Help with "Brown Wire Mod"

[toms89]

It's been about a month or so now and I have averaged 15.5-16.5 town/country driving. I have seen 18.5-19 on the highway at 68-72 mph

I can't contribute all of this to the "2hi mod" because I have been trying to drive with a much lighter foot I do not let the tach go past 2500 rpm and when I feel a shift coming I lightly let off the throttle, it seems to help a lot but I still love knowing that I am only in 2 hi and not constantly slipping clutches in the transfer case

Since you have a 2000 expy if you disconnect power from the A4wd it just keeps the transfer case from engaging the clutch as mentioned. Generally the vehicle is in 2wd mode unless slip is sensed via the gem module/anti lock brake sensors. It should make no appreciable difference in fuel milage as the complete front drivetrain is still spinning down to inside the transfer case because the wheels are spinning. Its just cannot apply power to the front drivetrain if the rear wheels were to spin.

My guess is its your driving style. I have pulled the fuse disabling my A4wd and noticed no difference in fuel milage myself.

Unfortunately we lack the center axle disconnect of the earlier expys and IWE's of the later ones that would keep the front drivetrain from spinning creating additional drag.

 

[Irwin]

My guess is its your driving style. I have pulled the fuse disabling my A4wd and noticed no difference in fuel mileage myself.

Unfortunately we lack the center axle disconnect of the earlier expys and IWE's of the later ones that would keep the front drivetrain from spinning creating additional drag.

I agree- it would be very nice to have a CAD, and no, I don't completely attribute the fuel mpg increase to the inline switch.

Like I said before, the biggest benefit for me is knowing that anytime the abs rings speed do not match my transfer case doesn't slip a clutch.

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.

 

[toms89]

I agree- it would be very nice to have a CAD, and no, I don't completely attribute the fuel mpg increase to the inline switch.

Like I said before, the biggest benefit for me is knowing that anytime the abs rings speed do not match my transfer case doesn't slip a clutch.

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.

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.

 

[toms89]

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.

I agree it kicks on far more often than most might realize but the only real disadvantage there since the front drivetrain is spinning anyways is the feel while turning. You can feel it come in and out... First time you notice it your like

 

[Hooch33]

It's been about a month or so now and I have averaged 15.5-16.5 town/country driving. I have seen 18.5-19 on the highway at 68-72 mph

I can't contribute all of this to the "2hi mod" because I have been trying to drive with a much lighter foot I do not let the tach go past 2500 rpm and when I feel a shift coming I lightly let off the throttle, it seems to help a lot but I still love knowing that I am only in 2 hi and not constantly slipping clutches in the transfer case

You are getting 18-19 MPG out of a 5.4 Expedition? Im having a hard time believing this.

 

[mc0311grunt]

Im going to have to try this mod.

 

[Irwin]

You are getting 18-19 MPG out of a 5.4 Expedition? Im having a hard time believing this.

Throttle in moderation. Get to speed quick but not obnoxiously. I don't let it shift past 2500rpm. I also drive a bit slower than most.

The biggest key to my mpgs I believe is/was maintenance. All bearings have been replaced, All fluids are fairly new and synthetic if possible.

The biggest thing for me is this rig is paid for, I drive a lot more than most so I need this to be as efficient as possible. If that means driving a touch slower than the norm that's ok by me.

The best mpg ever was a trip from Dundee MI to Oscoda MI. 21.2 on the highway round trip.

 

[FordandPolaris]

Throttle in moderation. Get to speed quick but not obnoxiously. I don't let it shift past 2500rpm. I also drive a bit slower than most.

The biggest key to my mpgs I believe is/was maintenance. All bearings have been replaced, All fluids are fairly new and synthetic if possible.

The biggest thing for me is this rig is paid for, I drive a lot more than most so I need this to be as efficient as possible. If that means driving a touch slower than the norm that's ok by me.

The best mpg ever was a trip from Dundee MI to Oscoda MI. 21.2 on the highway round trip.

That is very impressive. I am doing dances in the parking lot when I drive from home to college getting 13 highway haha.

 

[bdt61]

I plan on doing this mod pretty soon. Right now, I just keep the fuse pulled out haha. Keeping it in 2wd, I'm seeing an average of 21mpg highway and 14 town

 

[Hooch33]

That is very impressive. I am doing dances in the parking lot when I drive from home to college getting 13 highway haha.

yeah totally I highfive myself when I see 13 mpg, but that's only when im going downhill with a tailwind driving 5 feet behind a semi trailer.

 

[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