The purpose of Cutting Rotors

[Marika]

What's the purpose of cutting rotors?

Let's hear your thoughts, pro or con. Thanks.

[Ranger]

The purpose it to true them up and save them rather than buy new ones if the are worn unevenly, grooved more than 1/8" or have uneven deposits on them causing brake stutter etc. I have done many brake jobs without turning rotors and I prefer it that way it I can get away with it.

[Scotty]

Here is an article on the subject that I have found helpful:

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

I personally believe that turning rotors is necessary to true to the rotors surface (ie its thickness) and to provide a proper surface to expediate proper break in of the new pads. If there is any thickness variation, the new pads will quickly magnifiy the thinkness variation as they brake in and pulsing can become a problem. I always ask for a CLEAN UP, and tell them ONLY to take off as much as is necessary, no more. I have two sets of rotors and alternate them. Mike

[KHE]

I only have the rotors turned when I feel pedal roughness or if there are grooves deeper than .060".

[Bob D]

New pads get turned rotors. Period.

If the rotors are too far out of tolerance, then new pads get new rotors. Period.

If your'e going to do it, do it right!

[Rich]

Had the front brakes done on the Eldorado within the past year. Rotors were cut as per procedure according to the dealer. Afterward, I followed bbobynski's procedure for burnishing new pads with rotors.

Oddly, I needed to have the rear rotors replaced a few years ago at around 40,000 miles. Had fairly severe "seat-of-the-pants" shuddering from high speeds. New rotors corrected the problem. Now, a few years later (30,000+- miles) I think I am beginning to experience that same sensation during high speed braking. Are these cars prone to warping rear rotors???

Has anyone else had this symptom, and if so, what is the best cure? Do I just replace rear rotors every few years?

Thanks for the advice.

Rich

[chuckgann]

the best way to tell if its the rear rotors that need turning is to brake using the emergency break (dont slame it too hard, and not on a wet road as no abs with emergency) if you get the same shudder then its the rears, and yes these cars go through rotors pretty bad esp the front for us crazy city drivers...

[Scotty]

Had the front brakes done on the Eldorado within the past year. Rotors were cut as per procedure according to the dealer. Afterward, I followed bbobynski's procedure for burnishing new pads with rotors.

Oddly, I needed to have the rear rotors replaced a few years ago at around 40,000 miles. Had fairly severe "seat-of-the-pants" shuddering from high speeds. New rotors corrected the problem. Now, a few years later (30,000+- miles) I think I am beginning to experience that same sensation during high speed braking. Are these cars prone to warping rear rotors???

Has anyone else had this symptom, and if so, what is the best cure? Do I just replace rear rotors every few years?

Thanks for the advice.

Rich

I am going to be honest with you there are 2 camps, 1) the camp that THINKS it ok to put new brakes in without turning the rotors, and 2) the camp that turns or replaces the rotors when they do new pads. These days many of these auto 'mechanics' would rather replace the rotors than do the work to resurface them, and they will tell you that resurfacing them will lead to "warping". What you have to watch out for is inferior replacement parts, for awhile cheap inferior rotors were available from CHINA and they many still be available. These cars are NOT suseptible to 'warped rotors', bad rotors, or high speed vibration from the rotors, most of the problem comes from improper repairs, inferior parts, and or poor driving habits. I will give an example of a poor driving habit, holding the brake pedal down after a hard stop or when the brakes are HOT, causing a transfer of brake material to the rotor. I wonder if you put the parking brake on hard when the brakes are hot transferring material to the rotors. I hardly ever use my parking brake unless on a hill. In addition, I personally have never had any kind of high speed or even low speed shudder or vibration from the rear rotors. Please read this article for terrific information on this subject. Mike

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

[KHE]

My Cadillac shop manuals state that "Resurfacing of brake rotors should not be performed as part of routine brake maintenance. Resurface the rotors only if there is a complaint of pedal pulsation/roughness or if there is scoring deeper than .060".

There is no harm in resurfacing the rotors every time but the rotors will require replacement sooner. On a FWD car, rotor replacement is a piece of cake. The RWD cars, it is a bit more involved - you have to mess with the bearings, grease seals, all that bearing grease, repacking the bearings, etc..

