Based on your brief description, I'm not 100% sure this is your issue, however I did have the trouble outlined in this TSB. Mine issue was not so much when putting it in gear, but when I took off and stopped.
Driveline - Thump/Clunk on Acceleration/Braking
DRIVESHAFT - THUMP/CLUNK ON LIGHT
ACCELERATION FROM STOP OR WHEN BRAKING
AND COMING TO A STOP - RANGER 4X4 SUPER
This article supersedes TSB 03-26-2 to update the vehicle model years and service procedure.
Some Ranger 4X4 Super Cab vehicles may exhibit a low frequency thump type noise/vibration on light acceleration from a stop and/or when coming to a stop with light to moderate braking. This may be caused by axle wind up during acceleration or deceleration, creating a stick/slip condition at the rear driveshaft slip yoke splines.
A new type of grease is available which will greatly reduce the sticking/binding in the slip yoke during acceleration and deceleration. To service, apply the new grease to the rear driveshaft slip yoke splines. Refer to the following Service Procedure.
NOTE OTHER DRIVELINE NOISE CONDITIONS WILL NOT BE CORRECTED WITH THIS PROCEDURE. REFER TO THE APPROPRIATE RANGER WORKSHOP MANUAL FOR DIAGNOSIS AND REPAIR OF ENGAGEMENT CLUNK, TIP-IN/OUT CLUNK OR CLUTCH ENGAGEMENT CLUNK CONDITIONS.
1. Index (mark) the rear driveshaft to the rear pinion flange and the front of the driveshaft to the transfer case flange.
2. Remove the rear driveshaft.
SLIP YOKE DISASSEMBLY
CAUTION DO NOT, UNDER ANY CIRCUMSTANCE, CLAMP THE DRIVESHAFT IN THE JAWS OF A VISE OR SIMILAR HOLDING FIXTURE. DENTING OR A FRACTURE CAN RESULT, CAUSING DRIVESHAFT FAILURE DURING VEHICLE OPERATION.
1. Place the driveshaft on a suitable workbench. Do not damage the tube.
2. Mark the driveshaft and slip yoke on both sides of the boot. Mark the location of the clamp crimps so the new clamps can be installed in the same location (Figure 1).
3. Cut and discard the slip yoke boot clamps.
4. Remove the slip yoke from the driveshaft.
5. Thoroughly clean the boot making sure to remove all of the old grease and dirt. Inspect the boot for damage.
6. Inspect the lubricant on the driveshaft splines and in the driveshaft slip yoke for contamination. If contaminated, inspect the driveshaft splines and slip yoke for wear.
7. Using a stiff NON-METALLIC brush and a suitable solvent, thoroughly clean all the old grease out of the splines on the slip yoke and the driveshaft.
8. Use compressed air to completely dry both spline areas.
1. Install the slip yoke boot on the driveshaft (small opening end first).
2. Install and crimp the small slip yoke boot clamp using a keystone clamp installer (SST211-002).
3. Pull the boot toward the driveshaft to expose the splines. Completely coat all slip yoke and driveshaft spline surfaces with the grease supplied in the kit.
4. Position the large slip yoke boot clamp on the boot (DO NOT CRIMP).
5. Align the index marks and install the slip yoke on the driveshaft.
6. Set boot free length as follows:
a. Remove any excess grease from the slip yoke boot and driveshaft slip yoke surfaces.
b. Position the slip yoke boot in the slip yoke boot groove.
c. Set the boot length to 3" (76 mm) by sliding the slip yoke. Measure between the inner side of the clamps as shown in (Figure 2).
d. Bleed the air from the slip yoke boot using a screwdriver as shown in (Figure 2).
7. Crimp the large slip yoke boot clamp using SST 211-002.
1. Align the driveshaft front index mark with the mark on the transfer case flange and install the driveshaft. Torque the bolts to 82 lb-ft (111 N.m).
2. Align driveshaft rear flange index mark with the mark on the pinion flange and install the driveshaft. Torque the bolts to 83 lb-ft (112 N.m).
WARRANTY STATUS: Eligible Under Provisions Of New Vehicle Limited Warranty Coverage
OPERATION DESCRIPTION TIME
042307A Apply New Grease To The 0.7 Hr.
Rear Driveshaft Slip Yoke
BASIC PART NO. CODE
Former Ride: 2001 Ford Ranger XLT Off-Road (Stock)
Current Ride: 2007 Toyota Tacoma Off-Road SR5 (Stock)