need some help, please! rotor info. moderators?

[neunan]

im bitter. i just got my car back from a shop (put in the ACT clutch and clutchmasters flywheel) and soon after i noticed that my rotors were acting up, like they were warped. they're true Brembo cross-drilled and slotted rotors, racing style, made to dissipate heat better. obviously. i read somewhere that they run 82º cooler. anyway, the shop claims i overheated them by braking. i found that hard to believe, so i checked the torques on the hub-rotor bolts, and found them to range from 80-100+ ft.lbs, when theyre supposed to be at 40 ft.lbs. i pointed this out to the shop, and they claim that i overheated the rotors still. I NEED INFO to back up my claim that their overtorquing caused these rotors' warping! this is some bs...the shop owes me close to $400 for doublecharging me on the clutch job too. please help?

[HONDA_99]

if your Brembo cross-drilled and slotted rotors are stock size, you are stock with warped rotors and shop did not do any thing wrong.

torque for lug nuts is 80-90lbs/ft and not 40lbs/ft.

reason for those rotors to be warped is mass of them was reduced by cutting slots and drilling hole, so it makes them dissipate heat worse then stock rotors, not better.

i used to have brembo slotted rotors on my 94 & 99 Accords and front rotors on both cars were warped in few month of use without any kind of abuse, just normal driving. i end up putting stock rotors on 99 and i had to buy new set to 94 Accord.

but if you have big brake kit on your car and rotors are warped, shop might did some thing wrong to your car, but i don't what they could do.

[Dezoris]

Lets talk about this. Slotted rotors or cross drilled rotors, do not disapate heat.

The slots and the holes are to disappate gas created by the heating and breakdown of the organic material in the brake pads. This breakdown happens at a microscopic level. Now on a regular rotor this gas build up could cause gas being trapped between the pads and rotors, which reduces breaking efficacy. The slots and holes give the place for the gas to escape which keeps the pad making contact with the rotor.

This is an effect that only happens in race conditions, high speed braking for long periods of time.

These rotors do nothing for street use, and can actually reduce 0-60 braking times, as proven on big brake upgrades on the S2000 and ITR.

As far as warping the rotors, yes you can just as easily warp them as regualr ones, because they are becoming hotter in some ways then your stock rotors because of the pads, and the less surface area causing more work.

In road race conditions it is quite common to replace pads and rotors every race. And these people are using similar setups.

Sorry I can't agree with you.

[neunan]

i bought the car in november 2000 and im fairly sure it still had the stock rotors on it. i drove on those until this march and never experienced any warping. my driving has not changed at all, so unless these rotors noticeably increase heat, i shouldn't be experiencing any problems.

also the torque specs im talking about are not for the lugnuts, which are 80 ft.lbs, you were right about that. im talking about the rotor-hub bolts. maybe thats specific to only a few cars, as on my model Accord because the front rotors are inseparable.

let me quote somebody...
"What advantages do drilled and slotted rotors have? The most notable is they have an increased surface area to allow better cooling. Other advantages include lower rotational mass, better off-gassing properties, and increased wet performance. Do they run cooler? Yes! Based on the average of several controlled data samples these rotors run on average 82º cooler in the front and 27º cooler in the rear. The downside to drilled and slotted rotors, other than cost, is they are more prone to warp if not torqued correctly. They can also make a slight whirling noise during hard breaking."

i now notice that it says "increased surface area", which doesn't apply to me, but that is only one of the listed advantages.

here is the URL of that review in case anyone is interested.
http://www.volvospeed.com/Reviews/bremborotors.htm

im not arguing with anyone, im just trying to figure out what exactly happened and what i can do about it. so if you think its my fault, please tell me

[Dezoris]

Cooler in what conditions? 82 degrees? that is a huge amount, I assume in race conditions?

Well I won't argue that point since that is not your question. The accord setup is a true pain in the ass, and yes over tq'ing the hub will cause additional stress on the rotors, but it will be hard pressed to prove that and getting them to own up is an entirley differnt situation. If you can get them, to admit that they over tq'd the setup then you will need a statement from Brembo confirming that this warpage is caused by the stress of improper installation.

