2001 f250 7.3 engine, brakes have been redone, rotors turned, and pads are ceramic. When the brakes are used the front end shake. Brought it back, had the front brake calipers replaced. Still shakes. Can the ceramic pads cause the front end to shake, or can it be the front end it self? Thanks badwhisky1959@yahoo.com

 

i had some crrappy mud tires a long time ago, that felt shaky and terrible when braking

 

i would check the runout on the calipers, to see if they are warped or straight.

ceramic pads create heat, turned rotors indicate "used" rotors which may indicate thinner. means not as much mass to dissipate heat. infact regular rotors sometimes cant handle this heat. many times it is recomended to upgrade to drilled and slotted rotors to deal with the heat. These were developed for this reason.

soooooo all this boils down to is you may need new rotors... cant tell without looking at the truck myself, but you can check the runout, your local parts store may have a tool loaner program.

Often overlooked are caliper slider pins. Reciently mine would shake like your indicating yours are, but only when i turned left or right... what i found was my slider pins were rusted solid and would not slide causing problems. You may have changed the calipers but these pins are not part of the caliper, so check them too.

Good luck

 

When applying the brakes, sounds almost like warped rotors but if they turned them you would think they would have noticed that.

 

Ditto on the slide pins. Very common to skip that part. They allow the caliper to float along with the rotor. Very important. Every year, whether I like it or not, I take about an hour and clean and grease all four of mine.

 

What im thinking is...... the ceramic pads warped them after they were turned... and im positive they would have noticed upon turning, kinda hard not tooo, its impossible to turn a rotor and leave the warp in it

 

Are the lug nuts tightened with a torque wrench?

 

You’ve got problem rotors and they need to be replaced.

There are a lot of misconceptions being thrown in here.

First rotors are designed for thermal loading at their minimum thickness, then mass is added for service wear. Second, what are ceramic pads? They are not totally ceramic so they do not reject heat as a space shuttle tile would. Ceramic pads refer to the type of reinforcement fiber used, in this case potassium titanate rather then steel, organic or mineral fibers. The fiber reinforcement load is in the 10-15% range while the rest of the friction material components are the same across the board for all different classes of material save sintered metallic. Ceramic, low metallic and organic pads all have very similar thermal absorption characteristics, the only ones that have a higher thermal absorption / transfer rate are metallic and sintered. And the only ones that have a higher thermal rejection rate are those that use an underlayer between the steelback and friction material that is thermally insulating, like the ’99-’04 OE pads were.

Warped rotors tend to be a description for rotor with excessive runout and the cause for pulsation. The only time a high amount of runout will cause a pulsation is when the g forces of accelerating the caliper side to side become excessive, and this is when calipers are flipped back and forth on the slide pins under high-speed conditions. Typically you have to be at speeds in excess of 80mph and runouts higher then 0.006”, caliper mass and speed dependent.

What does cause pulsation readily is thickness variation and low friction hard spotting, with the exception that a high runout rotor pared with frozen sliding pins will also cause pulsation within the hydraulics and the subsequent frictional variation.

Studies have shown that the major service issue relating to rotor pulsation is during the machining of rotors. The first being that a bench lathe does not do a good job in achieving a low runout as necessary on today’s vehicles. Everyone looks to checking runout when a problem exists, but checking the runout when a turned rotor is installed on the vehicle to see if it proper is mostly ignored. A high runout condition (in the case of a Superduty anything over 0.0015” TIR) allows the rotor’s high runout location to wear when it contacts the brake pad under off-brake conditions, and the amount of rotor wear when the brakes are applied never makes up for this. Eventually you end up with a thickness variation across the rubbing surfaces, and all you need is 0.0008” variation for most people to notice the pulsation. That’s is less then most mechanics can consistently repeat when using a micrometer based on field tests.

This is also why over the last decade there has been so much of a push from the auto manufacturers for dealers to only use on car lathes. While still not as good as what is achieved in OE rotor production, the on-car lathes match the rotor and hub to achieve as close to 0.000” runout as can be done with a portable lathe. So a rotor gets turned on the bench lathe, its runout is high, thickness variation develops with the pulsation and the rotor is condemned that it “warped”, while in reality it was just poorly turned. Typically a rotor installed with 0.0060” runout will develop thickness variation in half the time of a rotor that is installed with 0.0030” runout due to the normal caliper rollback running clearances between the pads and rotor.

The second issue is when a rotor has developed a hard spot, something rarely caught during the lathe turning process, even with an on-car lathe. Hard spots have two issues. First is that being denser and harder then the parent cast iron material so it has a lower coefficient of friction. The second is that since it is harder and the lathe tool bit cannot tear into the surface so the hard pot stands proud of the rest of the surface, usually by a few ten-thousands of an inch.

