Brake shake with freshly machined rotors?

On Sat, 20 Jun 2009 16:28:59 -0400, Nate Nagel >
wrote:

>Anyolmouse wrote:
>> "Nate Nagel" > wrote in message
>> ...
>> | Hi all,
>> |
>> | got a bit of a puzzlement. Ever since I've had it, my '08 Impala has
>> | had a pronounced steering shimmy under braking - the harder you brake,
>> | the more the wheel shakes back and forth.
>> |
>> | I finally took it in for its first service in my care today, and asked
>> | them to balance and rotate the tires and also to turn the front
>> rotors.
>> | I ASSumed that this would take care of the issue (the tire balance
>> was
>> | because I was also having a shake at highway speed, not to address
>> this
>> | problem) but it did not - it's still doing it, and almost as badly as
>> it
>> | was before. The rotors show clear signs of having recently been
>> | machined; there's obviously marks in the iron that are not
>> | circumferential (I'm guessing they must have dressed it with a sanding
>> | disc or similar while spinning on the brake lathe after turning) so it
>> | doesn't appear to be a halfassed job on the part of the shop.
>> |
>> | I'd suspected that the cause of this issue was because the car sat for
>> | several months unused before I started driving it, so I just ASSumed
>> | that the brake shake was due to rust buildup on the rotors (except of
>> | course where the pads had sat, causing the rotors to wear unevenly
>> when
>> | the car was put back in service.) Of course, I suspect that also the
>> | rotors are undersized for the weight of the car, but that's typical,
>> and
>> | if it were simply warping, wouldn't it take a while to reappear after
>> | machining?
>> |
>> | Any ideas as to why this could be?
>> |
>> | nate
>> |
>> | --
>> | replace "roosters" with "cox" to reply.
>> | http://members.cox.net/njnagel
>>
>> I have a 2000 Safari that has the same problem. It was okay for a short
>> time after a complete brake job. When it came back I called my mechanic
>> and he asked if I had had the tires rotated. Yep, just had that done. He
>> said he was running into a lot of this problem with different brands of
>> cars, vans, etc. He said that the rotors are warping when the wheels are
>> torqued during the rotation process. I pointed out that the tire shop I
>> use, uses a torque limiting air ratchet and that should not be a
>> problem. He agreed but said that was a common denominator to all of the
>> brake pulsating/ shimmy problems he has seen.
>>
>> FWIW, If I intentionally brake heavy several times the pulsing problem
>> gets better and sometimes disappears. The rotors were still in specs
>> after being turned, but I think you may be right in thinking that they
>> are under engineered.
>>
>> You didn't say how many miles is on the car, but the suspension is the
>> only thing I can think of that would cause the the highway shimmy. More
>> specific, the front shocks or struts, which ever it has.
>>
>> I had a '93 S-10 that had bad bushings in the front A frame. It caused
>> the truck to veer to one side or the other under hard braking. There was
>> also a loud clunking sound when braking some times. It also exibited
>> some weird symptoms going down the highway. Sometimes, but not always,
>> the truck would get the shimmys after hitting a pot hole or going over a
>> bump. That all ws corrected when the bushins were replaced.
>>
>
>good point. maybe I will loosen/retorque lug nuts myself and see if
>that helps.
>
>nate


I have done that on my explorer and it did help.

On Sat, 20 Jun 2009 15:29:07 -0400, Nate Nagel >
wrote:

>Hi all,
>
>got a bit of a puzzlement. Ever since I've had it, my '08 Impala has
>had a pronounced steering shimmy under braking - the harder you brake,
>the more the wheel shakes back and forth.
>
>I finally took it in for its first service in my care today, and asked
>them to balance and rotate the tires and also to turn the front rotors.

Just a suggestion: when you take a car in for warranty work, never
ever tell them 'how' to fix it. When you suggest a repair technique,
that is what the do, nothing else, because that is what you asked for.
Instead, give them the symptoms, make sure they can duplicate these
symptions and say: "Fix it, warranty". Heck, even if it is not
warranty, don't suggest how to repair a fault! People make this
mistake over and over--the shop must do what you suggest even if they
know it won't fix the problem, and they cannot fix anything else
because you asked for a specific action to be performed.



> I ASSumed that this

Never assume. Let the shop/mechanic find teh problem.