As far as performance pads and rotors go, I junked a few sets on my mitsubishi, because I thought that I could be more agressive with them.

My Honda has not had that problem with the factory setup. I am approaching 70k miles, on the factory pads and rotors, and I still have 35k left in meat on the pads and 60% life on the rotors without them ever being resufaced once. And I actually race the Honda.

If you drive at high speeds over 70 MPH and use the brakes expect to warp them that is just the way it works. That is how all my rotors have been junked. Do you have hot spots on the brembos?

[neunan]

yea it will be hard to get them to admit to overtorquing, i thought of that AFTERi took 7 of them off. but for the 8th, luckily, it was overtorqued so much that i had to use an impact tool to loosen it. and i dont have an impact tool. so a professional that i know witnessed this(i went to him for the tool), and for further evidence im going to take my car into another shop and have the torques checked on the driveaxle hub-nuts, which appear to be overtorqued as well. my hope is that with the testimony of 2 competing shops, i will have enough proof.

well like i said, i havent changed my driving style at all since i changed brake setups, but yes i do drive at above 70mph fairly regularly, making trips on the interstate. i cant think of any times when i had to brake hard at these speeds, but im sure i brake lightly.

as for hot spots, an employee at the shop im upset with pointed them out to me, but as nobody else including me can see any, i think he was just...i dont know, misinformed? and he was pointed to the drilled holes. he asked me if i could "see the blue spots" and no, i dont see any.

[CXHatchback]

Shit, does this mean it's better that I not get aftermarket slotted/drilled rotors? I've never had a problem with warping, and I don't want one now.

[Dezoris]

I'll give you a quote from Comptech Sport
"Slotted or cross-drilled rotors are worthless for the street"

This is because of the gas buildup idea. The pads don't start gasing until extreme breaking conditions which unless you are running from the cops you will never see these conditions on the street. Even in auto cross. Your braking is relative to the vehicles acceleration and higher speed capability. I know my Civic is going to take me about 25 seconds to get to 100MPH. That is a long time, and on a track or least when I autox, I never get above 65MPH, and that is nothing a good set of carbon pads and normal rotors cannot handle IMO.

There are more things to look at besides Rotor design.
There is caliper clamping force, ABS, brake system condition (lines etc.) and brake booster effectiveness.

The fact is cars with good brake systems from the factory rarely see any benfit from big brake upgrades etc. In fact like I mentioned in the case of the ITR and S2000 BAER and Brembo big brake kits reduced effectiveness in some cases.

Now back to the case of the overtightening.
Yes it could cause premature warping. And on that basis, if the hubs were jacked, then they should cover the cost of labor and parts.
But warping and hot spots are two different things. If they can see glazing and blue on those rotors, regardless of how they were installed you heated them up, and that is going to be hard to get out of.
You are probably gonna have to take your lumps on this one.

[neunan]

once i have some free time im going to check the pads for glazing, but nobody ive asked other than the one guy claims to see any 'hot spots' or 'blue spots.'

CXHatchback, i dont think its a BAD idea, but from what these people are saying its not going to be a noticeable upgrade. ill get back to you on the glazing of the pads, because if they are, then ill probably just submit and say the warping was my fault, but im still fairly certain that the only reason they warped was because of this shop's negligence.

[curveball3110]

Hey everybody, on my Prelude I have slotted and x-drilled rotors (stock size) from Brembo and I must say that compared to the stock rotors these slotted and x-drilled ones give my car a much-needed "solid braking" feel. Whether slowing from 40 or 100, they do the job much better than the stock rotors. So why does everybody seem to dislike them so much? I sure don't. Peace

[Dezoris]

Originally posted by curveball3110
Hey everybody, on my Prelude I have slotted and x-drilled rotors (stock size) from Brembo and I must say that compared to the stock rotors these slotted and x-drilled ones give my car a much-needed "solid braking" feel. Whether slowing from 40 or 100, they do the job much better than the stock rotors. So why does everybody seem to dislike them so much? I sure don't. Peace

Let me ask you this did you replace the pads? When you did the rotors?

