Should I Replace/Turn Rotors When Installing New Pads?

x2 couldn't have said it better myself and don't blame anyone if you get a bad squeak or your pads don't last very long. Brakes are one of the last things you should skimp on. And to the person who mentioned the $30 rotors, trust me, you do not want economy rotors, especially on a Toyota truck which is very susceptible to rotor warping. Only put premium rotors if you want OE performance.

I'm a certified mechanic and I just laugh to myself at all the comments I read on the forums. Everyone thinks they know what they are doing and everyone is a mechanic nowdays. *sigh*

 

why would anyone go through the trouble of changing pads and NOT turn the rotors? i always have my rotors turned to get rid of the lip on the outside edge and to remove whatever deposits are stuck to the rotor surface.

to be sure, you don't have to have them turned ...but i would. ....and doing it my way, i never have squeeling brakes.

 

Back in my highschool/college days, I used to work in my uncles shop as a service writer. Granted that it has also been 15 years since I've done it and I'm definitely no mechanic myself, Tony's explanation is pretty much exactly the same attitude the mechanics took towards turning rotors. (If there's noticeable groves or pulsating, they would turn them, otherwise just run it.) I really have no idea how they treat newer vehicles though.

The way I always thought about it is turning them (usually because the owner ran the pads down so low the rivets were making groves in the rotors), would give the rotors an extra chance at life, but at a risk of causing them to overheat and warp more easily, and or course not being able to turn them in the future.

Also, I believe that back then, they would only turn rotors once or twice before telling the customer that there's a lot of risk of warping if they do it another time and leave it up to them to decide how to spend the money.

 

Rear drums don't wear out very fast. Inspect and replace pads if needed. Sometimes you need to clean them up and get a rebuild kit, but drums are tough. Remember only about 20% of braking come from you rear, that is why the drums last so long.

 

This post is probably one of the most inaccurate that I have ever come across. What makes it so bad is that this guy actually comes off like he knows what he is talking about.

I am not an automotive technician. I am however, an engineer. Folks a technician is not telling you to turn your rotors so that he can make some extra money. This is simply a problem of science.

The reality is that if the tech wanted to make some extra money then he simply would tell you NOT to turn them. Then the conversation would be about new rotors and pads later on. Generally this problem is at the molecular level on the surface of the rotor.

A build-up of pad material occurs with the extremely high heat that pads and rotors go through. And it will even occur when the pad material consistency has not changed at all. This heat transfer is far worse however when you go to a different type of pad with a different "recipe" or chemical make-up.

Nine times out of ten a rotor isn't "warped" at all. The rotor has pad material that has been transferred during hard braking or high heat.
Once it starts it begins to snowball and your braking performance gets worse and worse quickly.

All that any of you who doubt this need to do is a little bit of research. The right answer is out there for you. Also beware of extreme long life pads because yes they will last as long as the manufacturer claims that they will but, they sacrifice the surface of your rotor to do so.

Bing0

 

What about the thickness of the rotors??? I heard premium metallic pads wear them down...

 

im gonna pop in and say if you arent replacing your own pads.........its seriously one of the easiest things to do on these trucks

 

No offense but I’m curious about your age and personal experimentation with replacing pads without turning or replacing rotors. Book learning just isn’t the same as practical experience. The nice thing about brake pads is they are so easy to replace you can try not turning the rotors and if you’re not happy with the results the worse that can happen is you’re out of an hour of labor (less if you’ve done it many times) and +/- $50.

Not true, he could recommend turning them and the next time replace them because they are too thin to turn again. Makes $$ both times on the R&R of rotors and repacking the bearings.

 

I'm leaning towards BS on this.

I'd be interested in seeing your scientific data backing up your claims though. I'm not completely doubting you, but quite honestly, you're the one that sounds like you're trying to prove something.

At least your last paragraph does hold some validity in some cases, as some lifetime pads are just too hard and can chew up some rotors made with softer materials. It does vary based on both the rotor and the brake material though, as in many instances, the harder pads are just fine as well. If they weren't, they wouldn't have been an option for the last 20+ years.

 

i'm not sure what part of BingO's reply y'all are questioning. ..but this part is correct.

The "Warped" Brake Disc and Other Myths of the Braking System

by Carroll Smith Myth # 1 – BRAKE JUDDER AND VIBRATION IS CAUSED BY DISCS THAT HAVE BEEN WARPED FROM EXESSIVE HEAT.


