part one we described the TV
cable and how to set it to factory specification
at wide open throttle. We learned the idle starting point
of the TV valve was determined by the distance
the TV cable travels out as the "carburetors
linkage" is rotated back to its idle position.
This happens because idle position of the TV cable determines
the TV plungers starting position relative to the TV bushing. Subsequently this
TV plunger position determines the TV springs position which in turn determines
the TV valves starting position in the valve body. We also learned that
everything this transmission needs to know must be
communicated by TV feed fluid movement into the TV feed
orifice. The Pressure and volume of the TV feed
fluid into the feed orifice is 100% controlled by the TV valve as it moves to
subsequently expose more and more of the TV feed orifice as the vehicles accelerator
pedal is depressed. This requires a very precise relationship be established
by the coordinated effects between two components! The
distance the TV cable is allowed by the "carburetors linkage" to move
outward as the linkage rotates back to idle from W.O.T. and the length of the
Part Two we described where the TV fluid is
directed once it's allowed to enter the TV feed
passage. We learned that TV feed fluid
immediately effects line pressure,
up shift timing and light to medium throttle down
shift timing whereas heavy throttle downshifting
events are more controlled by TV fluid being directed
back to the TV plunger and TV bushing.
Heavy throttle up shifts and Down shifts are controlled by the TV
plunger's physical position inside the TV bushing
relative to the part throttle and forced detent downshift
ports. Part throttle downshifts are governed
by TV fluid allowed to enter the part
throttle downshift port at around 60% to 75% throttle
position. Forced or detent down shifts are
controlled by TV fluid allowed to enter the detent
control circuits when the plunger is 100% buried
inside the TV bushing. This physical positioning
of the TV plunger in the bushing is what allows TV
fluid to enter into the detent port!
important thing to be learned from Part Two is that proper control of these wonderful
overdrive transmissions requires full movement of the TV system including a correct
starting position where the TV valve is positioned right at the edge of
the TV feed fluid orifice at idle and a TV plunger that
gets completely buried then the accelerator pedal is depressed fully! The
fully depressed TV plunger position is very easy
to achieve at wide open throttle, also very simple
to verify. The correct starting position can be somewhat
complex to set up but is also very easy to
Three will describe incorrectly established relationships
between the "carburetors linkage" return of the TV cable and the length
of the TV spring. We call these incorrect relationships
"illnesses" since they will have detrimental
effects on the proper operation of these transmissions. Certain "illnesses"
can cause rapid failure while others will just prove
aggravating, irritating and frustrating. We will explain how to diagnose
an "illness" and offer ways to correct
(cure) these afflictions.
TV VALVE MOVEMENT
we have a TV valve moving over the TV feed fluid passage regulating the volume
and pressure of the fluid entering the TV fluid orifice as the TV spring forces
the TV valve to move as the TV plunger is moved by the TV cable. We show what
we believe to be a movement which is very close to perfect for most applications.
We will describe some exceptions in Part four "Behavior"
here is a properly adjusted TV system setting at its idle
position. Note the the TV plunger is positioned
somewhere between its fully out position and its
fully depressed position. Please not that the TV plunger is held in this
starting "position" by the TV lever. This is also true for the TV
valve. The TV valve is "positioned"
in the location above by the TV plungers position in the TV bushing and the length
of the TV spring.
is important to understand that the TV valve would no longer be positioned as
shown in the picture if the TV spring was either longer or shorter then the one
in the picture.
would also not be in the position shown if the "carburetor linkage"
had allowed the TV cable to travel a further distance out as the carburetor linkage
rotated back to its idle position. Same is true if the travel distance would have
the TV valve is not positioned correctly we like
to think of its incorrect position as an "illness"
which needs to be diagnosed and corrected. We call the "illness"
where the TV valve is positioned short of the TV feed orifice, short
spring syndrome or SSS for
short. The second illness where the TV valve is positioned beyond the edge of
the TV feed orifices edge is called long spring syndrome
of LSS for short.
Spring Syndrome - SSS
conditions will cause SSS. The first occurs
when some well meaning person "adjusts"
the TV cable again after performing a correct factory "set" procedure.
This typically happens when some knuckle head tells him that readjusting the TV
cable is a great way to "adjust" the transmissions
behavior. The second is a TV spring that is too
short to properly position the TV valve right at the edge of the TV
feed orifice after the cable has been "set" to factory specification.