> would take care of the issue (the tire balance was
>because I was also having a shake at highway speed, not to address this
>problem) but it did not - it's still doing it, and almost as badly as it
>was before. The rotors show clear signs of having recently been
>machined; there's obviously marks in the iron that are not
>circumferential (I'm guessing they must have dressed it with a sanding
>disc or similar while spinning on the brake lathe after turning) so it
>doesn't appear to be a halfassed job on the part of the shop.
>
>I'd suspected that the cause of this issue was because the car sat for
>several months unused before I started driving it, so I just ASSumed
>that the brake shake was due to rust buildup on the rotors (except of
>course where the pads had sat, causing the rotors to wear unevenly when
>the car was put back in service.) Of course, I suspect that also the
>rotors are undersized for the weight of the car, but that's typical, and
>if it were simply warping, wouldn't it take a while to reappear after
>machining?
>
>Any ideas as to why this could be?
>
>nate

Well, first, a warranty repair should be done ASAP after the flaw is
noticed. Don't wait for other problems to appear. Second, don't assume
what is causing a problem. Now the dealer can say the did what you
asked, and will be reluctant to do more.

Possibly bad rotors, as you suspect. They could easily be warped, or
have excessive runout. Can't say until diagnostics are performed.

On Sat, 20 Jun 2009 15:29:07 -0400, Nate Nagel >
wrote:

>Hi all,
>
>got a bit of a puzzlement. Ever since I've had it, my '08 Impala has
>had a pronounced steering shimmy under braking - the harder you brake,
>the more the wheel shakes back and forth.
>
Steering Wheel Pull/Shimmy When Braking
PROBABLE CAUSE: REMEDY

Uneven braking force: Check for mechanical or hydraulic problem.

Inoperative brake: Check for seized caliper, fluid leak or
restriction, worn or contaminated lining.

Weak or broken spring: Replace spring.

Worn shocks or struts: Replace struts or shocks

Deteriorated suspension bushings (especially control
arm pivot): Replace bushings.

Loose wheel bearings: Adjust or replace bearings.

Excessive disc brake rotor run-out: Replace both front or rear brake
discs or rotors.

Improper front wheel alignment settings: Adjust alignment to factory
specifications.

(From http://www.thepartsbin.com/suspension-steering.html)

--Vic

On Sat, 20 Jun 2009 17:18:02 -0400, PeterD > wrote:

>On Sat, 20 Jun 2009 15:29:07 -0400, Nate Nagel >
>wrote:
>
>>Hi all,
>>
>>got a bit of a puzzlement. Ever since I've had it, my '08 Impala has
>>had a pronounced steering shimmy under braking - the harder you brake,
>>the more the wheel shakes back and forth.
>>
>>I finally took it in for its first service in my care today, and asked
>>them to balance and rotate the tires and also to turn the front rotors.
>
>Just a suggestion: when you take a car in for warranty work, never
>ever tell them 'how' to fix it.

And when you do tell them you want something, ALWALYS get a price. I
learned that the hard way....I asked them to replace the brake
retainers figuring they couldn't be more then a couple bucks each.
When I got the bill I was about to call for the manager to figure out
why it was $70 higher then I expected till I saw what they price was
for the brake retainers......



When you suggest a repair technique,
>that is what the do, nothing else, because that is what you asked for.
>Instead, give them the symptoms, make sure they can duplicate these
>symptions and say: "Fix it, warranty". Heck, even if it is not
>warranty, don't suggest how to repair a fault! People make this
>mistake over and over--the shop must do what you suggest even if they
>know it won't fix the problem, and they cannot fix anything else
>because you asked for a specific action to be performed.
>
>
>
>> I ASSumed that this
>
>Never assume. Let the shop/mechanic find teh problem.
>
>> would take care of the issue (the tire balance was
>>because I was also having a shake at highway speed, not to address this
>>problem) but it did not - it's still doing it, and almost as badly as it
>>was before. The rotors show clear signs of having recently been
>>machined; there's obviously marks in the iron that are not
>>circumferential (I'm guessing they must have dressed it with a sanding
>>disc or similar while spinning on the brake lathe after turning) so it
>>doesn't appear to be a halfassed job on the part of the shop.
>>
>>I'd suspected that the cause of this issue was because the car sat for
>>several months unused before I started driving it, so I just ASSumed
>>that the brake shake was due to rust buildup on the rotors (except of
>>course where the pads had sat, causing the rotors to wear unevenly when
>>the car was put back in service.) Of course, I suspect that also the
>>rotors are undersized for the weight of the car, but that's typical, and
>>if it were simply warping, wouldn't it take a while to reappear after
>>machining?
>>
>>Any ideas as to why this could be?
>>
>>nate
>
>Well, first, a warranty repair should be done ASAP after the flaw is
>noticed. Don't wait for other problems to appear. Second, don't assume
>what is causing a problem. Now the dealer can say the did what you
>asked, and will be reluctant to do more.
>
>Possibly bad rotors, as you suspect. They could easily be warped, or
>have excessive runout. Can't say until diagnostics are performed.

