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Knocking noise from a front wheel - second gen Prius

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Posted by passerby on December 11, 2012, 7:08 pm
 
Hi all,

The Prius is 2nd gen (2009) with 67K on it now.

I have this noise I'm having a hard time explaining to the mechanics at the
dealership, perhaps because it has started right after the latest service when
they rotated the tires and replaced the oil in the front differential.

I can describe it as a rather soft knocking sound that seems to be coming from
the passenger side from wheel, with the frequency of once per revolution (or
twice - it turned out to be very hard to drive, count and look at the
passenger side wheel at the same time :) - need a huge mirror for that!) .
Well, it starts soft but becomes harder and I can even feel it of the steering
wheel after long and highway speed drives.

I brought it down to the dealership and they claim they could not find or hear
anything but the tire and the wheel look OK (tires almost brand new - about 5K
on this set yet, balanced before first installed), brake pads and the disk
look fine and no foreign objects. So, they said, it's safe to drive and don't
worry too much.

My wish for this noise to go away didn't materialize and I think it's getting
worse. So, I decided to ask for suggestions in this esteemed group before
bringing it to the dealership again. What do you guys think it can be? If not
the wheel/brakes, could there be something in the suspension that can make
such noise? The timing it started is very suspicious - could they have screwed
something up in the front differential while changing the oil there? Else
could they have bumped the wheel against something while rotating the tires?

Any suggestion and comment you can offer will be most welcomed!

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Posted by Le Forgeron on December 12, 2012, 7:27 pm
 
Le 11/12/2012 20:08, passerby nous fit lire :

Once per revolution... hmmm... of the wheel or steering wheel ?
If the wheel itself:
Check the tire, every section of it, on the rolling band. You might have
a screw or bolt incased in the outer part of the tire. visual inspection
should be seconded with manual inspection: pass your hand softly on the
tire, all over the part that get in contact with the ground.
(afterwards, you're good to wash your hands). You should have to move
the car at least thrice if you do not remove the wheel. Use a mark on
the side of the wheel to ensure you do not look always at the same spot.
(For easier spot, turn the steering wheel full way if possible)


Posted by passerby on December 12, 2012, 9:08 pm
 replying to Le Forgeron , passerby wrote:

The wheel, going straight. Actually, not sure if going in a circle would make
a difference - it only becomes obvious at about 15-20MPH and I've yet to find
a circle large enough to try that.


Thank you for your suggestion. I had it down at the dealership where they
claim they took it off and checked the tire. But come to think of it now: I
would rather check it again myself. They did say it's safe but I would feel
much better if I've seen it myself.


Despite it being synced with the wheel rotation (once per revolution), could
it still be something other than the tire?

Thanks!

--


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Posted by Le Forgeron on December 12, 2012, 9:53 pm
 Le 12/12/2012 22:08, passerby nous fit lire :

It could. On another car (not even a Toyota), I once met the same
symptom (1 clong per revolution). Turn out it was the ball bearing of
the wheel that was faulty (and expensive to replace) (might be due to a
chock of the wheel against a sidewalk). Check is harder: rotate the
wheel while it is off the ground (so the car must somehow be suspended
... the apparatus to change a wheel with the fifth wheel (if any) is not
secure enough, do not do that alone). Free rotation of the wheel made it
clear: clong every revolution.

Might be hard to perform on the front wheel (neutral N mode ?)


Posted by passerby on December 15, 2012, 8:08 pm
 replying to Le Forgeron , passerby wrote:

So, I did lift the wheel up with a tire jack and rotated it by hand while on
neutral. Then did it with the other one just in case. *Nothing* at all out of
the ordinary. I mean, I don't look at Prius wheels every day, but there was
nothing embedded in the tire, no tears on the tire or the rubber gaskets, no
sign of any oil dripping, nothing obstructing the wheel or could possibly come
in contact with the wheel, nothing seems lose. I've taken pictures of both
wheel wells while they they suspended, just can't quite figure out how to post
them here.  

And, no noise! Well, if you rotate them *very* slow, something in the
transmission appears to start biting and the wheel jerks while you're rotating
it. You can hear tiny "ticks" when you do that but not once per revolution,
more like 100 times per revolution. I think it's how CVT is working although I
cannot be sure.  

Anyway, this time the car was cold while I was doing it, I'm going to try to
do it after driving it 20 miles later today. perhaps something will change
when it's warm.

So, I'm still looking for ideas. One that I was pondering myself: could the
wheel be unbalances so badly as to literally lift itself up and then down? The
noise seems to be rather soft and rubbery rather than metal on metal.

Thanks for your suggestions, guys, please keep them coming!

 
--


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