Update: Warped Rotors

[Top Jimmy]

Got my CX-7 back this evening (by the way, it's an AWD Black Cherry Mica GT w/ Sand). The dealer swapped out the warped front rotors, replaced the front brake pads, changed the gas cap and did the PCM flash update (the flash is called XXB472FX SB 01--46/06 MIL/DRIVEABILITY PCM @ TCM FLASH in case any of you need to request if from your dealer).

The CX-7 is driving so sweet now. The vibration that I got in the steering wheel when braking at 65mph is gone. It actually seems to be more "peppy" after getting the flash update (might just be psychological though). Point is, it drives great now.

I have a question, though. When I got back from the dealer (about 10 miles from my house), like a dumbass, I rubbed my finger across the front and back rotors just to make sure the back ones were as smooth as the new front ones (because the dealer insisted nothing was wrong with the rear rotors), and to my surprise, the back rotors were almost cool to the touch. At worst, they were warm. The front rotors, on the other hand, almost burned a layer of skin off my finger because they were so hot (yeah, I know, I win the "Dumbshit of the Year Award" but that is beside the point here).

My (dumb?) question is, why are my front rotors so hot in comparison to the rear rotors? Maybe that would explain why the front rotors were warped after only 300 miles. Are the front one's supposed to be so damn hot in comparison to the rears?

 

[B1GHAM]

there will be a difference in heat associated with the front and rear brakes. This is due to the fact that braking bias is geared more towards the front brakes (esp. in heavier vehicles such as the CX-7).

What does this mean to you? More pressure is applied from the front caliper to the rotors to help stop the car. The pressure in turn creates more heat as a bi-product thus giving you hotter front rotors!

 

[giddyup]

I was under the assumption our cars had somekind of even brake distribution control. At least thats why I thought I dont get as much front end dive under hard braking as i used to in other cars??

 

[cmdavis3rd]

I was under the assumption our cars had somekind of even brake distribution control. At least thats why I thought I dont get as much front end dive under hard braking as i used to in other cars??

You can't have an even brake distribution on any car. One of two things would happen (there might be more, but for this example I will use two). 1) You will lock up the rears or 2) The back end will come around (more often if you are breaking in a slow curve).

Weight transfer is the simplest reason for not being able to have an even distribution. Essentially, when you get on the brakes, weight gets transfered to the front wheels. If you had an even brake discribution (ie. 50% of braking done with the front brakes and 50% the rear) then you would end up with not enough brake force in the front and one of the two situations above would occur since there is not enough weight over the rear tires essentially reducing traction.

Generally speaking, the front brakes do about 70-80% of the braking and the rears do the rest. That is why the front brake rotors are larged in OD and thickness and the calipers (can, not always) have more pistons and larger pads.

Front end dive is generally a marriage of fender gap and suspension firmness. If the fender gap is smaller and the suspension is stiffer then you will have less noticable nose dive. However, the amount of nose dive is no relation to how hard your vehicle brakes. If a car pulled .9g of linear braking and I was running steel rods in the suspension, then the only nose dive I would have would be from the tire sidewall compressing. Same would hold true for .8g and 1.0g of braking. If I was running springs and weak shocks then the nose dive would be more and more noticable.

 

[dmitrik4]

!!!!!

i thought perhaps that vibration during braking from highway speeds was in my imagination...guess not. my g/f hasn't noticed it, but i have.

have to get the rotors checked out at my first oil change.

 

[B1GHAM]

I was under the assumption our cars had somekind of even brake distribution control. At least thats why I thought I dont get as much front end dive under hard braking as i used to in other cars??

Its called Electronic Braking Distribution and it does control braking but in a different way. It controls the brakeforce to each wheel as needed to help bring the car to a hault esp. in emergency manuever situations. This however will still not change the way normal braking is effected. CMDavis is right.. under the guise of weight distribution, braking has to have a front end bias.

if %60-80 of the weight was shifted forward during braking, then there would need to be more braking force in the front wheels in order to help slow the mass down.

 

[singlemalt_18]

Its called Electronic Braking Distribution and it does control braking but in a different way. It controls the brakeforce to each wheel as needed to help bring the car to a hault esp. in emergency manuever situations.

Great discussion here...!

In addition to the brakeforce distribution, the CX-7 also has "peddle assist".

Typically, a female driver, (or any driver of smaller stature or body frame), is at some disadvantage under emergency or "panic" braking conditions, because they cannot physically apply the same amount of force to the brake peddle as a larger driver can deliver. This difference was significantly reduced with the advent of today's standard power brakes, but it still is a factor... just much less.

The peddle assist feature works by sensing the "speed" at which the brake peddle is being applied. When the system senses more velocity from a quicker press on the peddle, the assist kicks in to increase the force being applied to the brakes. This in effect minimizes any braking deficiency due to a persons size or strength.

I have only had one experience so far with a "panic" type situation, and I do believe I felt this feature at work. It was on dry roads, and I know there was some quick pulsing of the anti-lock at work; and even as my heart was still pumping, and the tingle of adrenaline could be felt from my fingertips to my ears... I felt like the CX-7 responded more from my reflexes, rather than brut force.

Take that RDX !!!

What good is going faster if you can't stop quicker?

 

[CXRabbit]

Take that RDX !!!

What good is going faster if you can't stop quicker?

LOL!

You're right though... Safety is a BIG deal for me when I buy a car and as far as the brakes go, the CX-7 just beats everything in it's class. I had a kitten bult out in front of me about 2 weeks ago and I KNOW with some of the other crossovers I would NOT have stopped in time (I was THAT close to hitting the poor little thing). At that very moment I was extremely happy to have chosen the CX-7!