[JIMDTS]

My thoughts are getting the rotors turned(resurfaced) are to get them smooth to remove any gouges or uneven wear pattern They can be only turned so much so that you don't make them too thin that you take away the strength due to heat and stress.Plus with them smooth your pads will last longer and no pedal pulsations ..I have some mechanic friends who put cheap pads bonded with no rivets on there cars and never turn the rotors and get very high milage on them Me I would rather turn them or just replace them if needed..and use a riveted pad the rivets cut into the rotors when they wear down that's why they use the cheaper bonded pads..I do most of that stuff myself if I have the time, pads, rotors claipers etc. much cheaper and I know what I'm getting.. I will put the better stuff on I just don't like to drive a car with shakey brakes..Heck I work with some guys who are a real piece of work One guy has been driving around with a brake warnung light on for about a year then goes to the shop for a brake job and complains about the price of a thousand or so all self induced damage that could have been avoided in the first place if he took care of it when the light came on..

Cheers

jim

[JasonA]

That's scary! But I think the definition of "worn brakes" varies a LOT depending on who you talk to. When I say my car needs brakes, Average Joe/Jane driver would probably run it another year that way. I can't imagine running brakes until the rivets are scoring the rotors! Same with tires. I REALLY err on the side of safety when I replace tires. When the tread is 1/4" or less (8/32"), I'm usually getting antsy and ready to replace them. Most Average Joe/Jane drivers probably run them to 2/32" or less.

[Scotty]

My Cadillac shop manuals state that "Resurfacing of brake rotors should not be performed as part of routine brake maintenance. Resurface the rotors only if there is a complaint of pedal pulsation/roughness or if there is scoring deeper than .060".

There is no harm in resurfacing the rotors every time but the rotors will require replacement sooner. On a FWD car, rotor replacement is a piece of cake. The RWD cars, it is a bit more involved - you have to mess with the bearings, grease seals, all that bearing grease, repacking the bearings, etc..

Kevin, You raise a good point about the rears, yes they are hard to do, and you are right, I do not turn those as often as a result. However, they do less work than the front, which as a result lessens their tendancy to overheat. I think it is evident from the lack of vents compared to the front.

The transfer of material takes place when the rotors and pads are hot. I think the transfer of material from overheating contributes to the rotor thinkness problems. As the pads are rising up and down over the rotors creating uneven pressure at points thereby causing wear. Guys here that are admittedly hard on their brakes have this pulsing problem. The transfer of material creates an intermittant drag due to the high spot, combined with the increased friction caused by the material itself.

I don't know if it is this thread, but I have had a few discussions, where a few members here tout the benefits of drilled rotors and their ability not to warp. This is undoubtedly due to their ability to cool better and dissapate heat quicker. Funny, we are told all the time that turning the rotors makes them thinner and which contributes to 'warped' rotors. Is it because they heat up faster because there is less material or heft to the rotor? Yet the material lost from drilling them does not contribute to warping, probably due to the increased ability for the rotor to dissapte heat as it is more like a heat sink. Since we know from that article that much of the 'warping' is actual material transfer, a material transfer that takes place most often when the brakes are overheated, the cooler the rotor the less the potential for pulsing.

Because we have such a divergence in people that have successes both turning and not turning the rotors, and with pulsing and not pulsing, I am thinking that a persons driving habits contribute to the 'warping' or pulsing that becomes evident. I think that if you have a heavy foot you will undoubtedly have pulsing problems especially if you hold the brake hard after hard braking. I am told that I am hard on my brakes and stop at the last moment. However if you are easy on your brakes and coast and slow down, rather than gunning it to the stop light and mashing the brakes, you have a lesser chance of pulsing. I think its possible, since the pad and rotor are perfectly flat, and because they are being ground together flat, that if the rotors are not overheated and the transfer of material is eliminated that they should wear perfect. However, add a worn hub bearing with runout to the equation and I wonder if all things would be equal then. I hope this makes some sense! Mike

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

[KHE]

Kevin, You raise a good point about the rears, yes they are hard to do, and you are right, I do not turn those as often as a result. However, they do less work than the front, which as a result lessens their tendancy to overheat. I think it is evident from the lack of vents compared to the front.

Mike,

I was talking about the front rotors in a rear wheel drive car. A lot more work to R&R the front rotors on a RWD car. Bearing repack, new grease seals, and setting the bearing clearance. Not difficult - it just takes much longer vs. a FWD car.

