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brown wire mod on my truck

Oh, and to answer Dogfriend's original question, yes, you can perform the brown wire mod. .

I wasn't asking the question, Jim was.

The mod that I was talking about is placing a switch in the brown wire circuit, not supplying 12v to the brown wire.

If you are going to supply 12v, I think placing a resistor in line to limit current is a good idea. I don't remember what the max duty cycle was when I did my test with the scan tool, but it was never 100%.
 



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Oops... sorry.... My confusion...

Y'all have got me curious now. I'll check it out as soon as I get home (meter is in my computer room). I'll stick the ammeter between the TOD relay and the TCCC and see what happens to the current through the circuit. If I get a 12V reading at that point when locked in 4wd, I can't see why applying 12V to it directly would be any different? If the system can generate 12V with the clutch connected regardless of the duty cycle, I can't see why powering it directly would be any different. The result is going to be X.X amps of current flowing through the circuit (That's my theory anyways... we'll know in an hour or so)

-Joe
 






the fastest i have driven in 4 hi...maybe 45..if that. I only really use it in deep snow/slush or on a trail when 4-lo isn't appropriate.
 






I think you really need to use an o-scope to see what the signal looks like. It should be a square wave if you are looking at current vs. time. I know that the scan tool was telling me that the duty cycle was 38.44% in 4Low. I think I saw higher than that when I got the wheels to slip in 4Auto, but it was only for a fraction of a second.
 






OK, I just went and re-measured the current draws in 4auto, 4high, and 4low. I didn't use an oscilloscope, but I think the results are still relevant.

In 4auto, the low reading (standing still) was .0242A. When I would step on the gas, it would vary, just as one would expect, but the peak came in when the wheels were slipping at WOT (loose gravel) and that measured 3.1A.

When I locked it into 4high or 4low, of course, as we've discussed before, the voltage drops off to a minimal duty cycle. However, once moving the least little bit, the current draw jumped directly to 4.31A, which is identical to the current draw when it's powered directly from a 12V source.

So, what's it mean? The way I see it, the Transfer Case Clutch Coil is drawing the exact same current through the circuit whether it gets the power from the TOD relay, GEM module, or an alternate 12V power source. That tells me that regardless of how the signal looks on a scope's screen, the resulting power consumption of the transfer case clutch coil is the same.

Now, that being said, I have two *theories* as to why the voltage drops off when stopped. First, it could be the electrical engineers' unnecessarily complicated algorithm for calculating the necessary duty cycle for the system. (i.e. garbage in = garbage out). The other possibility is that maybe if the vehicle sits stationary for an extended period of time, the clutch coil can overheat and burn open or short out the coil. The fluid being sloshed around when driving may be enough to prevent the unit from overheating when driving, but when stopped, it *may* be necessary for the system to reduce the power. Without knowing the specifics of the control system, I have no idea why that would be the case.

I did some digging a few years ago and came up with a contact at Borg-Warner. I'm going to see if I can dig them up again. Maybe they can shed some light on the control system (or at the very least, state conclusively if the power input into their t-case makes a difference).

For the time being, however, I'm sticking with my opinion that powering the clutch coil directly is no different electrically than powering it through the Control Trac system in 4high. The electricity that the clutch sees is, for all intents and purposes, the same.

-Joe
 






So, what's it mean? The way I see it, the Transfer Case Clutch Coil is drawing the exact same current through the circuit whether it gets the power from the TOD relay, GEM module, or an alternate 12V power source. That tells me that regardless of how the signal looks on a scope's screen, the resulting power consumption of the transfer case clutch coil is the same.

The amount of power is proportional to the duty cycle which is the percentage of time that the current is on.

http://en.wikipedia.org/wiki/Pulse_width_modulation

For the time being, however, I'm sticking with my opinion that powering the clutch coil directly is no different electrically than powering it through the Control Trac system in 4high. The electricity that the clutch sees is, for all intents and purposes, the same.

-Joe

On my truck, the scan tool read 13.33% duty cycle in 4 High, not 100%.

I don't know if it will burn out the TC clutch over an extended time. But IMO it is a likely possibility. I suppose one could obtain a TC clutch and apply 12V to it and see how long it lasts.
 






OK, I've been chewing on this one all night....

I understand the theory behind PWM. However, in this case, we're still dealing with modulating the pulse width on a 12V DC voltage. So, no matter how much you modulate the pulse width, you're still going to end up with an effective voltage somewhere between 0V and the supply voltage for any givent current draw.

However, the exact effective voltage will be a function of the current draw of the item downstream. Pulse-width modulate to a dead short and the voltage will be zero. PWM to a resistor, and until you exceed the currenty carrying capacity of that resistor, the measured voltage will vary. Exceed that current carrying capacity, and the measured voltage goes to Vmax and the current remains constant (which is exactly what I'm seeing in 4high and 4low).

The amount of power is proportional to the duty cycle which is the percentage of time that the current is on.
http://en.wikipedia.org/wiki/Pulse_width_modulation

I understand what you're saying, but I believe that once the current carrying capacity of the resistive load downstream of the PWM source is exceeded, the voltage maxes out and the current through the circuit remains constant. I believe that's what we're seeing with the clutch coil here. Otherwise, when we apply a direct 12V to the coil, wouldn't the current through the circuit be three times greater than the current measured through it with a 33% PWM power supply?

Look at it another way: If I lock in 4high using the OEM system, and it calls for a 13% duty cycle, the system moves 4.31A of current through the clutch. Now, if we apply a constant 12V source to the system, shouldn't the clutch consume 7.5 times that amount of power?

We know it still flows 4.31A of current with 12V applied directly, so the clutch coil isn't consuming any more power. 4.3A is 4.3A no matter what the voltage, and in this case, we already know that the effective voltage as measured at the BWM switch 12V regardless of the source, so isn't the net effect the same power consumption by the clutch and, therefore, the same function?

Putting it another way, amperage flowing through the clutch is the same. (Effective) Voltage input to the clutch is the same. Therefore power consumption is the same.... isn't it? Is there an EE in the house??
 






im confused if i do this mod in 99 it has auto, 4 high and 4 low, if i do the brown wire mod, will ill still be able to us 4 high and 4 low, i dont want to elimanate 4 wheel drive i just want to lock my front diff, please explain this to me.
 






It will not lock your front diff. It will unlock lock your transfer case to allow you to have 2wd.
 






No. There was a lot of interest in doing that, but you would need to supply a PWM signal on the brown wire to get 4 high.

If you just supply a constant 12V, you risk burning out the coil that engages the clutch.

PWM signal?
 












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