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Home » Public Forums » GMCnet » Re: [GMCnet] Transmission vacuum modulator leaking?
Re: [GMCnet] Transmission vacuum modulator leaking? [message #326961] Sat, 09 December 2017 23:27 Go to previous message
jimk is currently offline  jimk   United States
Messages: 6734
Registered: July 2006
Location: Belmont, CA
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Senior Member
There will be evidence there.

On Sat, Dec 9, 2017 at 9:24 PM, Jim Kanomata wrote:

> Just disconnect the Vac hose at the intake and see.
>
>
> On Sat, Dec 9, 2017 at 9:15 PM, Gordon Gibson
> wrote:
>
>> Hello all
>>
>> In the process of putting the coach to bed for winter, a new problem
>> seems to have surfaced. I am getting white smoke (sometimes a lot of it)
>> coming
>> out the tail pipe intermittently. First time I noticed it was after
>> stopping for lunch on a 200 mile drive. Starting back up I had white smoke
>> blowing for longer than I would expect from condensation. It stopped
>> fairly quickly and I did another 100 miles with no reoccurrence. Then
>> yesterday
>> I drove it to the gas station to fill the tanks up - just far enough so
>> that the temp gauge reached its normal operating level. White smoke on
>> starting up, and all the way home.
>>
>> Today I started the coach and had white smoke for the first 5 - 10
>> minutes, then it stopped. I checked fluid levels - coolant level seems
>> normal,
>> but ATF was a bit low. I added a half a quart then started up to measure
>> the level again....and the white smoke really came billowing out.
>>
>> My guess is a leaking diaphragm in the transmission vacuum modulator that
>> is allowing ATF to be sucked into the intake manifold. Does this sound
>> right? The tranny was rebuilt about 8,500 miles ago so the modulator
>> should have been replaced at that time. But the engine seems to be running
>> too
>> smoothly for it to be a cracked head or leaking head gasket. Besides,
>> the coolant level is holding steady. No coolant sludge on the engine oil
>> dipstick either.
>>
>> I know the right thing would be to lift the coach, pull the rubber hose
>> off the modulator and check to see if ATF drips out - but I just have dinky
>> car axle stands and am unwilling to crawl under the coach in my city
>> driveway just supported by the bottle jack. Building ramps is a project
>> for next
>> summer.
>>
>> So if this diagnosis sounds right to the group I will head to a tranny
>> shop Monday morning. Looks to me like the modulator should be very quick to
>> R&R. at a garage with a good floor jack and a pair of good axle stands.
>> They are forecasting 8 inches of snow for Tuesday so I'd really like to get
>> this fixed and the coach put away beforehand....
>> --
>> Gordon Gibson
>> 1976 23" Norris Upfit
>> Montreal West, Quebec, Canada
>>
>> _______________________________________________
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>>
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
>



--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502

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