Resistor mod ver2.0
 

So after a bit of trouble trying to source a "dropping" resistor for my 92 LS-L I figured I just fab one up myself. I looked online at digi-key and selected a variable resistance resistor. Its adjustable from 0-50ohms. I currently have it set at 28.5ohms. Works GREAT!!!

http://search.digikey.com/scripts/Dk...-50-nd&x=0&y=0

P/N AVT25-50-ND Shipped came out to (IIRC) $8.50

http://i17.photobucket.com/albums/b86/BVM03/015.jpg

http://i17.photobucket.com/albums/b86/BVM03/016.jpg

Hope this helps those looking to do the same thing! Enjoy!!!!

Re: Resistor mod ver2.0
 

What is it for?

Re: Resistor mod ver2.0
 

longassname's

Re: Transmission resistor mods - differences?
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.


And from Trevor
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 and back stop, 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.

It will be appreciated that increasing the resistance in the circuit, or opening the circuit by omitting the dropping resistor, has two outcomes. Firstly the PWM voltage during closed periods falls to zero, resulting an increase in its effect, thus increasing the line pressure and making shifts more abrupt. Secondly, as an undesirable issue, shock loads applied to solenoid valve “A” are increased.

The resistor should measure between 9 and 15 ohms to be within specifications and is usually close to 12 ohms.

Re: Resistor mod ver2.0
 

Ok, I have seen modified ones, but never quite like that.

Re: Resistor mod ver2.0
 

This method I have the ability to change the shift firmness to my personal taste. Quite easily at that.

Re: Resistor mod ver2.0
 

Yea, I made an adjustable one about five years ago.
It was a simple thing, using a variable resistor.
But I could not tell the differance between the low setting and the high setting...
That is why I settled on the 20.6 OHM resistor that just works.
(With out tripping the Power Light.)
I am glad that you used my research to come up with this.:)

Re: Resistor mod ver2.0
 

Coming up with my own method enabled me to actually GET what I wanted. :lol:

I'd leave it at that.:cool:

Re: Resistor mod ver2.0
 

Ok so what exactly are you trying to do with this mod?

Re: Resistor mod ver2.0
 

What do any of us intend to do with any mod? :lol:

What am I trying to do? Hmmm well since you asked.

I wanted a dropping resistor as it is supposed to help with shift firmness per this forum.

I was "unable" to secure one via the normal method due to whatever it was... I dont really care at this point.

I looked online at what was needed and gave myself some flexibility with the design. I am able to increase or decrease the resistance as I try to dial in the right shift firmness. Its not perfect but it avoids the whole one size fits all and negates the core availability problem.

I built it, tested it and offered the results and how to duplicate it FOR FREE to the forum.


FFS.

Re: Resistor mod ver2.0
 

have you fabricated a bracket to mount it with?

Re: Resistor mod ver2.0
 

I used a small L shaped bracket I had laying around in my yellow bins of death.

Re: Resistor mod ver2.0
 

The dropping resistor is in series with the A solenoid to drop the 12V signal from the TCU to about 5V to suit the 3ohm solenoid. The standard resistor is 12 ohms the solenoid is 3 ohms, so 0.8 amps flow in the system, to have the line pressure change, to suit the throttle position.

If we use a higher resistance of 20.6 ohms, the total series resistance is now 23.6 ohms to flow 0.5amps. This increase will have the line pressure 37% higher than it was. The maximum line pressure will not increase, only the lower pressures are increased.

This can help a terminally ill box to survive, in helping the band not to slip in 4th at low speed, but it will also increase the pressure to the C solenoid by the same amount, that can cause the transfer clutch to bind at low speed turning.

As for firming up the shifts. The TCU lowers the line pressure when the shift is to take place, so you are not really fixing the soft change, just making it feel better.

The Quick Change does it right.:) it prevents the pressure drop, and the 50% power cut during the shift, to remove the time lag, and allow the shift firmness to suit the throttle position.

Harvey.

Re: Resistor mod ver2.0
 

The resistor circuit has no individual relationship with throttle position. Solenoid A is controlled by means of a combination of signals delivered the full voltage, as well as the resistor circuit. The resistor circuit, due to the reduced voltage, is not capable of properly moving the solenoid.

Line pressure is adjusted by means of the pulse width and the length of time the valve is open. If the resistance/resister is increased, a point will be reached, whereby the solenoid will not remain held in for a complete cycle. N.B. Altering the resistor can not provide a degree of adjustment.

If the resistor is reduced in value, below an optimum figure all control via the TCU will be eliminated. There is no half way or adjustable position.

At an intermediate fixed throttle position, the "QC" totally eliminates control of line pressure via the TCU. At and from a specific point any control relative to throttle position, is eliminated.

Re: Resistor mod ver2.0
 

I don't think every body would agree with you.:rolleyes:

Harvey.

Re: Resistor mod ver2.0
 

Those with real interest in the subject, should go here for definitive information. ---

http://www.subaru-svx.net/forum/showthread.php?t=53241