Warped rotors, why?

[jseabolt]

For some odd reason, when I hit the brakes on my 2003 Baja, 78,000 miles, there is a shimmy in the steering wheel. I'm assuming the rotors are out of round perhaps?

 

I checked the pad depth at around 70,000 miles thinking the pads were about worn out because a few times when I hit the brakes I thought I heard brake squeal. I went ahead and bought a new set of pads.

 

I pulled the front and rear calipers off the passenger side. Well, when I measured the thickness of the pads compared to the new pads, they were only half worn. I think the new pads are 13mm and my original pads were like 6.5mm. So I put the calipers back on and took the new pads back. So my guess is the pads won't need to be replaced until I have about 140,000 miles on the car. Which is a far cry compared to my first car which was a 1981 Honda Prelude. On that car I was putting new pads on the front every 20,000 miles!

 

I am not hard on my brakes. I usually downshift and use the engine as a brake when going down hills, don't ride my brakes, etc.

 

Is this normal for rotors to warp like this? I'm assuming they got hot at some point. Or are they just out of round from normal usage? I wouldn't imagine they would get out of round if the brake pads are only half worn.

 

If I have them turned will they stay true or once warped they loose their temper and will warp again?

 

The shimmy is not too bad but I'm concerned this might wear out the wheel bearings over time. I've done front wheel drive wheel bearing replacements and it's not fun. I'd rather just bite the bullet and buy new rotors if I have to.

 

 

 

 

[idosubaru]

Yes the rotor is the cause of your symptoms.  I wouldn't call it normal, but it happens.

 

I've switched to high quality grease, not using cheap pads, check the slide pins often (when swapping on winter tires, rotating, etc), and replace brake pad clips usually once in the life of the vehicle.  Since i've started doing this I don't think I've had a rotor issue yet.  Living in the rust belt is hard on the slide pins and clips.  I'm not sure if that's coincidence or related - but i was having an occasional warped rotor before that.

 

Check all the brake pads - it's common for one pad in a caliper (not even both in the same caliper) to be warn significantly more.  Usually due to sticking caliper slide pins or sometimes rust/black build up on the pad clips causing the pad to push against, but not release from the rotor. 

 

Usually you can tell which rotor it is if you pay close attention and replacing in pairs is 100% pointless. 
Buy one rotor

Replace the side you think is the culprit
In the event you didn't guess correctly, install the used rotor you just removed on the other side since now you've "confirmed" it was the other side causing the vibrations. 

 

I used to have rotors turned all the time, shop across from my office does it, so it's easy.  I never noticed issues with turned rotors.

i don't know the efficacy of turned rotors but i think it would largely depend on driving conditions/use and isn't a huge concern.  

 

If you're replacing with aftermarkets and still have OEM rotors, I would probably keep the OEM rotors and turn them, they're probably materially higher compounds. 

 

2000+ Subarus have slide pin bushings - you can't use regular brake caliper grease on those, you need high quality silicon based grease like Sil Glyde or equivalent.  It's waaaaaay better product than the old school, commonly used Permatex green bottle stuff.   The bushings will swell with regular grease and stick or seize in the caliper pin bore.

[gbhrps]

jseabolt,

 

78 000 miles, but a 14 year old car, and I'm willing to bet that you've never changed the brake fluid and flushed the system. Most manufacturers want you to change the fluid every 4 years, others every two. Brake fluid absorbs water from the air and it starts rusting the brake lines and caliper bores and pistons on the inside.

 

Check your reservoir. If the fluid isn't clear, but amber to dark brown or black, your fluid has started to corrode the pistons in their bores, and most likely making them stick and not releasing properly when you release the brake pedal. It may cause the caliper to seize entirely. Then your rotors heat up because the pads never release completely, which can cause warping of the rotor.

[keith3267]

Before you do anything, try this.  Find a lonely road and do a fast (not lockup) stop from about 60 mph.  Actually let off the brakes at about 5 mph to prevent a hot spot from forming.  Then get back up to 60 and lightly test the brake.  If there is still a shimmy, repeat the fast stop and test again.

 

Most of the time, one or two hard stops will clear up the problem.  If it doesn't, then the rotors need to be checked for run out with a dial indicator.  I would test before machining or replacement.  But I'd say that 90% of the time, one or two hard stops solves the problem.

 

People who are easy on their brakes sometimes don't get the rotors hot enough to clean them off, but they do get hot enough for some of the binders from the pads to accumulate on the rotors.  The hard stops heats the rotors up enough to burn off the residues, but it won't "unwarp" the rotors if they are truly warped.

[idosubaru]

Most of the time, one or two hard stops will clear up the problem.

