Tranny Resistor Replacement: The affordable way!

[kuoh]

Not necessarily, the higher rating only means that it is capable of dissipating more power before the resistor is damaged. That or the manufacturer is overstating their ratings, i.e. 110 amp alternators that only put out 95. To absorb more power, you need a bigger surface area to dissipate heat. In the same packaging, 20 watts of heat is 20 watts of heat.

FYI: I replaced with the OEM resistor as well, and I'm still getting intermittent code 11's, so it looks like an ATF and solenoid change is in my near future.

KuoH

Originally Posted by sperry

The heat of the resistor is a good point. 'Course I'm using a 25W resistor than a 20W (which is the OEM rating), so it should run a little cooler than stock.

[sperry]

Originally Posted by kuoh

Not necessarily, the higher rating only means that it is capable of dissipating more power before the resistor is damaged.

Let's say a resistor can handle a max temp of say 200 degrees before it's damaged.

A 25W resistor will "max out" when you put 25 watts of power through it. A 20W resistor will "max out" at only 20 watts. So if you put 20 watts through both resistors, the 20W will be maxed and the 25W won't be, right?

So, by extension, if the packaging is the same, and you put the same amount of power through both resistors, the 25W resistor will be cooler than the 20W resistor, no?

[kuoh]

No. Resistors dissipate power in the form of heat. Where did you think that power would go? It's more like a 20 watt resistor dies at 200F and a 25 watt resistor will hold out till 250 or....it has more area to dissipate the additional heat so the internal elements can stay under 200F. The numbers are just figurative ofcourse.

KuoH

Originally Posted by sperry

Let's say a resistor can handle a max temp of say 200 degrees before it's damaged.

A 25W resistor will "max out" when you put 25 watts of power through it. A 20W resistor will "max out" at only 20 watts. So if you put 20 watts through both resistors, the 20W will be maxed and the 25W won't be, right?

So, by extension, if the packaging is the same, and you put the same amount of power through both resistors, the 25W resistor will be cooler than the 20W resistor, no?

[Budfreak]

i did this to my resistor about 9 months ago almost exactly the same way. i used the same brand and wattage of resistor but first i tried a 25 ohm and didn't think it was firm enough so i added in another 10 ohm. my tranny shifts pretty firm and smooth most of the time. i still get my little flair sometimes from 2-3 and i've already done the brake band and so on so i think it's my tps causing it because it only usually does it between 1/2 and 3/4 throttle.

[dan_j_b]

I have a bag of those resistors left over from when I did mine if anyone needs one, PM me

Dan

[Budfreak]

Originally Posted by dan_j_b

I have a bag of those resistors left over from when I did mine if anyone needs one, PM me

Dan

got a 15 ohm?

[dan_j_b]

I have 7 - 10 ohm 25 Watt resistors. Sorry, no 15 ohm

[UPnorth362]

So less resistance= shorter, firmer shift and more resistance= longer, softer shift? is there any damage not running the resister. Would it hurt to use a rheostat and change resistance while the car is running?

[Nomake Wan]

Originally Posted by UPnorth362

So less resistance= shorter, firmer shift and more resistance= longer, softer shift? is there any damage not running the resister. Would it hurt to use a rheostat and change resistance while the car is running?

Think ya got it backwards, there. Less resistance is softer, more resistance is firmer. Budfreak said 25 ohms was too soft, so he bumped it up to 35 ohms and that was firmer.

[Budfreak]

Originally Posted by Nomake Wan

Think ya got it backwards, there. Less resistance is softer, more resistance is firmer. Budfreak said 25 ohms was too soft, so he bumped it up to 35 ohms and that was firmer.

Note: 25 OHMs was too soft for ME. Others might not agree as I lean towards accelleration and racing use.

[Trevor]

So that you guys no exactly what you are about, it is I hope worthwhile to again publish my explanation of all that is involved:-

DUTY SOLENOID VALVE "A". This is a pulse width modulated duty solenoid valve, ( Sometimes known as a pulsoid). The device is incorporated in the SVX transmission control system, in order to adjust line pressure in the following manner :-

The fluid line is provided with a bleed or bypass via an on/off device, in the form of an electrically operated valve. This solenoid valve is opened and closed repeatedly, in a rhythmical manner by a control current which is turned on and off by the transmission control unit (TCU) at a very fast rate. The valve is a normally closed device, and remains closed in the event of the loss off a control current.