Often when there is a hard spot in the rotor the first few brake applications will have pulsation due to the difference is coefficient of friction of the smooth hard spot and rougher softer cast iron. But as the softer material burnishes smoother and friction material transfer forms over the entire surface, that pulsation will go away. However in time that slightly higher and much harder, less easily abraded surface will be thicker by the 0.0008” necessary to develop the hydraulic and frictional pulsation that the driver will complain about. This typically takes 5k-15k miles for it to take effect. And again a rotor is condemned to have warped, when in fact the hard spot was the problem.

 

wow Jack very educational... i like learning new things...

 

Thanks Mark,

There is just a lot of beliefs that get toss around even from mechanics, and it gets picked up as knowledge. The industry started doing a lot of research into pulsation about 20 years ago and being on both the OE and aftermarket sides of the business it always amazed me how little of the OE testing and research gets over the the aftermarket side. Even within the auto manufacturers a fair amount the knowledge base from the OE side does not make it into service side.

For the last 10 years whenever I hear/read the term warped rotors I just start hitting my head on something hard. It's easy to look at the surface facts and conclude what is happening, but it's not until we really start to measure, test, observe what is happening we keep making the same error. There are probably a thousand people here that have had rotors turned and within 10k miles had pulsation return. Less mass - quick return of the problem and it makes sense.

Ford was the first to get on-car lathes into the dealers 12 years ago. And they paid for the lathes! Ford never buys anything for the dealers! And all the other manufacturers have followed in time. But even doing it with those tools if the hard spotting is not noticed by the mechanic, the problem will return anyway. A lathe just cannot remove all the crystallization with the rotor.

Ceramic fiber reinforcement has certainly improved the quality of organic pads and allowed for the replacement of semi-mets in many higher load conditions, like in the 6-7000lbs class. But they still have their issues, and since the formulas are closer to the lighter duty organic type pads, some of the older issues crop up. Late model Silverado and Tahoe vehicles have a fair mount of issues with metal pickup on the pads surface resulting in severe scoring depending on the operating conditions. So it's not the great hope that some think they are.

 

Jack is it possible for me to see the material that you have, maybe some online resources

 

Fleet Trucks: two 2002, one 2004 and two 2009; all have brake pad wear issues. Have changed out pad, rotors, caliper and glide pins. Doing much better. The 2009's had brakes wear out metal to metal within 17,000 miles from new vehicle purchase. Thought maybe it was snow removal grounds maintenance related. The two new trucks experienced the same issues. All the new glide pins seemed to help. Does anyone else question the reasoning to having the rubber bushing on the lower glide pins? The calipers I question even needed replaced. Reasonable price made it easier to just go ahead and replace the calipers on the high mileage trucks. I don't like the rubber bushings on the Ford parts so I went with aftermarket glide pins without the rubber bushings. It may just be me but I think the rubber causes the lower glide pins hang up which then causes the disc pads to wear and eventually you have metal to metal damage of the rotors. This usually happens with the trucks whose operator plays their am/fm stereo up loud and can't hear the metal to metal noise until it is too late. Preventative maintenance only applies when you have a periodic inspection of the fleet vehicles during engine services. While engine oil and filter is being changed and oil is draining take your time and spin each tire and if you can't you had best do more investigation of the caliper glide pins. Remove tire/wheel, remove bolt on calipers. Hang caliper up out of the way. See if the glide pins are hanging up inside their bores. If the bottom one is hard to move in or out - remove/clean bore and pin/re-lube with synthetic caliper grease/re-assemble. If the disc brake pads are not wearing even, (one thicker than the other),(wedge shaped wear), anything other than both pads wearing about the same thickness - then change out. I prefer severe duty disc pads for fleet maintenance vehicles. Usually the operators over load and abuse the vehicles so heavy duty parts usually pay for themselves. If anyone has any other advice on the Ford Truck brake issues I would like to hear more. Issues are usually an end-user/owner problem. It is all in how the vehicle is being worked/utilized and if your preventative maintenance program happens to be catching the problems before any real damage to the vehicle has occurred. Just like the commercial school bus fleet/owner operators - they are required to complete a brake and king pin re-certification inspection once every 6 months. Most do a good job. Yet we've had to go out on a few road calls after the 9 month school year begins for brake failures. It seems their brake pads fell out of their brake calipers. Signing a re-certification certificate the state police check during school bus inspections and not actually inspecting the brakes, which is obvious to use technician/mechanics, is a pretty sad state of mind to even consider and also a law enforcement ticket-able offense of "failure to maintain the vehicle" when it is a commercial vehicle inspection that the school bus just passed. So it is very important for any of us performing brake inspections for us to take such brake inspection serious. No matter if it is a semi-tractor trailer/school bus/work trucks or your family vehicle - brakes have to work each and every time we need them. We very rarely have issues with our fleet of vehicles with air brake systems - it seems it is more hydraulic brakes with our fleet of hydraulic brake vehicles. Brake shoe and brake pad wear patterns help when trying to address brake system wear. Over looking glide pins and slides are a common cause of repeat wear patterns.