 

Are you serious? Never heard of this.

 

Brake fluid is unlikely to be the issue. People routinely drive 200,000 miles without changing fluid and never have issues. I'm not recommending that, I'm just saying the common automotive talk about hygroscopically induced caliper cancer is a far cry from real world situations of robust vehicles like Subarus. The difference between online tech talk and real world is huge. I wouldn't apply that to any other ndnifacturer as I'm not familiar with others, maybe it's more accurate amongst other companies, I wouldn't know. But not Subarus.

 

I've seen two Subarus leak fluid from compromised calipers/drum components. They were both rusted, frame rotting, ill maintained, sat for extended periods of time 3 digit Craigslist specials.

[jseabolt]

No I've never changed the brake fluid in my Subaru. I know DOT3 fluid turns black after a year or two but I figured if the reservoir cap is sealed, moisture should not enter the system.

 

I'll try the hard stop method. I am quite easy on my brakes. The car is a 5 speed so I never need to tap or ride the brakes going down a hill like with an automatic.  In fact unless I have to make a panic stop (someone in front of me slamming on their brakes) or an approaching traffic light changing while going faster than I should, I usually don't start braking until I'm doing 20 mph.

 

Although when going down hills in my Chevy van, I always gear it down into 3rd or 2nd on long hills to avoid riding the brakes.

 

This maybe apples to oranges but where I work we have these Hyster fork trucks with drum brakes and some people never hit the brakes (has a Monotrol accelerator) so eventually the brakes get out of adjustment and when I hit the brakes it will throw me forward. So I start at one end of the warehouse and back up tapping the brakes and this usually fixes it.

[somick]

No I've never changed the brake fluid in my Subaru. I know DOT3 fluid turns black after a year or two but I figured if the reservoir cap is sealed, moisture should not enter the system.

During braking the temperature will rise and the moisture will boil and turn into steam.  Steam's hydraulic characteristics are not what we need in the braking system.  The pedal may go down to the floor.

 

Changing the brake fluid is a cheap/inexpensive insurance.

 

Good luck,

Sam 

[idosubaru]

I figured if the reservoir cap is sealed, moisture should not enter the system.i

 

That's what happens in practice on average well maintained daily driven Subarus. That's why tons of people drive 200,000 miles and never have issues without ever changing brake fluid.

 

In theory brake fluid is hygroscopic, but how often that happens is miniscule and not usually in well maintained, average daily driven Subarus.

Of course changing it is a good idea - it's not the first place to think/consider for diagnosis of an existing issue - it's not going to fix your current issues.

[keith3267]

Are you serious? Never heard of this.

 

Very serious, you should try it sometime when ever you get brake shudder.  There are several conditions that can cause brake shudder, this only works for one of them.  But consider the cost of trying this first and its a no-brainer.

 

Modern disc brake systems are not sealed.  The old all drum systems were sealed.  The reason is that in the old drum brake systems, the brakes were mechanically adjusted for wear, so the brake fluid level remained fairly constant.

 

In a disc brake system, the adjustment for wear is simply moving brake fluid from the master cylinder to the calipers.  As the brakepads wear down, the caliper piston moves out to compensate (actually just doesn't move back as far when you let off the brakes) which enlarges the reservoir of fluid in the caliper.  There is a small vent in the cap of the master cylinder to let in air, otherwise a vacuum would form in the master cylinder and the brake pads would get sucked back to their original positionand soon the pedal travel would be so long that the brake would not work very well.

 

I flush my brake lines when ever I change my pads.  I never add fluid between pad changes because with most vehicles, the min line in the master cylinder corresponds to the pads being worn out.  When the fluid gets low, I inspect the brakes and unless there is a leak, the pads are always near their wear limit.

[CNY_Dave]

Could it be a rust ridge on the inner our outer edge of the pad swept area?

 

Doesn't take much rust to raise a whole lotta fuss.

[bratman2]

What Keith3267 is describing is common on Moto Guzzi Norge motorcycles. Us older farts buy them, they are fairly big and heavy, have awesome Brembo brakes that get lightly used. Then brake shudder shows up from uneven pad compound on the front discs. Don't ask me how I know. So he may have a point. If nothing else it would be easy to try it. I have resorted to using more front brake on my Norge and switching to a different pad compound. !

[1 Lucky Texan]

it isn't impossible for rotors to 'potato chip' just very, very unlikely on daily drivers.

 

as said, uneven pad deposition occurs from 2 things, light use or clamping down on hot brakes to wait for a train or a light. If bedding in procedures do not help - or the problem gets worse after a bed-in procedure, you probably need new rotors or have them machined. In an overheat situation, I've read that there can be a spot on the rotor that has a different temper and replacement is the best option.

