1985 Dodge 3/4 ton 4 WD, PU. I need to change the u-joints on the front axles.?

Here's your best answer. Before you take it apart, start the truck and put lever into 4 wheel lock mode, and make sure the 4x4 light comes on. This way the slider-coupler will be engaged and will hold on to inner spline, so when you re-install outer shaft, they will line right up. If you leave it in 2 wheel drive, then you will HAVE TO unbolt the vac actuator to re-align the coupler and shaft.

looks simple

1.Raise and support the vehicle on jackstands.

2.Remove the four flange retaining bolts and lockwashers from the constant velocity U-joint at the transfer case. Matchmark the parts to reinstall them in the same position. To prevent the constant velocity joint from turning while removing the nuts, utilize a press bar.

3.Remove the nuts and lockwashers from the U-bolts at the differential flange and remove the U-bolts.

4.Support the driveshaft and separate the U-joint at the front the driveshaft yoke, pulling backward to clear the flange. The driveshaft should never be allowed to hang by either universal joint.

5.Remove the driveshaft.

To install:

6.Before installing the driveshaft, wipe the areas with a clean cloth and inspect the surfaces for scratches, nicks, dents or burrs. If there are any of these correct the problem before proceeding.

7.Support the driveshaft and slide the U-joint into the front the driveshaft yoke, pushing forward past the flange.

Be sure to install remarked parts with the same orientation as before removal.

8.Install the U-bolts, then tighten the nuts and lockwashers for the U-bolts at the differential flange.

9.With the marked parts reinstall them in the same position. Replace the four flange retaining bolts and lockwashers for the constant velocity U-joint at the transfer case.

you need the repair manual on this one before you even start to remove any parts because once you get it tore apart it may be difficult to get back together again,both answers are good on this one but without a manual you may have problems getting it back together,good luck.