Spectacular rear brake rotor near-failure

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Chuck Branscomb wrote:

MikeWhitney wrote:

I have some theories about how this happened - any comments?

What's your thinking Mike? Can you tell where the crack originated on either rotor? Unless they are using thinner cross-sections in their design, I'm stuck on the material properties or a manufacturing error.

Chuck - think this had anything to do with it?

Chuck Branscomb · **Posted:** Mon Feb 11, 2008 4:25 pm

MikeWhitney wrote:

Chuck Branscomb wrote:

MikeWhitney wrote:

I have some theories about how this happened - any comments?

What's your thinking Mike? Can you tell where the crack originated on either rotor? Unless they are using thinner cross-sections in their design, I'm stuck on the material properties or a manufacturing error.

Chuck - think this had anything to do with it?

Hard to tell what that is...rear wheel bearing play causing rotor contact with caliper/bracket?

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Chuck Branscomb wrote:

MikeWhitney wrote:

Chuck Branscomb wrote:

MikeWhitney wrote:

I have some theories about how this happened - any comments?

What's your thinking Mike? Can you tell where the crack originated on either rotor? Unless they are using thinner cross-sections in their design, I'm stuck on the material properties or a manufacturing error.

Chuck - think this had anything to do with it?

Hard to tell what that is...rear wheel bearing play causing rotor contact with caliper/bracket?

It *appears* from the picture that the rotor is in fact slightly touching the pad carrier at full-tilt-bookie cornering or curb-hopping. It is so slight though that I have trouble believing that it could cause such rotor failure.

I am surprised that the hub can be seeing so much flex relative to the caliper bracket on the trailing arm. There is no discernable play in the bearings -- but maybe they should be replaced just-in-case?

Aaron Buckley · **Posted:** Mon Feb 11, 2008 4:58 pm

Chuck Branscomb wrote:

Hard to tell what that is...rear wheel bearing play causing rotor contact with caliper/bracket?

Hey Mike... can you throw up pictures of what was left of the pads? I think that would answer Chuck's question, and put some light on other possibilities.

Either way, scary stuff and I'm glad it was found on the trailer

- AB

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Graham Jagger wrote:

I don't consider this to be a defect. It's a plain old rotor. Never designed or intended for track use or race pad use. It did what they do. Failed due to heat stress over X thermal cycles. The cracks appeared at the places where the metal was weakest.

I talked to the guys at Bimmerworld about this. They use Balo rear rotors on all their IT cars, World Challenge cars, and customer race cars. They have never seen or heard of cracking like I experienced. Radial cracking, yes, but not catastropic cracking starting from the hub center.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Aaron Buckley wrote:

Chuck Branscomb wrote:

Hard to tell what that is...rear wheel bearing play causing rotor contact with caliper/bracket?

Hey Mike... can you throw up pictures of what was left of the pads? I think that would answer Chuck's question, and put some light on other possibilities.

Either way, scary stuff and I'm glad it was found on the trailer

- AB

Hey Aaron - I didn't take pics of the pads - they look very good. Perfectly straight wear with no taper. I also never experienced a long pedal which would be expected with a lot of pad knockback. So I'm a bit confused about that.

Chuck Branscomb · **Posted:** Mon Feb 11, 2008 5:06 pm

MikeWhitney wrote:

It *appears* from the picture that the rotor is in fact slightly touching the pad carrier at full-tilt-bookie cornering or curb-hopping. It is so slight though that I have trouble believing that it could cause such rotor failure.

I am surprised that the hub can be seeing so much flex relative to the caliper bracket on the trailing arm. There is no discernable play in the bearings -- but maybe they should be replaced just-in-case?

Did this happen on both sides of the car in the same way?

Regardless, it would be somewhat consistent with the way the rotor cracked that it was loaded side-to-side (i.e. view the rotor face as a cantilever beam so the stresses would be highest toward the fixed end). It might only take a few major stress cycles (i.e. major contact with bracket cycles) to start a crack that then progresses as the load area decreases...or we're barking up the wrong tree since those bracket marks were made after the rotor had started to degrade...

Given the way the rotor cracked apart near the root like that though it makes me wonder about flex.

