Help with "Brown Wire Mod"

[tsgrpr97]

I see it as backwards from the way you describe it. The clutch is generally not engaged. It engages only when it does sense slip (A4wd). It will then vary the duty cycle then so you may turn. If its locked you cannot turn without the tires slipping.

I think there's some misunderstanding of the a4wd system. I've been reading up for a while between the ford service manual and borg warner literature. The TOD system doesn't measure wheelslip via the abs sensors. There are two output speed sensors mounted on the transfer case. 1 sensor for each driveshaft. At vehicle start, the clutch coil is energized at a duty cycle of 10% and it will remain at ten under ideal conditions. If as little as 1/2 rpm difference between front and rear driveshafts is detected the TOD will attempt to compensate.

Because its so sensitive, its critical that the tires be of matching circumference and equal pressures. A 7mm difference in circumference of a tire on the rear axle is enough to cause the system to attempt to correct for that difference and magnify the drag you feel when turning at full lock.

From what I've read another common cause of the drag while turning may be the front and rear output speed sensors on the tcase sending erroneous data.

Another issue might be to make sure the tcase is filled with a mercon equivalent and not mercon v. the mercon (I'm thinking) might allow for more slip at tight turn conditions.

I can't imagine any measurable increase in mpg from deactiviating the clutch because when the truck is cruising (with matching tires) the axle speeds should be well within 1/2 rpm of each other leaving the duty cycle of the clutch at its minimum, so any drag there would be insignificant. The killer of the gas mileage is the live front axle, which will be there spinning regardless of the clutch.

Going by memory, I think Ford stated the difference in mpg between the axle with the center disconnect and the live axle in the a4w system to only be like 1mpg difference, if that. For a while I was toying with the idea of replacing my axle with an earlier one with the disconnect, buying one of those conversion kits to operate it manually, and doing the brown wire mod. But thinking back what killed it was the fact that for all that trouble I "might" gain 1mpg. Its not worth it.

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[tsgrpr97]

I understand ford made these to last a "lifetime" but I feel that the A4WD kicks on more than one would actually realize, and in my opinion it's an unecessary soccer mom frill.

Borg warner built it to last a lifetime. Its a good reliable unit and that's why many manufacturers install them in their vehicles. IIRC BW was developing the auto 4wd system with isuzu in the late 80s. They were originally incorporating a differential between the input and the clutch to allow the slippage needed for turning manuevers, when they realized that by manipulating the duty cycle of the clutch instead of "on or off" and balancing the fluid there was no need for the differential and with the computer program they developed TOD was born.

Its a very sophisticated unit. Its natural at first to second guess and think of ways to bypass or modify it. But all the concerns I had were put to rest after I invested the time to really get to know it.


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[Canadian Expy]

The main reason anybody should be doing the Brown Wire mod is for
Rear Wheel Burn outs

 

[mc0311grunt]

I did this mod. Other than being able to do a burnout I have seen no gains whatsoever. Granted I just removed the fuse but mileage has stayed the same. I might actually do the switch and everything when I get started on racing. Id rather throw slicks on the rear than do awd launches