I am going to try and put this entire thread together much as I did the 4R70W Diary, so those just needing basic info do not have to sift through a lot of chatter throughout the thread. I will create and link another comment thread for those comments - which is here: http://www.explorerforum.com/forums/showthread.php?t=182072 and until at least the first half of this Diary is done, lock this thread. (unlocked for now as the first half is done) Much of this initial info came from the FORD manual, with some edits. While the initial part might not make a lot of sense to some, once the pictures start coming in I hope to try and explain what this all means in 3d nuts and bolts inside the TC. I always think theory of operation is essential to any component you are working on, and this is no exception. This first stuff is important to understand how this TC works though and I recommend reading and at least trying to comprehend it... even without pictures. I admit it is not easy. GENERAL DESCRIPTION OF THE CONTROL TRAC 4405's OPERATION The Borg-Warner Control Trac 44-05 transfer case was used in the Explorer (4WD) vehicles starting in 1996. The transfer case transfers power from the transmission to the rear axle, and also to the front axle when electronically activated. Mechanical Operation In the 4X2 mode, torque from the transmission is transferred to the input shaft which, in turn, drives the rear output shaft that drives the rear axle assembly. Though the input shaft and the rear output shaft are independent of one another, there is a mechanical gearing interconnect that locks them together as a unitary assembly during normal operation. That through power from the transmission is transmitted to the back wheels for a 4X2 engagement. Shifting to 4WD is done electronically by energiizing the electromagnet, which in turn actuates a very interesting electromechanical ball ramp clutch assembly. (More on this later) The electromechanical ball ramp clutch assembly drives the drive sprocket after the generic electronic module (GEM) activates the clutch coil. The drive sprocket turns the chain which rotates the front output shaft and front driveshaft. In other words the input shaft and output shaft are locked, and the eledctromagnet actuates the gearing (through a clutch) that adds the sprocket attached to the chain drive, which then adds the front output shaft to the equation. (Confusing enough?) The high-low shift is accomplished when the reduction shift fork moves the reduction collar to lock the planetary gear set to the output shaft. Torque from the input shaft is then transmitted through the sun gear, which then turns the front planetary gear set front planet The front planetary gear set front planet which is now engaged provides transfer case speed reduction. Transfer Case Functions There are three modes on the transfer case, Auto, 4WD Low, and 4WD High. Neutral is only available as a dealer installed option. C-Trac Function This is the interesting part. The C-Trac transfer case transmits torque to the front wheels through an electromechanical shift assembly after a predetermined change in speed between the front and rear driveshafts is detected. These driveshaft speeds are determined by two Hall effect sensors which send a signal to the generic electronic module (GEM). If the GEM detects a change in speed between the front and rear driveshafts, it activates the transfer case clutch coil with a varying current to minimize the change in driveshaft speeds. Low Range Function In 4WD Low Range, the transfer case electromechanical clutch locks the front and rear driveshafts for maximum 4WD traction. The transfer case motor also rotates the shift cam to move the reduction fork to the 4WD low range position. This low range shift is accomplished through a planetary gear set which changes torque to the driveshaft from 1:1 to 2.48:1 ratio. This is the transfer case being rebuilt in this thread. GENERAL DESCRIPTION OF THE AWD 4405's OPERATION The all-wheel drive (AWD) transfer case is a two-piece aluminum, chain driven, viscous clutch type unit. This produces a system in which all-wheel drive is always activated. All-wheel drive transfer case is automatic and has no external controls. The viscous clutch is a non-repairable, torque distribution device. The internal construction of the viscous clutch consists of alternating plates that are connected to the front and rear outputs of the transfer case. The viscous clutch is filled with a high viscosity fluid which flows through slots in the plates. The resistance to shear causes the plates to transmit torque at the needed ratio. The ratio that torque is transmitted at is approximately 35% front and 65% rear. A front differential compensates for the difference between the inner and outer wheels. However, when one driveline component travels farther than another, there will be driveline or torsional windup that must be released. Operation Torque is transmitted through the input shaft to the planet carrier assembly. Torque flow continues through the gear ring to the rear output shaft. Torque also flows from the planet carrier assembly to the sun gear shaft, which is splined to the drive sprocket. The drive gear is connected to the driven sprocket by the drive chain. Torque continues through the driven sprocket to the front output shaft flange. The viscous clutch provides the connection between the gear ring and the sun gear shaft. The AWD is not being rebuilt in this diary. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Initial note: Some changes occurred in 98 when the Vehicle Speed Sensor was moved from the transfer case to the rear differential. For that reason a 1998 4405 will not provide a necessary VSS input to a 97 or 96.\ model year vehicle.