If your old rotors were junked or worn, then there is your answer.
Brake feel has nothing to do with effectiveness.
It may feel better but your stopping distance may not have changed.

Nobody hates slotted or cross-drilled rotors, they just don't do anything on the street.

[curveball3110]

Yeah, I used Axxis Metal Master Pads and replaced the pads with the rotors, but my old rotors were in fine condition.
I just figure that the vents and drill holes release heat / energy under any conditions, and that's always a good thing, right?
By the way, how does brake feel have nothing to do with effectiveness?

[Dezoris]

Lets draw an analogy just for fun.

Lets say you are driving 30 MPH, and you open your car door and stick your shoe out and try to stop the car from moving.

1.)Why can't you stop the car?
2.)What If you could stop the car with your foot which would stop the car faster? Your bare foot or a shoe, or better yet a boot?
3.)How would you reduce the heat generated by you putting your foot on the ground?

Think about those things and answer.
And thing of your foot as the pad, your leg as the braking system and the ground as the rotor.

As far as brake feel, are you speaking of pedal travel? stiffness in the pedal? Because these things can be change by minor adjustments in the system. How does pedal feel equate into higher more efficent clamping force?

I'll await your answer.

[curveball3110]

1) I can't stop the car because I can't put enough pressure to the ground to make my foot effective in stopping the car.

2) My bare foot would be like the old pads. Using a boot would be like new pads.

3) But if there were "slots and drilled holes" in the ground, it would reduce the heat generated by the contact of my foot with the ground, enabling a quicker stop, correct?

And as far as brake feel goes, yes I mean pedal travel. When I tapped the old brakes just for a second, they didn't do much to slow me down and the pedal experienced a lot of travel right away.

Now, when I tap the new brakes just for a second, the pedal is very stiff (enough to stop you from low-mid speed w/o fade) but will start to fade if you try to completely hold it while decelerating from a higher speed. Once it starts to fade pedal travel is the way it used to be before the new rotors/pads.

This is how I understand it: when you have braking system "A" with a very stiff feel (i.e. less pedal travel), when you do engage the brakes it provides better response (quicker stopping) over system "B" that doesn't have a stiff feel (i.e. experiences a lot of pedal travel, "sloppy"). This happens because there is so much tension* (I don't know if that's the right word) in system A's brakes that the slightest change in pedal pressure can cause the brakes to have a higher more efficent clamping force than system B's can produce. Is that how the equation works out? Peace

[Dezoris]

Originally posted by curveball3110
1) I can't stop the car because I can't put enough pressure to the ground to make my foot effective in stopping the car.

2) My bare foot would be like the old pads. Using a boot would be like new pads.

3) But if there were "slots and drilled holes" in the ground, it would reduce the heat generated by the contact of my foot with the ground, enabling a quicker stop, correct?

And as far as brake feel goes, yes I mean pedal travel. When I tapped the old brakes just for a second, they didn't do much to slow me down and the pedal experienced a lot of travel right away.

Now, when I tap the new brakes just for a second, the pedal is very stiff (enough to stop you from low-mid speed w/o fade) but will start to fade if you try to completely hold it while decelerating from a higher speed. Once it starts to fade pedal travel is the way it used to be before the new rotors/pads.

This is how I understand it: when you have braking system "A" with a very stiff feel (i.e. less pedal travel), when you do engage the brakes it provides better response (quicker stopping) over system "B" that doesn't have a stiff feel (i.e. experiences a lot of pedal travel, "sloppy"). This happens because there is so much tension* (I don't know if that's the right word) in system A's brakes that the slightest change in pedal pressure can cause the brakes to have a higher more efficent clamping force than system B's can produce. Is that how the equation works out? Peace

Ok so what makes the car stop.
You have a good idea thus far.

Lets clear up your issues


Clamping force: The clamping force of a caliper in pounds is the brake line pressure multiplied by the total piston area of the caliper in a fixed caliper and two times the total piston area in a floating design. To increase the clamping force it is necessary to either increase the line pressure or the piston area. Increasing the pad area or the coefficient of friction will not increase clamping force.


