Cracks in my rotors, but only "skin deep"? Should I worry?

[Sparky]

I started getting this vibration at highway speeds recently so I went out and visually checked a few things that I could without getting the jack out (I don't have a good place to jack things up so I have to go somewhere to do it... kind of a pain). In the process I noticed what looked like cracks on my rotor on the passenger side... no, both rotors on the passenger side! Crap. Then I realized the apparent cracks don't only go through the cross drilled areas, but kind of randomly all over. One other thing is these apparent cracks are only "skin deep" so to speak. The crack lines do not extend into the chamfers of the slots and and holes, or the edges of the rotors

First I've seen this kind of thing before. I've seen pics of cracked rotors, but they were obviously cracked, and always through the holes. Not these rather random looking cracks. Some of them I can barely feel with my fingernail, others I can't even do that on. Braking seems unaffected. I did the front brakes in August and the rears in September last year, and have put 12k on the fronts and 10k on the rears.

Also, only the passenger side rotors seem to have this. I didn't notice any on my driver side rotors, which makes it even stranger.

Front passenger side:

Rear passenger side:

As you can see, some go through the holes, but not all, and the lines don't go deep at all.

I'm going to contact the manufacturer of the rotors and see what they have to say.

Thoughts?

 

[Wyle]

If I'm looking at the right areas, those look amazingly straight and long for cracks. Weird.

Especially when it continues through a hole.
View attachment 18958

They almost look like score marks from something. Did you have them turned when you changed pads? Either way, I would think any mild score marks from sliding rotors around would be gone after 4-6 months of use.

 

[Boricua SS]

they almost look like they were machined that way, and its starting show??

i would monitor them closely, as brakes arent something to mess with on a 5000+ lb SUV...

 

[Sparky]

4600 pounds actually

Brakemotive is a sponsor on another site I'm a member of, so I fired those pics to them to get their input. Given that they are not deep at all (and quite random) I'll probably just monitor them for the time being as you said, unless Brakemotive or someone else recommends otherwise. As mentioned they seem to be functioning quite normally.

No, I never had them turned. The pads and rotors were done at the same time.

 

[jrSS]

Like u said u were going to do..... get ahold of the manufacturer. Great idea. Kinda weird tho

 

[Sparky]

OK here's a stupid thought that I didn't think of until now - could it just be left over from the crosshatching? Like, some of the crosshatches were machined a little deeper than others, so now that most are worn down I'm left with just these visible? They do follow that general pattern actually, particularly the marks in the last pic. And that would explain why they are so long, straight, and fine.

If so, I feel stupid

 

[fishguy1123]

Either way it works out, please let us know! I'm planning on replaceing mine with the brakemotive stuff in the spring so any input would be great.

 

[gmcman]

could it just be left over from the crosshatching? Like, some of the crosshatches were machined a little deeper than others, so now that most are worn down I'm left with just these visible?

I dunno but they appear to be fairly deep for crosshatching. I have seen hairline cracks run perfectly straight through the holes just like yours but the number of cracks makes me think they are either machined like that or they are ready to come apart on you.

I know you don't want to hear this but this is exactly why I avoid these rotors like the plague...unless i was racing. When you drill and slot rotors there is less metal under the pad surface to be used for braking. For the street I would speculate with all things being equal that solid blanks would be smoother and stop faster.

Keep us posted on what the manufacturer says.

 

[blazinlow89]

Dang I am still waiting on my set of these.

How long ago did you put them on, it is a very good possibility that they are the original cross hatching. The lines are to perpendicular and follow each other. It was more random and maybe you had some larger curves then I would think otherwise.

I would almost bet on it

View attachment 19282

This is just a general pic off of his ebay listing. Between machining tolerances, and common things that can vary during repetitive machining they might be slightly deeper than usual.

 

[Chickenhawk]

I agree that these are left-over machining marks. I would be very interested in what the manufacturer says about this.

If these are the left-over crosshatch machining marks, I cannot believe how inconsistent they are and how they are all at random depths. Personally, I think the manufacturer has a LOT of 'splainin' to do here.

By the way, while I can see a marginal use for grooved rotors, it should be pointed out that cross-drilled rotors actually decrease overall braking performance, through less mass to dissipate heat and less cross-sectional area for the pads to clamp against.

Rifle shooters who need consistent results with barrels that can be cold to warm to hot have barrels with GREATER mass and greater surface area to dissipate heat, not less. Plus, no extreme-use professional application uses cross-drilled rotors, and that includes ambulances, fire trucks, police cars, aircraft and nearly every single race car on the track.

