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I don't visit this forum chapter much and I don't talk that much on any forums about brakes anymore because it like pushing a rope, up a hill. I spent 30 years in the friction material industry and 25 of that managing vehicle testing. I worked on the P131 Superduty launch since '97.
Since before 2000 I was on forums explaining that you have to have really poorly manufactured rotors to have thermal warping, and I'm against the use of that word for what 99% of the pulsation issue is, and that is thickness variation of the rotor. It's called DTV in the industry.
We get to the condition of DTV due to the installed runout of the rotors and the abrasive characteristics of the friction materials. From there we can get to developing hardened areas of the rotors which cannot be machined out. And once that occurs, further use of the rotors after the machining leads to earlier DTV conditions since now you have areas of the rotor that wear more slowly then the other normal area.
Friction material transfer leading to pulsation is a condition with organic, non-metallic friction material. Its high point of occurrence was doing the early '90s when asbestos was first being removed out of friction material and there wasn't a good understanding of the change in chemistry needed. It occurred when friction heated up faster then the rotors, and the hotter material deposited excessively on the cooler surface. It was a temporary condition and since cold brake stops are abrasive rather then the normal adherent friction once a transfer layer is established on the rotor, the cold stops quickly remove that transfer layer. Lincoln Towncar's of the early 90's were very prone to it and it's a shame that people who were just outside of the friction industry use what was a short time period issue to explain other conditions. Every good braking event needs the establishment of a transfer layer and its at a molecular level deposit on the opposing surface (rotor) that's brown or grey in color.
Rotor DVT has always been problematic in causing brake-on pulsation, but it has become more of an issue as brake pad life has extended out. The issues of the early '90s brought forth much more study of the rotors conditions and tolerances. If you scan SAE paper titles, especially those given at the annual SAE Brake Colloquium event you'll find a treasure trove of rotor studies. And since the late 90's you also can find numerous articles in service industry magazines like Brake and Front End, most written by Larry Carly, who took the information gathered and somewhat presented at those SAE events to get the service industry to understand that it ain't warp.
After the launch of the Superduty in '99 there was an influx of warranty due to brake pulsation. While the Ford pass car groups were hit deep into addressing rotor pulsation issues, the light truck group hadn't seen the issues extensively as they were still in the Disc/Drum experience. Disc/Disc brakes (as on the '90 Towncar) changes the brake balance and overall operating conditions. Two changes were immediately done to the P131 platform, a change in the hubs for both bearing clearance and flange width to present a more stable mounting, and the second change was to the rotors. One to accommodate the thicker flanges with a reduced hat depth, and the tolerances for runout (TIR) were tightened. But even that had to be changed again with the launch of the Excursion, as during launch it was found that the Excursion with its softer suspension was more sensitive to the pulsation feel. The initial production of the Excursions had their rotors turned as they came off the assembly line to improve runout. That situation was a windfall for Pro-Cut lathes, as Ford Engineering found turning the rotors mounted to the hubs was the best way to insure minimal runout. In fact it proved out so well during engineering trials and the initial launch of the Excursion until tighter tolerance rotors came through the pipeline, Ford ended up giving a ProCut lathe to all of the dealerships. Ford never gives tools to dealerships. And today you'll find on-car lathes the recommended method for all vehicle brands, domestic and foreign. The Excursion experience greatly helped launch Pro-Cut's expansion and benefitted Joe Willey and Paul Hooper success.
The quality of the rotors matter greatly, not only how well they are machined but how well they are cast and thermally stress relieved before machining. Rotors are an area (like brake pads) were you get what you pay for. And while there is a premium for Ford (or GM, Chrysler, etc) to tag their name on a part, they are usually the best produced product. In fact I still have boxes of new rotors for my Superduty, the "blue box" OE assembly line parts, not the Motorcraft red box aftermarket grade. Not that they aren't a good product, the Federal-Mogul rotor plant that makes them as Wagner rotor had to upgrade the facility at a cost of ~$10 mill to meet the specs Ford required. The Wagner rotors were a top line product in the aftermarket field, just not up to what Ford required.
