Warped Front rotors

[murphsubaru]

My 99 Forester continues to warp front rotars. I thought I corrected this problem with the last brake change by replacing the front pads, rotors, caliper pins and carage barackets. A few months later one of them is warped. Any suggestions.

[idosubaru]

sounds like you did it all correctly:

new pins and clean out the bores (or replace if possible) they slide in.

new boots, new pad clips, grease the pins.

 

supposedly driving style is a culprit....braking and then holding onto the brake pedal - like interstate driving, then hitting a red light and holding the hot rotors and pads together. here's an in depth technical article:

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

 

were your rotors brand new?

 

maybe there are higher quality rotors or pad combinations less susceptible to the problem.

[987687]

Did you get good quality rotors and pads?

I've found that the cheapo cheap rotors will warp very easily.

[89Ru]

Interesting article.

 

It suggests that higher end pads can deposit material unevenly onto rotors. The rotor is not really warped, it just has uneven pad material stuck to it (they call it pad-imprinting). If not corrected, the pad material can morph into something hard, baked on, that only gets worse. The article suggests that changing out pads to semi-mets can fix the problem if its not too far along. It also suggests a bed-in procedure to help avoid the problem in the first place.

 

Some pads are sold "burned in." I think this might be the same as "bed-in." It seems like this is only half the solution since a properly bed-in rotor has a thin layer of pad material evenly deposited on it. Perhaps pads and rotors could be sold together, already bed-in, but that jacks up the cost, inventory, and if done after the point of sale, could delay the shipping time and is probably not the best idea.

 

One solution is to learn how to bed-in a set of rotors and pads and have a back-up set of abrasive pads. Or just run abrasive pads in the first place and live with the dust and higher temperature fade (probably not advised for mountains or towing).

[Caboobaroo]

How are the condition of the struts? If they are original and the car has over 150k, I would replace them. With worn struts, the car pitches forward under braking making the front brakes work harder to stop the vehicle and with faster braking, can actually warp the rotors easier.

 

For a stock replacement, use KYB GR2/Excel G struts. These are the closest to OEM for your car as KYB made the originals.

[1-3-2-4]

Interesting article.

 

It suggests that higher end pads can deposit material unevenly onto rotors. The rotor is not really warped, it just has uneven pad material stuck to it (they call it pad-imprinting). If not corrected, the pad material can morph into something hard, baked on, that only gets worse. The article suggests that changing out pads to semi-mets can fix the problem if its not too far along. It also suggests a bed-in procedure to help avoid the problem in the first place.

 

Some pads are sold "burned in." I think this might be the same as "bed-in." It seems like this is only half the solution since a properly bed-in rotor has a thin layer of pad material evenly deposited on it. Perhaps pads and rotors could be sold together, already bed-in, but that jacks up the cost, inventory, and if done after the point of sale, could delay the shipping time and is probably not the best idea.

 

One solution is to learn how to bed-in a set of rotors and pads and have a back-up set of abrasive pads. Or just run abrasive pads in the first place and live with the dust and higher temperature fade (probably not advised for mountains or towing).

 

Organic pads will make this feeling, Since I was due for a pad change I switch over to ceramics, I've put over 30K on and no more warped feeling, I did the same on my last legacy I had too plus hardly any dusting up of the wheels which is a plus.

[bstone]

You can cut a hole in the floorboard and just use your feet to stop, like they did in the Flintstones. No more rotor warpage!

[presslab]

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

 

I've seen that article before; must be true, 'cause it's on the internet! He does say "This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures." so he's admitting he sees warped rotors (run-out) but blames it on the material transfer. Which came first, the chicken or egg? Any run-out means the rotor is warped, regardless of how it occurred! It's a contradiction.

 

Anyway anyone who has turned a warped rotor on a lathe (as have I) can obviously see that the rotor has actually warped, and it's not just a high spot from material transfer. I'm not saying that material transfer doesn't happen too, but I'm firmly in the warped rotor camp as I've warped mine more times than I would care to admit. :-\

 

After extensive thermal cycling (from heavy braking) residual stress that is formed when the rotor is cast is said to cause the rotors to warp; I believe that. Next set of rotors I get I'm going to try the cryo treated ones. The cryo treatment is said to greatly reduce the residual stress in the cast iron.

[CNY_Dave]

I have suffered through the material-deposition pulsation, and I think it is technically correct (the best kind of correct) to say the primary result is not a warping of the rotor, as the rotor material isn't being bent, but that material is preferentially removed from the softer areas, leaving the hard area where the pad material was deposited higher.

 

Of course since the high-spot/hard-spot gets hotter than the rest of the rotor, there well could be some heat warping from uneven heating.

