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Warped rotors - who's experienced this?


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36 replies to this topic

#1 GeneralDisorder

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Posted 27 November 2009 - 12:05 AM

I don't tend to experience this on my cars but after having bought a few Legacy's over the years I've noticed a tendancy for them to warp rotors. I've replaced:

'94 Legacy GT Wagon: warped front rotors @ 165k.

'91 Legacy Turbo SS: warped rear rotors (vented) @ 160k.

I now have another '91 Legacy sedan that likely has warped rear's @ 215k and it's had this problem before. I'll put the dial indicator on it tomorrow and find out for sure, but according to the maintenance reccords the rears have been turned before for this issue and were "too thin to take a third turn!" according to the reccords from the dealer. I put all new pads on today and only then could I tell the rotors were warped as it was down to the backing plates on the old pads.

What's the deal with these? Is this a pretty consistent issue? I've never had a problem with rotors warping on EA's - to the point that I almost never actually replaced a set - just pads and sometimes have them turned. With all this warping though I would be leary of taking material off an already thin design

GD

Edited by GeneralDisorder, 27 November 2009 - 12:07 AM.


#2 Durania

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Posted 27 November 2009 - 12:44 AM

My 2000 2.5RS had warped rotors when I bought it at 95k. I put two new front rotors on it soon after buying it along with pads and still had a violent front end vibration. I finally ended up just having to bite the bullet and have all 4 rotors turned. It was a completely different vehicle after that.

#3 GeneralDisorder

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Posted 27 November 2009 - 12:51 AM

I replaced the front's on my Turbo only to find no change to vibration (which really seemed like a front rotor kind of vibration), but it was the rear's all along. It seems to be the same with this '91 I'm working on now - the vibration seems like it's from the front but with the maintenance history and what I know from my turbo I'm betting it's actually the rear's. I'm going to actually check tomorrow with a dial indicator.

GD

#4 heartless

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Posted 27 November 2009 - 07:07 AM

Now you have me thinking...hmmm

have a vibration on my 90 LS wagon, not violent, but definitely noticable.
Front end was completely redone recently - new tierod ends, ball joints struts, alignment, etc...was thinking i needed to rotate tires (which i will probably do anyway) but now I cant help but wonder....

Put new pads on all around last year, but still has the same rotors...:confused:

#5 grossgary

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Posted 27 November 2009 - 07:10 AM

Yep - EJ's go through rotors more than old school stuff. Like you, I never bother with rotors on XT6's. On EJ's i'm starting to have them turned or buy new rotors much more often.

Heavier? More HP?

#6 89Ru

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Posted 27 November 2009 - 08:37 AM

What happens when lugs are loosened with full weight on the wheel? Can this warp a rotor against the pads?

What causes warping? Uneven heat transfer to the wheel...rapid cooling...do alloy wheels have an effect on this?

Bad wheel bearings can contribute to overall wheel temp, I suppose just one hard braking with a hot wheel could warp a rotor.

Just wondering if there is any correlation between EJ's vs. EA's (heavier, alloy wheels, tendency for bad wheel bearings...)

In my limited experience (one EA, two EJs) the only one I've had rotor problems with is the EA...front rotors have been warped its *entire* life. Even new rotors warped soon after installation. I've just learned to live with it and figured early in its life the hub warped somehow...

Just read that Endwrench mentions marking the rotor and hub to match at reinstall...I'll be doing this from now on.

Tire guy...Impact wrench...hub rust...oh my!

#7 Allpar Mod

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Posted 27 November 2009 - 09:16 AM

Aside from use, the most common cause of warped rotors are overtightening with impact guns. Loosening the wheels should have no effect on the rotors.

All rotors will show some signs of warpage eventually from the constant heat transfer that occurs. Disc brake rotors always are in contact with the pad so there is constantly heat in place. This becomes greater during braking, significantly during hard braking. The repeated heating and cooling of metals cause warpage.