This is a picture of a Pro-Cut lathe turning a rotor on a Ford Excursion. You'll notice the rotor is a brand new rotor. This was part of a study for Ford Service to find out how often the tool bits wore, how many rotors before bits had to be replaced.
I can't emphasize enough how imported installed rotor TIR is. The service manual of the Akebono caliper years, 1999-2004, specs out 0.0015" maximum for the front rotors on the 4x4. The 4x2 is a little more tolerant at 0.0020" as they have a more stable hub. The assembly line spec however was 0.0010", 5 ten-thousands tighter. Ford doesn't like to eat warranty. For almost 10 years my facility ran Superduty brake tests. Every test had to have the rotors measured for surface finish Ra and installed rotor runout. Out of close to 400 rotors on Superduty vehicle tests we found one OE rotor that did not meet installed spec. We mounted it on the wall.
The installation of a rotor on a hub can influence runout. All machined items have runout, the hub flanges and the rotor itself. There were times when the first install of a rotor on a hub exceeded 0.0015", when the high point of the hub matched the high point of the rotor. Rotating the rotor on the hub 180 degrees cancels out the tolerance stack of assembled parts.
These are outtake pictures for a training manual I did with the Superduty brake service. I had to turn in all company info when I left the company, but I found I still had some images from when I did work at home. This actually was showing used rotor runout for a section of turning rotors on a bench lathe, if you had to do it because you didn't have an on-car lathe. And the only way to match what an on-car lathe does is to mark the rotor as it's installed, then fit the rotor to the bench lathe to match the runout. Guys who bench turn always want to debate how well they can work a rotor, including those who came to our "Train the Trainer" workshops we used to do, corporate guys who trained the individual shops. When you have the instrumentation that can accurately measure a rotor better then what you can do with dial indicator in a service situation find it's a different story.
These were outtakes because of the glare on the dial. This used rotor measured 0.0008" runout.
Runout is important because of off-brake wear, the main cause of DTV unless you want to live in the early '90s. And it's why the warranty on new Superdutys was the highest for people who lived in less trafficked areas and didn't run heavyweight. You always end up with one pad lightly touching a rotor. And the predominance is higher when the slide pins start to rust and the piston seals harden from heat aging, loosing the ability to pull backache pistons for maximum clearance. There is a test procedure for evaluating this condition on a vehicle. Ford keeps it on highways close to Dearborn, Chrysler runs Detroit to Chicago and back with brake applications a certain points on the way.
And along with having one pad lightly touching the rotor you also have rotors and hubs with some runout. The highpoint of rotor lightly touching the rotor say at the outer pad for a continuous time wears that high point, reducing it. The problem is on the exact opposite side on the inner surface the runout causes the rotor surface to be farther away from the inner pad, or most likely it won't be toughing at all. Well, until the wheel rotates 180 degrees. Usually a mounted rotor has the high point of the outer surface in one area, but the high point of the inner surface is 180 degrees out. So the outer rotor surface wears away at one spot, the inner rotor surface may wear away 180 degrees later. When the thickness variation or out of parallel of the rotor rubbing surfaces gets to about 0.0008" the wedging of the pads from the thin to thick sections cause a pushback of the hydraulic pressure (pedal pulsation), and the resulting increase in hydraulic pressure also causes a high brake torque level, causing a slight tug on the steering wheel as the vehicle is pulled to one side for a millisecond.
If the friction material is abrasive enough to the rotor, the on-brake events can keep the rotor trued from the off-brake wear. But that's a varying situation, based on not only the abrasiveness of the friction material, but the operating conditions of distance between brake applications and how much energy needs to be dissipated at the time of deceleration, determined by vehicle weight and speed.
This is a graph of a vehicle run on the DTV test program. It was setup with one rotor installed with a high runout on purpose. The measurements of the rotor are done with a test instrument sold by Link Engineering utilizing capacitance probes that fit into a modified brake caliper bracket so they are taken at the same location each time. Their site does not show the probe installation.
