Nubo

Back when the squeaky brakes became an issue I remember someone presented a rather involved "bedding" process for the brakes, which involved repeated and increasingly strong braking. I have to admit I didn't give it that much credence at the time. But, here is another article in which the author gives more detailed reasons on why they feel the procedure is useful and effective. Having experienced "warped" brake rotors before, I was particularly interested in that they claim to never have encountered a truly "warped" disc but rather the problems are often a result of issues that the "bedding" process is supposed to prevent...

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

beachdog

Good article, Nubo.

Since the causes and remedies are known, it is interesting that Ford never did anything about the brakes in the Taurus. Every single Tuarus that I have driven (rentals!) have all had severely "warped" rotors. You would think that the manufacturers would figure out a way to "pre-bed" the brakes. It would make the owners a lot happier and reduce their warranty costs.

TeamRX8

iTrader: (25)

squeaky brakes and warped rotors are two entirely different issues, they are not related

TCReedy1

Warped Rotors are simply and only due to poor design. As we all know - under braking, the rotors get very hot indeed - even on a standard passenger car, a heavy slow down or stop from freeway speeds can induce temperatures as high as 750°F. On race and rally cars (which tend to use Carbon rotors) this gets up to 1200 to 1500°F hence the red glow you often see.

Warpage occurs in metals because when they get very hot and then cool again, stresses build up at molecular and grain boundary level, causing the "flat" bits to bend slightly. There are three answers only within the known laws of physics. One is to keep the rotors cooler (hence vented front discs which are the ones always doing 70% of the work) or better quality materials or thicker heavier cross-sections which allow for greater strength. Some of it has to do with residual machining stresses as well - nearly all normal and vented rotors are cast and machined. The machining leaves residual surface stresses which don`t help unless the rotors are stress-relieved or annealed. All this costs mucho-money in the auto world. Most OEMs like Ford, GM, DCX would not dream of putting this additional piece & tooling cost into their rotors and it proves considerably cheaper to **** off their customers by telling them Rotors are wear out items and are not covered under warranty.

Ford are by far the worst because they drive their tier one suppliers to ridiculous, shitty, barely sustainable profit margins - hence the suppliers do everything possible in their world to supply the cheapest, nastiest components like Rotors and everything else that goes into a Ford (known fact - not personal opinion). Japanese motor companies like Toyota, Honda, Nissan are typically very good with customer "feel" items like rotors..because they know wobbly rotors just pisses off the driver, they tend to go for thicker (hence stronger) sections. This philosophy applied to vehicles tends to explain why the Japanese are panning the US OEMs to death in sales, quality and driver-returnability.

Thats the game folks!

Tom

Huhwha

Not sure I can agree with this. My former '00 Maxima would shake your fillings out slowing down from highway speeds. Nissan knew about this and would machine the rotors when I bitched enough, but they never stepped up to the plate and dealt with the underlying issue - poor quality parts. Great car, but this was a major annoyance and very visible to both driver and passengers - not too smart imho.

bfulmer

The warped rotor thing is more complex than you may think. The bedding procedure talked about is to ensure an even friction material deposit on the rotor. This will ensure that the friction level is the same around the entire rotor. If this is NOT true, you will experience brake "shudder". Brake shudder feels like you are not decelarating smoothly but you will NOT feel the brake pedel move up and down when this occurs. If you have a so called "warped" rotor you will not decelerate smoothly and you DO feel the the pedal move up and down. Lets call this pulsation. Two very different things. Now, what causes "warped" rotors and pulsation? Actually, most if not all "warped" rotors are NOT due to excessive heat especially on street cars. You will boil brake fluid, fade linings, and lose your brakes long before you warp rotors due to heat. Racing application use better brake fluid and lining that don't easily fade and still don't warp rotors very often. "Warped" rotors are caused by uneven rotor wear. This is why is takes time for the "warp" to develop. You change you rotors and everything is good for a while but the pulsation comes back after 10,000 of 20,000 miles. The unever wear is caused by the rotors having high lateral runout (LRO). I like to picture LRO as your rotor looking like a potato chip but MUCH more subtle. You will not be able to see LRO and this must be measured. LRO will not in itself cause pulsation, its the uneven rotor wear DUE to LRO that will cause thickness variation in the rotor. Thickness variation causes pulsation which is felt in the pedal!! So, "warped" rotors are actually rotors that have thickness variation. So why does LSO cause thickness variation and uneven wear? When you release your brakes, the lining settle out very close to the rotor. If the rotor has LRO, the lining will rub on the high spots while your driving down the road off the brakes! This rubbing of the high spots will eventually cause the rotor to wear unevenly and now you have the thickness variation I spoke of.

Hope this helps

olddragger

iTrader: (3)

Great info guys. So if my rotors are smooth now, no shutter,shimy, good stopping etc then i can just pop in the new pads and bed them in correct?
OD

alnielsen

iTrader: (4)

Sorry, but no. You need to have the rotors turned on a lathe to give a new surface to the pads. The old surface will have grooves on the surface. These grooves will reduce the life of your new pads. Turning old rotors on the lathe will also introduce grooves on the new surface of the rotor, so you need to have the shop put a "non-directional surface" on the rotor. Warped rotors can not be repaired on a lathe. They have to be replaced. My Chrysler van was warping rotors. With the wheels off, if you spun the rotor slowly, first one side of the rotor would touch one pad then later would touch the other pad. This did cause a vibration at highway speeds.

dannobre

iTrader: (3)

I change pads between track days.....I have never machined the rotors due to just changing pads.......they do need to be machined...but changing pads is not a reason that I do. Otherwise, I'd have no rotors left :D

bfulmer

There is no need to have your rotors machined when you switch to race linings. In fact, most of the dealers I know of will not machine rotors anymore because its really tough to machine them without introducing/elimination LRO. We've even tried to machine the rotors while mounted on the vehicle but this is still not good enough. If you have pulsation, most dealers I know of will just replace rotors. The description on the Chrysler van was in fact LRO as I described above. This LRO will not cause the pulsation but over time will cause thickness variation. Machining the rotors probably eliminated the thickness variation but it's really tough to eliminate all the LRO. Just think, if there is a little corrosion between the rotor mounting surface and the lathe then the machining operation could have introduced MORE LRO. The pulsation may come back because LRO could still exist.

