Service Tips
1. Hop, skip or bounce can be normal, especially if the vehicle has been operated in turns on hard, dry pavement. However, you should explain to the owner/operator that 2WD should be used, except when off road or on snow or ice.
2. To determine if driveline windup is causing delayed shifts to 2WD, jack the vehicle or lift it on a hoist with the wheels free to rotate. This should release the driveline windup, if it is present, and the transfer case will complete its shift, if windup is the problem.
NOTE: VEHICLES VARY IN TERMS OF HOW "TIGHT" THEY ARE. SOME VEHICLES HAVE A LOT OF "GIVE" IN THE SYSTEM. SOFTNESS IN SUSPENSION AND MOUNTS WILL ALLOW THE DRIVELINE TO ABSORB MORE WINDUP BEFORE IT AFFECTS PERFORMANCE. IF DRIVELINE WINDUP OCCURS, THE SYSTEM WILL TIGHTEN LIKE A GIANT RUBBER BAND UNTIL THE TIRES START SLIPPING. A "TIGHT" VEHICLE WILL SIGNAL THE WINDUP SOONER, USUALLY BY A LOT OF CHATTERING NOISES.
Figure 17:
3. If the system slips under load, find what has broken or is slipping. To locate where slip is taking place, put marks at various possible slip points (see Figure 17). Test drive the vehicle, then check to see if marks at different points are still in the same relationship to each other. This will help you determine where the slippage is taking place or where to look for broken parts, if any.
a. On vehicles with auto hubs, find a place where you can do your test, mark the components, then drive without backing up. Stop and check the marks to see if they are in the same relationship to each other. If you back up before checking your marks, the hubs may reindex and not reveal the problem.
4. If the problem is clearly driveline windup and not broken parts, check tires and vehicle loading.
5. If the transfer case shift control motor operates properly and nothing happens, you will have to service the transfer case. If a manual shift lever fails to shift the transfer case, you will also have to look inside. Be sure you have eliminated driveline windup as a cause.
6. If a vehicle is operated in 2WD with the hubs locked, the driver may report driveline noise. This occurs because the 4WD components are in motion instead of at rest (the normal condition in 2WD with the hubs unlocked). However, it is important to remember that excessive noise may be a sign of a serious problem.
7. A problem can arise if the vehicle is equipped with a limited slip front axle and the front tires are worn differently or are slightly different sizes. In this case, operating in 2WD with hubs locked can result in steering pull like a limited slip rear axle. This will disappear when the hubs are unlocked.
8. Maintenance of the hubs is important. Easy shifting from one operating position to the other requires smooth movement of the inner clutch ring. This ring slides on splines which must be clean and well lubricated. To prevent dirt and water from entering the hub unit, the oil seals must be very carefully installed. If the vehicle is operated where the hub is constantly submerged in water or mud, the hubs should be serviced more frequently. The important thing is not to run for long periods with dirt and water in the hubs. Start with a short service interval and check for water and dirt. Stretch out the interval as experience shows how dirty they are actually getting.
"TOUCH DRIVE" - NEW ELECTRONIC CONTROL MODULE FOR 1991
A new electronic control module has been installed on the 1991 model Ford trucks with "Touch Drive," built after 8/6/90. The new module features a different computer logic to control shifting.
With the previous module, it was possible for the driver to select 4L directly from 2WD. However, the control module actually shifted the vehicle into 4H first, then checked to see if the vehicle was stopped and that the automatic transmission was in neutral (or the manual transmission clutch was disengaged). If these conditions were not met, the actual shift wouldn't take place. Instead, everything would be make ready for the moment when the shift could be completed. This was called pre-staging.
During pre-staging, the Low Range light flashed. This confused some customers. In addition, pre-staging and the flashing light sent confusing signals to the new E40D transmission's electronic controller.
The new module solves both these problems. With the new logic, if the driver selects 4L when in 2WD, nothing will happen, because the transfer case controller ignores the 4L signal. The driver must make the shift to 4H first, then, while stopped, shift to 4L.