 

If I haven't zoomed around enough to get on the brakes hard, I sometimes will feel a little brake judder coming on. I will make certain I have a road that will allow at least 1/2 mile for cool-down and, while maintaining 30-40mph, left foot 'drag' the brakes. That usually helps or cures the problem. I might repeat it if it hasn't cured the issue. The 3 times I went to a track event, I did a procedure beforehand more like the one described by Keith above - just to make sure i had good , smooth rotors.

 

check here (other good reading there too); http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

Edited November 29, 2016 by 1 Lucky Texan

[jseabolt]

Changing brake fluid. In theory this makes sense but here is my problem.

 

When you "flush" the brake system, all you are doing is putting fresh fluid in the reservoir, lines and hoses. When you open the bleeder screws, the old fluid is still left in the caliper because the bleeder screw and hose fitting are usually located at the top. I've never seen a brake hose mounted to the bottom of a caliper so new flush can actually pushes the old fluid out. 

 

The only way I could think of to remove the old fluid is to remove the caliper from the mounting bracket, remove the bleeder screw and turn the caliper up side down and let the old fluid drain out. Then you have to consider any funk buildup in the system is going to settle to the bottom of the caliper. 

 

So how are you going to get that stuff out unless you extract the piston? I guess you could shoot some brake cleaner through the bleeder screw hole and clean it out that way but I don't know if this stuff would harm the seals or not.

 

The last brake repair I did was on my 98 Chevy van a few months ago. One day I hit the brakes and heard this scrubbing sound. HMMM? Sounds like the pads are wore. But modern cars should have squealers that rub against the rotor before it get's metal to metal.

 

So I pulled the caliper like most cars, two Allen head bolts with sleeves that surround the bolts. I discovered the inside pad was almost down to the metal but the outer pad still had about 1/8" friction material and the squealers were bent! 

 

When I remove the other caliper, I noticed that the sleeves that the bolts go through came out with them. But the sleeves on the offending wheel were still stuck in the caliper. I sprayed some PB baster around them and worked them out with a pair of vice grips. It looks like the sleeves on the offending wheel were zinc plated and the ends that go into the caliper had rusted. Where the sleeves on the other caliper are aluminum.

 

I know you can buy new sleeves but I just sanded the rusted ends down, greased them with anti-seize compound and turned them around backwards so the non rusted ends are now in the caliper.

 

I haven't had any issues.

 

However one difference between my van and my Subaru is, there is no vibration when I hit the brakes but rather they pulsate at low speeds. I think there the rotors have developed hot spots at some time or another and that is what I am feeling.

[keith3267]

jseabolt.  Some people, and car enthusiasts who work on their own cars are the worse, are just way too anal about getting every last drop of old fluid out of their car when doing a fluid exchange.  This includes oil, ATF, PS fluid, brake fluid and coolant.  It isn't necessary.  I know people that leave the drain plug out of the engine for 24 hours when doing an oil change.

 

I do a brake flush when I change the pads.  The caliper pistons are drawn as far back into the cylinder as they can go so any residual brake fluid is minimal.  After the flush, the residual old fluid will migrate into the fresh fluid so worse case, it is like fresh brake fluid with a 1000 miles on it.

 

If I get 90% of the old fluid out and replaced with new, I am happy.  In the case of transmissions, I believe in drain and fill, starting early and doing it frequently so it never gets contaminated enough to do any damage.

[CNY_Dave]

 

jseabolt.    I know people that leave the drain plug out of the engine for 24 hours when doing an oil change.

 

.

 

Don't underestimate the benefits of a nice, dry start!

 

:o :o :o

[bstone]

I had the same issue as the OP. Turns out my calipers were original and just rotting away. I replaced them, put in new fluid, bled the brakes, and now braking is smooth and so is rotor wear.

[1997reduxe]

yeah do your self a favor and get good new rotors even powerstop, but better oem, and some good rebuilt calipers and nice pads, replace it all and the fluid.

i mean if im reading correctly these rotors are 13 years old? or if they were replaced may have been an off brand?

the cause is right in your avatar pic of your car: snow.

i used to live in pennsylvania and aside from the salt the winter is a killer, youve had 13 of them.

i figured out over time especially after the rotors are older and thinner not up to original par, that say youre driving along on a trip and they get heated off and on, at least theyre pretty warm, then you hit a big slushy patch, then they dry off and heat up with some braking, then more slush. maybe this happens 100 200 times on a good snowy day? thats when a lot of the warping happens i think.

Edited December 4, 2016 by 1997reduxe