Transmission resistor mods - differences?

[WestCoastSVX]

Unless I missed another thread somewhere, I think it's time we put together a list of all the transmission resistor modificaitons out there and what each of them do. With at least 3 on the market, varying price from $10 up past $100, plus the old "just unplug it" method, what are the differences?


1) Unplug the resistor behind the battery

2) Smallcar shift kit

3) Harvey's Quickchange

4) Old Tom's custom resistor

Feel free to post facts, opinions, concerns, etc. This should be interesting. Please keep it civil though. :)

[svxfiles]

Unless I missed another thread somewhere, I think it's time we put together a list of all the transmission resistor modificaitons out there and what each of them do. With at least 3 on the market, varying price from $10 up past $100, plus the old "just unplug it" method, what are the differences?


1) Unplug the resistor behind the battery

2) Smallcar shift kit

3) Harvey's Quickchange

4) Old Tom's custom resistorhttp://www.svxfiles.com/custom.html#resistor

5) ECUTune TCU upgrade.http://www.ecutune.com/tcu.htm

Feel free to post facts, opinions, concerns, etc. This should be interesting. Please keep it civil though. :)

I have used all of these.:)

I really like the combination of 4 & 5!
Mine raised the line pressure without any harsh shifting or codes, and LAN's lets the SVX stay in a lower gear longer.
Now, (while driving like a grown-up) when starting out my Red 93 will go all the way across an intersection before it upshifts.

[AyeJaye]

I've been wondering about this too. What exactly does the resistor do, and what are the benefits to modifying/replacing/unplugging it?

[longassname]

Resistor mods increase the line pressure during times that the tcu is trying to reduce the line pressure. People have been using them to try to defeat the slow, sloppy shifts that SVXs came with from the factory. While it is possible to get at the sloppy shifts that way it's better to do it through the hydraulics because then you can increase line pressure when the tcu isn't trying to reduce the line pressure. Increasing the maximum line pressure increases torque holding capacity. Increasing torque holding capacity so that the brake band and high clutch do not slip prevents your transmission from burning up. Changes can also be made to increase lubrication of the planetary sets and bearings. The most common failure in SVX transmissions after high clutch and brake band burn out is failure of the thrust bearing on the rear support.

Resistor mods also mainly firm up shifts and don't dramatically speed up the shifts. They will speed the shift up a little because anything that reduces slippage during the engagement time will make the clutch pack or band being activated grab quicker. Valve body mods can speed up the shifts dramatically because there are modifactions made specifically and seperately to the fluid circuits that are slowing the shifts--not just line pressure. I have the valve body modifications for the SVX dialed in now. Shifts in transmissions with my modified valve bodies are instantaneous, firm, and smooth.

The short of it is that a good valve body not only shifts better than a resistor mod--it makes your transmission last much longer.

[oab_au]

I've been wondering about this too. What exactly does the resistor do, and what are the benefits to modifying/replacing/unplugging it?

The short story, is that the resistor allows two separate signals to operate the A solenoid, without interfering with each other.:)

The long story is that the resistor is part of the electrical circuit that allows the line pressure to vary with the throttle position, that is the torque that the transmission has to handle. When the load is light, there is no need for a high line pressure as it would only waste power, so the pressure is lowered in line with throttle position.

The signal that is sent to the A solenoid, that controls the line pressure, passes through the resistor to drop the voltage from a 12 Duty cycle signal to a 5 volt duty cycle, as the solenoid is a 5 volt unit. If this was the only line controlling the solenoid we would not need the dropping resistor.
This is the circuit of the two control lines.
http://www.subaru-svx.net/photos/files/oab_au/39636.JPG
There is another signal from the TCU that is used to reduce the line pressure at other times, like when the change is going to take place. The pressure is reduced by a 5 volt duty cycle signal that is sent to the A solenoid. This is why the dropping resistor is needed. If the throttle signal is 'wide full open' the voltage through the resistor is almost zero volts, so the A solenoid is turned off supplying full line pressure to the box. When the change is to happen the TCU sends a 3 volt signal to the A Solenoid to turn it on again to reduce the line pressure. If there was no dropping resistor, the zero voltage signal on the Throttle line would short out the 3 volt signal from the TCU. The resistor isolates the two voltages.:)

Altering the resistance of the dropping resistor, changes the relationship between the Throttle position and the line pressure, to make it higher that it would have been. It is still lowered during the shift.

The Quick Change is the only one to keep the line pressure from dropping while the band and clutches are engaging, and the only one to keep the engine from cutting the power, while the change is made.

Harvey.

[Trevor]

The long story and correct story, is that the resistor does not, and can not, separate two signals. It does not, and can not, prevent one from shorting out the other. It is a fact that only one signal is involved and therefore the impossible is not required.

Pulse width control of solenoid “A” involves the application of voltage from two circuits, but these act in combination and together form a single means of control.

The TCU combines each and every available input required and involved in adjusting line pressure via solenoid ”A”. A single signal is then computed and delivered to the solenoid via two circuits. As is logical and practical, there is no separation of the signal, as has been wrongly claimed.

SVX Transmission Line Pressure Control.

Line pressure is initially controlled via pulse width modulated, (PWM) electrical, normally closed, solenoid valve “A”. When open, this valve bleeds off pressure, rather than interrupts pressure, as a means of control. It provides precise control, but has only limited capacity. Therefore amplification is necessary, in order to achieve final control of the overall operative line pressure.

The adjusted pressure from solenoid “A” is applied as pilot control pressure, to a fully hydraulic pressure modifier valve. The pressure modifier valve, in turn controls the main pressure regulator valve. The result is a system of amplification, in two stages.

Solenoid valve “A” is controlled by means of a PWM signal, delivered by the transmission control unit, (TCU) via a direct circuit. This electrical signal comprises a series pulses, delivered at a fixed frequency of nominally 50 cycles per second. The length of the pulses, rather their frequency, controls fluid output from the valve.

The dropping resistor circuit.

It will be immediately apparent that the sudden on off pulse width modulated duty, to which normally closed solenoid valve “A” is subject, tends to cause what could be called a hammering of the valve seat, even though this is largely reduced/damped by the flow of the controlled fluid.

The dropping resistor introduces a second series of current pulses, applied in parallel with the control signal. These pulses are applied across the off cycles, so as to check the travel of the armature as it moves, thus reducing both shock and noise. These secondary parallel signals mean that in effect, during the closing/closed period, the voltage does not fall completely to zero.

This second series of pulses must be at a lesser level than the control signal, hence the dropping resistor. A resistor with a high current rating is required, which can not be mounted within the TCU enclosure.

Full voltage from the direct circuit operates the solenoid and quickly opens the valve. The low voltage dropping resistor circuit, holds in the solenoid and thus controls the point at which the valve is allowed to close. Therefore controlling the length of the low voltage pulse, sets the overall pulse length.

The full voltage direct circuit signal, comprises a very short fixed length pulse. This is immediately followed by an independent low voltage pulse, from the resistor circuit. The sum of the two provides the total pulse length delivered during each cycle.

It will be appreciated that increasing the resistance in the circuit, or opening the circuit by omitting the dropping resistor, will upset the normal pulse length, thus increasing the line pressure and making shifts more abrupt. Secondly, as an undesirable issue, shock loads applied to solenoid valve “A” are increased.