| [GMCnet] Update on Tranny [message #84063] |
Tue, 11 May 2010 10:26  |
fbhtxak
Messages: 191
Registered: April 2006
Karma: 0
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Senior Member |
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Dan,
Further to Ken's and Jim's comments...
Does the engine RPM increase when the TH425 "downshifts".
You won't necessarily know that if you don't have a tach.
In '03 driving to Tucson/GMCMI from East TX, the fan clutch
suddenly engaged near El Paso and would not disengage.
'Sounded similar to "transmission downshift" and felt
somewhat the same way - until I focused on the tach. Prior
to "failing safe", the clutch would "gently" engage - but
only for a short time to reduce the coolant to the
thermostat set point (190F). That happened mostly when
leaving a "super slab" for fuel or on non-super slabs when
going through a small town. 'Would usually disengage after
about 1-2 minutes... The reason it "felt" like a downshift
was because of the sudden, long duration fan load on the
engine. It was a long drive from El Paso to Tucson with the
"roar of the fan". 'Replaced the clutch at Tucson...
'Agree with Ken and Jim - although a long shot, the "noise
and sensation" you experienced may not be what it appears to
be...
Fred Hudspeth
'78 Royale - Tyler, TX
'82 Airstream Excella 28' Motorhome - Anchorage, Alaska
From: Ken Henderson <hend4800@bellsouth.net>
Subject: Re: [GMCnet] Update on Tranny
To: gmclist@temp.gmcnet.org
Message-ID:
<AANLkTikrUAzPXGOz7IMSNqEaHATbDXs4lWbdHX8X-EQj@mail.gmail.co
m>
Content-Type: text/plain; charset=ISO-8859-1
Dan,
Don't feel bad if that's what's happening. Crossing the
Texas panhandle in '96, driving our '90 Airstream Land
Yacht, every time I slowed down the transmission
downshifted. We spent that night at Palo Duro Canyon, from
where I called my RV dealer friend in NC. He called back
the next morning, after talking to his service manager, with
the same diagnosis.
The Airstream had an auxiliary electric fan. After I
installed a manual switch parallel to its thermostatic
control, and used it, the symptom never recurred.
Talk about embarrassed -- worse than having my pants fall
down!
Ken H.
On Tue, May 11, 2010 at 2:10 AM, Jim Maher
<hasbeen24@msn.com> wrote:
>
>
> Dan, sometimes I just get these crazy thoughts that jump
back into my
> mind from earlier days. Bear with me while I run this by
you and see
> what you think. When GM came out with what they called the
HOT chassis
> in 1986 I was working as service manager at an RV
dealership here in
> the Phoenix area. We started to get complaints from
customers along
> the same lines that you are stating, namely "the
transmission is
> shifting down". I have not read the full story on yours so
I may be
> way off the mark. What we found was not the trans dropping
down a gear
> but the fan kicking in to cool down the engine
temperature. We proved
> this by watching the temp gauge rise, fan kicking on with
the loud
> roaring noise, temp gauge lowering. If you have a
tachometer it would
> be another way of determining if it is actually dropping
down a gear.
> I know you had a new engine installed and if they
installed a new viscous fan assembly along with it that
would be a different sound to you.
> Hope this helps, Jim
> _______________________________________________
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| Re: [GMCnet] Update on Tranny [message #84071 is a reply to message #84063] |
Tue, 11 May 2010 11:09  |
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WD0AFQ
Messages: 7111
Registered: November 2004
Location: Dexter, Mo.
Karma: 207
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Senior Member |
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Thanks Fred. I wish that was it. At 60 mph my tach is running around 26-2700 rpm. When the thing kicked, @ 60 mph, I looked and the tach was at 3500. I never run the engine over 3 grand, and normally about 26-2700. I do love hotrodding but not in a 12,000 pound beast with a car engine and tranny.
Dan
3 In Stainless Exhaust Headers
One Ton All Discs/Reaction Arm
355 FD/Quad Bag/Alum Radiator Manny Tran/New eng.
Holley EFI/10 Tire Air Monitoring System
Solarized Coach/Upgraded Windows
Satelite TV/On Demand Hot Water/3Way Refer
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