The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.
When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.
With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, (FIGURE 1) discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, (FIGURE 2) a few where the friction surface had collapsed in the area between straight radial interior vanes, (FIGURE 3) and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. (FIGURE 4)
In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.
In order to understand what is happening here, we will briefly investigate the nature of the stopping power of the disc brake system.
THE NATURE OF BRAKING FRICTION

Friction is the mechanism that converts dynamic energy into heat. Just as there are two sorts of friction between the tire and the road surface (mechanical gripping of road surface irregularities by the elastic tire compound and transient molecular adhesion between the rubber and the road in which rubber is transferred to the road surface), so there are two very different sorts of braking friction - abrasive friction and adherent friction. Abrasive friction involves the breaking of the crystalline bonds of both the pad material and the cast iron of the disc. The breaking of these bonds generates the heat of friction. In abrasive friction, the bonds between crystals of the pad material (and, to a lesser extent, the disc material) are permanently broken. The harder material wears the softer away (hopefully the disc wears the pad). Pads that function primarily by abrasion have a high wear rate and tend to fade at high temperatures. When these pads reach their effective temperature limit, they will transfer pad material onto the disc face in a random and uneven pattern. It is this "pick up" on the disc face that both causes the thickness variation measured by the technicians and the roughness or vibration under the brakes reported by the drivers.
With adherent friction, some of the pad material diffuses across the interface between the pad and the disc and forms a very thin, uniform layer of pad material on the surface of the disc. As the friction surfaces of both disc and pad then comprise basically the same material, material can now cross the interface in both directions and the bonds break and reform. In fact, with adherent friction between pad and disc, the bonds between pad material and the deposits on the disc are transient in nature - they are continually being broken and some of them are continually reforming.
There is no such thing as pure abrasive or pure adherent friction in braking. With many contemporary pad formulas, the pad material must be abrasive enough to keep the disc surface smooth and clean. As the material can cross the interface, the layer on the disc is constantly renewed and kept uniform - again until the temperature limit of the pad has been exceeded or if the pad and the disc have not been bedded-in completely or properly. In the latter case, if a uniform layer of pad material transferred onto the disc face has not been established during bedding or break-in, spot or uncontrolled transfer of the material can occur when operating at high temperatures. The organic and semi-metallic pads of the past were more abrasive than adherent and were severely temperature limited. All of the current generation of "metallic carbon", racing pads utilize mainly adherent technology as do many of the high end street car pads and they are temperature stable over a much higher range. Unfortunately, there is no free lunch and the ultra high temperature racing pads are ineffective at the low temperatures typically experienced in street use.
Therefore - there is no such thing as an ideal "all around" brake pad. The friction material that is quiet and functions well at relatively low temperatures around town will not stop the car that is driven hard. If you attempt to drive many cars hard with the OEM pads, you will experience pad fade, friction material transfer and fluid boiling - end of discussion. The true racing pad, used under normal conditions will be noisy and will not work well at low temperatures around town.
Ideally, in order to avoid either putting up with squealing brakes that will not stop the car well around town or with pad fade on the track or coming down the mountain at speed, we should change pads before indulging in vigorous automotive exercise. No one does. The question remains, what pads should be used in high performance street cars - relatively low temperature street pads or high temperature race pads? Strangely enough, in my opinion, the answer is a high performance street pad with good low temperature characteristics. The reason is simple: If we are driving really hard and begin to run into trouble, either with pad fade or boiling fluid (or both), the condition(s) comes on gradually enough to allow us to simply modify our driving style to compensate. On the other hand, should an emergency occur when the brakes are
cold, the high temperature pad is simply not going to stop the car. As an example, during the mid 1960s, those of us at Shelby American did not drive GT 350 or GT 500 Mustangs as company cars simply because they were equipped with Raybestos M-19 racing pads and none of our wives could push on the brake pedal hard enough to stop the car in normal driving.
Regardless of pad composition, if both disc and pad are not properly broken in, material transfer between the two materials can take place in a random fashion - resulting is uneven deposits and vibration under braking. Similarly, even if the brakes are properly broken, if, when they are very hot or following a single long stop from high speed, the brakes are kept applied after the vehicle comes to a complete stop it is possible to leave a telltale deposit behind that looks like the outline of a pad. This kind of deposit is called pad imprinting and looks like the pad was inked for printing like a stamp and then set on the disc face. It is possible to see the perfect outline of the pad on the disc. (FIGURE 5)
It gets worse. Cast iron is an alloy of iron and silicon in solution interspersed with particles of carbon. At elevated temperatures, inclusions of carbides begin to form in the matrix. In the case of the brake disk, any uneven deposits - standing proud of the disc surface - become hotter than the surrounding metal. Every time that the leading edge of one of the deposits rotates into contact with the pad, the local temperature increases. When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness. Drat!
PREVENTION

