Anyone else warp rotors ALL the time?
 

I seem to be changing rotors every year. Last time I made sure to rebuild the front calipers in case they were binding. No go. Rotors are warped. Front bearings are good and adjusted - checked today. Tie rods and ball joints are good. Struts less than a year old. I know, I know, there's a school of thought that says rotors don't warp but rather material builds up on the disc. But these are warped.

I think winter had something to do with it. From -35 to operating temp and then back to -35 on an average day may be doing it. Thoughts?

Anyone have good things to say about Frozen Rotors for our cars? This is driving me nuts.

I've heard about two things -

1) in the 951's there are separate air intakes going direct to the rotors that people convert to 944 use, and

2) titanium sheets that sit between the pads and calipers to help dissipate the heat.

These aside from the regular drilled/slotted rotor designs, both also to help dissipate heat.

Guess you're in a 944? Turbo? You didn't say, nor did you say your rotor setup, which I'm assuming is stock.

Make sure your lug nuts are torqued evenly to specs. And greasing the caliper slide rails won't hurt either. Are the rotors seated properly against the hub? If there is dirt between the rotors and the hub the rotor will not turn true and will warp. Are these new rotors that have not been turned before? A older thin rotor will not dissipate heat as well as a new rotor and could overheat and warp. What is your driving style? If you are locking up all four you may have the installation correct but may just be overheating them.

Good luck!

how are you determining that they are warped? which rotors are you using, and which pads?

I'm no expert, but for my own interest, I would like to know what style of driving was done to lead to this condition. I can see you are in Alberta, but I think it would also help to know how the car was stored, if you had hot rotors and then drove through one of those flood-level puddles one summer day, if this happens all of a sudden or takes a year, when you notice the warpage, etc... AH I see you added detail just this minute, thanks...

@ChrisRL - regular rotors on NA early 944. I did try the beefier 911 rotors, cross-drilled, and the car ate those too!

@djnolan - new rotors (not machined). Greased caliper on rebuild as suggested. Lug nuts? Maybe. I change wheels twice a year and check bearings every time I do. Dirt between hub and rotor unlikely. I'm pretty careful. Still, I'll be more careful next time.

I drive all highway miles during the week. Sometimes very fast, yes, but I don't mash the brakes, don't ride them, and try not to keep the pedal down when at stop signs. I'd say they get plenty of opportunity to cool evenly. Rarely do I abuse the car. Which is not to say I don't thrash it from time to time. They respond well to being driven hard. But mostly I just tool along the highway.

Pads are Metal Master, i believe. Rotors are Brembo. Our host had a great deal on them.

@ Bukowski - car doesn't get stored. I drive I almost every day, regardless of the weather. It does sit outside in the driveway overnight. Big deal - lots of cars do.

metal masters are a terrific pad, but they do need some work every once in awhile...at least in the applications I've used them for.

Bedding Your Brake Pads in the RIGHT Way | Corner Balance

good instructions to follow

Ah yes. I bedded the pads. 8 to 10 braking cycles from 85 to 25 mph. Followed by a drive with no braking to cool them. Can't verify 400 degrees.

I must have missed something somewhere...

Any thoughts on the cryo rotors?

Thanks for the replies, guys. Much appreciated - as always.

I think this may have overheated a stock rotor. I bedded the pads. 8 to 10 braking cycles from 85 to 25 mph. Maybe work up to this gradually. Also make sure your lug nuts are torqued, so the rotors dissipate heat evenly to the hub, and are seated flat.

I'm fairly convinced one of the rotors on my wife's Forester warped due to metallurgy issues. I had replaced the OEM rotors with Brembo at one point, and the brake pulsation (just from one rotor) kept getting worse over the course of a year. If parts aren't properly stress relieved during manufacturing they can continue to relieve stresses built up during the process especially when subjected to heat cycles. You may want to try another manufacturer. I was surprised it happened with a Brembo, but no mfg. is perfect.