Nubo

As long as the grooves are not too deep it probably isn't necessary to turn the rotors. The grooves are concentric with the rotational axis and the new pads will quickly conform to the shape. The concern, as I understand it, has more to do with initial braking and contact surface area (i.e. braking performance) during the break-in period. If the grooves are too deep the brakes will be inadequate initially even though they'd probably be fine after a while. But it wouldn't be safe to drive around waiting for this to happen. Service manuals usually indicate how deep the grooves can be before turning is needed.

samsong

My experience supports this. I don't machine the rotors unless out of spec, just change the pads. Never had uneven stopping, pulsation issues after 16 years, 180+K on my car (changed rotors once at 120K with the third or forth set of pads).

Racer X-8

Hey, I have a question. Every once in a while, you find yourself in a situation when you have to brake hard, coming to a complete stop. In those situations, is it preferable to release the brakes, and even more preferable if you have room to, to let the wheels roll a little as soon as possible. My thinking is that the brake pad acts as a heat sink, conducting heat, while the rest of the rotor is cooling by convection and heat transfer to the air. Hence, you wind up with rotor warpage (LRO). For this reason, I like to release the brake and preferably let it roll at least 1/2 revolution after a hard stop. Anybody have info on this? My MX-6 has 220k miles on it and looking back, a lot of mainenance expenses on it is in the front brakes. Last time I had the brakes serviced, I replaced the front rotors. The guy asked me if I wanted the cheap ones or the good ones. Hehe. First time I was asked that. BTW, Pep Boys suks - don't go there for service, especially for brake jobs. I have my reasons if you want to hear some stories...

Georgia8er

I agree there is no reason to turn the rotors unless they are warped. Then yes, that will take care of the problem. Also when putting on new pads, spray some water on the concrete where you're working and gently rub the pad surface. This evens out the pad before use and results in less squealing and general noise from the pads.

TCReedy1

God Don`t you just hate all this? I`m sure bedding-in is effective but why the hell should anyone have to do it in the first place? It still boils down to design for function. If the design is wrong, then sooner or later the rotor will warp or even crack.

Of course things are different for those guys doing track days and events. That puts additional and more frequent heat and wear-tear into the brakes and so maintenance & new pad needs rise accordingly. We ordinary street Joes would like out rotors to last the lifetime of the car though. Where does it say in the owners manual that rotors are a service item? Does it give a change interval for rotors? Nope. It does give an LRO spec and thickness spec in the service manual though. Interestingly, if one of those is compromised, Mazda still expect you to pay for the replacements.

I took my RX8 (37000 miles) to my dealer and they would have nothing to do with it. Even though they acknowledged warpage last year and skimmed the rear ones...the chances of my getting new ones out of Mazda are squat!

Never again.

Tom

Nubo

I will actually try to avoid keeping the pads on the rotors if I know the brakes are particularly hot. Well, at least the front ones. If I need to come to a prolonged stop in that situation I'll use the handbrake to hold the car. That only engages the rear brakes. The front brakes do most of the work stopping the car and will generate most of the heat.

dannobre

iTrader: (3)

Last thing you want to do is put on the parking brake when the brakes are hot. It's the first thing they teach you at a track day. I've seen people that forgot...and spot welded there pads to the rotors :D

Racer X-8

Actually, more like a braze. :D Darn now that's hot! Must be hot like when they glow red at night for that to happen, huh?

TexasKyle

I have to disagree that you can't warp a rotor due to excessive heat. I am, among other things, a certified thermographer and have used a high dollar (60K) infrared camera to shoot different makes and model vehicles. My friend has a newer Dodge Ram truck that was going thru rotors. Just by chance, I was playing with the camera in a parking lot after lunch time one day and there was a Dodge and a Chevy Truck parked pretty close to each other. The Dodge's front wheel centers were almost 300 degrees hotter than the Chevy's. I noticed this on several occasions. Yes, the Dodge guy could have been breaking harder etc etc. Just an observation I have personally made with the right equipment to make it. I believe the Dodge just had poorly designed cooling for the brakes.

(I am no mechanic or engineer....just making an observation)

rxeightr

Racer X-8 -- I have done this for the 30+ years I've been driving, and am a believer it does make a big difference in not getting warped rotors. I also try to pump the brakes when coming to a stop, or going downhill.

When driving an automatic transmission car, I'll put it in neutral at a stop light so I can take my foot off the brake pedal.

Nubo

I wasn't referring to parking a hot car on a level surface, but referring to the OP's situation: driving on roads when there are times when you have no choice but to stop and sit at a light with hot rotors. Sometimes you're on an incline and don't have the option to sit in neutral. In this case I figure it's better to have the rear pads touching the rotors instead of the front ones. His idea of rolling a few inches at a time could still be used in conjunction. Your only other option with a MT would be to sit slipping the clutch. Or maybe get out and chock a wheel :D