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Part Three: "Illnesses"

In 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 TV spring.

In 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!

Most 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 verify.

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Part 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.

 


NORMAL TV VALVE MOVEMENT

 

Here 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"

 

 

Pictured 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.

It 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.

It 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 been shorter.

Whenever 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.

Short Spring Syndrome - SSS

 

Idle PositionW.O.T. Position

 

Three 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

Regardless 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.

 


SSS CONDITION

 

SSS 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?

The other leading cause of failure is overheating which is also easy to prevent!

SSS 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.

Another 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.

This 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.

Our advise is never drive a vehicle that has an SSS condition until is fixed!

 

Long Spring Syndrome - LSS

Idle PositionW.O.T. Position

 

The 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 appropriate.


LSS CONDITION

This 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 "illness".

If 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'

 

If 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"

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