That being said, I would give that the actual decrease in performance would be so tiny as to be unnoticeable in regular service, and if owners do this for the looks, then so be it. Just as long as they understand it is strictly for looks, not performance. (Plus, I would rather run premium cross-drilled and grooved rotors from a reputable manufacturer than cheapie economy solid blanks from a no-name any day, but that's just me. Brakes, shocks and tires and three places I do not compromise on.)

 

[gmcman]

I agree that these are left-over machining marks. I would be very interested in what the manufacturer says about this.

+2, after looking at the rotor above it's fairly obvious there alot of fine marks in the braking surface.

 

[Sparky]

Sorry forgot to update.

Brakemotive forwarded the pics on to their tech, who said that there should be nothing to worry about and it does look totally superficial and said with some more use they should go away as the rotor wears. The rep also said that if after a while they don't, or seem to get deeper or worse to certainly let them know.

For what it's worth, these two rotors are the ONLY ones I've seen like this and I know several people who have Brakemotive brakes without any deeper marks, so I wouldn't hold it against them. As I mentioned they work normally and I never would have noticed had I not been poking around the suspension on that side.

 

[blazinlow89]

Good to know, I look forward to installing my soon.

My guess is that they change tooling without doing any adjustment to compensate for the new bit/end mill etc. That could have caused the grooves to be slightly deeper than others. Machining tolerances are critical. I have seen 15lbs block of aluminum thrown because some idiot put the blank in the CNC vice wrong. It is not pretty.

 

[MacMan]

......Plus, no extreme-use professional application uses cross-drilled rotors, and that includes ambulances, fire trucks, police cars, aircraft and nearly every single race car on the track......

While I agree with the rotors used in most NASCAR applications, the rest of your statement is far from accurate.

I have been in racing for 40+ years, and have worked on dirt modifieds, USAC sprint and Silver Crown cars, pavement winged midgets, and also dirt winged sprint cars. MANY of the cars race in those series use cross drilled rotors.

And don't let BMW/M series, Mercedes AMG, or Corvette, etc, etc engineers know they're doing something wrong on their high-end cars.....I seem to remember seeing a LOT of cross drilled rotors on their highest performance cars.

All that being said, on a TrailBlazer/Envoy, regular smooth rotors are the way to go.

 

[Sparky]

Only reason why I got slotted/drilled was because that's what Brakemotive sells. If I had my way they wouldn't be drilled - and a while back they didn't have drilled ones - but oh well.

 

[Chickenhawk]

While I agree with the rotors used in most NASCAR applications, the rest of your statement is far from accurate.

I have been in racing for 40+ years, and have worked on dirt modifieds, USAC sprint and Silver Crown cars, pavement winged midgets, and also dirt winged sprint cars. MANY of the cars race in those series use cross drilled rotors.

And don't let BMW/M series, Mercedes AMG, or Corvette, etc, etc engineers know they're doing something wrong on their high-end cars.....I seem to remember seeing a LOT of cross drilled rotors on their highest performance cars.

Thanks for the information on sprint cars! My experience has only been with endurance and road racers.

You are correct that some race cars do use cross-drilled rotors but a lot seem to take off the cross-drilled rotors and install slotted or solid rotors, such as this Corvette race car:

Plus, BMW, AMG and Corvette street cars use cross-drilled rotors for looks. Thats why people buy those vehicles. (The slight loss of performance is not critical in these street applications because they tend to have superior brakes anyway.)

However, I have tested a lot of police cars on race tracks and looked under a lot of aircraft landing gear assemblies in my time and have never seen cross-drilled rotors, so I stand by my statement.

 

[Guano]

I'm on my 2nd set of Brakemotives (& those are not) & will never go back to solid (couple off reasons why).

 

[Sparky]

I'm on my 2nd set of Brakemotives (& those are not) & will never go back to solid (couple off reasons why).

Which are you referring to?

 

[marshall@pcm]

Definitely looks like machining marks.

 

[HARDTRAILZ]

all things being equal that solid blanks would be smoother and stop faster.

That makes perfect sense, but swapping my front rotors to drilled and slotted, made mine stop faster. The braking feels like it is harder too. I just did the front because I got a steal off ebay on the pair of rotors only and wanted to try em.

However I did do solid on the rears when they needed it because I had metal on metal and could not wait for shipping on drilled ones.