While the right disc continued to be worn true to a lower runout, there came a point where Disc Thickness Variation became high enough over the 0.0008" threshold where the driver could feel pulsation.
But not only is rotor installation important, so is the selection of friction material.
Anyway, enough for tonight or maybe this thread. As I said I don't post about brakes as much as I used to. And I'm not even going to proof this.
It looks like there is NO rotors, better than the other,
What are you using currently? On Rock Auto Raybestos advertises their runout tolerances, and you can compare those to Wagner, Motorcraft, and Powerslot. Jack also mentioned getting new rotors cut, if you can't get them down under the runout spec. I'd known Ford bought on-vehicle lathes for dealers to reduce warranty work but I didn't know they did it off the assembly line, if you get new rotors and they don't measure out, that might be your best bet to get more than a year out of your brakes.
TooManyToys, by no means am I questioning your knowledge, as mentioned above, probably the best thing I've read on how the braking system deals with heat but do have a question. Based on what I gleaned from your post, rotors don't really warp, please correct me if I'm wrong - but it's <usually> the pads that cause the issue. My question is that in the past I've just replaced the pads (not on my truck, when I was younger and poor) but the issue didn't go away.
First, I have a decades long problem with people using the term "warp", because everytime there is a pulsation issue that term is used and the connotation is they thermally warped like vinyl record. And the problem with that is all the true reasons are therefore ignored and thrown under the rug. So a new rotor gets thrown on, not of the causes are not addressed and we are back to the same issue. An examples noted above, a rotor was worn to the point of thickness variation, the owner "would get to" the problem in time so cementite formed at the thicker areas, the rotors turned and within 10 to 15k miles we are back to pulsation because the were resistance cementite is again proud. The rotors are declared warped because of heat since it was turned thinner, but exceeded the minimum thickness limit. Heat didn't cause the reoccurring issue, the hard region within the rotor did. When an engineer designs a rotor they work through the numbers of thermal absorption and rejection for the application, and it's well defined science. They use those values as the minimum spec, then add 0.0060" or whatever for wear and machining. I've never encountered any rotor or drum designer who didn't do that.
And during the design phase there are numerous test procedures to evaluate the rotor for the application, and changes are made to fine tune. sometimes its for thermal issues and other times for noise. The rotor most times is the loudspeaker of brake noise, so the two rubbing discs may be added to in mass to alter their natural harmonic, or the cooling vane structure can be altered, by it's design or by the vane count. Aftermarket companies tend to use the mould patterns they have for the side of the rotor and do not necessarily match the OE design.
The are three basic designs for rotor vanes, straight vane, curved directional and post. Each one has it's own characteristic for cooling and NVH. And cooling can depend on what the operating characteristics of the vehicle may be. While heading down the mountain grade at full GVW you may want a design that throws aa lot of air through the rotor at moderate, but that design may not be the best application for the other situation of high brake heat, city traffic, where the low speeds don't get a lot of air to flow though the vanes.
More then a decade ago I showed this on another forum. At the onset of the Superduty launch Ford's priority was lower brake temperatures. OBS trucks with the disc/drum setup since the early '90s had issues with high temperature. In the Pacific Northwest, brake fluid boil and rotor cracking were often problematic, but that brake design is a poor pairing, a disc brake up front and a drum brake in the rear. The torque outputs are linear for a disc brake while a duo-servo drum are logarithmic, so there is a lot of massaging done with prop valves and it's never perfect. So it's typical to move the brake bias to the front axle rather then deal with the mess at the rear axle. Disc/Disc gets you the freedom of making a more balanced braking bias.
But Ford was still hyper. This is an image of the difference in the rotors between the early Akebono based braking system compared to the latter KH/TRW system. Both rotors were designed and supplied to Ford for the SDs by TRW. The earlier rotors are a post vane construction, the latter years back to a straight vane construction.
I've never seen the post vane construction in an aftermarket rotor for the '99-04 Superdutys. It costs too much to make.
I got sidetracked to the question.
