Technically Speaking
- Author: Wayne Colonna, Technical Editor
Delayed engagements in forward and reverse, slipping in forward and reverse, or a no-move condition in forward and reverse has been and continues to be a complaint with the Isuzu Trooper’s 30-80LE transmission and the Toyota 4Runner’s A340H transmission. Usually the call comes in on the hotline after the technician has removed the transmission several times and all looks fine. The technician checks line pressure and finds it to be within specifications as well.
The cause of this complaint (as many have learned over the years) is found to be in the transfer case. This is often overlooked, as the transfer case is not disassembled to separate it from the transmission. So it goes to the bench as a unit for just the transmission to be worked on. But inside the transfer case closest to the transmission is the transfer direct-clutch drum that the sealing rings just love to dig into. The severity of the wear determines the degree of the complaint; i.e., delayed engagements, slipping or no movement. Technicians often misdiagnose this problem by blaming the transmission for the problem when all along it has been in the transfer case.
A more-recent occurrence of a transfer-case malfunction being misdiagnosed as a transmission problem is the BorgWarner 44-05 in the Ford Explorer. The complaints are varied. We hear that it falls out of gear while on throttle or that it falls out of gear while coasting and that at times there is a ratcheting noise. All of these complaints are thought to be occurring in the transmission, and the unit is removed several times. Valve bodies and solenoids, and even whole transmissions, have been replaced in an attempt to be rid of this problem.
When it is finally revealed to the technician that the problem is in the transfer case, he discovers after disassembly that either the fork tips have burned away because of low oil levels, causing excessive play, or the fork’s shift rail has egg-shaped the holding boss in the rear-case cover, causing the excessive shift-fork play.
According to Mike Weinberg, president of Rockland Standard Gear and a contributing editor to Transmission Digest, the geometry of the fork and cam is such that an excessive side-load force is placed upon the fork rail, which causes the wear in the rear cover. Additionally, the electronic shift-control system, known as Control-Trac, in the Explorer’s 44-05 transfer case may help to further accelerate this problem. When the transfer case is in auto 4WD, if the tires have insufficient air pressure, are worn unevenly or are the wrong size, the generic electronic module (GEM) may observe a slip ratio via the front and rear speed sensors and activate the electromagnetic clutch in the transfer case in an attempt to equalize driveshaft speed. This clutch engagement adds additional force through the output shaft to the fork, and with the side-load problem, the fork’s shaft will wear the rear case much more quickly.
So if a 4R44/55E or a 5R55E transmission has a BW 44-05 transfer case behind it and the vehicle is neutralizing on or off throttle with a noise, don’t be fooled into thinking it’s the transmission. Chances are you have a transfer-case problem.
One extra note: If the fork tips are replaced and the leak stopped, or the rear case is replaced along with any needed associated parts, the problem will be resolved for a time, but the side-load problem remains. Mike redesigned the cam as well as other components needed to relieve this side-load problem, eliminating this concern permanently. You can reach Rockland Standard Gear at 845-753-2005 if you need a unit.