What does this mean? That your clamping force of your caliper and brake subsystems has nothing to do with pad design or makeup nor does it have anything to do with the type of disc used

Now you need to understand

Coefficient of friction: A dimensionless indication of the friction qualities of one material vs. another. A coefficient of 1.0 would be equal to 1g. The higher the coefficient, the greater the friction. Typical passenger car pad coefficients are in the neighborhood of 0.3 to 0.4. Racing pads are in the 0.5 to 0.6 range. With most pads the coefficient is temperature sensitive so claims that do not specify a temperature range should be viewed with some suspicion. The optimum is to select a pad with a virtually constant but decreasing coefficient over the expected operating range of temperatures. As a result, the driver does not have to wait for the pad to heat up before it bites, and the pad fade will not be a factor so that modulation will be easy

Ah ha so now you see that finding the pad of the right material and heat range effects your braking efficiency. You don't want a pad race pad for the street, because you have to heat it up to its approriate heat range before it bites. Not to far of from racing tires where their operating range is higher, so getting them to stick requires more heat.

The difference is here you pick a pad for your car based on driving habits, much like you would tires.
If you are on the brakes non-stop and generating excessive amounts of heat then you want a pad and rotor combo designed to bite or grip at higher temps.

On the street we want bite right away thus a pad with a lower operating temp, and the trade off is fade at higher temps, (excessive braking or high speed braking) or reduced bite.

Here is a run down of types of materials


Carbon/carbon brake: A braking system in which both discs and pads are manufactured from carbon composite material. Utilized in every form of racing where they are not outlawed, carbon/carbon brakes offer significant reduction in rotating mass and inertia along with much greater thermal capacity and dimensional stability in use. The disadvantages include cost, a certain amount of lag time while heat builds up (especially in the wet) and some difficulty in modulation. Contrary to popular belief, the coefficient of friction is no better than that of state of the art carbon metallic pads and cast iron discs. A major advantage on super speedways is the reduction of gyroscopic precession on corner entry.


Carbon metallic: This is a trademark of the Performance Friction Corporation. Pad friction compounds containing large percentages of pure carbon along with various metallic elements. Pioneered by Performance Friction Corporation these compounds offer very constant coefficients of friction vs. temperature characteristics along with increased thermal capacity. The disadvantage is that, since they both operate at higher temperatures and their temperature rises to operating temperature faster than other compounds, they increase thermal shock to the disc and increase thermal conduction to the caliper pistons and brake fluid. As a result, it is recommended to not use drilled discs with carbon metallic pads.

Thermal shock or disc exposure to extreme temps causes a break in the bonds of the metals used in the discs which can cause cracking.

Thermal shock is different from bluing which is a result of thermal stress on cast iron rotors, but is normal for brakes that are exposed to hard braking, it will however lead to shorter rotor life

Here is some ifo relating to new brake setups and why it is important to install them correctly, and to allow a break in period


Bedding in: There are two types of "bedding in" with regard to brakes:
1. Bedding of the friction material. All friction materials contain volatile elements used as binders. In the initial thermal cycling of the material these volatiles boil off, forming a gaseous layer between the friction material and the brake. A bedded pad will exhibit a layer of discolored material from 1.5 to 3 mm thick.

2. Bedding of the disc. Before using a new disk, all machining and preservative oils must be completely removed following the disc manufacturer's recommendations. Usually it involves washing with soap and water or using one of the proprietary "brake clean" compounds. The disc should then be mounted and checked for run out. It should be bedded in with a number of moderate stops with lots of cool off time between stops, gradually increasing the severity of the stops until the entire surface of the disc is evenly discolored. This will prevent thermal shock, distortion and the formation of "hot spots" (regional deposition of pad material which results in a permanent transformation of the cast iron underneath the deposit) and ensure maximum disk life. [/i]


