Is there such a thing as an automatic transmission modulator valve?

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my_two_cent - 09 Mar 2008 08:23 GMT

Folks;

I'm having a problem with automatic transmission fluid getting into my
cylinders and burning. It happens only occasionally, but in reading
about other cars, the advice is to replace the "modulator valve".

None of my three Miata manuals mentions an AT modulator valve and none
of the online or catalog parts suppliers has any. I haven't found any
discussion of this on this group.

I'll call the dealership on Monday morning, but if anyone knows how
fluid can get from the transmission to the tailpipe, please let me
know what and where it is.

(It's not engine oil coming through the valve guides, rings or PCV
valve. It's not coolant. It's not excess fuel from a stuck injector.
Might be aliens, but I'm pretty sure it's ATF coming out the pipe.)

1996 Miata M Edition with 137k miles. No wisecracks about the auto --
only way to get the spouse to swap cars.

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Ken Lyons - 09 Mar 2008 18:38 GMT

> Folks;
>
[quoted text clipped - 5 lines]
> of the online or catalog parts suppliers has any. I haven't found any
> discussion of this on this group.

There is a "vacuum diaphragm" on the U.S. driver's side of the transmission
just above the pan. The transmission usually doesn't run right when this
goes bad.
http://forum.miata.net/vb/archive/index.php/t-222712.html

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Ken Lyons '97 Brilliant Black/'90 Classic Red
Inside the Beltway
[Remove the first two digits to reply]

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my_two_cent - 11 Mar 2008 16:29 GMT

> "my_two_cent" <kwea...@gmail.com> wrote> Folks;
>
> There is a "vacuum diaphragm" on the U.S. driver's side of the transmission
> just above the pan. The transmission usually doesn't run right when this
> goes bad.http://forum.miata.net/vb/archive/index.php/t-222712.html

That thread mentions a device that sounds exactly like the modulator
valve. I called the dealership parts department yesterday and the
friendly fellow who called me back said that I could get a modulator
valve and he remembered "back in the day" that failures of those
valves could cause smoking.

I like the advice to pull off the vacuum line and swab for ATF. I'll
do that first.

I've ordered the replacement and will get it on this weekend. Thanks
for your response, it is really helpful to get confirmations and it
seems like this valve will be really easy to replace. I get nervous
when I don't have one of my trusted manuals to guide me.

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my_two_cent - 16 Mar 2008 17:08 GMT

> I like the advice to pull off the vacuum line and swab for ATF. I'll
> do that first.
[quoted text clipped - 3 lines]
> seems like this valve will be really easy to replace. I get nervous
> when I don't have one of my trusted manuals to guide me.

I pulled off the air line and a fingerful of ATF poured out. Replaced
the valve and no smoking and the transmissions shifts more smoothly.
Add one more item that can cause tailpipe smoking to the list of
symptoms.

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Ken Lyons - 17 Mar 2008 01:57 GMT

> I pulled off the air line and a fingerful of ATF poured out. Replaced
> the valve and no smoking and the transmissions shifts more smoothly.
> Add one more item that can cause tailpipe smoking to the list of
> symptoms.

Thanks for getting back to us with the results. I'll certainly keep this in
mind if our '90 auto ever has the same symptoms.

Signature

Ken Lyons '97 Brilliant Black/'90 Classic Red
Inside the Beltway
[Remove the first two digits to reply]

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