You can have situation of rotors distorting from heat. I'm never measured it with any OE or OE standards rotor on a Superduty. I've seen it with Jeep Grand Cherokee because of their sheet metal stamped hat section and I've seen it with very cheap rotors that are sold in the aftermarket where hey are not stress relieved during manufacture. So it's possible.
98% of our work was done with OE rotors, and part of our test work was to take Superduty brakes up to the point where you could get the brake pads to burn, then measure the time they continued to burn. That's not a NHTSA procedure, but a Ford internal. Still never got a rotor to thermally permanently distort. (All rotors will distort like a Belleville washer if you get them hot enough due to the restraint of the outer rubbing disc to the hat section, but they return to a flattened state. This is why some racing designs use a floating disc with an assembled connection to the hat, it matters when your in a racing environment).
So, what kind of temps did we test to .... New production vehicles have to meet FMVSS 105 or if under 7715 lbs GVW, FMVSS 135. This is the outline. BTW, aftermarket pads have no regulatory requirements for performance unlike what Europe does.
What an OBS F350 does during the second fade which simulates running down a mountain pass at 60mph loaded to GVW.
That's actually damn good for fade resistance, a pedal effort under 75lbs while maintaining target deceleration. Your breaking 1500 degrees F. Rear drum brakes are not working too much.
An '99-04 F350 SRW Superduty running the same sequence. The driver got a little anxious around stop 12 more then he had to and pushed higher on the PE.
No real fade. Both front and rear brakes are actively dissipating energy, no prop valve so the hydraulic pressures are equal, and overall temperatures are lower because of the brake bias moved to better balanced condition of Disc/Disc. Look at the change is pedal travel, gaining almost 2 inches of travel at the highest pressures. Also the ambient is a higher temp.
An '05-08 F350 running the same test sequencee. Different friction, different rotor design.
Still excellent fade performance, but temps are higher. So for all the hype of the bigger brakes on the 2nd generation of the brake system, temps are not cooler running the same vehicle GVW weight. Gee, who would have thought.
Post test measurements completed after the test above.
So after running through two fade sequences and all the stopping distance applications at GVW noted in the test comparison, not significant change in on-vehicle measured TIR. That's very typical of the 2,500 FMVSS tests I reported on in my career. And also note the TIR is under 0.001" before and after the test, just as on the assembly line.
Now you can stress distort a rotor on a vehicle when tightening the wheels. It was one of the ways we would dial in a rotor to a specific runout for the DTV test noted much earlier. If you wanted 0.0020" runout you could torque it into that distortion when using a steel wheel. With any aluminum wheel you have to shim between the rotor and hub because aluminum wheels have a more equal contact points to the rotor. Shimming is equal to getting some dirt or rust debris between he rotor and hub, or in cases of extreme rust development, a situation we call rust jacking. It's why somewhere in the 2006 time frame Ford started to apply an anti-rust grease coating on the hub mating surface where the rotor contacts. It wan't just so you didn't have to pound off a rotor from the hub.
Bryan mentioned earlier about Raybestos advertising rotor machining specs for runout and thickness variation. Unfortunately Raybestos is still in the aftermarket world.
The Ford service manual spec as I mentioned earlier is 0.0015" maximum indicated runout, 0.0010" on the assembly line for 4x4.
Their stated runout and parallelism depends if your paying around $60 or $100 per rotor. As I stated before, price matters if you can trust the company. I'm glad to see they publish some specs.
All hubs are going to have some runout, and whatever that runout is projects to about twice that value out to the rotors rubbing surfaces. With a rotor that has 0.0020" runout I can get that into mounted service spec most likely by indexing the rotor on the hub matching the higher runout of the rotor to the low runout of the hub, but unless I have a real crappy hub, it's going to be tough with the 0.0040" runout rotor.
And it's the high runout areas that is going to wear thin and increase the thickness variation or put of parallel that will cause pulsation. A rotor will high runout and parallel rubbing surfaces will just move the caliper on it's slides back and forth. A rotor transitioning from thick to thin will vary hydraulic pressure and brake torque that causes the pulsation in vehicle, pedal and steering wheel.
Exceeded my word count for today.