There is only one way to prevent this sort of thing - following proper break in procedures for both pad and disc and use the correct pad for your driving style and conditions. All high performance after market discs and pads should come with both installation and break in instructions. The procedures are very similar between manufacturers. With respect to the pads, the bonding resins must be burned off relatively slowly to avoid both fade and uneven deposits. The procedure is several stops of increasing severity with a brief cooling period between them. After the last stop, the system should be allowed to cool to ambient temperature. Typically, a series of ten increasingly hard stops from 60mph to 5 mph with normal acceleration in between should get the job done for a high performance street pad. During pad or disc break-in, do not come to a complete stop, so plan where and when you do this procedure with care and concern for yourself and the safety of others. If you come to a complete stop before the break-in process is completed there is the chance for non-uniform pad material transfer or pad imprinting to take place and the results will be what the whole process is trying to avoid. Game over.
In terms of stop severity, an ABS active stop would typically be around 0.9 G’s and above, depending on the vehicle. What you want to do is stop at a rate around 0.7
to 0.9 G's. That is a deceleration rate near but below lock up or ABS intervention. You should begin to smell pads at the 5th to 7th stop and the smell should diminish before the last stop. A powdery gray area will become visible on the edge of the pad (actually the edge of the friction material in contact with the disc - not the backing plate) where the paint and resins of the pad are burning off. When the gray area on the edges of the pads are about 1/8" deep, the pad is bedded.
For a race pad, typically four 80mph to 5 and two 100mph to 5, depending on the pad, will also be necessary to raise the system temperatures during break-in to the range that the pad material was designed to operate at. Hence, the higher temperature material can establish its layer completely and uniformly on the disc surface.
Fortunately the procedure is also good for the discs and will relieve any residual thermal stresses left over from the casting process (all discs should be thermally stress relieved as one of the last manufacturing processes) and will transfer the smooth layer of pad material onto the disc. If possible, new discs should be bedded with used pads of the same compound that will be used going forward. Again, heat should be put into the system gradually - increasingly hard stops with cool off time in between. Part of the idea is to avoid prolonged contact between pad and disc. With abrasive pads (which should not be used on high performance cars) the disc can be considered bedded when the friction surfaces have attained an even blue color. With the carbon metallic type pads, bedding is complete when the friction surfaces of the disc are a consistent gray or black. In any case, the discoloration of a completely broken in disc will be complete and uniform.
Depending upon the friction compound, easy use of the brakes for an extended period may lead to the removal of the transfer layer on the discs by the abrasive action of the pads. When we are going to exercise a car that has seen easy brake use for a while, a partial re-bedding process will prevent uneven pick up.
The driver can feel a 0.0004" deposit or TV on the disc. 0.001" is annoying. More than that becomes a real pain. When deposit are present, by having isolated regions that are proud of the surface and running much hotter than their neighbors, cementite inevitably forms and the local wear characteristics change which results in ever increasing TV and roughness.
Other than proper break in, as mentioned above, never leave your foot on the brake pedal after you have used the brakes hard. This is not usually a problem on public roads simply because, under normal conditions, the brakes have time to cool before you bring the car to a stop (unless, like me, you live at the bottom of a long steep hill). In any kind of racing, including autocross and "driving days" it is crucial. Regardless of friction material, clamping the pads to a hot stationary disc will result in material transfer and discernible "brake roughness". What is worse, the pad will leave the telltale imprint or outline on the disc and your sin will be visible to all and sundry.
The obvious question now is "is there a "cure" for discs with uneven friction material deposits?" The answer is a conditional yes. If the vibration has just started, the chances are that the temperature has never reached the point where cementite begins to form. In this case, simply fitting a set of good "semi-metallic" pads and using them hard (after bedding) may well remove the deposits and restore the system to normal operation but with upgraded pads. If only a small amount of material has been transferred i.e. if the vibration is just starting, vigorous scrubbing with garnet paper may remove the deposit. As many deposits are not visible, scrub the entire friction surfaces thoroughly. Do not use regular sand paper or emery cloth as the aluminum oxide abrasive material will permeate the cast iron surface and make the condition worse. Do not bead blast or sand blast the discs for the same reason.
The only fix for extensive uneven deposits involves dismounting the discs and having them Blanchard ground - not expensive, but inconvenient at best. A newly ground disc will require the same sort of bedding in process as a new disc. The trouble with this procedure is that if the grinding does not remove all of the cementite inclusions, as the disc wears the hard cementite will stand proud of the relatively soft disc and the thermal spiral starts over again. Unfortunately, the cementite is invisible to the naked eye.
Taking time to properly bed your braking system pays big dividends but, as with most sins, a repeat of the behavior that caused the trouble will bring it right back.

