Keith Browning Posted September 18, 2011 Share Posted September 18, 2011 What I find interesting is that the word "warped" continues to be improperly applied when the discussion of brakes comes around. Brake rotors simply DO NOT WARP. Such a physical attribute on a part like this would require distortion from significant and improper assembly or damage. I beleive this mis-understanding leads people down the path of an incorrect or ineffective repair. The real reason you get a vibration or shimmy when applying your brakes is caused by brake rotor thickness variation. This is condition is caused by rotors that have excessive amounts of lateral run-out that in turn causes the rotor to wear on one side at a particular spot on the rotor as it moves toward and touches the brake pad while it is rotating with the brakes un-applied. This also happens on the other plane of the rotor 180 degrees opposite on the rotor. What you end up with is brake rotors that are thinner in two spots on the rotor. This condition develops over time. When you apply the brakes, the pads are forced back into the caliper at the thicker spots of the rotor and the caliper forces the pads closer when the thinner spots of the rotor return. This translates in brake fluid pressure being forced back, or pumped, to the master cylinder causing movement in the brake pedal which you the operator feel in your foot. If the variation is great enough the force can react with the rotating mass of the rotor, hub, wheel and tire which can transfer into the steering and even through the chassis as a vibration which you the driver might also notice in the steering wheel or in the seat if the problem is in the rear brakes. If your truck is having repeated problems with brake vibration, looking for high priced or gimmicky solutions like cryogenically molecularly modified brake rotors (sounds flippin fancy don't it) will NOT solve your problem. You need to identify the cause of the run-out in the hub and rotor assembly and correct THAT which will allow your rotors to rotate "true." Measuring run-out on the hub itself will tell you a lot. Removing rust and dirt from the hub where the rotor mounts to it can also reduce run-out. Machining the rotors on the vehicle, mounted on the hub will result in rotors that rotate true however starting off with good parts that have a minimum of run-out to begin with is best overall. Another cause for brake vibration on Super Duty trucks is rust or pitting of the rotor surfaces typical of trucks that sit for periods of time. Iron based metals such as the metals used to manufacture brake rotors rust when in contact with moisture and air. In these situations rust forms on the surface of the rotors with the exception of where the brake pads are covering the rotor surface. What you end up with is a rotor surface with rusty areas over the majority of the rotor where the amount of friction differers from where the non-rusty areas are. The result is a momentary grab in the brake caused by variations of the finish of the rotor surface. The longer the truck sits unused, the heavier the rust and pitting will be and the greater the variations in the surface finish of the rotors will become. The obvious fix is to drive the vehicle more frequently or store the vehicle indoors where humidity levels are lower and more constant. The reason for slotted, vented or drilled brake rotors if to increase heat dissipation that can reduce brake fading and pad material transfer caused by excessively high surface temperatures of the rotors and pads under high load / high speed conditions. When that occurs it is similar in theory to the rust scenario in that you have affected the friction surfaces in an un-even or erratic manner. Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted September 18, 2011 Share Posted September 18, 2011 Amen to that. I don't do brake jobs. They just aren't gravy like people think. The rust up here is very hard on rotor finishes and machining them on or off the vehicle is usually a bad idea. Our shop replaces a lot of rotors and most people cannot understand why they cannot be machined. I will say that we see a bunch of "warped" rotors <snickers> come from our detail department. They spray that damn tire gloss shit on everything but the actual tire and as soon as you drive away, presto a lateral run-out condition is set up! Quote: looking for high priced or gimmicky solutions like cryogenically molecularly modified brake rotors Speaking of, has anybody put on a set of them new "gray" rotors for the Flex/Taurus brake noise TSB? Them things are friggin' heavy! Adds a 100 pounds of sprung weight to the car. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted September 18, 2011 Share Posted September 18, 2011 Brake rotors simply DO NOT WARP. Actually, they do warp, but this does not cause brake pulsation. I have seen (parallel) runout in huge amounts, like 1/4", that caused noise from the caliper being banged back and forth on its slides, but there was no brake pulsation. It will also cause a low or soft pedal, which is common these days. Originally Posted By: Keith Browning The real reason you get a vibration or shimmy when applying your brakes is caused by brake rotor thickness variation. This is condition is caused by rotors that have excessive amounts of lateral run-out that in turn causes the rotor to wear on one side at a particular spot on the rotor as it moves toward and touches the brake pad while it is rotating with the brakes un-applied. This is the correct description of what causes pulsation. In ASE test writing, it's hard to write a question on this topic that is technically correct and does not "fall out" of the first set of tests it is presented on. (The initial time it is presented the question is graded but not scored) Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted September 18, 2011 Share Posted September 18, 2011 "I'm sorry sir, these rotors are just too thin to be machined" They weren't warped though. