Nomo,

Sorry for taking a while to get back to you I went and rode practice for race this weekend. The Expedition t-case has a a wide variety of wierd problems. One that I've seen quite a bit lately is the shift motor causing uncommanded shifts into 4x4, Ford has revised the shift motor to correct this but I've seen the shift motor also cause internal damage has well before the revised motor could be installed. I've seen GEM also cause shift problems has well. Some of the older Expeditions had quite a few problems with the fluid getting burnt and the speed sensers start acting up and causing uncommanded shifts. Most all the problems with the T-case have been related to electrical problems I have actually seen very few cases break without somthing electrical causing it.

 

MXRACER514 -

Seems like you know alot about the AWD functions of the Expedition. I have a 2001 EB Expy 4x4 and the 4X4 light is flashing on the dash. I don't believe that my AWD is working at the moment. I have heard that the flashing 4X4 is related to some bad speed sensors. I also heard that there 3 of them. Can you tell me where they are located so I can check them or replace them? Is it something that I can do? I live in Fairbanks Alaska and having AWD is kinda nice when not using 4WD.

Thanks for the reply.

- Tony

 

I recently sold my 03 explorer, the clutch packs were worn out, and replaced and I still had shudder under moderate to hard acceleration, maybe the other axle was bad to. Also I live in a cold climate with snow covered roads much of the year, I found the awd with the automatic engagement of 4x4 high (I think) to be a real pain. With 4x4 high the diff would pop on sharp turns on semi dry pavement, but if you didn't engage 4x4 high the automatic system was always turning off and on. Also my explorer would turn over and start just fine but it would immediately die at temps below -37 deg celcius, like I said, cold, but other cars would start just fine if they were plugged in, as was mine. I am not sad to see it go. Oh yeah and the 4wd wasn't that good to begin with, my 2000 f150 with the limited slip locks up the rear end immediately, the explorer never did.

 

Chiuaa,

Try disconnecting the battery, waiting a few moments, and reconnecting it. Sometimes an old explorer I had would do that, and after ford hammered me for $60 to disconnect the battery, I started doing it myself. And for what its worth, my 95 explorer 4x4 was quite capable offroad

 

I personally feel Ford should have left the 2WD option on all of the Expy's. I had a 98 and drove it in 2WD throughout warm and non wet weather. 4AWD is nice when it is snowing or it is wet out. I now own a 99 Expy and it doesn't have 2WD option, only 4AWD, 4HI, and 4LO. I hate not having the 2WD option because it makes the steering alittle harder, on dry pavement when I have to merge onto the highway you can feel the front end engaging and disengaging constantly until I let off the throttle (I have the 5.4 and rear wheel spinning is common) so as the rear wheels try to spin the front end is engaging. I personally am afraid of the extra wear and tear of the t-case and front driveline. I have un-plugged the motor on the t-case and now it is running almost true 2WD. I am in the process of getting the vacuum diaphram so that I can un-lock the front axle like the 97 and 98 models. I have observed a slight gas mileage increase from un-plugging the t-case. The only thing I have observed by un-plugging the t-case motor is the 4x4 light flashes.

 

There's a much easier way than retrofitting the front axle.... more on that in a moment though.....

Let me clarify a few things. First, between the Explorer and the Expedition, we're talking about four distinct vehicles with three VERY different systems.

The basics. Control Trac is not the same thing as AWD. AWD uses a center differential (either viscous or gear-driven) to drive BOTH front and rear driveshafts at all times. The ControlTrac 4WD system is essentially "Rear-wheel-drive-until-it-slips" at which time the GEM engages the transfer case momentarily to drive all four wheels, then releases and checks for a slip condition again. It is AUTOMATIC 4 wheel drive, not all wheel drive.

With the Control Trac System, the clutch in the transfer case is either on or off. There is no "partial" application of the 4wd in those systems. However, the GEM monitors the throttle position, vehicle speed, wheel speeds, etc to determine when 4wd is needed, and varies the duty cycle of the transfer case clutch as it sees fit.
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First, the Explorer. '95-96 model years with the V-6 used the Control Trac system in conjunction with a 2-speed transfer case and a center axle disconnect. The driver had their choice of 2wd, 4 auto, and 4 low.

For the '97-'01 V-6s, Ford did away with the Center Axle Disconnect and went to a live axle in the front in conjunction with the Control Trac system and the 2-speed transfer case. This gave the operator the ability to select 4 auto, 4 high, and 4 low.