 

[singlemalt_18]

Lucky Dog!

You're right though... Safety is a BIG deal for me when I buy a car and as far as the brakes go, the CX-7 just beats everything in it's class.

I had a kitten bult out in front of me about 2 weeks ago and I KNOW with some of the other crossovers I would NOT have stopped in time (I was THAT close to hitting the poor little thing). At that very moment I was extremely happy to have chosen the CX-7!

SO WAS THE CAT !!!!!!!

...and I just have to ask - is this what they mean when someone says "I had a kitten!" ???

LMAOWTIME (Laughing my ass off with tears in my eyes!)

 

[dmitrik4]

actually, the big advantage of pedal assist isn't that some drivers aren't strong enough to apply full braking, but that most drivers simply don't, even in panic situations. most drivers don't use the brakes as hard as they can be used, even when they think they are.

 

[Alpha Wolf]

Just curious.

Warped rotors are usually caused by one of two things.

1. Constantly dragging the brakes heating the rotors up to a temp where they warp.

2. Someone takes your tires off and then improperly tightens your wheel lugs causing them to warp. Ie. Failure to use an X pattern and failure to use a Torque wrench but uses a very large Impact wrench which way over tightens the lug nuts.

Just wondering if you had any brake or tire work prior to this occuring or if you or anyone else who drives likes to drive with two feet with one on the gas and another on the brake pedal.

Also driving off with the parking brake partially activated will heat up the rear rotors enough if driven far enough but thise would not affect your front rotors.

 

[Top Jimmy]

Just curious.

Warped rotors are usually caused by one of two things.

1. Constantly dragging the brakes heating the rotors up to a temp where they warp.

2. Someone takes your tires off and then improperly tightens your wheel lugs causing them to warp. Ie. Failure to use an X pattern and failure to use a Torque wrench but uses a very large Impact wrench which way over tightens the lug nuts.

Just wondering if you had any brake or tire work prior to this occuring or if you or anyone else who drives likes to drive with two feet with one on the gas and another on the brake pedal.

Also driving off with the parking brake partially activated will heat up the rear rotors enough if driven far enough but thise would not affect your front rotors.

I'm guessing the rotors were warped during the manufacturing process (a bad batch maybe?). I bought the car with 87 miles on it and noticed the warped rotors at about 350 miles (that is the first time I drove at highway speeds).

I was very easy on the brakes after I bought it so if the warpage occurrred after my dealership received the vehicle from the manufacturer, the warpage had to have occurred in the first 87 miles the vehicle was driven (test drives, etc.). I don't know a whole lot about cars but I am doubting rotor warpage can occur in the first 350 miles due to excessive heat or even if the lug nuts were too tight. This is what makes me think the rotors came that way from the manufacturer.

 

[kailua]

Like everyone else said. Majority of the braking force is on the front wheels. If you look at the brake calipers and pads the front are alway larger (almost twice the size as the rear.

 

[Int3grity]

you want to know something I think top Jimmy might be on to stomething here I thought this was normal in the car I noticed this the first time I drove the car that the brakes vibrate alittle almost as if I am braking to hard when I am not hell I thought the car just came with cheap brakes or something.

it sort of went away a little but more or less it now happens like your driving at 40mph then the stupid light is about to change out of nowhere so you have to stop with adequate distance my steering wheel shakes. I have also noticed alot of brake dust and I have not even been driving the car ruff I been gentle because I want my car to last.

 

[offset_98]

Braking:
Front: 80%
Rear: 20%

 

[mikey1981]

you want to know something I think top Jimmy might be on to stomething here I thought this was normal in the car I noticed this the first time I drove the car that the brakes vibrate alittle almost as if I am braking to hard when I am not hell I thought the car just came with cheap brakes or something.

it sort of went away a little but more or less it now happens like your driving at 40mph then the stupid light is about to change out of nowhere so you have to stop with adequate distance my steering wheel shakes. I have also noticed alot of brake dust and I have not even been driving the car ruff I been gentle because I want my car to last.

or it could just be that ur tires need to be balanced. My car got delivered out of balance & alignment. that would be my first guess before i would consider the rotors being warped.

the 7 has dbl piston brakes all around, and the breaks are actually a larger size in the back. If your truck isnt breaking well, id bring it in. cuz this thing breaks better than any car ive ever driven.

 

[bane1240]

me too - I think

Just got my CX-7 on Saturday and yesterday it started shimmying in the steering wheel when braking at all speeds but only real noticable from about 40mph up under hard braking. There should be no shimmying at all. Following up with dealer tomorrow. Vehicle has 600 miles on it.

 

[protogizzle]

The problem that occurs is when the CX-7's and ('s sit on the lot for awhile. I have personally had to machine the rotors on many new cars. It is caused by the vehicles staying stationary in one spot for long periods of time. The rotors then continue to build up rust on the parts of the rotor that are not covered by the brake pads. When you take off and drive for sometime the rust goes away but the rotor now has a low spot causing the pulsation. For future owners of the cx-7 and 9's, take a good test drive to check for pulsation. As for the wheel balance shimmy, it is probably flat spots int he tires from sitting. Due to gas prices, sport utes aint movin like they used to. Hope that will help. And for those who may wonder, I am a Mazda Master Tech.

 

[wannabe]

Just got my CX-7 on Saturday and yesterday it started shimmying in the steering wheel when braking at all speeds but only real noticable from about 40mph up under hard braking. There should be no shimmying at all. Following up with dealer tomorrow. Vehicle has 600 miles on it.

check dates before you post this thread is over a year old.