Home » Public Forums » GMCnet » Transmission vacuum modulator leaking?
| Transmission vacuum modulator leaking? [message #326958] |
Sat, 09 December 2017 23:15  |
gibsongo
Messages: 116
Registered: October 2012
Location: Montreal West, Quebec, Ca...
Karma: 0
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Senior Member |
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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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| Re: [GMCnet] Transmission vacuum modulator leaking? [message #326959 is a reply to message #326958] |
Sat, 09 December 2017 23:25  |
Dave Stragand
Messages: 307
Registered: October 2017
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Senior Member |
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Can you check it for fluid at the carb/manifold end of the vacuum line? That should be accessible from the top.
> On Dec 10, 2017, at 12:16 AM, 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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1978 Transmode (403)
Pittsburgh, PA
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| Re: [GMCnet] Transmission vacuum modulator leaking? [message #326960 is a reply to message #326958] |
Sat, 09 December 2017 23:24 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
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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| Re: [GMCnet] Transmission vacuum modulator leaking? [message #326972 is a reply to message #326960] |
Sun, 10 December 2017 10:16 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Gordon,Leave it hitched up until Spring. It not going to hurt
anything.
JR WrightMichigan
-----------------------------------------From: "Gordon Gibson"
To:
Cc:
Sent: 10-Dec-2017 15:16:28 +0000
Subject: Re: [GMCnet] Transmission vacuum modulator leaking?
Thanks for the answers guys. But one more question - If I disconnect
the modulator vacuum line from the intake manifold, will the coach
still be
drivable? It's a fairly short distance to the storage place, but once
there, the coach will be moved from time to time And if I do this, I
assume
that I should be capping the vacuum port on the manifold. Should I
also be capping the line to the tranny vacuum modulator?
--
Gordon Gibson
1976 23" Norris Upfit
Montreal West, Quebec, Canada
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Transmission vacuum modulator leaking? [message #326980 is a reply to message #326960] |
Sun, 10 December 2017 15:26 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Gordon,Your looking for a modulator for a TH-425 GM transmission out
of a 1975 Oldsmobile Toronado 7.5L 455cid V8. This is a good starting
point to get you into most of the autoparts computers systems.
I will give you some part numbers here, you should be able to cress
them to a Canadian number at Canadian Tire Store:
AutoZone part# MV105 and I have used this several times on number of
transmission.
Others that are available from RockAuto.com are:
ATP JX67Fram part#FM2331AC Delco 89057785 fits both the TH400 & TH425
transmissions as do all of these modulators.Airtex/Wells
7R1003Standard Motor Products TM15
JR Wright
Michigan
-----------------------------------------From: "Les Burt"
To:
Cc:
Sent: 10-Dec-2017 17:45:48 +0000
Subject: Re: [GMCnet] Transmission vacuum modulator leaking?
Gordon,
Once you have determined if the modulator is at fault, I suggest you
make a few calls first thing Monday morning to see if a local auto
parts or trans shop can supply the modulator quickly. The answer to
that quest will quickly help you decide whether to procrastinate.
Les Burt
Montreal
'75 Eleganza 26'
> On Dec 10, 2017, at 12:28 PM, Billy Massey wrote:
>
> Requires no adjustment.
>
http://www.buyautopartsonline.ca/catalog-1/itemdetail/acdelco-professional-c
/> > anada/89057789
>
> -----Original Message-----
> From: Gmclist On Behalf Of Gordon Gibson
> Sent: Sunday, December 10, 2017 11:18 AM
>
> Ken,
> I get it, but...first I need to confirm the problem. Then I have to
source
> a modulator. As Les Burt mentioned, that will probably involve
getting it
> shipped from somewhere- most probably the US, which always takes
twice as
> long as one would hope. Just this morning we got several inches of
wet white
> fluffy stuff, and there's another 10 or so on the way on Tuesday.
I've
> changed enough starters and water pumps lying under a car in the
snow and
> slush
> to find procrastination an appealing course of action.
>
> Also - I thought I read somewhere that the modulator needed to be
adjusted
> by turning an internal set screw a given number of turns then fine
tuning
> form smooth shifts. Is this the case
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Transmission vacuum modulator leaking? [message #327049 is a reply to message #326960] |
Tue, 12 December 2017 11:41 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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There is no time for real rust to form so do not be concerned about rust on
cylinders unlees it sits ariund for few month .
On Tue, Dec 12, 2017 at 9:39 AM, Jim Kanomata wrote:
> Make sure your fluid has harly any Anti Freeze as that will cause the
> bearings to lock up.
>
> On Tue, Dec 12, 2017 at 9:09 AM, Billy Massey wrote:
>
>> Would it be advisable to insert some radiator stop leak and head out for
>> Boremanns at first light? Only slowing down for fuel and fluids.
>>
>> bdub
>>
>> On Tue, Dec 12, 2017 at 10:49 AM, Gordon Gibson > gordon.gibson@videotron.ca>
>> wrote:
>>
>>> Once again, thanks for the helpful comments guys. Given what I think
>> to
>>> be the nature of the problem, procrastination has ceased to be an
>> option and
>>> I am trying to find a a garage to fix it. My preference would be to
>> bring
>>> it back to Borrmann's Garage in Bluevale ON (500 miles away) but that's
>>> probably not a wise idea.
>>>
>>> My experience is that it's hard to find good garages to work on GMCs.
>>> The truck places don't like to work on motorhomes and their
>> preferences go
>>> to
>>> diesel motors. Garages focused more on cars often don't have service
>> bays
>>> big enough and they don't like tying their lifts up for days while
>>> searching for parts or having machine work done.
>>> --
>>> Gordon Gibson
>>> 1976 23" Norris Upfit
>>> Montreal West, Quebec, Canada
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
> 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
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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