Neither front nor rear seams to have any issue, but I did keep my front in case cracks develop, but for 20K they have been an improvement over previous.

 

[gmcman]

That makes perfect sense, but swapping my front rotors to drilled and slotted, made mine stop faster. The braking feels like it is harder too. I just did the front because I got a steal off ebay on the pair of rotors only and wanted to try em.

However I did do solid on the rears when they needed it because I had metal on metal and could not wait for shipping on drilled ones.

Neither front nor rear seams to have any issue, but I did keep my front in case cracks develop, but for 20K they have been an improvement over previous.

I would have shortened your quote but my Droid isn't very user friendly.

What pads are you using? That's where the money makes the most diference IMO.

 

[gmcman]

While I agree with the rotors used in most NASCAR applications, the rest of your statement is far from accurate.

I have been in racing for 40+ years, and have worked on dirt modifieds, USAC sprint and Silver Crown cars, pavement winged midgets, and also dirt winged sprint cars. MANY of the cars race in those series use cross drilled rotors.

And don't let BMW/M series, Mercedes AMG, or Corvette, etc, etc engineers know they're doing something wrong on their high-end cars.....I seem to remember seeing a LOT of cross drilled rotors on their highest performance cars.

All that being said, on a TrailBlazer/Envoy, regular smooth rotors are the way to go.

Would it be a fair asumption that drilled rotors in the application of dirt racing would give the dirt somewhere to go when the brakes are applied?

 

[HARDTRAILZ]

I would have shortened your quote but my Droid isn't very user friendly.

What pads are you using? That's where the money makes the most diference IMO.

Advance auto replacements that were 20 or 30 bucks.

 

[blazinlow89]

Mine are warped so anything will make a huge difference.

 

[MacMan]

Would it be a fair asumption that drilled rotors in the application of dirt racing would give the dirt somewhere to go when the brakes are applied?

Drilled rotors, or even slots in rotors are not there to allow dirt out.

The purpose of slots/holes are to allow the gasses that are produced by the pad/rotor heating and friction to have a place to vent to.

If a very high performance vehicle used a smooth rotor, the gas would get "trapped" between the pad & rotor, since it had no place to go, and the pads would actually "float" on a cushion of the gas, giving poor stopping and a soft-feeling pedal.

Please note the front and rear rotors in the pics:

 

[gmcman]

Drilled rotors, or even slots in rotors are not there to allow dirt out.

The purpose of slots/holes are to allow the gasses that are produced by the pad/rotor heating and friction to have a place to vent to.

I do know that outgassing was a problem at high pad temps and was a problem back in the earlier days with inferior pad materials and bonding agents. However with the absence of asbestos, outgassing has become more of a non-issue and really not an issue on ther street. Take some pads (I don't know which) to the track and you may experience this.

 

[HARDTRAILZ]

Wouldnt the holes/slots provide better braking since the is a bit more biting edges into the pad, even though it would cause more pad wear. !t makes sense to me at least and I do have better braking.

Just tossing out thoughts, I know from my experience I prefer the drilled/slotted performance and will likely do them again, but I would like to know the thoughts on all aspects of this stuff.

 

[v7guy]

from my reading the slots do act as a knife edge cleaning any potential glaze on the pads off. Obviously at reduced pad life. I've seen the drilled rotors crack all over because of the holes. I run some porsche rotors with brembo calipers on my track day firebird and those rotors have holes cast into them (opposed to drilled like most rotors, cast decreases stress risers). i've not personally had any problems with cracking but other guys have. I've seen it enough to steer clear of drilled rotors.
In the end more mass in the rotor will absorb more heat and keep the pad cooler. Accordingly I usually go for the heavier (non slotted/drilled) rotor. In the end it's probably a wash, I'm not trying to set a time at a road course, just need to stop on the highway. Maybe I should try some slotted rotors.

 

[ieatglue]

Those def. don't look like cracks to me. Cracks are pretty crooked. Here's an example of what mine looked like after checking them due to a steering wheel shudder...

 

[Pittdawg]

Those def. don't look like cracks to me. Cracks are pretty crooked. Here's an example of what mine looked like after checking them due to a steering wheel shudder...

Was the shudder only present on hard braking?

 

[Sparky]

Since this is bumped (sorry Pittdawg I can't help you with your question), I'll update. I've noticed as I've driven the truck that those lines are slowly fading, which reaffirms what Brakemotive said about them just being a few milling marks that were a bit deeper than normal. Totally nothing to worry about