 

for 15$ I'd turn them. dont' replace your oem rotors for some 30$ rotors. PLEASE don't.

 

now that we have answered with the "company answer" how many of us have done a "pad slap"?

 

x3

 

I would suggest replacing your rotors or having them re-surfaced.

I replaced just my pads about a month ago and within a few days my brakes began squeaking when I lightly applied them. It started to get worse as time went by and was really annoying. When I swapped them out I used the shims and put disc brake quiet between the shim and the pad which I have always done. I also lubed the pins that hold the pads thinking they might bind a little and cause uneven contact which leads to squeaks.

I determined the sqeak was probably coming from the glazed rotors since I already took the other steps necessary at the time of the pad change to prevent squeaks.

I ended up replacing the rotors and now the squeak is gone. The reason I replaced them was because the only time I have to do the brakes is at night and weekends when the places who can turn them are closed. I think I paid around $90 total for both front rotors from advance auto parts.

 

I had 60000 on my 02, 3 sets of pads and it was pulasting...saw the GB on the PS rotors and I got those. Kragen's was $40 a piece for blank rotors so $85 was a good deal to me for slotted. It is easy to take the rotor out. Remove the two caliper bolts, hang up the caliper and bang the rotors with a rubber mallet. Take them and have them turned, replace the pads and good to go.

 

The biggest part I have a trouble with it is that he starts out by saying that this is taking place on a molecular level, but offers up no proof. Well, I guess if molecules are present, then it is happening on a molecular level...

As far as cast iron being porous and collecting pad residue, by all means. This can happen on new and old rotors and doesn't really relate to rotors being turned or not when pads are replaced though, as the pulsating effect can happen any time during the lifetime of the pads or rotors, depending on the conditions during the last time the car has stopped.

I see no problem with the theory that the pads and rotors should be broken in, or "seasoned" (cooking with cast iron reference). Personally, I dont think its necessary, but it is a sound theory none the less. I think that most drivers brake responsibly enough that it isn't an issue, and those that dont will always have pulsating brakes anyway, with ABS helping them.

The only thing I can think of is if the ceramic in pad A particles aren't the the same consistency as the ceramic in pad B, the braking wouldn't be exactly the same if rotors were turned so it had completely new brake material. I suppose under some situations, this could potentially be the case if the new pad materials broke down into a much coarser material then the original, but even then, I suspect that the materials are close enough to the same and it is swapped out often enough that it isn't a problem.

I believe the warping issue has more to do with someone getting their brakes done, driving the distance home (basically riding the brakes the whole time testing them), then deciding to test even more by locking them up a few times, causing the large deposits to form in one spot, in which they've basically just re-seasoned their rotors incorrectly. The same thing as if they were to go down a long hill, riding the brakes the whole time then coming to an abrupt stop.

This will happen if someone turns the rotors or not though. It just seems to happen more often just after brakes are changed because the drivers are going too far on testing in order to feel secure in their new brakes.

 

I was only stating facts as I have perceived them from my own personal experience with braking systems as well as personal research. For me, being right is not important. Recognizing that I personally don't know the right answer in the first place is the beginning to finding out the right answer.

I want my brakes to be as perfect as they can possibly be. I do research to that end. Much of what I have accepted as fact and science comes from StopTech.com. These folks have done scientific research for the racing industry. Using electron microscopes they have determined that the different pad materials and high heat cause previously glazed rotors to form cementite deposits on them. Which is the primary cause of pulsating brakes.

I was surprised to read where one of you said "we know what the company answer is..." Do we disregard empirical evidence because we just have to be right? Not me. Braking is a science and the answers are out there if you want to find them. As for how old I am? I am 45 and I have done my own brake work for many years. Though I don't see how this establishes or negates credibility, the question was asked.

I will always have my rotors turned before changing pads. I am fully persuaded that this is the way to go. The danger is in making sure that you have someone turning them who knows what they are doing. The last thing that I want is some careless moron taking off any more material than is necessary or trying to do it too quickly.

My .02

Bing0

 

I love good brakes!

I always do my brake myself. I almost always use new discs since I love for the brake job to feel good all the way to the last day before changing.

 

no offense to those who disagree but humtaco has got it right!

 

Turning rotors is only as good as the lathe operator.

I've heard it said that there should be a couple of thousands of run-out on each side for release of gases but before I switched to 'buy new' I have had rotors with detectable runout on a test drive - me no likee.

I have yet to do my Taco's discs and drums so we'll see.