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted September 18, 2011 Author Share Posted September 18, 2011 Actually, they do warp, but this does not cause brake pulsation. I have seen (parallel) runout in huge amounts, like 1/4"... Not sure at what level I care to disagree with you on that point because this write up is the result of some input from a braking engineer and I have some trouble buying into this 100%. But I am glad I posted this and we are discussing it. I am a believer in that all rotor concerns related to runout and thickness variation are caused by "something" be it improper installation, other worn or damaged brake/hub/bearing/suspension parts, abuse and damage. Are we splitting hairs here as to the terminology or the cause? I would not consider a 1/4" of lateral runout "warpage." I consider that damage. I also think that the word parallel technically shouldn't be used to describe something that varies... just sayin. Enjoying your popcorn Brad? Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted September 19, 2011 Share Posted September 19, 2011 Not sure at what level I care to disagree with you on that point because this write up is the result of some input from a braking engineer and I have some trouble buying into this 100%. But I am glad I posted this and we are discussing it. I am a believer in that all rotor concerns related to runout and thickness variation are caused by "something" be it improper installation, other worn or damaged brake/hub/bearing/suspension parts, abuse and damage.Are we splitting hairs here as to the terminology or the cause? I would not consider a 1/4" of lateral runout "warpage." I consider that damage. I also think that the word parallel technically shouldn't be used to describe something that varies... just sayin.IIRC, the car with the 1/4" runout was a regular at our shop (it was a Nissan Sentra) and I believe we did all service to it. I don't think damage was caused by us or anyone else, I think we replaced a rotor(s?) and a caliper(s?) and shipped it. I remember the complaint being noise under braking and the rotor looked perfect to the eye, but we drove it in the air (FWD) and I was shocked to see how much runout it had. The cal was bobbing back and forth causing the noise, and there was absolutely no pulsation. I think the pedal was higher after we fixed it.You do believe in warpage, you are just calling it something else. Yes, we are agreeing and splitting hairs.I'll take you on any time, bro, come at me. I'll meet you in the parking lot after school. :twack:This is all in fun. I, of course, have the utmost respect for Keith. :notworthy:Another forum I belong to was just shut down because of serious fighting, namecalling, and other childish BS among the participants. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted September 19, 2011 Author Share Posted September 19, 2011 @ Bruce One thing I can definitely say about this group, we don't fight. We discuss and debate things... they way it should be. Now, if you want to see something warped I'll show you a picture of my dEck. The boards do not have a runout problem. They are definitely warped! Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted September 19, 2011 Share Posted September 19, 2011 I read that wrong at first, substituting an i in deck...... Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted September 19, 2011 Author Share Posted September 19, 2011 I think we now know WHO is warped here. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted September 19, 2011 Author Share Posted September 19, 2011 Ain't that the pot callin the kettle black! Quote Link to comment Share on other sites More sharing options...
mrbudge Posted September 19, 2011 Share Posted September 19, 2011 Many years ago there was a TSB released for Pinto's, of all things, for brake pulsation. The cause was pad material transfering to the rotor causing inconsistent friction between the pad and rotor. The fix was to replace the pads with a more agressive pad that actually removed the pad material from the rotor. I believe that this is still very common, as I have put a great many dials and micrometers on rotors to identify a 'warped' rotor, only to find runout and thickness variation are well within tolerances. A fine cut with the on car lathe to remove surface deposits cures the brake shudder every time. I do not believe in re-surfacing a brake rotor during a 'brake job', however. New rotors go nicely with new pads, machining the rotors to my mind only makes the rotor that much closer to the end of it's service life, especially if half if it is rotted away. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.