 

I have heat-warped rotors in the past (on other cars), and it was always at a very 'short wavelength', that is, the ripples were very close together.

[ocei77]

[quote name=presslab;1155218

Anyway anyone who has turned a warped rotor on a lathe (as have I) can obviously see that the rotor has actually warped' date=' and it's not just a high spot from material transfer. I'm not saying that material transfer doesn't happen too, but I'm firmly in the warped rotor camp as I've warped mine more times than I would care to admit. QUOTE]

 

Let me wade in.

 

The only way you can really be positive, is to get a new set of rotors and check for run out before use. Use them as stated so that deposits form, check for run out again. Turn so you are only removing deposits not real metal and compare .

 

Because metal is removed under complaints of "warped", we don't have a baseline,to say how they were at installation.

 

Another factor is the floating caliper design that many cars use nowadays.

 

When I install a new set of rotors or pads, I use the bed in procedure as outlined by Baer. It's a little more involved , but I have never had an issue since using it.

 

O.

[idosubaru]

I've seen that article before; must be true, 'cause it's on the internet!

i did say "supposedly", I'm not 100% convinced nor put much weight in it.

 

"This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures." so he's admitting he sees warped rotors (run-out) but blames it on the material transfer. Which came first, the chicken or egg? Any run-out means the rotor is warped, regardless of how it occurred! It's a contradiction.

i can see the possibility of reading that without a contradiction..."this...results in the condition typically called run-out". he's referencing, metaphorically speaking...using words to explain something in lieu of their precise technical meaning. happens all the time in auto world. but it doesn't matter, it's just an article and not that important, the link can be deleted!

[1 Lucky Texan]

the paragraph just prior to the statement quoted has a list of presupposed conditions too.

 

I think also, there's a difference between 'thickness variation' and something shaped like a Pringles potato chip that would have the same thickness all around. (actual warpage)

 

I suspect, more often than not, pad deposition is causing pedal pulsation and probably other problems on road cars. Of COURSE, rotors (and wheels for that matter) can be installed incorrectly or be bad from the factory.

[presslab]

The only way you can really be positive, is to get a new set of rotors and check for run out before use. Use them as stated so that deposits form, check for run out again. Turn so you are only removing deposits not real metal and compare .

 

My thought is that the heat cycling is "relaxing" the grain structure in the cast iron, causing the warpage. So even if it had no run-out before use it could get some run-out after heat cycling. And then maybe this run-out will cause depositing of material, I don't know.

 

i did say "supposedly", I'm not 100% convinced nor put much weight in it.

 

i can see the possibility of reading that without a contradiction..."this...results in the condition typically called run-out". he's referencing, metaphorically speaking...using words to explain something in lieu of their precise technical meaning. happens all the time in auto world. but it doesn't matter, it's just an article and not that important, the link can be deleted!

 

Sorry I didn't mean anything against you for posting it.

 

Run-out is well defined terminology in metrology, although warpage could mean a lot of things I suppose. On a brake rotor two problems that I would consider warpage would be circular run-out (potato chip braking surface), and perpendicularity (dished braking surface). Mmm, it's making me hungry.

http://www.brownandsharpe.com/applications/intro-to-coordinate-metrology/geometric-dimensioning-and-tolerancing

 

I think also, there's a difference between 'thickness variation' and something shaped like a Pringles potato chip that would have the same thickness all around. (actual warpage)

 

Yeah that's a good point. Although the way I read Carroll's article is that he says the deposits cause hot spots which then lead to subsequent run-out. So in his mind he explains away even true run-out (not just thickness variation) as caused by these deposits. He also states these deposits are "more often not" visible.

 

So basically any unexplained warpage is caused by invisible deposits on the rotor. These deposits are caused by using the wrong pads, improper break-in, or stopping with superheated pads allowing them to transfer material. Hmm, all those things are the customer's fault! Oh, that's right, Stop-tech sells brakes so any complaints of warped rotors are not their fault. Makes perfect sense now.

 

We'll never get the true backstory from Carroll as he passed away 10 years ago.

[idosubaru]

well, i don't link to normally or put much into that article anyway so it's probably not helpful and better left out. glad you pointed it out. i was wondering why this guy is having issues with new components as well, I've had it happen before too.

 

Actually I just did - I also had rotor vibrations less than 20,000 miles after a brake job...wish I knew why. new pads and greased/maintained calipers/slides. I had to install a new rotor just a couple weeks ago.

 

maybe it's struts as someone mentioned, though that's kind of hard for me to imagine...though they are original and 200,000 miles although there are no notable symptoms (maybe I won't say that once i finally replace them and see how it's supposed to drive). LOL