tranny resistor
 

Several threads discuss the resistor disconnected, small car mod- however does anyone know how the transmission uses the resistance or lack of resistance in adjusting shifting. I seen 60 ohms, 100ohms recommended.


John

I can't help with a technical explanation, but here is some basic info:

Low or no resistance = higher hydraulic pressure = harder shifts.

Higher resistance = lower hydraulic pressure = softer shifts.

Too much resistance = too low hydraulic pressure = no shifts(?), lots of slippage, creating excessive heat = BAD, ultimately dead tranny.

I thought I had read that the maximum resistance to use was 62.5 ohms. Sorry, I can't find that thread to confirm.

Good Luck,
Dan

I'm using 35 ohm in mine with no noticable problems. I'm planning on playing with it next weekend and dropping it to 20 ohm and see how it changes.

Correction.
 

The above should read :-

HIGH resistance, or OPEN CIRCUI i.e. no resistor or connection, = harder shifts. (Less or no bias supply.)

LOWER resistance, = softer shifts. (Increased bias supply.)

Too LOW a resistance, (excessive bias supply), = too low hydraulic pressure = no shifts(?), lots of slippage, creating excessive heat = BAD, ultimately dead tranny.

N.B. Specified value 12 ohms. Maximum resistance 15 ohms. Minimum 9 ohms. (All as specified in the Subaru Manual.)

The resistor circuit provides a steady positive bias supply, which is applied, in addition to a variable pulse width modulated control current. The resulting modulated current pulses duty soleniod A, in order to adjust fluid pressure as required.

Trevor

I won't argue with you because you have much more experience than I and you are quoting the Bible (Subaru Manual).

I only know what happened with my car. My transmission was very 'firm' when it shifted between gears and almost 'clunked' into gear when I went from neutral to reverse or drive. When I tested my original resistor it read 0 ohms (shorted, not open). When I installed a 10 ohm resistor purchased at my local electronics parts store, the transfer between gears softened.

Dan

Dan,

What you report is indeed strange. A resistor will usually go open circuit in the event of a fault, as it is physically near impossible for a short to occur without some external conductor being involved.

Did you make your measurement while the resistor remained connected to the car wiring ? Could it be that you were reading infinity in lieu of zero ohms as this could be an easy mistake to make.? Do you still have the faulty resistor ?

The 10 ohms resistor which you have installed is of course within the specifications and you have fixed things properly.

Please be sure that I am trying to assist rather than argue. Particularly to be sure others are not led in the wrong direction. What is more there are still some unanswered questions regarding this circuit.

Cheers, Trevor.

Trevor

I'm sorry, when I just reread my post. it did sound a little snotty . . . :o

Yes, I do still have the faulty resistor. I'll recheck it, it'll be a couple of days. My number one priority on my next day off will be a cracked radiator in my wife's SVX.

Dan

im curious, anyone know what the watt rating on the stock resistor is? it looks to be a 10+w style, the hard ceramic casing is a give-away. anyone knwo for sure. id like to do some resistor play, but i want to avoid frying resistors, i cant stand the smell of fried electronics. lol (magic purple smoke... :D)

But starting fires with a 1/4 or 1/2 watt resistor can be so much fun . . . I used to 'remote start' campfires when I was in Boy Scouts.

Check out this thread, sperry states that 20 watt is OEM, he didn't say where he got the info from but I like his write up on how to replace the stock resistor!

http://www.subaru-svx.net/forum/showthread.php?t=29344

Dan

I'm using 25 watt resistors in my setups.;)

Resistor wattage.
 

The current flowing in the circuit, depending on the tolerance variation of the components, is 1.3 A for the lowest resistance, 0.7 A for the highest resistance. At the highest voltage of 14 V, the wattage is from 18.6 W to 10.05 W.
So a 25 Watt resistor is needed.

Harvey.;)

What is the recommended maximum resistor value? I have 100 ohms and I still feel like it is not shifting quickly/firm enough. Someone wrote that the solonoid needed a minimum current for longevity.

Harvey,

Simple ohms law does not apply in respect of calculating current on several counts, even if it were accurately appled.

It should be appreciated that a second parallel supply circuit is also involved here and more so that this circuit is intermittent. Most important, is that the end load is purely inductive rather than resistive. Variable inrush currents will apply. The time base of the parallel control signal will comprise the basis for current variations.

However it does appear, specifically on the practical basis of what others have reported, that 25 ohms is a good safe compromise.

Your old mate, Trevor.

P.S. Still waiting on you taking up my long standing wager/challenge regarding the operation of the solenoid.

The solenoid remains continually activated via a separate circuit, which applies a modulated voltage thereby intermittently energising the solenoid in order to control pressure. Disconnection of the resistor, or increasing the resistance, should therefore have little effect on the life of the solenoid.

However that said, with the resistor disconnected the solenoid does become fully de energised during each cycle of the control signal, but the fluid flow should prevent any hammering. Then again this could be the designed function of the resistor and bias supply.

The 100 ohms you have in the circuit should prevent trouble light indication, while it is unlikely that the shifts are being softened to any degree. Experiment by disconnecting it.