 

Great information guys! I have experienced everything mentioned here except the ceramic pad part. My research showed that the ceramic is more prone to sacrificing the rotor to save the pad and that I was better off with semi-metallic. To see Jack specify the OE pads as the only thing better than the semi-metallics reassures me the time to research was not wasted.

That being said - as soon as I read the thread title, my first thought was "slide pins". I've had all 4 of mine cause issues (bought my truck used). Slide pins aside, I had a caliper flat sieze - so I'd say start looking at those calipers after 10 years or 200,000 miles.

 

I don't make or sell friction and haven't worked in the industry for over 3 1/2 years.

 

1stLtDan,

The lower pin bushings were added to go back to the 1st gen caliper design that had inherent slide resistance. Overall there were 3 design levels with the ’99-’04 Akebono brake calipers. The 1st and 2nd gen versions were like the aftermarket ones mentioned, without bushings. However the 1st gen had the internal lipped slide boots (like the rear brake) so that design had the sliding resistance.

I actually do the same as you and just remove the lower rubber bushing. While we all lubricate the slide pin bores, as the rubber bushings move back and forth they wipe the bracket’s bore of any silicone where the bushing resides and soon you develop rubber adhesion to the bore. I’m sure many have seen an older metal part mated with a rubber seal or O-Ring and when it’s removed there is residual rubber left on the metal. Things got lost during the maturing and engineering fixes that ultimately got Kelsey-Hayes released as the ’05 and up caliper supplier.

Since the sliding pin boots are formulated like all brake rubber parts, resistant to brake fluid but not petroleum products, we typically use silicone grease to lube the slides so the boots won’t swell from the petroleum and loose the sealing integrity at the lips. However, some people seem to have good luck using a light coating of anti-seize on the pins and bores without issues – so far. I’m trying that with silicone based anti-seize which would definitely not cause the boots to swell, not readily available.

There is an easier way to check for slide pin freedom instead of taking off the wheels. From under the truck back off the caliper slide pin bolts about 3-4 turns, then push the bolts and pins side to side. If they move easily, you are good to go and it’s easy to do while you are waiting for the oil to drain during that process. Just make sure that when you tighten the slide bolts back down the sliding pin flats are in the right indexing to the caliper housing.

The company I worked for supplied not only pass car /light truck, but CV and transit vehicles as well. One of the techniques I used to leave fleet operations with was to use a infrared gun to shoot the brake temperatures at each wheel when fleet vehicles came in at the end of a days run. While each axle would have it’s own temperature level if the left and right brakes on one axle showed too much disparity, one brake was not working correctly. Once a site starting doing this the mechanics would learn the temperature profiles and could easily spot a problem child before the problem worsened to the point of shucking pads or linings, requiring a road call.

Pad life is greatly dependent of the vehicles duty cycle and friction material choice. Every friction material formula has it’s own bell curve for wear. You mentioned snow removal and that could be one of the highest temperature operations a truck experiences. Many think the cold air keeps the brakes cooler, but that just shifts the temperature profile by the difference in air temp. A trucks brake might be at 700°F when plowing during the 30°F winter, while the same type of driving in 100°F summer heat will have it at 770°F. Of course this depends on the type of plowing that is being done.

While a high speed stop from 60mph dissipates a lot of energy into heat, if the stops are not frequent the brake will cool off substantially at speed with the air being pulled through the rotor’s vanes. The real problem are stops that occur rapidly and at low speeds under 30mph where air is not pulled through the cooling vanes in much quantity. And before someone mentions it, drilled and slotted rotors won’t help here. And snow plow trucks going back and forth in a parking lot really kicks up temperature and it can be at the point where friction material wear can be high, friction compound dependent.

Lets say this is data from a 10,000lb 4 wheel disc braked truck running city traffic

If you look at the two sections highlighted for the highest temperature excursions and then look at the vehicles speed during these times you'll see that it was running at lower speeds doing normal brake applications every 0.1 miles for about 15 brake applications. Low energy stops (speed) but a lot of them with no cooling air.