Part Two: TV feed fluid
of Part two is explain where the TV feed fluid is directed to once it enters
the TV feed passage. Once explained, it will
become clear that these transmissions need a TV system that buries the TV
plunger inside the TV bushing at W.O.T.and positions the TV valve at the
correct position inside the TV bushing at idle!
graphic is a reasonably accurate representation of a Th-700R4 Throttle Valve
(TV) system in the correctly set factory position for a Chevrolet C/K pick
up with a 350 CI engine with TBI
Quoting GM again, not
to be redundant, but to again focus our attention on the functions controlled
by the TV cable system!
TV cable used with the 4L60 transmission should not be thought of an automatic
downshift cable. The TV cable used on the 4L60 controls line
pressure, shift points, shift
feel, part throttle downshifts and the
detent downshifts. The function of the (TV) cable
is similar to the combined functions of a vacuum modulator and a detent cable."
The five activities
listed above are influenced by the TV valve movement. As the TV Valve starts
feeding TV fluid into the feed orifice (blue circle),
it's directed to three places as it enters the passage shown below (area
shown in transparent red). TV fluid passes through the spacer plate
(green circle in bottom picture) into the transmissions
pressure boost circuit where it instantly boosts line pressure. This fluid
also feeds to the circuits that control up shift timing and feel called MTV.
The transparent red fluid also feeds the port
shown (purple circle in top
picture) directing TV fluid back into the
TV bushing and TV plunger (See heavy throttle upshift
and downshift control section below) to assist plunger movement so
the pedal pressure isn't excessive. This fluid also feeds the part throttle
(Green arrow) and detent (Yellow
arrow) ports in the TV bushing.
The picture below has a hole (Green
circle with explanation in the spacer plate TV fluid flows through after entering
the passage in the valve body indicated with the transparent red color in
the picture above. This fluid
are plenty of "cross over" effects between these three circuits
which we will not even attempt to explain since this article is only meant
to provide an overview of the TV System
and its effect on these transmissions. When you read the following few paragraphs,
it should become clear that all activities
of these transmissions are effected by the TV valve system. The following
information is offered to help the owner / installer understand why the
TV valve must have a correct starting (idle)
position and a correct wide throttle position,
not just one or the other. By the end of Part Two it should
be obvious that some aspect of the transmission management will not be correct
unless the TV system is managed correctly through its full spectrum of movement!
The TV feed fluid
is directed into three control circuits which subsequently control or effect
Line pressure management and upshift
and downshift timing and feel are fed directly as fluid enters the feed orifice
Pressure: The TV feed passage (green
circle on spacer plate above) directs TV fluid to the transmissions
pressure boost system, via the line bias valve. The transmissions line pressure
will rapidly rise as fluid enters the TV feed passage and will typically have
it's full boost effect
by the first
65% of accelerator pedal movement
off the idle position! The need for instant pressure rise to off
set any increased input of torque into the transmission by the
engine is CRITICAL!
AND DOWNSHIFT TIMING AND FEEL
and downshift timing and feel:
This fluid circuit is called modulated
TV up. The MTV up
control circuit is designed to appropriately delay upshift timing with increases
in accelerator pedal application. The further the accelerator pedal is depressed
the later and firmer we want the transmission to up shift. This circuit has
effects on up shifts timing and feel occur during light
and medium accelerator pedal settings and less "noticeable"
effects after the TV system passes 1/2 throttle.
However, this circuit does effect less obvious things
all the way from idle to W.O.T.
second circuit is the modulated TV down circuit,
this circuit starts having its affects during heavy
to full throttle settings and has
little or no effect at light to medium throttle settings. This circuit
works hand in hand with the next
part throttle and detent ports located in the TV bushing.
throttle upshift and downshift control
fluid entering the TV bushing (left picture above) comes from the TV feed
orifice (blue circle-right picture) which is being fed by the movement of
the TV valve over the feed orifice. This fluid progressively increases in
volume and pressure as the TV valve is activated. We've tried to illustrate
these by color and transparency change.
throttle port and detent port in the TV bushing.