The quality of the brake parts will have a direct correlation with warpage, mostly how bad and how soon.

#8 grossgary

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Posted 27 November 2009 - 10:03 AM

the most common cause of warped rotors are overtightening with impact guns. Loosening the wheels should have no effect on the rotors.

All rotors will show some signs of warpage eventually from the constant heat transfer that occurs. Disc brake rotors always are in contact with the pad so there is constantly heat in place. This becomes greater during braking, significantly during hard braking. The repeated heating and cooling of metals cause warpage.

The quality of the brake parts will have a direct correlation with warpage, mostly how bad and how soon.

Most of us are aware of this, but this it just general auto information, not anything specific to the question concerning EA/EJ differences.

Older vehicles are more poorly maintained...grease, caliper boots, seized calipers, not babied like newer cars, cheaper brake parts are used....but even still have fewer warped rotors?

#9 frogstar7055

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Posted 27 November 2009 - 12:26 PM

Tighten lug nuts with a torque wrench to spec.
Over tightening with lug wrench or impact WILL cause rotors to warp over a very short period of time.

#10 davebugs

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Posted 27 November 2009 - 12:39 PM

Quality of rotors VARIES WIDELY.

The ultimate "you get what you pay for".

I just paid 80 each for my DD and I could have gotten the cheapest for 20.

Typically the pads last, and the rotors crap out on my DD. OEM rotors last 100k, cheap aftermarkets last 20k, decent aftermarkets last 60k. I went OEM this time. Infact come to think of it they basically cost 1.00 for each 1k I get out of them. And I'm only talking rotors - so given everything works (no caliper hanging up), is lubed (slide pins and such), it just depends how much you like doing brake jobs.

If over 100k miles the cost is literally the same (actually it'd be more when you figure the pads with the rotors as I do) and one way I get to do it one time, and the other 5 times - guess which one I'm gonna choose?

YMMV

#11 GeneralDisorder

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Posted 27 November 2009 - 05:13 PM

I put the dial indicator on the rotors (bolted down to the hub with all 5 lug nuts), and the runout is between .002" and .0025" on all 4 rotors.

Per my Haynes manual, the acceptable max runout is .0039" so I'm within the specs here.

It doesn't seem to vibrate till the brakes heat up - are they just warping under the heat load because they are so thin - having been turned at least twice by the dealer?

Or is the Haynes manual innacurate or the spec too wide?

All pads are new - all slide pins greased. Lug nuts torqued to spec.

??!?

GD

Edited by GeneralDisorder, 28 November 2009 - 01:44 PM.


#12 grossgary

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Posted 27 November 2009 - 06:23 PM

I've definitely had rotors that vibrate only when heated. I've had some that would only vibrate coming off of highway exit ramps at high speed, but otherwise felt normal. Fairly good vibrating too, not just a light pulsing.

#13 GeneralDisorder

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Posted 27 November 2009 - 06:45 PM

I've had some that would only vibrate coming off of highway exit ramps at high speed.


That's EXACTLY what these do. They don't even seem to do it on side-streets *after* getting off the freeway - but that off-ramp makes them SING. The wheel vibrates a good inch in either direction.

On the one's that have done this was it the front's that were to blame or the rear's? I had a constant pulse on my turbo that was the rear's.....

The rotor's don't give me any clue - they are all about the same runout wise..... it *feels* like maybe it's from the front's but I can't be sure - my turbo felt like the front's too but after changing them it made zero difference.

GD

#14 grossgary

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Posted 27 November 2009 - 08:28 PM

On the one's that have done this was it the front's that were to blame or the rear's?

Oh man R you're taxing my memory, it's been awhile and I can't even recall which vehicles did it, but I know I distinctly remember it like you said - it stood out how bad it was in specific instances and not noticeable any time else.

I'm inclined to think the fronts...either because i'm blindly assuming it, have a faint memory, or seems those would get the hottest in that situation.

