never machine rotors unless there is a noticeable uneven wear on the rotor or deep score marks.
The work hardened surface of the rotor resists wear, and removing it reduces the strength and the life of the rotor.
Rotors quickly work harden or glaze with use, so removing that finish only has a very temporary effect on brake performance. One downside is that the brakes take a little time to bed in, normally like 5 or 10 hard stops from about 80 kilometres per hour. Knowing that, you can take a short and careful drive, and repeatedly left foot brake until the brakes get a bit hot and bed in. You will know when the pedal feels right.
I also never use OEM pads (purely for cost reasons), but I do use premium quality pads from big name aftermarket vendors who are also OEM supplier, like Bendix or Hardie Ferrado. These suppliers might be different in your part of the world. They can normally provide an equal or better compound at a substantially lower cost to OEM.
I do not use semi metallic like "Metal King" as I think they are to abrasive on rotors.
Things to consider when choosing a compound to suite you are:-
Noise.
Pad life.
Rotor wear.
Braking power (friction properties).
Fade resistance.
Dust colour and appearance.
Corrosive nature of dust build up on wheels.
It also always pays to ensure the callipers are free to float easily on the pins, the pads move freely on their mounting blocks, that they have sufficient clearance in the blocks to allow them to move freely even when very hot, and that the calliper pistons move freely and retract properly, so that the brakes do not drag. This is important for avoiding steering pull to one side as the brakes are applied and to get maximum pad life and fuel economy.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
I agree with Pat. It a money maker for the shop that does the turning. First, they don’t have to test drive or measure the run-out on the rotors it they machine them. Second, after machining there is a significant increase in probability that the rotors will need be replaced because they will be too thin to meet minimum specs. I have even see shops machine new rotors just to be sure they are true. Why measure the run-out for free when you can charge to turn the new rotor??? I used to work in a shop that always turned rotors and drums, new and reused.
The origin of this practice was with brake drums. A large lip would develop over years of service. I used to turn the drums and arc the shoes to match in the old days. If you did not, a spongy brake peddle would result until the shoes wore in. If the new friction material was riveted/bonded on slightly to one side, the friction material would hit the lip. The shoes would wear in quickly and often the automatic adjusters would not catch up with the accelerated wear. Some cars and trucks did not even have automatic adjusters. A low brake pedal would result until you back up the car/truck several times while hitting the brakes or returned to the shop for adjustment. This was not good for customer relations; hence, we always turned the drums to get rid of the lip.
The origin of this practice was with brake drums. A large lip would develop over years of service. I used to turn the drums and arc the shoes to match in the old days. If you did not, a spongy brake peddle would result until the shoes wore in. If the new friction material was riveted/bonded on slightly to one side, the friction material would hit the lip. The shoes would wear in quickly and often the automatic adjusters would not catch up with the accelerated wear. Some cars and trucks did not even have automatic adjusters. A low brake pedal would result until you back up the car/truck several times while hitting the brakes or returned to the shop for adjustment. This was not good for customer relations; hence, we always turned the drums to get rid of the lip.
It all depends on the pad composition used previously, driving habits, and of course if the rotor is wearing flat. I've never once re-machined or replaced rotors on any of my personal cars, but then, if the brakes start squealing or if the build-up pad compound on the rotors starts to delaminate and cause a pulsation, I'm not going to get angry with myself for poor work. Paying customers are an entirely different story! The job has to absolutely positively be done right the first time.
Measuring runout doesn't enter into it - you have to measure runout either way. Properly machining the rotors requires that you measure runout on the vehicle, mark high and low spots, then chuck into the lathe to match, *then* ensure that runout is zero when installed. Yes, it's a pain in the tail. No, most people don't do it. On the other hand, ensuring zero runout on new rotors practically eliminates pulsation problems forever, barring bad castings, so *new* rotors get runout measured and, if necessary, a clean-up machining.
Why is it that there's never enough time to do it right, but always enough time to do it twice?
Measuring runout doesn't enter into it - you have to measure runout either way. Properly machining the rotors requires that you measure runout on the vehicle, mark high and low spots, then chuck into the lathe to match, *then* ensure that runout is zero when installed. Yes, it's a pain in the tail. No, most people don't do it. On the other hand, ensuring zero runout on new rotors practically eliminates pulsation problems forever, barring bad castings, so *new* rotors get runout measured and, if necessary, a clean-up machining.
Why is it that there's never enough time to do it right, but always enough time to do it twice?
- Thread starter
- #7
I had thought the glazing of the rotor somehow caused rapid wear of the pads. Sounds like this isn't so. Years ago I worked on a machine that used a large disk brake. Once the disk glazed up the brakes would squeal. I had to rough up the disk with a grinder to get the noise to go away. Any idea why a glazed surface would cause a squealing?
