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Old 12-09-2018, 05:28 PM   #1
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One rotor much hotter than other 3 - cause of vibrations?

Hey guys,

As many of you know, I have been trying to track down this annoying vibration / wobble that I've been experiencing through my steering wheel for past year or so. Today, another forum member was generous enough to let me swap wheels with him to see if that was the case, but the problem persists. However, when I was replacing the wheels after the test drive, I noticed that my driver side front rotor was a good bit hotter than the other three. When I got home, I used my IR thermometer and confirmed - all 3 were between 85 and 95 degrees F and the driver left was at 115-120 F depending on the part of the rotor I pointing the thermometer at. Could this be responsible for the vibration and wobble? Would it be a warped rotor issue? Unbalanced rotor? Sticking caliper? What's the best way to check for these?

In case anyone asks, the following have been done already in hope of figuring this out and have not solved the issue:

Tie Rods Inner (L+R)
Tie Rods Outer (L+R)
Drop Links (Front)
Struts (All 4) + Mounts/Bearings
Lower Control Arms (All 4)
Front Track Arms (L+R)
Rear Trailing Arms (L+R)
Wheel Bearings
Tires (All 4)
Sway Bar Bushings (All 4)
Alignment (Thrice)
Wheel Balancing (5 times and counting...)

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Old 12-09-2018, 06:54 PM   #2
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Have you measured the rotors for thickness? If the rotors are warped, you should feel it at almost any speed with your foot on the brake. Does it pull that way, when you step on the brakes? I don't remember from previous posts, what is your brake service history?
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Old 12-09-2018, 07:28 PM   #3
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Here's a question...does the frequency of the vibration increase as the speed of the car increases. Asking b/c as the rotational speed of the wheel increases the time between the peaks and valleys of a warped rotor passing by the brake pads should decrease thereby leading to an increase in the frequency of the vibration.

Just a guess on my part of how the physics of a warped rotor translates into the feel in the steering wheel. My experience with an unbalanced tire suggests things could be more complicated in that I've felt stronger vibrations at speed.
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Old 12-09-2018, 07:49 PM   #4
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I like the idea of the rolling road test. Also, have you checked the front wheel bearings? My $0.02
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Old 12-09-2018, 09:04 PM   #5
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You have been extremely patient over this, good on ya! The hot rotor is interesting. Don't know what year or system you have, but the ABS can activate either brake independently on the front on all years if a difference in rotational speed is detected and is usually a series of pulsations.. You might want to inspect your wheel speed sensors.
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Old 12-09-2018, 09:04 PM   #6
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Have you measured the rotors for thickness? If the rotors are warped, you should feel it at almost any speed with your foot on the brake. Does it pull that way, when you step on the brakes? I don't remember from previous posts, what is your brake service history?
I have not measure the rotors yet, but that is on my list now. It does not vibrate any more when I touch the brake, but the car does pull to the left when I accelerate at a low speed or even letting the car roll on a decline.

I bought the car at 76k and it is at 88k, I have not done anything to the brakes during that time.
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Old 12-09-2018, 09:09 PM   #7
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Here's a question...does the frequency of the vibration increase as the speed of the car increases. Asking b/c as the rotational speed of the wheel increases the time between the peaks and valleys of a warped rotor passing by the brake pads should decrease thereby leading to an increase in the frequency of the vibration.

Just a guess on my part of how the physics of a warped rotor translates into the feel in the steering wheel. My experience with an unbalanced tire suggests things could be more complicated in that I've felt stronger vibrations at speed.
Yes, the vibration does the worse at speed - I took her up to 85 or so on my way home today and the vibration was at a higher frequency. Thank you again!
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Old 12-09-2018, 09:10 PM   #8
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I like the idea of the rolling road test. Also, have you checked the front wheel bearings? My $0.02
I replaced the front wheel bearings about 500 miles ago - did not make much of a difference. Haven't checked the rear bearings with the rotor off, but the wheels do not move at all at both 9&3 and 12&6. Can you explain what you mean by rolling road test?

Last edited by speedyspaghetti; 12-09-2018 at 09:38 PM.
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Old 12-09-2018, 09:25 PM   #9
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Originally Posted by speedyspaghetti View Post
I replace the front wheel bearings about 500 miles ago - did not make much of a difference. Haven't checked the rear bearings with the rotor off, but the wheels do not move at all at both 9&3 and 12&6. Can you explain what you mean by rolling road test?
Again don't know what model or year you have, but the wheel bearings on some years have the speed sender as part of the bearing and need to be installed correctly.
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Old 12-09-2018, 09:37 PM   #10
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Again don't know what model or year you have, but the wheel bearings on some years have the speed sender as part of the bearing and need to be installed correctly.
It's a 2002 S - it does not have PASM or TC, so I don't know if that has anything to do with it.

In regards to your other reply - thanks haha... it has been quite the journey. There have been times when I have wanted to just sell the car and maybe move onto a 60s Mustang to restore or an S2000 as an alternative to the Boxster... but I just love this car too much and I know how amazing it is when it is functioning properly... I don't want to give up on it yet.