I would think you have one of those temperature guns? Those things are awesome, get one if not, you'll start using it for all sorts of stuff you couldn't think of before having one. Next time you go down a ramp hit them all and see if temps tell you anything. I'm sure you know, the rotor temps are all over the place depending how/where you hit them. If one is that bad I would think it would stand out, but I just got my temp gun this year and never used it in those situations.

#15 GeneralDisorder

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Posted 27 November 2009 - 08:49 PM

Yeah I do have one - I know just the off-ramp to try that on too. I wonder if I could rig up a K type thermocouple for my DMM to sit just a few thousanths from the rotor surface and then run that into the cabin :eek:

Might be a mute point - I just tore the passenger side front apart for an axle - bad DOJ and blown boot. Original axle to the car. I have all the maintenance reccords - no mention of axles except the tech notes they were "making noise but boots intact" at around 160k. Green painted joints too so they are OEM. Axles have gone 215k and the driver's side still has intact boots!

I may do front rotors while I'm replaceing that DOJ.

Looks like the wheel bearing on that side wants replacing too - sounds dry and I knew I heard some wheel bearing while I was on the freeway :rolleyes:

GD

Edited by GeneralDisorder, 27 November 2009 - 08:51 PM.


#16 grossgary

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Posted 27 November 2009 - 10:50 PM

MORE EJ wheel bearing fun!

I have another rear one too, this is getting really old!

#17 Allpar Mod

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Posted 28 November 2009 - 12:35 PM

GD queried....

Or is the Haynes manual innacurate or the spec too wide?


I have had experience with Haynes manuals for vehicles other than Soobs and I have found inaccuracies, blatent ones also. It wouldn't surprise me if they were wrong about the runout.

I know I was making generalities rather than addressing specific Subaru issues. They are still pertinent to our cars.

If a rotor has been cut multiple times, it wouldn't surprise me if it needs replaced. You have to remember that every time that you cut metal off, there is a weakening of the rotor as a whole.

#18 grossgary

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Posted 28 November 2009 - 12:49 PM

Is the runoout/tolerances, is that something they can look up, standardized or marked on the inside of the rotor - aren't there numbers in there? I often take a stock of rotors to the shop across the street from my office - I just drop off a stock of rotors and never tell them what they are from and they turn them. Not sure what numbers they're using to test and turn?

Nearly every post offering suggestions is still ignoring the question and point of this thread. Newer stuff having more warped rotors than older. That's the issue he's referring too, not all the possible idiosyncrasies of rotors, he's well aware of that.

These suggestions only underline the entire point of him starting this thread, because an older car should have worse conditions....older, cheaper parts, maintained worse, other poorly maintained systems, etc.. older cars should be having more rotor issues.

#19 GeneralDisorder

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Posted 28 November 2009 - 01:43 PM

Yeah - I'm mostly concerned with why this is occuring more often with the EJ brake design and if anyone has found what's causing it/how to avoid it.

It's obviously not a rotor quality issue - the ones I've replaced have all been OEM rotor's. And they may have lasted a good long time - 100k perhaps. But with the EA stuff they last FOREVER. I've never replaced a rotor on an EA81 or EA82 for warpage. They last right up till they are too thin and very often beyond. To the grave of the car. They may be grooved, worn, etc - but they still stop the car adequately and I haven't had a great desire to replace any of them.

Some may consider it "normal" for rotors to warp after a time - I'm not of that camp. I consider that it's possible to design them to NEVER warp and that's what I would like if I can get it.

Gary - they are marked for minimum thickness on the inside of the casting. Mine are marked 22mm minimum thickness and they are at a little over 23mm currently as measured with my micrometer. There is a definite ridge where they have worn since last being turned and I'm assuming they were turned when the pads were last replaced as they were all within mm's of the backing plates.

