: front or rear rotor problem? how to tell



iametarq
09-04-10, 08:57 PM
Braking at high way speeds this weekend I notice there is noticeable shaking. I can feel it in my seat and in the steering wheel. I do not feel it in the brake pedal, it does not push against me.

My front rotors and pads are about 1.5 years. Rears I can't remember, but the sensors are not telling me anything is due for changing.

Which brings me to my next question. After reading this whole article about "no such thing as warped rotors" http://www.brakeandfrontend.com/Article/71319/brake_tech_feature_8_myths_that_could_be_holding_y ou_back_from_performing_the_best_brake_job.aspx what do you when your rotors are "warped" Do you just replace them, if that is my problem? or do you get them resurfaced?

Thanks!

RippyPartsDept
09-04-10, 09:39 PM
you can get them resurfaced if they haven't already been resurfaced a bunch of times, but usually you can find rotors in the aftermarket that are under $50 (sometimes even $25)
the sensors only will tell you when the pads need replacing

Dadillac
09-04-10, 09:44 PM
Braking at high way speeds this weekend I notice there is noticeable shaking. I can feel it in my seat and in the steering wheel. I do not feel it in the brake pedal, it does not push against me.

My front rotors and pads are about 1.5 years. Rears I can't remember, but the sensors are not telling me anything is due for changing.

Which brings me to my next question. After reading this whole article about "no such thing as warped rotors" http://www.brakeandfrontend.com/Article/71319/brake_tech_feature_8_myths_that_could_be_holding_y ou_back_from_performing_the_best_brake_job.aspx what do you when your rotors are "warped" Do you just replace them, if that is my problem? or do you get them resurfaced?

Thanks!

Let me go out on a limb here and assume that you have ceramic pads right? If so get rid of them and go semi metallic. But either way you will need to resurface or replace your rotors.

Don

iametarq
09-04-10, 10:03 PM
I do not believe they are ceramic. I'll have to check my receipts when I get back home on Monday. The pads are AC Delco from Rock Auto. The rotors are from my local parts store since they were less expensive.

The rotors have never been resurfaced.

Is my problem more than likely the fronts? Assuming my vibrations are from the fronts, do I really have to replace the pads when I resurface the rotors? They are only about 1.5 years old and the pad thickness is nearly new looking.

JimD
09-05-10, 12:28 AM
Just to swerve back to your thread topic for a heartbeat, the front or rear question can be answered by applying and holding your park brake pedal at "high speed". Not to worry; the park brake pedal on your year/model will not lock down when the transmission is in R or any forward selection.

Give some thought to how much energy (heat) is required to "warp" an OEM rotor (you are in uncharted waters using aftermarket parts). Unless you are off-road racing your car every weekend I doubt if your rotors are warped.

One common possible cause of your symptoms is improper wheel lug nut torgue value and sequence. My tire retailer offers free rotation every 6,000 miles and I take advantange of the offer. But I drive home and reset each lug nut to 100 lb ft with my torque wrench using the proper sequence.

Another possible cause of your symptoms is "uneven pad material deposit on the rotor surfaces". This can be easily corrected by making a series of ten 'hard stops' from 45 mph without activating ABS and not coming to a complete stop. You will smell brake pads and see some brake pad smoke; that is good. Several applications might be required to lay down a consistent thickness layer of pad material on the rotor surfaces.

FWIW: My high mileage '98 Seville does not "shake" under braking at any speed. And my OEM parts brakes have not been touched in more than 94,000 miles.

Good luck....

iametarq
09-05-10, 12:33 AM
Thanks Jim,

My front rotors are not OEM. I am going to try your hard stop method before I do anything tomorrow. Before this weekend the car has never had any shakes/vibrations when braking.

No racing here. But daily dirt road driving, unfortunately.

Thanks for the reminder on the hard stops. I'll find somewhere to do that tomorrow hopefully.

Dadillac
09-05-10, 11:32 AM
The ceramic pads require quite a bit of heat to work. So the rotors heat up quite a bit while braking. Then when you come to a stop your pads are on the hot rotor and this will allow the pad material to transfer onto that part of the rotor. This is the pulsation that you are feeling. Semi metallics run way cooler so this issue doesn't happen near as often as ceramics. If you resurface the rotors and continue with the ceramics you will more than likely have the issue reoccur within 5,000 miles.

Since the front brakes do most of the braking due to weight transfer I would suspect the fronts are the culprit. But the parking brake test is a good one to try. Just don't stay on the parking brake too long. You will heat the rear brakes up fast this way and that will create the same issue you are having now even if the rears are fine.


Don

iametarq
09-05-10, 11:56 AM
My parking brake is disconnected. :( I had to disconnect the cables because they need to be replaced. They were not releasing all the way whenever I would use it.

EDIT: Finding an empty 55 mph road in Flint, MI is difficult! I found a parking lot that was clear but couldn't get to much over 30 before having to brake. :(

I did about 10 near stops, and could smell the brakes when done but I don't think it was enough. It feels a little better but I will probably get the front rotors turned. After running my finger nail over them when back to where we are staying they are nicely grooved. Probably due to all of the sand/gravel on the road my wife has to drive back at home ever single day to get to work. *sigh.

