Tech: 1994 Toyota Camry has thumping noise when brakes are applied

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m6onz5a - 23 Jul 2007 18:32 GMT

My friend has a '94 Camry with 4 wheel ABS, and when the brakes are
applied at low speed you hear a thumping noise in the front end
drivers side.

Both axles are good and have the sensor ring. Both ABS sensors have
been replaced, and it still made no difference.

But, when you unplug either front ABS sensor the thumping noise stops
but of course the ABS light is now on-on the dash. When you plug
either sensor back in the thumping starts back up.

Any ideas???

Thanks a bunch
Chas

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qslim - 23 Jul 2007 21:25 GMT

Does the thumping noise vary with wheel speed? Is it a rapid vibration like
the ABS activating? Is it felt in the pedal?

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m6onz5a - 24 Jul 2007 11:07 GMT

> Does the thumping noise vary with wheel speed? Is it a rapid vibration like
> the ABS activating? Is it felt in the pedal?

No it only does it as you are slowing down like under 20 mph. It's a
definite thump thump thump noise coming from the front drivers side. I
beleive the thumping slowed as the vehicle slowed down. Not sure if he
feels it in the pedal or not.

Chas

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Comboverfish - 24 Jul 2007 15:35 GMT

> > Does the thumping noise vary with wheel speed? Is it a rapid vibration like
> > the ABS activating? Is it felt in the pedal?
[quoted text clipped - 5 lines]
>
> Chas

If it goes away when you unplug a speed sensor, I can't help but
believe it is a purely ABS related issue. The system will default to
standard hydraulic braking and turn on the ABS light, which sounds
like your description.

Toyota MDT in MO

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m6onz5a - 07 Sep 2007 19:35 GMT

> > > Does the thumping noise vary with wheel speed? Is it a rapid vibration like
> > > the ABS activating? Is it felt in the pedal?
[quoted text clipped - 12 lines]
>
> Toyota MDT in MO

Problem solved! BOTH ABS sensor rings had a nick in them causing the
thumping. Once replaced the problem is now gone.

Thanks for everyone's help
Chas

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Comboverfish - 23 Jul 2007 23:12 GMT

> My friend has a '94 Camry with 4 wheel ABS, and when the brakes are
> applied at low speed you hear a thumping noise in the front end
[quoted text clipped - 11 lines]
> Thanks a bunch
> Chas

Two obvious possibilities:

First I would check the sidewalls for the size of all four tires (need
to be the same), and compare tread depth. To go a step further, I
might check the rolling distance of all of my tires by marking them
with fresh paint, rolling the car forward until the two paint marks
leave spots on the ground, then refreshing the same spots on the tires
and rolling the tires until the paint marks are left on the ground
once more. Without disturbing the paint on the ground, measure each
pair center-to-center and compare all measurements (should all be very
close).

If there is an electric/hydraulic failure that doesn't cause the ABS
ECM to enter failsafe, the system may be operating any time the brake
pedal is pressed. Usually this is a wheel speed sensor or tone ring
issue. They do not always "set a code" or cause the ABS system to
shut down. I am leaning towards this type of failure as I would
suspect that you have checked tire sizes already. Of course, I have
actually seen a worthless "mechanic" hang a high $$ EHCU/modulator
assembly on a Prius that really only had one wrong sized tire. After
he ordered and installed the part I decided to tell him what the real
problem was. I would have helped him earlier, but this is the way he
has always "diagnosed", yet seemingly he'll never get fired. Rant/job
hatred over. Sorry.

Toyota MDT in MO

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m6onz5a - 24 Jul 2007 11:05 GMT

> > My friend has a '94 Camry with 4 wheel ABS, and when the brakes are
> > applied at low speed you hear a thumping noise in the front end
[quoted text clipped - 25 lines]
>
> If there is an electric/hydraulic failure that doesn't cause the ABS

> ECM to enter failsafe, the system may be operating any time the brake
> pedal is pressed. Usually this is a wheel speed sensor or tone ring
[quoted text clipped - 9 lines]
>
> Toyota MDT in MO

Thanks for the info guys. I'll pass it along to my friend. Hopefully
it's something simple like the wrong size tires.

Chas

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