GD

#20 Allpar Mod

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Posted 28 November 2009 - 07:18 PM

It's entirely possible that a particular braking system could put demands on the rotors that would promote warping. This might be the specific issue that you are concerned with. I apologize if it sounded like I was ignoring the root question, but I've never heard of a specific issue with brake rotors in any particular year range or product line within the Subaru marque. The Jeeps we've owned, yes. Not the Soobs. That's not beyond the realm of possibility. Personally, I never owned any car or light truck that didn't ever have a warped rotor or two. That's both foreign and domestic. I've owned my share over the years. I do have to admit that the ones that had the least issues with this were the three Loyales we owned, '89, '90, & '91.

Let me ask you guys this....is it possible that this could be a climactic thing? By this, I mean that rotor warpage could be due to the climate in the part of the country one is in? reason why I ask this is I just remembered a recall on our Jeep rotors for premature wear in climates that use road de-icing substances. The recall was model year specific so it wouldn't be hard to imagine a similar problem within a specific year range of any other vehicle.

Just throwing something out there...a possible reason, maybe.

#21 GeneralDisorder

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Posted 28 November 2009 - 08:48 PM

Let me ask you guys this....is it possible that this could be a climactic thing? By this, I mean that rotor warpage could be due to the climate in the part of the country one is in? reason why I ask this is I just remembered a recall on our Jeep rotors for premature wear in climates that use road de-icing substances. The recall was model year specific so it wouldn't be hard to imagine a similar problem within a specific year range of any other vehicle.

Just throwing something out there...a possible reason, maybe.


Hhhhmmm - that's interesting as we use a lot of that junk out here. That's all we use actually - no salt in OR. Just gravel and chems.

What was it about the jeep rotors? That's got to be some serious de-icing chems to break down a cast rotor..... what the hell!?

GD

#22 abog

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Posted 28 November 2009 - 09:29 PM

Hey guys, as I remember the main difference in the rotors on EJ series cars and on EA cars are the way they are retained, with the EA cars the rotors are bolted in place to the hubs and do not rely on the wheel studs to locate them. The EJ series are dependent on the studs and nuts. You will find that a slight variation in wheel torque on an EJ car will usually show a large variation in assembly run out. At the dealership during the first couple of years of EJ cars we had a terrible problem with brake pulsation. After much experimenting and trial and error we settled on only using the factory recommended on the car brake lathe to turn any EJ rotors. This set up cut the rotor on the hub, with the wheel nuts torqued to spec. While not perfect this method significantly reduced the short term reoccurance of the pulsation. Basically what is happening is as the wheel is torqued the run out of the hub changes dramatically and will be very different than just the hub alone. I have found that alloy wheels change the run out more than the steel wheels. So by turning the rotors as they will run on the car they are less likely to pulse. The EA series didn't have as dramatic a change because they were attatched in such a way that they remained moreconsistant regardless of wheel torque.

#23 GeneralDisorder

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Posted 28 November 2009 - 10:21 PM

Interesting - I did check the run-out with the rotors bolted down to the hubs but as noted this only occurs after the rotors have heated up so.....

What's was the conclusion on this only occuring when heated? I can drive around town and it never has an issue.

And it does make some sense - the EA hubs are bolted seperately to the wheel and to the disc so no changes in wheel torque can affect the EA rotor's.

Could it be that the wheels and/or hub are not true and sandwitching the rotor between them causes them to warp when they get hot?

GD

Edited by GeneralDisorder, 28 November 2009 - 10:25 PM.


#24 grossgary

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Posted 28 November 2009 - 10:45 PM

Don't know the conclusion GD, but on the ones I've seen they'll continue to that for a long time and not "get worse" so to speak. Wonder what cleaning up the hub and wheels would do - get rid of corrosion and spots?

#25 GeneralDisorder

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Posted 28 November 2009 - 11:09 PM

Now that I'm really giving it some thought and all - I wonder if this tendancy to warp rotors plays into the overall lack of bearing life on the EJ's - the wheel bearings would be pulsating with the rotors.....

What a mess.

GD




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