DickRasmussen · **Posted:** Mon Feb 11, 2008 5:15 pm

FYI, I don't recall details (as usual :oops:

) but Mustangs used HARD have similar problems. Wheel Bearing Flex seems to be contributor, especially with heavy cars on sticky tires.

Aaron Buckley · **Posted:** Mon Feb 11, 2008 5:50 pm

I think Chuck and Dick are on the money. The wheel bearings might need to be inspected. When you think of the number of turns on VIR, that's a lot of spots to hit the caliper and get it glowing cherry red, which could easily have done that kind of damage to the rotor.

As to the pedal travel remaining consistent, I would think that would be due to the your fronts compensating somewhat. I would expect that your pads on the other wheels and see if they are worn even more than this rotor's pads. That might show some compensation. Granted, this is just a guess

As to the parking brake crack, it makes you wonder if removing them for the track wouldn't be an awful idea. - AB

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Aaron Buckley wrote:

I think Chuck and Dick are on the money. The wheel bearings might need to be inspected. When you think of the number of turns on VIR, that's a lot of spots to hit the caliper and get it glowing cherry red, which could easily have done that kind of damage to the rotor.

As to the pedal travel remaining consistent, I would think that would be due to the your fronts compensating somewhat. I would expect that your pads on the other wheels and see if they are worn even more than this rotor's pads. That might show some compensation. Granted, this is just a guess

As to the parking brake crack, it makes you wonder if removing them for the track wouldn't be an awful idea. - AB

There is hardly any wear on that caliper bracket though -- no lip, just barely through the rust. There is also no mark on the rotor from the contact. I'm really not convinced either way, just throwing out information...

Also FYI if you didn't notice -- it's happening on both sides. All 4 pads came out straight and looked fine.

DickRasmussen · **Posted:** Mon Feb 11, 2008 7:28 pm

Mike,

You need to work on your cutting technique . . . :lol:

http://groups.msn.com/SVTCobraR/bremborotorfailure.msnw

As you can see these are old pics (2001)

I could not find any detailed posts from a couple of years ago when this issue surfaced again. I don't know if a solid cause was determined or publicized.

Pete Guthrie · **Posted:** Mon Feb 11, 2008 11:16 pm

i have done that twice on my car. it was on the front brakes, i drove for a hour on it to another SC store, to replace it. I put it on that night and bedded it on on the ride to track in that next morning.At CMP, my car eats brakes badly. I only have been there twice total, broke both times. (baaad juju)
so now i run vir and roebling. when you dont have abs, and it feels like you do. Often that is a baad sign, ive done that twice, it was before i went to nx2000 front rotors. Fellow se-r owners take note: the stock front rotors are not up to real track abuse. Do the nx2k change, then find a set of 14'' wheels with a good ID. With this set up on stock pads, it will still fit. If you goto carbotech pads, you will need either spacers or 15'' wheels. But on the street nx2k rotors and stock pads will fit fine.

Karl Shultz · **Posted:** Mon Feb 11, 2008 11:54 pm

Mike, I've been doing the track thing for about ten years now. I have *never* seen a failure like that...and you got two of them in one weekend! Do let us know what the vendor has to say, if anything.

Most curious to me is that it happened in the rear and not the front. That seems really strange to me.

Adam Ligon · **Posted:** Tue Feb 12, 2008 12:07 am

Also what about caliper guides?

Worn, sticking, non lubricated guides can cause draggin issues which wold generate heat, etc. Just another idea

Arthur McDonald · **Joined:** Fri Aug 29, 2003 1:54 am **Posts:** 2052

MikeWhitney wrote:

Edit - pic #3 might be misleading. This is the inside of the parking brake surface -- not the actual rotor brake surface. One of the cracks appeared to start there.

Clearly, you need to cut out using the handbrake in tight turns

I picked up a huge braking vibration during a school at Mid-Ohio. Upon inspection, I found that one of the front rotors had a large radial through the inner face of the rotor. Swapped in a spare, went back on track, and viola, the vibration was just as bad. The other front rotor was badly warped, and the broken rotor wasn't causing any (detectable) vibration.

Is there any kind of ducting feeding cold air to the rear brakes? Perhaps they're getting hit by too cold an air stream.

THSCC Forums

Spectacular rear brake rotor near-failure

Who is online