[Gmecm] Re: Geting rid of electronic transmission.

[Danny Sauer]

davesnothereman wrote regarding 'Re: [Gmecm] Re: Geting rid of electronic transmission.' on Thu, Mar 02 at 17:40:
> >> Where did this idea come from that the cooler only work in tcc
> >> mode?
> From a GM trans class, based on observed fluid flow.

Ask for a refund. :)

In this transmission class, did they go over the main cause of
transmission failure?  It's heat.  Thinking back, we might recall that
the torque convertor, when run below its stall speed, is slipping a
lot.  This slippage both causes a lot of heat (see #1 cause of
transmission failure, above) and shear degredation of the transmission
fluid - causing decreased ability to lubricate.  That makes heat.  I
refer back to "#1 cause" again here.

Now, let's think back to the transmissions that failed.  Given a
lockup-style convertor, the stall speed can be raised a little because
the TCC will be locked up under normal operating conditions.  Raising
the stall speed alows a little better responsiveness.  But what if the
TCC was disabled?  Then under normal "driving around town at low
speeds" conditions, the TCC would no longer be able to operate.  But
the engine wouldn't be revving high enough to be in full stall, so
there'd be a lot of slippage in the convertor.  This generates a lot
of heat (#1 cause of failure).

In most stock vehicles, the only cooling capacity is the
in-the-radiator cooler.  On the hot side of the tank, for faster
warm-up.  This cooler has a very limited capability for cooling a
transmission, though it's adequate for normal use.  Notice that most
towing packages add an auxilary cooler just because of some extra load
- still less heat that a constantly slipping convertor will generate.

With this in mind, and remembering that "heat kills transmissions", do
you think maybe it's more likely that the transmissions died due to
excess heat build up from the slipping convertor beyond the ability of
the whimpy stock cooler to dissipate heat, or more likely that GM
totally redesigned their transmissions on the advent of lockup-style
convertors such that fluid only flows through the cooler when the TCC
is locked and the tranny is generating a minimum of heat?  Be careful,
and remember that there were some TH350s that had a lockup convertor
but were otherwise laregly unchanged from the non-lockup versions...

Let's say that all of that silly "theory" is unbelivable.  After all,
I'm a Unix systems administrator, not an ASE-certified GM transmission
technician.  What the heck do I know about transmissions?  Well, right
now, on my lap, is the factory service manual for the 1995 B platform,
book 1 of 2.  On page 7A-14A-13 (about halfway through) the words
"4L60-E Transmission fluid flow and circuit descriptions" appear in
bold type, and on the pages that follow, there are full color diagrams
showing all of the circuits in a 4L60E, and where fluid is flowing in
every gear for each possible gear position.  It starts with Park, then
Reverse, then all four gears with the indicater in overdrive, etc.
It's really a very good reference for diagnosing tranmission issues,
and for learning things that they skip over in GM Transmission Class,
so it seems.  In every illustration, there's a little picture of a
transmission cooler.  In every illustration, there are little red dots
with arrows indicating flow from the pump to the pressure regulator,
then the convertor clutch valve, and then into the cooler.  Those dots
and arrows indicate that there is flow through the cooler in every
gear for every position of the shift lever.  Both when the TCC is
locked and when it's not.

Anyway, you're half right - no TCC may well cause premature failure,
especially in a vehicle operating at low RPMs at low speeds when
there's low airflow over the trans case and through the radiator.
It's not because fluid's not flowing through the cooler, though, it's
because the cooler capacity is simply inadequate for the increased
load.  The old-timer's Corvettes probably don't fail because 1)
they're performance vehicles designed with extra heat in mind and 2)
they usually have shorter gears, so they're revving more in town.

--Danny