Machining trues the rotors and maximizes wear surfaces. If the rotor surface is flat, free of grooves, has no noticable wear (radius) on the edges or run out, the pads will last about the same amount of time whether the rotor is machined or not. If you machine rotors that fit all the criteria above, whatever you gain in pad life will be lost in rotor life.
A shop will always machine rotors because they can't afford for things not to work right the first time, every time.
A shop will always machine rotors because they can't afford for things not to work right the first time, every time.
In the 'old' days, that's the 50's and 60's for me, I always turned my brake drums...everytime I put on new shoes...new drums after they were too thin to turn.
With disc brakes, I never machine them and only replace them if they become warped (my '95 Chrysler LHS) or damaged by a broken pad (my 91 Dodge PU), replacing BOTH rotors. Point of fact, unless there is seriously agressive wear, I will still use them allowing a little extra time to bed in new pads! My old 83 Turbocoupe went well over 200,000 miles on the same discs and my wifes Lincoln is now over 131,000, but will need replacement next time as they have become warped. On my vintage Mini race car I am still on two year old Brembo discs and now on my fourth set of EBC Greens...on my vintage Lotus Cortina race car, I am still using OEM discs installed in 1988, using the old Repco MetalMaster pads (I still have a stash of them)!!! The big secret is to match the rotor material and mfgr. with the proper pad and if your discs need resurfacing, they need to be REPLACED, IMO!
Rod
With disc brakes, I never machine them and only replace them if they become warped (my '95 Chrysler LHS) or damaged by a broken pad (my 91 Dodge PU), replacing BOTH rotors. Point of fact, unless there is seriously agressive wear, I will still use them allowing a little extra time to bed in new pads! My old 83 Turbocoupe went well over 200,000 miles on the same discs and my wifes Lincoln is now over 131,000, but will need replacement next time as they have become warped. On my vintage Mini race car I am still on two year old Brembo discs and now on my fourth set of EBC Greens...on my vintage Lotus Cortina race car, I am still using OEM discs installed in 1988, using the old Repco MetalMaster pads (I still have a stash of them)!!! The big secret is to match the rotor material and mfgr. with the proper pad and if your discs need resurfacing, they need to be REPLACED, IMO!
Rod
bentwings1
Mechanical
- Mar 8, 2006
- 48
- 0
- 0
I do as patprimer, izzums and evelrod, I don't surface my rotors or drums. I also use the cheapest softest pads and shoes. It's a lot cheaper to replace shoes and pads than rotors and drums. My Dodge diesel dually has 150k on the original brakes and they are like brand new. It will stop a 10,000 pound trailer like it wasn't even back there. Not that I don't use the trailer brakes, but it will stop easily with out them.
My old SuperCoupe had over 200k onthe original rotors too.
However as noted the brake shop can't take a chance on having problems so they must turn rotors and drums. I worked in an auto shop for years and always turned them with the care noted above. The last thing I wanted was a come back for brake problems. Also if someone has a crash you can rest assured the first thing the lawyer looks at is who serviced the brakes and how. You won't have a chance on thin rotors with grooves in them or slick smooth rotors. The bottom line is if you do them for yourself don't turn them. If you do them for someone else turn them or replace them.
My old SuperCoupe had over 200k onthe original rotors too.
However as noted the brake shop can't take a chance on having problems so they must turn rotors and drums. I worked in an auto shop for years and always turned them with the care noted above. The last thing I wanted was a come back for brake problems. Also if someone has a crash you can rest assured the first thing the lawyer looks at is who serviced the brakes and how. You won't have a chance on thin rotors with grooves in them or slick smooth rotors. The bottom line is if you do them for yourself don't turn them. If you do them for someone else turn them or replace them.
Well I have like 60,000 to 70,000 on some brake pads and shoes that were only supposed to last 30,000 or so. And that is on the NONturned drums and rotors.
Also in my flying days, the small planes that I rented had rotors that were grooved and worn worse than anything you would want to use on your car. Don't ask I don't know.
The only reason to have to turn them is if the metal backing has rubbed on them. Or the gooving is way deep.
Otherwise they live just fine.
Also in my flying days, the small planes that I rented had rotors that were grooved and worn worse than anything you would want to use on your car. Don't ask I don't know.
The only reason to have to turn them is if the metal backing has rubbed on them. Or the gooving is way deep.
Otherwise they live just fine.
I have to disagree with most all of you, our shop pays the techs the same whether we replace or machine the rotors, so it is not a money maker for the shop to machine them because it takes there techs longer to machine than to replace (less productivity) and the shop doesn't make money off the markup of a new set of rotors. Up here in the northeastern US rotors are always severely rusted and grooved due to our winter road conditions so they are never in a condition where we can just slap pads on them. In fact scoring, grooving, or heat checking on the rotors fails state safety inspection. We measure the rotor thickness before we machine them, based on experience we know how much material we will machine off and whether or not the rotor will go below minimum thickness requirements when we machine them. I really hope that there aren't too many shops out there that aren't competent enough to machine rotors because it certainly isn't brain surgery.