As for the speed sensor - what could be tripping the ABS come on so frequently? Is there a way to check the speed sensor? When I replace the bearings, I did not notice any sort of sensor attached to them.
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Old 12-09-2018, 09:49 PM   #11
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On your front and rear uprights there are two connectors, one is the brake pad wear sensor. The other is the speed sensor. You remove one bolt and pull the sensor out. make sure the hole the sensor inserts into is clean and you can see the reluctor rotating inside as you rotate the wheel. Also the sensor is magnetic and can become fouled by ferrous particles. Attached has the speed sensor. Usually recommended to remove while doing wheel bearings.

https://www.pelicanparts.com/catalog/SuperCat/1050/POR_1050_BRKHYD_pg4.htm#item17

Last edited by 911monty; 12-09-2018 at 09:59 PM.
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Old 12-09-2018, 10:16 PM   #12
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On your front and rear uprights there are two connectors, one is the brake pad wear sensor. The other is the speed sensor. You remove one bolt and pull the sensor out. make sure the hole the sensor inserts into is clean and you can see the reluctor rotating inside as you rotate the wheel. Also the sensor is magnetic and can become fouled by ferrous particles. Attached has the speed sensor. Usually recommended to remove while doing wheel bearings.

https://www.pelicanparts.com/catalog/SuperCat/1050/POR_1050_BRKHYD_pg4.htm#item17
Ah gotcha - yeah I had that removed when I did the bearing because I had to pull the caliper to get access and I undid this to get my wrench in there. Is it possible that it became faulty in some other way? Would it give a code?
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Old 12-10-2018, 06:58 AM   #13
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Don't ignore the calipers! When I had exactly the same problem on my Mercedes CLK it wasn't the rotors, but it was sticking calipers. The wheels were getting so hot that the plastic caps on the valve stems partially melted! A set of rebuilt calipers fixed the problem.
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Last edited by Anker; 12-10-2018 at 02:27 PM.
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Old 12-10-2018, 09:09 AM   #14
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Don't ignore the calipers! When I had exactly the same problem on my Mercedes CLK it wasn't the rotors, but it was sticking calipers. The wheels were getting so how that the plastic caps on the valve stems partially melted! A set of rebuilt calipers fixed the problem.
Ok, this is promising. Did you feel any impact on the steering of your car when you had this issue? Is it possible to do this myself with a caliper rebuild kit? Or would it be better to just buy a rebuilt set?
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Old 12-10-2018, 12:02 PM   #15
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Don't ignore the calipers!
If it has been sticking long enough, that particular pad will be 'thinner' [QUOTE]

PS: I meant to say that the pad will be thinner than the pad on the opposite wheel (but same position)


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Last edited by Gilles; 12-10-2018 at 09:11 PM.
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Old 12-10-2018, 12:42 PM   #16
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+ 1..

Not sure about the vibration but pretty sure about the overheated rotor..

PS: If it has been sticking long enough, that particular pad will be 'thinner' but once I removed the piston and clean it (polished)
with steel wool and replaced the seals = no more sticking caliper
Fingers crossed...hopefully this is the issue. I'm probably due for new rotors anyway, so I'll probably replace the front rotors + pads, even if the caliper is the issue here.
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Old 12-10-2018, 12:45 PM   #17
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Ok, this is promising. Did you feel any impact on the steering of your car when you had this issue? Is it possible to do this myself with a caliper rebuild kit? Or would it be better to just buy a rebuilt set?
Whoa - Hold on a minute...

You've already thrown a ton of $$ and parts / labor chasing this issue to no resolve. Reputable shops dissuade this behavior... the rest do not and keep going until your wallet says otherwise. If you've been directing them what to R&R that's one thing... If they've been leading the money parade I'd spend time learning to DIY or at the very least find a better shop.

Now, pull the wheel and inspect the caliper, pads and rotors to see if issue is there before ordering anything else. Otherwise you'll continue this expensive madness.

Post pics here if you need help.

Good luck
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Old 12-10-2018, 01:12 PM   #18
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Whoa - Hold on a minute...

You've already thrown a ton of $$ and parts / labor chasing this issue to no resolve. Reputable shops dissuade this behavior... the rest do not and keep going until your wallet says otherwise. If you've been directing them what to R&R that's one thing... If they've been leading the money parade I'd spend time learning to DIY or at the very least find a better shop.

Now, pull the wheel and inspect the caliper, pads and rotors to see if issue is there before ordering anything else. Otherwise you'll continue this expensive madness.

Post pics here if you need help.

Good luck
The shops I've gone to, besides the ones that suggest wheel balancing/alignment/new tires have all said "oh well, it's not that noticeable" and give me a list of things it could be without being definitive about anything. All of thats part I replaced I did myself, so definitely saved some labor costs, although my sanity may have been affected You're right though - I'll get the car up on jack stands soon and see if I can take a deeper look at the brake assembly. I bled the system recently, which I imagine would've helped with the caliper, but I guess if it is stuck, bleeding would not "unstick" it.
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Old 12-10-2018, 01:46 PM   #19
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Not on my Boxster, but my old Forester...I had a sticking calliper that wouldn’t completely release.
I would get these crazy random harmonic vibrations that would come and go; highway speeds were the worst. The entire vehicle would start to shake... subtle at first and gradually becoming violent enough to make me pull over and stop.
Pull off the highway, stop for a bit and start driving again and sometimes the behaviour would repeat itself, but not regularly.
Took the car to my Subaru wrench and he thought I was full of **************** until he test drove it and experienced it for himself.
Yep, a bad caliper that wouldn’t release fully.
Caused a goofy random harmonic vibration through the right front/left rear brake circuit that would cause both calipers on that circuit to randomly chatter.
A new caliper and pads on the right front wheel and new pads on the left rear and all returned to normal.

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