[Scotty]

Kevin, You raise a good point about the rears, yes they are hard to do, and you are right, I do not turn those as often as a result.  However, they do less work than the front, which as a result lessens their tendancy to overheat.  I think it is evident from the lack of vents compared to the front.

Mike,

I was talking about the front rotors in a rear wheel drive car. A lot more work to R&R the front rotors on a RWD car. Bearing repack, new grease seals, and setting the bearing clearance. Not difficult - it just takes much longer vs. a FWD car.

I see I did misunderstand. But your post made me do some thinking and that is what fell out. LOL... That I turn or resurface the rear rotors less than I do the front. Due to the rear doing less work and not causing the pulsing as readily. And that its most probably due to the reduced heat buildup in the rears and my driving habits. Mike

[Scotty]

Same with tires. I REALLY err on the side of safety when I replace tires. When the tread is 1/4" or less (8/32"), I'm usually getting antsy and ready to replace them. Most Average Joe/Jane drivers probably run them to 2/32" or less.

People think I am nuts because I change my tires between 45000 and 50000 miles. I have a friend who says he will sue because he does not get the 80,000 mile warranty (hes an *smurf*). I believe that a tires ability to pump out water is diminished at about 45,000 miles and my most important goal is safety in the wet weather as I have had a couple of accidents in the rain. I give my old tires to my uncle and he is thrilled and does not drive in the rain, lol... Mike

[jgr7]

I'm not sure if it is the same for cars, but when I had my street bike the dual drilled front rotors never warped, and I used them pretty hard. One thing that I learned is that the drilling reduces unsprung weight up front, and helps cooling. The thing that most people don't talk about though is that the pattern of the holes, at least on my bike were placed in a row of 3 then a row of 2 then a row of 3 and so on. When you looked they were spaced this way so the entire surface of the pads were groomed by the holes as they were not chamfered. It made the pads wear out faster but you always had a real good surface on the rotors. If I had been riding around town and not doing any hard braking for a little while I would notice the brakes didn't seem as strong, so out on the hwy I would head and take it up to 100 or so and the get on the brakes pretty hard, this would clean them up and make them work lots better.

Jeff

[Logan]

I've used the China rotors on several cars without a single issue.

I dont know how they do it...prison labor or something. Here, we can get 2 new fronts for $40.

They are not worth even turning.

[Scotty]

I've used the China rotors on several cars without a single issue.

I dont know how they do it...prison labor or something. Here, we can get 2 new fronts for $40.

They are not worth even turning.

Maybe it was the beginning of China manufacturing rotors but I have a close friend that runs a NAPA parts and he said that they had lots of problems with the rotors made in China, including voids in the casting where the brake pads wore through the rotor into a void. He also said they did not wear well and cracked. Realizing the potential for a wheel being locked up by this type of thing I have never purchased the rotors. I am glad to see you have not had problems hopefully he received a bad batch. Mike

[JIMDTS]

Hi jason

I change my tires if they are bad or even look bad depends on the car I have never went over 50k on any tire but some of them at 50k looked real good and had enough thread that they probably could go another 25k or so.On some cars like high performance cars when I would drive them hard tires don't last too long it's either pedal to the metal or slamming on the brakes and sliding around turns..so no tire lasts..too long

I have a friend who is really nuts about tires and it's really funny He swears that tires are only good for 2500 miles and every 2000 to 2500 it's new tires and everyone at this bar I stopn is always asking him to buy his old tires He says he won't sell them because they are bad tires and just gives them away I keep telling him he's nuts go to at least 5000 or 10,000 and his comeback is did you ever have a blow out. Plus the guy drives like an old lady always the speed limit or less.And these are Michelin tires every 3 or 4 months he is buying tires. Maybe one of these times I'll grab a set..But usually it's not a tire size I could use.

Cheers

Jim

[KHE]

I have a friend who is really nuts about tires and it's really funny He swears that tires are only good for 2500 miles and every 2000 to 2500 it's new tires and everyone at this bar I stopn is always asking him to buy his old tires He says he won't sell them because they are bad tires and just gives them away

Does he have any 235-70R15 in whitewalls????

I'd go broke buying tires every 2500 miles....