Brake pedal problem

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mbdiesel@gmail.com - 20 Jul 2006 03:57 GMT

All,

I have a strange issue on my 1985 300SD. The car has 215K miles and
rotors and pads were changed less than 10K miles ago. Brake Fluid was
also flushed.

When coming to a stop, sometimes the front brakes make the noise
similar to ABS pumping noise and at the same time the brake pedal
pushes upwards before allowing you to push in to come to a stop. My
guess is that the ABS speed sensor is going bad or gone bad. Last week
this issue was occuring everytime .....then this week it did not happen
for about 3 days....sometimes the problem goes away during the same day
between starts and also comes back between starts. Any thoughts?

thanx.
anil bharucha

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Richard Sexton - 20 Jul 2006 05:34 GMT

>All,
>
[quoted text clipped - 9 lines]
>for about 3 days....sometimes the problem goes away during the same day
>between starts and also comes back between starts. Any thoughts?

Sounds to me like the rotors are no longer perfectly round and flat.

One thing that can kill them is riding the brakes down a big hill then
sitting there at the bottom at a stop sign with the brakes on. The
rotors, very hot, cool unevenly where the pads contact them and warp.

Rotors are cheap and easy to replace. Figure one one set per 100K miles
or so.

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Tiger - 20 Jul 2006 15:27 GMT

I would clean the ABS sensors... with brake cleaner... you have to clean all
the cogs and surrounding area to avoid ABS malfunction.

Another thing to do is change the brake light switch. The ABS takes the
trigger from that switch and then the computer takes over. Sometime the
brake light is on or the other switch inside it is on that ABS is active
during your driving time.

Last thing to do is check your rotor for trueness. It is possible you got a
binding caliper that keeps too much pressure on the pad when not active.

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mbdiesel@gmail.com - 20 Jul 2006 19:02 GMT

Tiger,

Thanx for the informative response. One thing I forgot to mention in
my original post was that my emergency brake pedal has some play in it
and the light stays on if not tied up with a small rubber band. I need
to replace the cable and the switch as well.

I was not aware that ABS was somehow tied into the switch circuit. I
will check out other things you suggested.

Anil Bharucha

> I would clean the ABS sensors... with brake cleaner... you have to clean all
> the cogs and surrounding area to avoid ABS malfunction.
[quoted text clipped - 6 lines]
> Last thing to do is check your rotor for trueness. It is possible you got a
> binding caliper that keeps too much pressure on the pad when not active.

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