Now that you have that down lets get to the pedal effort you were talking about. This is called modulation. The stiffer and tighter the pedal is the less force is transfered to the clamping system via the booster, and master cyl. The higher the pressure in the brake lines and more pedal travel you have equals more force.
More pedal travel=Higher system pressure/clamping force harder to modulate

Stiffer pedal/tighter=Less pressure easier to modulate

Modulation: The term given by the process by which the skilled driver controls the braking torque to maintain maximum retardation without locking wheels. Because the human being modulates most efficiently by force rather than displacement, effective brake modulation requires minimum pedal travel and maximum pedal firmness

The pads and rotors do not change this. They may increase your systems ability to increase hydrolic pressure though.

Mechanical pedal ratio: The brake pedal is designed to multiply the driver's effort. The mechanical pedal ratio is the distance from the pedal pivot point to the effective center of the footpad divided by the distance from the pivot point to the master cylinder push rod. Typical ratios range from 4:1 to 9:1.The larger the ratio, the greater the force multiplication (and the longer the pedal travel)


This ratio can be adjusted by the installer.
So now you can see that brake modulation is key for controlling your braking to keep teh car stable, and has nothing to do with actual with
braking efficiency or braking tq.


There seems to be a misconception of what a ventilated disc is.
this is a ventilated disc

This is a cross drilled rotor and ventilated disc



This is a slotted ventilated disc


You asked about the cross drilled rotors and how they help cool the brake system. Well here is the short answer, air cools them, and without ducting running to your brake discs they are hardly more effective than your standard ventilated disc. The slotted rotors are for gassing, when the pads reach their operating temps or higher they start to gas or breakdown and the slots are there to allow the gas to escape.

So you are reducing suface area on cross drilled rotors, and they are also more prone to cracking unless, you have a system used by porsche that uses ceramic coatings, on their caliper, special brake fluid, stainless steel brake lines, venting all the necessary items to aid in convection

Convection: One of only three heat transfer mechanisms. Conduction and radiation are the other two. Convection is the transfer of heat by fluid flow. Air can be considered to be a fluid in a thermal model of a brake system when it is moving and is contact with the heated surfaces of the disc or drum. In the case of a solid disc the air moving over the surface of the disc is very random and turbulent, but still functions to provide some cooling. In the case of a ventilated disc, by the pressure of a forced air duct or by induced flow that is a result of the centrifugal acceleration of the air already in the vent of a rotating disc, air flows through the vents. The air absorbs thermal energy along the vent path. In this way, the heat generated by the braking system of an automobile is transferred to the moving air stream and away from the brake disc.

As far as cross drilled rotors go,
The advent of carbon metallic friction materials with their increased temperatures and thermal shock characteristics ended the day of the drilled disc in professional racing. They are still seen (mainly as cosmetic items) on motorbikes and some road going sports cars. Typically in original equipment road car applications these holes are cast then finished machined to provide the best possible conditions by which to resist cracking in use. But they will crack eventually under the circumstances described in another section. Properly designed, drilled discs tend to operate cooler than non-drilled ventilated discs of the same design due the higher flow rates through the vents from the supplemental inlets and increased surface area in the hole. That's right, inlets, the flow is into the hole and out through the vent to the OD of the disc. If discs are to be drilled, the external edges of the holes must be chamfered (or, better yet, radiused) and should also be peened.
Thanks to By Stephen Ruiz, Engineering Manager and
Carroll Smith, Consulting Engineer at STOPTECH LLC



So basically what kind of pads do you have?
And do you have all the other equipment on your brake system to make these modifications noticable? No, no one usually does.
Throwing on a sport pad is the easiest way to increase your COF, and will increase efficiency. Increasing rotor size will also help, but, not without sport calipers which OEM we don't have, even with this upgrade, the system requires true stainless steel teflon brakeline, and a possible upgraded booster and master cyl. to accomodate the increased pressure needed to keep clamping force up, along with race/syn brake fluid. This is the proper way to do it, the way to actually get noticable 60-0 braking distance reductions.

So if you could mustard reading through all that, why did adding a big brake setup not reduce stopping distance on the S2000?