Skiller.
09-09-10, 11:49 AM
I seem to have this too, but my car shakes without the brakes applied also. When braking, it only shakes the steering wheel slightly with LIGHT pressure on the brake pedal. If I hit the brakes hard at 60, there is no shaking all the way down to 0. Of course, I also have shaking at highway speeds...Can a bad tie rod end cause this? My pads and rotors are a few months old...

hellamint
09-09-10, 05:37 PM
I have a 2007 STS AWD. When I am braking at around 40 MPH, my car shakes (applying light to medium brake pressure). The steering wheel nor the brake pedal shake at all. What could be the cause of this?

FYI: I just bought the car a week ago (CPO). Is this something the dealership would fix under warranty?

RippyPartsDept
09-09-10, 06:50 PM
check with the dealer ... brake pad changes are wear items and obviously not covered but if there's a problem with some other brake parts it might be covered...

Submariner409
09-10-10, 07:25 PM
I have a 2007 STS AWD. When I am braking at around 40 MPH, my car shakes (applying light to medium brake pressure). The steering wheel nor the brake pedal shake at all. What could be the cause of this?

FYI: I just bought the car a week ago (CPO). Is this something the dealership would fix under warranty?

Before you try the dealer, get on a quiet stretch of highway or open rural road. Make several aggressive slowdowns to <10 mph from 60 - 70 mph, just short of ABS operation; do NOT come to a complete stop each time and if you do have to stop, do NOT hold the brakes on - shift to N and take your foot off the brake. There's a very good chance that your rotors have pad resin buildup, and what you have just done is scrub the rotors clean: practically every disc brake city/near suburban vehicle suffers from this vibration and the brakes need to be exercised from time to time. Why not hold the brakes when excessively hot ?? More pad deposits......and, BTW, brake rotors (cast iron) do not warp.

RippyPartsDept
09-10-10, 10:54 PM
Sub, if you get your rotors really hot then go through some water (say a foot deep - enough to really get a good amount of water on the rotors) could that warp cast iron rotors? or is it just no possible?

Submariner409
09-10-10, 11:05 PM
Sub, if you get your rotors really hot then go through some water (say a foot deep - enough to really get a good amount of water on the rotors) could that warp cast iron rotors? or is it just no possible?


They'll crack first. The warp factor (:yup:) is exactly why cast iron - high quality cast iron - is used for brake rotors worldwide. (Aircraft brakes applied at 230 mph - full max OMG !)

I've posted this before, but.......extremely fast road, sports, and race cars generate enough braking heat to have the rotors run at cherry red at the end of a switchback or tight chicane turn - they then go back to 150+ mph on the straights, cool down, and do it all over again for 12 or 24 hours. If there was ANY warpage the front end (maximum braking force percentage) would come out of the car LONG before LeMans, Sebring, Daytona, or Monaco was over....

RippyPartsDept
09-10-10, 11:50 PM
ok, i thought that i heard somewhere that a hot rotor if taken through water could warp.
we have a lot of areas in town where the road becomes part of the retention ponds when it rains hard for a few hours
one particular stretch right yards down the road from our shop (in front of the benz/gmc/buick/(pont) dealer) gets really deep
http://www.wwaytv3.com/wilmington_roads_flood_rain_comes_quickly/07/2009
it's kind of hard to see in the picture, but that's waist deep!
doesn't always get that deep, but that stretch will get at least a foot of water a couple times a year

RippyPartsDept
10-03-10, 10:21 PM
ok so we had the wettest september ever
it rained all week starting last sunday night, and stopped on friday
we got around 25 inches of rain
there was flooding again
http://image.weather.com/web/multimedia/images/slideshows/car/car23.jpg
jim cantore from the weather channel was reporting from the parking lot of the golden corral earlier in the day (which is about where this photo was taken from)
this stretch of road gets blocked off by barriers, but for some reason people still drive around/through them

we've probably had about 10 flooded cars towed in this week (and we're one of about 10 dealerships in town) a couple were only minor floods and are back out on the road already

iametarq
10-19-10, 11:40 PM
I took my front rotors in to get re-surfaced, finally. Now I have them back, can't test drive until I get my new front hub coming in on Friday.

I hope the shake goes away, if it does not, I will get the rears re-surfaced. All the pads still have a lot of life on them.

I am 99% sure I have ceramics on my front brakes right now, don't feel like digging through the car file right now... The brake shop also told me this was more than likely the last time I'd be able to turn the rotors. They would more than likely be too 'thin' at the next time around. Really? Ceramics wore out my rotors? Dang.

Submariner409
10-20-10, 06:41 PM
The brake shop also told me this was more than likely the last time I'd be able to turn the rotors. They would more than likely be too 'thin' at the next time around. Really? Ceramics wore out my rotors? Dang.

Any brake rotor with over 75,000 miles is living on borrowed time - rotor wear is perfectly normal and really doesn't have a heck of a lot to do with pad material - I just had to put front rotors on the truck at 75,000 and I'm easy on brakes............

iametarq
10-24-10, 11:40 AM
Well to update this thread, I put the re-surfaced rotors back on the front of the car yesterday and ALL the pulsing/vibrating when braking is totally gone. Its smooth braking again. Glad I did not have to take the rears off too. :thumbsup: Easiest $24 spent on the car. Reused the pads, etc.

stoveguyy
10-26-10, 12:58 PM
did you have a bad hub? loose bearing? or maybe abs light?

iametarq
10-26-10, 05:39 PM
did you have a bad hub? loose bearing? or maybe abs light?

Neither, just shaky braking at any speeds over 45 mph. as others state here I believe it was due to the build up of brake pad material on the rotors.