As the TV
valve feeds TV fluid into the feed orifice, part of this fluid is fed to the
TV plunger through a port in the TV bushing. This fluid increasingly
assists in moving the plunger against TV back pressure to prevent the throttle
feel from becoming too great. As the TV plunger moves down the bore of the
TV bushing it will eventually pass over the part throttle port. The
TV plunger must travel 50% to 75% of its full available travel distance inside
the TV bushing before it reaches this port. This fluid effects heavy throttle
upshifts and under the right circumstances will cause downshifts. These downshifts
are normally a single gear.
port fluid feed. The TV plunger
must be moved all the way to the end of its available
travel to allow TV fluid to enter into the
detent port of the TV bushing. Fluid entering
this port does a number of things but we
feel one of the most important is its
effect on two gear down shifts (sometimes
three gear)! We are continually amazed
at how many people with these transmissions don't realize their transmissions
are capable of doing double gear downshifts because theirs never has. TV
fluid can only enter this port when the TV plunger is completely
buried at W.O.T. For the part throttle
and detent down shift fluids to have their proper effect on downshifting
and upshifting, the TV plunger must move from the
systems 50% throttle position to its W.O.T. position!
pressure management has its greatest effects during the first 50 to 65% of TV
valve movement. Light and medium throttle up shift timing and feel is
managed during the first 50 to 60% of TV valve movement.
Wide open throttle upshifts are heavily influenced during the last
30% of TV valve travel. Part throttle port in the
TV bushing only gets fed after 50% to 75% TV
plunger movement. The fun two gear downshifts
are initiated by TV fluid directed through the
TV bushings detent
port. This port is only fed when the TV plunger
is completely buried inside the TV bushing at W.O.T.
Each of the
three TV fluid feeds described in the
preceding paragraphs has
its own specific effect
on these transmissions during a
designed range of movement as the
TV plunger moves from its idle position to wide open throttle
position. Line pressure is controlled during the first half of movement, up
and down shifting during the full range of movement and the part throttle /
detent ports effects only occur after half throttle to W.O.T. Once you understand
that "all positions" have effects
on specific transmission management activities, you will then understand how
important it is to establish a correct full
movement TV cable system.
the information provided in Part Two is to make one point crystal clear. A correct
starting position of the TV system and a correct
ending position of the TV system must be established for all
functions to perform correctly! Getting the correct
(W.O.T.) ending position is very easy
to do using the factory TV cable adjustment procedure. The trick
is to get the correct starting position of this system.
The correct starting position is determined by two factors, length
of the TV spring and the distance the TV
cable is allowed to return once the correct TV cable W.O.T. relationship
is "set". A method to fix the relationship between these two factors
in stock applications will be offered at
the end of Part Three.
of Part Two
one of these wonderful overdrive transmissions to operate properly, the TV
system must start with the TV
Valve positioned at the edge of the TV
feed orifice with the accelerator
pedal in its idle
position and end up with the TV plunger
completely buried inside the TV bushing when the
accelerator pedal is fully depressed!
the following procedure, the installer can easily check to be sure the TV plunger
is positioned correctly relative to the feed orifice, moves instantly with even
slight applications of the accelerator pedal and confirm that the TV plunger
is mechanically positioned against the face of the TV bushing at W.O.T.
procedure will require the use of a second person. Connect a 0-300 PSI pressure
gauge to the transmissions pump diagnostic port on the drivers side of the bell
housing. Perform the TV "set"procedure, start the engine and check
for the following:
here for an explanation of how to hook up a 0-300 PSI gauge
- First; your
pressure gauge should read the same with the TV cable connected or disconnected.
A slight pre-load of 2 to 4 lbs at idle will not normally produce any adverse
- Second; when
the TV cable is connected and adjusted correctly, even slight movements of
the TV cable where it exits the cable housing should produce instant
- Finally; have
your assistant depress the accelerator pedal fully and hold it there. Using
a set of pliers, try to pull the TV cable further out. If you can not, then
this demonstrates the TV Lever is firmly against the face of TV bushing at
this W.O.T. position.
- If your system
doesn't pass these tests, they can be fixed! The fix process may require the
removal and reinstallation of the transmissions pan a few times but it is
not that difficult to do. Delayed pressure response
can be very serious and needs to be addressed A.S.A.P.
Three will explain how to determine which "Illness" your
transmission has and how to cure the problem.