Nate Nagel > wrote in :

> Hi all,
>
> got a bit of a puzzlement. Ever since I've had it, my '08 Impala has
> had a pronounced steering shimmy under braking - the harder you brake,
> the more the wheel shakes back and forth.



Of maybe some help:
<http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml#>
<http://www.brakeandfrontend.com/Article/39171/diagnostic_solutions_servicing_brake_rotors.aspx>
<http://www.brakeandfrontend.com/Article/38661/advanced_brake_diagnostic_tools.aspx>



>
> I finally took it in for its first service in my care today, and asked
> them to balance and rotate the tires and also to turn the front rotors.
> I ASSumed that this would take care of the issue (the tire balance was
> because I was also having a shake at highway speed, not to address this
> problem) but it did not - it's still doing it, and almost as badly as it
> was before.



Did anybody make certain the tires spun ABSOLUTELY true with NO
hop, wobble or snaking BEFORE balancing was attempted?

ANYthing but dead-true will result in unsatisfactory performance.
And those much-vaunted Hunter road-force machines tend to cover up
or disguise inept mounting, so they're not much of an answer.

I've had many years of tire replacements on several cars as personal experience
in this matter, many of those replacments being followed by highly
inconvenient and annoying multiple re-visits to the garage that did the work
in an attempt to get them to fix the vibration, which they rarely could.

I finally gave up and asked my mechanic if he could install tires for me.
he said sure. What a difference. So far, glass-smooth EVERY time.
Even though his "bedside manner" isn't that great, I worked up the nerve
to ask him why he was able to do this and nobody else appears to be able to.
He explained the problem in great detail, and showed me physical
evidence of why so many places have problems with comebacks due to
vibration, using my own tires (mounted by somebody else) as one example.

The upshot? Basically, inept technique. Mounting tires properly is not
difficult at all, but does require some very basic knowledge of some
very simple things. Problem is, most tire monkeys receive little training,
and their bosses understand little to begin with.





--
Tegger

Tegger wrote:
> Nate Nagel > wrote in :
>
>> Hi all,
>>
>> got a bit of a puzzlement. Ever since I've had it, my '08 Impala has
>> had a pronounced steering shimmy under braking - the harder you brake,
>> the more the wheel shakes back and forth.
>
>
>
> Of maybe some help:
> <http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml#>
> <http://www.brakeandfrontend.com/Article/39171/diagnostic_solutions_servicing_brake_rotors.aspx>
> <http://www.brakeandfrontend.com/Article/38661/advanced_brake_diagnostic_tools.aspx>
>
>
>
>> I finally took it in for its first service in my care today, and asked
>> them to balance and rotate the tires and also to turn the front rotors.
>> I ASSumed that this would take care of the issue (the tire balance was
>> because I was also having a shake at highway speed, not to address this
>> problem) but it did not - it's still doing it, and almost as badly as it
>> was before.
>
>
>
> Did anybody make certain the tires spun ABSOLUTELY true with NO
> hop, wobble or snaking BEFORE balancing was attempted?

I can't answer this question (see below)

>
> ANYthing but dead-true will result in unsatisfactory performance.
> And those much-vaunted Hunter road-force machines tend to cover up
> or disguise inept mounting, so they're not much of an answer.
>
> I've had many years of tire replacements on several cars as personal experience
> in this matter, many of those replacments being followed by highly
> inconvenient and annoying multiple re-visits to the garage that did the work
> in an attempt to get them to fix the vibration, which they rarely could.
>
> I finally gave up and asked my mechanic if he could install tires for me.
> he said sure. What a difference. So far, glass-smooth EVERY time.
> Even though his "bedside manner" isn't that great, I worked up the nerve
> to ask him why he was able to do this and nobody else appears to be able to.
> He explained the problem in great detail, and showed me physical
> evidence of why so many places have problems with comebacks due to
> vibration, using my own tires (mounted by somebody else) as one example.
>
> The upshot? Basically, inept technique. Mounting tires properly is not
> difficult at all, but does require some very basic knowledge of some
> very simple things. Problem is, most tire monkeys receive little training,
> and their bosses understand little to begin with.