All 4x4 V-8 Explorers from '95-'01 came with the AWD system, which uses a center differential and drives BOTH driveshafts at all times. The V-8s do NOT have a two-speed transfer case.
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Now, with the Expeditions, for '99 (and '99 IIRC), they had four choices: 2wd, 4 auto, 4 high, and 4 low. These systems used a vacuum-actuated center-axle disconnect and a 2-speed t-case, very similar in design to the Explorer, essentially, just on a larger scale. In 2wd, the front driveshaft didn't turn, and the CAD was disconnected. In 4 auto, the CAD was engaged, essentially turning it into a live axle, and the automatic controls for the t-case were active (again, 2wd until the rears slip). In 4 high, the CAD stays locked, and the transfer case locked for a 50/50 power split front to rear. Of course, 4 low adds low range to the mix.

(As a side note, all the '97-03 F-150s used the same front drivetrain setup, but with a completely different transfer case)

In '00 (I think) they did away with the 2wd position on the dial, and eliminated the CAD on the front axle, again, essentially like the Explorer, only super-sized.
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Disclaimer: I have not personally tried this mod on an Expedition, but the wiring schematics are identical to the Explorer, and should work.... in theory. Try this mod on the Expedition at your own risk (but I'd just about guarantee it'll work)]

Now, if you have a Control-Trac equipped vehicle (Explorer or Expedition) that is NOT equipped with a 2wd position on the switch, there is a way you can get true 2wd. It's known in the Explorer circles as the "Brown Wire Mod" and works wonders to get rid of the annoying clunking as it engages and disengages on dry pavement. You won't see any performance or mileage gains as the front wheels are still turning all the same components (halfshafts, diff, driveshaft, etc), it just prevents the transfer case clutch from locking the front and rear driveshafts together.

 

[text was too many characters so I had to continue it here]

Here's a little more background.... The Control Trac system uses the GEM, a Transfer Case Shift Motor, and a Torque On Demand relay to work the transfer case. In the dash, when the GEM senses it needs to engage the transfer case (from throttle position, speed, wheel slippage detected, etc) it tells the TOD relay to engage and disengage the transfer case up to and including a 100% duty cycle as necessary to maintain the same driveshaft speeds front and rear. When you select 4 high, the TCS relay engages the transfer case clutch full-time, locking the transfer case. Selecting low range simply tells the GEM to tell the TCS relay to shift the planetary gears in the transfer case in addition to applying power to the clutch coil.

Now, both the TCS relay and TOD relay send power to the transfer case via a brown wire (Hance the name for the mod). Cutting this wire prevents power from flowing to the Transfer Case Clutch Coil and, therefore, prevents the Transfer Case Clutch Coil from locking. Installing a switch in between where you've made the cut allows the operator to select whether or not the transfer case engages in auto mode, essentially disabling the 4wd.

Now, there's an added bonus: If you install the switch in the brown wire, the transfer case low range/high range function is completely unaffected. That means you can select low range from the **** on the dash, then turn the Brown Wire Mod switch OFF, disconnecting the front driveshaft, and leaving you in 2WD LOW range. This is handy if you are trying to pull shrubs without tearing up the lawn too bad, or need to make a tight turn on a trail (saves the hassle of disengaging low range to go back to 2wd first!). Simply lock and unlock the front half of the drivetrain at will!!


Hope I didn't confuse everyone too badly....

-Joe

 

Thanks again for the info....I once got your message about the "brown wire mod" but unfortunately I didn't come across it. The 98 Expy were the last until 03 to have the 2WD option on the dial (I know though there are a very few amount of 99 - 02 Expy's that have the 2WD option on the dial because I personally came across one). I have a 99 and it doesn't have the 2WD option nor the vacuum actuated motor on the front axle. There is a place for it, but it isn't there. I will again look for the brown wire, but I'm wondering if it is just a different color because the wiring harness is a bit different from an Explorer and an Expedition.

 

The '99 Expedition wiring diagram shows it as being a brown wire.... it comes from the Transfer Case Shift Relay and the TOD relay... Not sure where it's located on an Expedition offhand, but if you follow the brown wire from the connector on the transfer case back, it's got to be there somewhere. If you look at the plug on the transfer case, you'll have a brown, and orange, and a yellow. The orange and yellow come from the TCS relay and the brown comes from both the TCS and TOD relays. There is a splice somewhere where the two meet, and you want to make sure that the switch you install is downstream of the splice (if you want the ability to disconnect the transfer case in low range).

I can tell you that on the Explorer, the TOD relay was on the passenger side of the stereo opening, and the splice with the wire was in the upper right hand corner of the same opening, behind the GEM. That's probably not the case on the Expedition, but you never know.... Also, I believe the wiring harness for the transfer case comes up through the floor along the transmission hump underneath the driver's seat somewhere.... it shouldn't be too hard to find since you can find the plug on the transfer case and work your way back.

-Joe