| 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
| I ASSumed that this would take care of the issue (the tire balance
| because I was also having a shake at highway speed, not to address
| problem) but it did not - it's still doing it, and almost as badly as
| 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
| 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,
| if it were simply warping, wouldn't it take a while to reappear after
| Any ideas as to why this could be?
| replace "roosters" with "cox" to reply.
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.
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