You just described the exact problem that was driving me nuts on my 944
for literally years until I found a local Porsche club guy who had his
own tire machine.

However I have yet to report success because both my rim and tire
exhibited runout and I haven't had a chance to swap the tire (on a
straight rim) back on the car to see if it is acceptable or if I need
another new tire.

But back to the problem at hand, I am limited to two repair shops for
work on this car unless I want to pay for the work myself (fleet car) so
it may simply remain unresolved, much as it bothers me (I know it can't
be good for ball joints, tie rod ends, etc.) Or if I end up with a
windfall sometime soon, I may take it to a GOOD shop and just point and
say "fix."

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

You can machine warped rotors all you like, but it will not make any
difference as far as the warping is concerned. The lathe will just follow
the warp in the rotor and cut it the same, only thinner. Sounds like you
need a new set of rotors. I would check the rear brakes to make sure they
are operating as well, usually warped rotors result from either too much
effort on the part of the front brakes trying to stop the car (excessive
heat), or a mechanic overtorquing the wheel nuts upon reinstallation and
unintentionally causing the warpage in the rotors.

How much pad lining is left on the front pads? Did they re-use the original
pads, or install new ones? When they re-installed the caliper sliding pins,
did they clean and then grease the pins and sliders so that the caliper
slides freely?

Just my 2 cents,
Sharky

"Sharky" > wrote in message
news:acf%l.32875$PH1.11637@edtnps82...
> You can machine warped rotors all you like, but it will not make any
> difference as far as the warping is concerned. The lathe will just follow
> the warp in the rotor and cut it the same, only thinner.

Absolute caca.. If you do it right, you can definitely machine the rotors,
and
if you reinstall correctly this can last a long time.

I suspect you had some bad experiences, Sharky.

Sharky wrote:
> You can machine warped rotors all you like, but it will not make any
> difference as far as the warping is concerned. The lathe will just follow
> the warp in the rotor and cut it the same, only thinner. Sounds like you
> need a new set of rotors. I would check the rear brakes to make sure they
> are operating as well, usually warped rotors result from either too much
> effort on the part of the front brakes trying to stop the car (excessive
> heat), or a mechanic overtorquing the wheel nuts upon reinstallation and
> unintentionally causing the warpage in the rotors.
>
> How much pad lining is left on the front pads? Did they re-use the
> original
> pads, or install new ones? When they re-installed the caliper sliding
> pins,
> did they clean and then grease the pins and sliders so that the caliper
> slides freely?
>
> Just my 2 cents,
> Sharky
>

50-75% pad left, original pads, and no idea if they lubed it. If I'd
done it myself I'd have lubed it, but I don't feel like working on
company car myself. I did change the oil when I first got it because it
was due on time but not on mileage (so I couldn't get them to pay for
it) and I was so paranoid, even though I've never screwed up an oil
change in my life.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

On Sun, 21 Jun 2009 00:32:06 GMT, "Sharky" >
wrote:

>You can machine warped rotors all you like, but it will not make any
>difference as far as the warping is concerned. The lathe will just follow
>the warp in the rotor and cut it the same, only thinner.

Really? So how do they make them in the first place!!! Do you think
they just come from the casting bed already machined?



Sounds like you
>need a new set of rotors. I would check the rear brakes to make sure they
>are operating as well, usually warped rotors result from either too much
>effort on the part of the front brakes trying to stop the car (excessive
>heat), or a mechanic overtorquing the wheel nuts upon reinstallation and
>unintentionally causing the warpage in the rotors.
>
>How much pad lining is left on the front pads? Did they re-use the original
>pads, or install new ones? When they re-installed the caliper sliding pins,
>did they clean and then grease the pins and sliders so that the caliper
>slides freely?
>
>Just my 2 cents,
>Sharky