Brake shake with freshly machined rotors?

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

Nate Nagel > wrote:
>
>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?

Maybe you have a shimmy that is unrelated to the actual braking system.
Checked the tie rods? All the bushings? Get under there and start
tugging on stuff and seeing if you can feel any play in anything in the
front end.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
> Nate Nagel > wrote:
>> 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?
>
> Maybe you have a shimmy that is unrelated to the actual braking system.
> Checked the tie rods? All the bushings? Get under there and start
> tugging on stuff and seeing if you can feel any play in anything in the
> front end.
> --scott
>

Car has only 21K miles on it (about 4K of which are mine) it'd be pretty
pathetic if it had worn out suspension components already.

I didn't mention that it had a slow leak when I first got it and I'd
noticed that the steering wheel was slightly off center, so when I left
it to have the tire plugged I told them to check/correct the alignment.
One would think that that would involve doing all that you suggest.

nate


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

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.
> 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?

My guess would be a bad tire. Did they rotate them? It could also be a
sticking caliper, but then you would probably feel it in the brake pedal
also.

-jim


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

"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.

--
"We have no government armed with power capable of contending with human
passions unbridled by morality and religion. Avarice, ambition, revenge,
or gallantry, would break the strongest cords of our Constitution as a
whale goes through a net. Our Constitution was made only for a moral and
religious people. It is wholly inadequate to the government of any
other." --John Adams, October 11, 1798

Anyolmouse

jim wrote:
>
> 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.
>> 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?
>
> My guess would be a bad tire. Did they rotate them? It could also be a
> sticking caliper, but then you would probably feel it in the brake pedal
> also.
>

Yes, the tires were supposedly both balanced and rotated, and I know the
tires are bad. They're Goodyear Integrity, the same crap tires that
were on my last car. Unfortunately there's not much I can do about that
unless I want to pay for new ones out of my pocket.

nate


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

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

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

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.
> 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


There could be hard spots on the rotors. And perhaps while it was
sitting the area where the calipers were that did not rust is now
either harder or softer then the rest of it from that, although I
would not give that high odds. I had a impala back in the 70's that
did what you were describing and they only fix that worked was new
rotors.

"Anyolmouse" > wrote in message news:Uvb%l.13440
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.

Those things dont always work they way they should. I have had two sets of
rotors warped
because of them.

"Nate Nagel" > wrote in message
...

>
> good point. maybe I will loosen/retorque lug nuts myself and see if that
> helps.
>
> nate

It's worth a try, but I doubt it will help..

As said before, tires are a possibility, bad machine work is another, and
tire/rotor
reinstallation (on some models) is a third.

I had some rotors cut once and when I remounted them on the GM product, you
could SEE
the wobble. The machinist didnt set up the lathe correctly.

If you dont still have the Coxco (?) link, let me know and I will find it
for you.