Last edited by TooManyToys.; 03-29-2018 at 10:03 AM.
Reason: Added info.
Over twenty years of owning F150's and various SDs. Every single one of them had front brake issues (warping and overheating); until I upgraded to Brembos. It's a huge investment, but solves your braking issues. Remember, the factory installs the minimum equipment. Ford truck brakes are notoriously undersized for the weight that they have to stop. Just my humble two cents.
Over twenty years of owning F150's and various SDs. Every single one of them had front brake issues (warping and overheating); until I upgraded to Brembos. It's a huge investment, but solves your braking issues. Remember, the factory installs the minimum equipment. Ford truck brakes are notoriously undersized for the weight that they have to stop. Just my humble two cents.
Hawk Pads: $70
Pair of Power Slot rotors: $300
Same results, whole lot less money.
Also, as has been covered extensively in this thread already, rotors do not warp.
Sorry to hear you were having such poor results with your brakes, but from the mid '90's since I learned the importance of mounting and choosing rotors for the lowest runout, and choosing a proper friction material to compliment the rotors for the driving situation, I've not had one of our families personal vehicles have a brake pulsation issue. And I've used the factory rotors.
As I noted above, friction materials can have an impact of the situation, just like the driving conditions, due to off-brake vs on-brake rotor wear. Unless your rotors have zero runout, which they can in time is they are worn to that state, you have the risk of developing DTV if the off-brake wear exceeds the corrective wear during on-brake. That's a difficult concept to wrap you head around.
The problem with the '99-04 Superduty factory setup was the friction material was a very rotor non-abrasive, low-wear material. So your on-brake wear might not get to the point of a corrective action, mostly with longer distance between brake applications or lower weight stops. In true commercial local applications, it trended fine. Back in the '02 time frame on the forums I often suggested people flip to PFC "Z" pads, the OSB front brake friction material, or move to Hawk LTS, which is a mid-metallic friction. I preferred at the time the "Z" pads as they were lower in metallic and had a flatter friction/temperature response. Hawk LTS need more heat in them to up the friction, so cold stops, and the Superduty tends to run cold in most common driving conditions, don't perform as well as the perception of their brake effect is. However, PFC stopped making that material, suggested their Carbon Metallic in place which was not the same performance, so then I went to suggesting Hawk LTS. I still run Hawk LTS as the re-release of PFC "Z" I do not trust. Ford Motorcraft line of Super Duty for the Superduty although is an alternate replacement. So often a change to a more rotor aggressive aftermarket pad masks a poor installation of a rotor or its manufacture, as long as it can wear the rotor true before the rotor develops DTV (thickness variation). In the marketplace the combination of "Frozen Rotors" and Hawk LTS pad made great penetration, promoting how great cryogenically treated rotors were, but the fact was you just needed standard rotors with the aggressive LTS pads.
Ford was aware of rotor wear importance and relied on their European side to assist in their friction material selection for the '03 F-150 and Expedition, so they brought in Jurid and Ferodo to supply the front and rear brake pads respectively. If you were the owner of a Job 1 vehicle you experienced the issue of black rims from rotor and friction material dust. These materials never should have been adapted a USA based vehicle and both the rotor and friction material wear was horrendous. Within 200 miles of driving owners complained of the wheel condition, and if kept in place, both pad and rotor life were compromised. But the objective was met, they wore the rotors true, the rotor wear for the same exact test conditions between the lighter trucks to the Superduty was a factor of 10. Before the typical Job 2 timeframe, the vehicles were already were having a friction material changeover, and in the case of the Expedition, and change in the vacuum booster to accommodate the change in brake pads. Federal-Mogul supplied those materials.
An example of how the wheels would be after a typical Durability/NVH 2,000mile test.
Again you can adjust for the rotor's installed condition and manufacture tolerances by means of the friction material. Sometimes you can go overboard, as Ford did; you need to pick your Goldielock's situation. But it's easier to get the rotors mounted true then play the game of picking the right friction material, either too little wear or black wheels.
03-27-2018, 10:32 PM
