The 2006 Jeep Wrangler with the 42RLE 4 speed automatic transmission is known for a problem with the shifter linkage. They used a small plastic bushing to connect the shift arm to the linkage arm on the transmission. This plastic bushing is known to break and/or pop off.
There is a simple fix for this problem. You can replace the plastic bushing and small plastic nipple with a much stronger 3/8 grade 8 bolt. All you need is a wrench and/or ratchet and a drill. Anyone can implement this fix.
You'll need the following...
A drill, a 3/8" 16 1 and 1/2 grade 8 bolt, a 3/8 drill bit, an aircraft (lock) nut, and two 3/8 washers.
Before beginning, place the Jeep in Park, apply the parking brake and chock the wheels.
IMPORTANT: The transmission may potentially change gear during the course of the install, so DO NOT rely on the Park gear to hold the vehicle in place!!
Step 1: The broken linkage
This is what the broken linkage looks like. This happened to me on the Rubicon trail, and we bound the linkage with mechanics wire in order to get off the trail.
Step 2: Remove linkage arm
Locate the linkage arm on the driver side of the transmission, it should be easy to see. Remove the linkage arm by loosening the bolt on the top of the arm where it comes out of the transmission, and pulling straight up. This bolt clamps the linkage arm to the transmission. There is a square nut which sits in a square groove in the linkage arm. If you remove the bolt completely, this square nut may fall out and you'll need to feel around a bit to retrieve it.
Step 3: Drill out the plastic nipple
Place the linkage arm in a vice, and drill out the plastic nipple with the 3/8 drill bit. The drilled out nipple is pictured sitting on the linkage arm. You should file away the rough edges around the hole.