After passing through this modulated solenoid valve, the continually interrupted pressure is in the form of a pulsed flow. When the peaks level off with the troughs, there is a resulting overall steady reduced pressure. The level of this pressure is adjusted by varying the on/off intervals. Most often the length of the on time is adjusted and the number of on/off pulses per second is kept constant. The usual rate is around 50 cycles per second.

The resulting adjusted output pressure is therefore delivered as a rapidly fluctuating stream. The system incorporates an expansion chamber as a smoothing element, which works as a sort of cushion. This device is usually in the form of a cylinder and piston or diaphragm, backed by a coil spring.

In the SVX system the component is described as a Pressure Modifier Accumulator. The high pressure peaks in the stream press the piston outwards and become rounded off, while the low pressure troughs are filled in as a result of the piston moving inwards under spring pressure. The end result is a smoother level of pressure, such that controlled devices are not materially affected. An increase in the volume of fluid controlled, is achieved by transferring the solenoid regulated pressure, to a pressure modifier valve and a regulator valve.

It should be clear that by “chopping” the fluid supply in an adjustable way, pressure control is achieved economically using a simple poppet type solenoid valve, with few mechanical or electrical complications. However the valve remains in a continuous cycling mode, which imposes rather arduous mechanical stresses.

THE DROPPING RESISTOR CIRCUIT.

It will be immediately apparent that a sudden on off cycle tends to cause what could be called a hammering of the valve seat, even though this is largely checked by the viscosity of controlled fluid flow. The dropping resistor introduces a second series of current pulses applied in parallel with the control signal. These shorter pulses are applied during the off cycles and timed to check the travel of the armature as it reaches the closed position, thus reducing both shock and noise. These secondary parallel signals in effect, “round off” the closing period and reduce the closing shock.

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 relative electrical off time is increased thus increasing the line pressure and therefore makes shifts more abrupt. Importantly as a second issue, increased shock loads are applied to the valve. The resistor should measure between 9 and 15 ohms to be within specifications. The usual is about 12 ohms.

It is a documented fact that the line pressure control solenoid is the first to fail, due to having by far the most arduous duty to fulfill. Failure is usually mechanical, resulting in the valve seat not closing properly and as a result line pressure is markedly reduced. The end results can be drastic, especially in respect of transmission friction surfaces.

The fault will not necessarily be registered as a fault code, as the armature of the valve can be in the fully closed position with the problem confined to a worn or obstructed valve seat. In the event of an open electrical circuit, which should register, the valve being normally closed, will fail safe and result in maximum line pressure.

[Trevor]

Originally Posted by UPnorth362

So less resistance= shorter, firmer shift and more resistance= longer, softer shift? is there any damage not running the resister. Would it hurt to use a rheostat and change resistance while the car is running?

I hope that my previous explanation will assist in answering your queries.

You could use a rheostat, dependent on the drawbacks I have explained. However a device off sufficient wattage will be rather bulky and difficult to source. A better idea would be a rotary selector switch and several resistors providing selectable steps in resistance.

[Crazy_pilot]

Since this thread goes back a bit, are there any reports on the longevity of this fix? The comment was made that the heat in the engine bay could degrade the wires used to adapt the resistor to the SVX connector wires. Any problems to report on that front?

[UPnorth362]

The heat from the engine bay is not enough to degrade any type of good quality wire. Over time the shielding my become hard, but its not a part with alot of movement so it should not be a problem. Also with a 20 or 25watt resister there shouldent be substantial heat emitted. From my calculations, with 20ohm resistance there should be no more than 15watts passing through the circuit at 14.4volts. varying temps will of course vary these measurements.

[UPnorth362]

Also a note to the users here. I work for a large specialized electronics company and have access to just about every type of electronics component available. If anyone is looking for something in particular, let me know.