The last cause of the TV valve being positioned "short"
of the TV feed orifice is when
the TV cable was allowed to travel too long
a distance outward when the"carburetor linkage" rotated back
to idle from the correct Wide Open Throttle position
of the cause, the result is still the same. The TV
valve is positioned short of the leading edge of
the TV feed orifice at idle. SSS
can simply be defined as a condition where the TV valve
must be moved some distance before it reaches
the edge of the TV feed orifice where it can begin
its management influences. The distance the TV valve must travel before
it can begin to "manage" will determine how serious the condition is.
is potentially a very dangerous condition since the vehicles accelerator pedal
will be signaling the vehicle's engine to make increasing amounts of torque before
the TV valve even starts to signal the transmissions
pressure boost system to raise line pressure to off set
this increasing twisting force. Severe SSS will lead
to very rapid transmission clutch / friction
failure since clutch clamping pressure will
be lagging behind engine torque input! Mild SSS afflicts
a large percentage of Th-700R4 and Th-2004R transmissions because of the natural
"shortening" of the TV spring that occurs
during the millions of cycles this spring is put through during it normal lifetime.
If the TV spring is not "re-calibrated"
during the rebuild and installation process,
this "illness" will still be present when
its installed back into the vehicle. This condition will lead to a much shorter
service life then it gave the first time around. We believe that "mild"
SSS is the root cause of almost all friction failures in these
transmissions especially high gear friction failure. Food for thought; if a transmission
is capable of providing 300,000 miles of normal service but "fails"
at 125,000 miles instead, is that acceptable?
other leading cause of failure is overheating which is also easy to prevent!
also delays the signal to delay the up shift timing, consequently the transmission
will "usually" short shift ( commonly
called stack shifting) as it sequences up through the gears. Stack shifts are
shifts that occur earlier then is appropriate for the specific throttle setting
at the time. While this condition can be quite irritating, it normally doesn't
hurt anything. Low pressures, on the other hand, are very serious and can easily
go unnoticed until it's too late since a little bit of slippage can be very hard
to detect. Whether you know about it or not, it will still
accelerate friction wear.
affect from the condition of SSS
is its affect on downshifting. Downshifting will be delayed relative to accelerator
pedal position or be non -existent altogether. This is especially noticeable while
trying to get a forced or detent downshift which relies on the TV plunger being
totally depressed into the TV bushing at W.O.T. If your transmission is late
to downshift or doesn't two gear (detent) downshift, I would be very suspicious
of an SSS condition.
condition is very easy to identify using a 0-300 PSI gauge to confirm instant
pressure response with even the slightest movement of the TV cable. (Insert link)
The installer can easily remedy this condition.
advise is never drive a vehicle that has an SSS condition until is fixed!
Spring Syndrome - LSS
other incorrect TV set up condition is what we call
Long Spring Syndrome (LSS).
This condition exists when the TV valve is positioned
in such a way as to cause TV feed fluid to be prematurely
feeding into the TV feed orifice. This condition will be influencing
the transmissions control circuits even though the accelerator
pedal is still in its idle position. We know of four things that will normally
cause the LSS "illness". First is
when the vehicles accelerator pedal will not rotate the "carburetor linkage"
to its full W.O.T. position and the accelerator pedal is then used during a
factory "set" procedure to "set" the W.O.T. position.
Second cause would be a "carburetor linkage" which
causes the TV cable to return a distance shorter than required to position
the TV valve at its correct starting position. Third
is a TV spring that's too long
which subsequently will not allow the TV valve to
position correctly at the edge of the TV feed orifice.
This LSS condition rarely causes damage but
can result in some very frustrating behavior. LSS
causes the TV valve to be positioned in such a way
as to allow TV feed fluid pressure and volume to
feed into the TV feed passage before the accelerator
pedal is depressed at all! This condition signals
for higher line pressures and instructs the up
shift control circuits to start delaying the up shift
timing before the accelerator pedal is even depressed
at all! Common symptoms of LSS are late hard up shifts compared to the
accelerator pedal position during light to medium throttle driving situations.
Late hard shifts during light throttle driving situations gets very old in a hurry.
Downshifting may occur too early and can sometimes causes "shuttling"
between overdrive (4th) and 3rd gears. The transmission may produce double down
shifts at inappropriate times, of example, it shifts from overdrive (4th) down
to second gear (2nd) gear when a shift into third (3rd) would have been far more
condition is also very easy to diagnose using a 0-300 PSI pressure gauge attached
to the transmission pump diagnostic port on the drivers side of the transmission.
When you're certain your TV cable system is
achieving the correct W.O.T. relationship between all of its components; the accelerator
pedal completely depressed, the "carburetor
linkage" rotated to its mechanical W.O.T. stop and the TV
plunger totally buried into the TV bushing.
Perform the following test; first start the engine and let it idle. Record the
reading on the pressure gauge. Disconnect the TV cable and "gently"
start allowing the cable to return into the cable housing. If at any point the
pressure reading drops lower then the pressure you originally wrote down, you
have an LSS condition! How much the pressure
drops will determine the severity of your transmission LSS
your transmission has an LSS condition but
passes the following drive test (click on the link below) and you are happy
with its overall behavior, you should probably leave it alone!
Click here for our 'Test driving procedures'
you now are certain your TV cable is set up correctly with no signs of SSS
or LSS but it still doesn't behave the way
you would like, you should now proceed to Part Four "Behavior"