On my personal vehicles at times i have done a complete brake job with new rotors, and other times i have just cleaned and lubed the hardware and slapped pads on. Both ways the vehicle stops safely, however when braking from high speeds (100mph+) you do notice a difference with the grooved unmachined rotors. But as i said before my experience is up here in the rust belt, down south your rotors may last forever.
-Jon
On my personal vehicles at times i have done a complete brake job with new rotors, and other times i have just cleaned and lubed the hardware and slapped pads on. Both ways the vehicle stops safely, however when braking from high speeds (100mph+) you do notice a difference with the grooved unmachined rotors. But as i said before my experience is up here in the rust belt, down south your rotors may last forever.
-Jon
patprimmer
New member
I have never seen really rusty rotors, except on a boat trailer.
We do not have ice and snow, therefore no salt.
Daily use cleans of any surface rust well before pitting begins, so your argument is not valid here, although I see your point where salt is used and especially if the rotors see a good dose of salt and are left to stand for a week or two.
I have never felt a difference in the pedal between machined rotors and not machined after 1000 miles of use, as the surface of the machined rotors will have work hardened and glazed just like the non machined ones, and the pads will be totally bedded in on the non machined ones by that time.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
We do not have ice and snow, therefore no salt.
Daily use cleans of any surface rust well before pitting begins, so your argument is not valid here, although I see your point where salt is used and especially if the rotors see a good dose of salt and are left to stand for a week or two.
I have never felt a difference in the pedal between machined rotors and not machined after 1000 miles of use, as the surface of the machined rotors will have work hardened and glazed just like the non machined ones, and the pads will be totally bedded in on the non machined ones by that time.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
I live in the winter salt belt in Indiana and have always just put new pads on, even if the rotors were grooved. I did have a rust related brake failure when the friction material/backing pad interface was undermined by rusting and the pad finally came off during a brake application. Jons999--interesting that the state safety inspection acually requires that the rotors be examined. Any states I lived in with a "safety" inspection considered the brakes OK as long as the car did not crash through the back wall of the shop.
Much of the time, the rotors get rust lines or pits to the point that the brakes pulsate violently before the pads are worn out. The rest of the time, by the time the pads' life is over, they are rusted/grooved badly enough that machining would require removing an excess of material to get to clean metal. nevermind the damage that the rust does to the lathe bits. It is common to get over 50% of the width of the braking surface covered with rust.
Interestingly, cars with ATE brakes seem immune to this problem, which leads me to believe that pad composition plays a large role in it. Perhaps someone else could chime in about specific pad compositions, but the compositions that never have rotor glaze/rust problems leave a satiny finish on the rotors, but create copious amounts of brake dust as a downside.
Interestingly, cars with ATE brakes seem immune to this problem, which leads me to believe that pad composition plays a large role in it. Perhaps someone else could chime in about specific pad compositions, but the compositions that never have rotor glaze/rust problems leave a satiny finish on the rotors, but create copious amounts of brake dust as a downside.
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3
- #16
GregLocock
Automotive
Sure, different pad materials chew the rotor up to a greater or lesser extent.
It's just another compromise in the black art of pad selection.
Incidentally worst case for rotor wear is often freeway driving, grit builds up on the rotor and then gets scuffed between the pad and the rotor.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
It's just another compromise in the black art of pad selection.
Incidentally worst case for rotor wear is often freeway driving, grit builds up on the rotor and then gets scuffed between the pad and the rotor.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
- Thread starter
- #17
Thanks for all the input guys. I finally got around to changing the pads. I saw something I hadn't seen before. There's a small spring attached to the inner pad that looks like it's supposed to apply a small force or moment to the inner pad. It's so small I can't believe it does much when the pistons are energized. Must be there for when the pistons aren't energized. Any ideas?
patprimmer
New member
To stop rattles.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
diskullman
Industrial
After working for an automotive parts distributor (and buying parts at their cost), I don't even question about turning rotors. Turning a rotor for my 98 Dodge Stratus cost $13.00 each at my local parts store. A new replacement rotor (Chinese) cost $7.oo each. Now, multiply these facts times all the brake jobs, local shops, and brake lathe operators, and there goes thousands of US workers made expendable by cheap Chinese imports.Kinda scary
Russell Giuliano
Russell Giuliano
BiPolarMoment
Mechanical
BobM3: I've heard there is often a part called an "Anti-rattle spring" or on some cars an "anti-rattle clip"--ironically, it is sometimes the source of rattles to spite its name (happened on my friend's car).
Can anyone confirm or disprove the veracity of this site:
Can anyone confirm or disprove the veracity of this site:
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