Edit, I'd also suggest you go with a cryo treated rotor. This is a common way to minimize distortion in mfg'd item when conditions are severe. The process of putting the parts in liquid nitrogen (at least I think that's what we used) causes the grain structure to be very fine. And in the process of the grain structure recrystallizing the new crystalline structure is not only a lot more stress free, but will resist warpage from extreme heat cycles.

Perhaps you're getting too much cooling out of your rotors?

The car was designed around an ideal operating temperature of literally 100 F warmer. Considering the rotor is pretty much a fan, things cool off a lot faster at those temps, and the faster you drive the more cooling you get.

The first thing I'd try would be to block off the openings in the backing plate.

^ That's an interesting take on things.

@ djnolan - my bad, then, for overheating them right out of the gate.

@ MB968 - alright then. I'm going to try a set of cryos on the front, but given the advice here I'm going to take some extra steps on the install.

I'll post results too, and my process, and maybe 8 months from now I'll be singing a different song.

that bedding procedure is not enough to overheat the combo he is running

how long after your intial break in are you noticing the pulsation? mileage wise?

6 to 7 months. Say... 8 to 10K kilometers. Seems to happen in the spring, which is why I suspect winter extremes.

I'd say it's the temperature there, or another problem in the hub rotor wheel assembly.
My rotors are still good since late 2005, just did first pad change and all is fine here

We'd have to see the rotors, if they are actually worn, actually warped, etc. I have had some issues with pitting on the rotors on my Audi, which I think were from poor metallurgy and use/wear. This seems to cause a brake shudder when the rotors are hot, but they are OK when cold. I have never had problems with the Zimmerman rotors I use on the P-cars. I like Metal Master pads (for the street) also.

Before the Audi rotors got pitted I had to re-bed the pads from time to time with a few hard stops. The rotors at this point are close to the wear limit but IMO they should not have started acting up like this. I have not found a record of the purchase (probably 4-5 years ago.)

There are a lot of cheap rotors on the market now and it is possible the cheap ones are kinda crappy.

rotors almost NEVER warp. it is incredibly uncommon. in over 30 years of doing this, i have seen exactly 2 warped rotors. all others were claimed to be warped, but actually is was just deposits. if they are truly warped, you will be able to measure it with a run-out gauge very easily.

see the stoptech site on this. it is very informative. it also gives the correct bedding procedure, which is not what you are doing, and varies a bit, depending on the type of pad.

i would never run cryo on a car i wanted to drive hard. it reduces braking capability and increases braking distance (that's why none of them show braking distances). it does make rotors last longer though, which is what they advertise, so for a street car, this might not be a horrible thing.

as for the problem, i would look carefully and measure the calipers. if they are not seating squarely, and putting the pads exactly parallel, you could be creating hot spots very easily.

are you changing the pads every time you change the rotors? what pads are you using?

Do you have the notches on brake pistons angled properly?

Two of my recent vehicles have had warped rotors; runout was well outside the max. limit on both. On my 3000 GT Vr-4, warped rotors are a common issue; mostly on earlier models, though mine was on a '97 which has much larger rotors from the get go. It shouldn't have had the issue, but it did. I agree warped rotors isn't common, but it does happen. I've had 3 or 4 cases over my car days.

As to coefficient of friction, even though the cof for the steel will be reduced by the cryo treatement, the change will be insignificant compared to the combo of the brake pad and the rotor (i.e. the cof of the pad >> rotor), especially as regards to adherent friction which is the main player for perf. pads.

Check out the website at
http://stoptech.com/technical-support/technical-white-papers/bed-in-theory-definitions-and-procedures/brake-pad-bed-in

The article gives an easily understandable writeup on abrasive vs adherent friction and the role that bedding-in plays to make sure the layer of pad material that gets transferred to the rotor to insure max. friction/stopping. The article also covers rotor warpage, as well as unevenness of the transfer layer of pad material that can also cause unevenness in braking as mentioned by Flash.

Check the runout of your rotor to make sure you are dealing with the correct cause.