I did this mod today, but I did it without pulling the selector mechanism out of the transmission. My goals were a) minimize disassembly and b) get the shift knob in the right position, which for me, meant keeping the knob in the same position for the odd gears, and letting the knob not go as far back in the even gears. Here's what I did:
First, the additional things you'll need are a Dremel with a flex-shaft and grinding stone, and you'll need to make a special tool. The special tool is needed to press out the stud. It is simply a piece of flat steel, 3/16" or 1/4" thick, 1/2" or so wide, and about 2" long. Drill and tap a hole in the center. Grind the end of a screw to a blunt point. (The piece of steel in this picture is only 1/8" thick, but it bent during use.)
1. Put front end on ramps or jack stands.
2. Measure knob positions. You don't really have to do this, but it is good to know. I found that the stock throw third to fourth was about 4-1/16". Third gear:
3. Select third gear and tape the shift knob in position.
4. Remove the large splash shield under the engine and the air intake. Cover or plug the intake on the car so nothing will get in there. I also removed the weight on the end of the selector arm, but this may not be necessary.
5. Pry the end of the shifter cable off of the ball stud. Check that the shift knob is still taped in position.
6. Cover the area around the selector arm.
7. From underneath the car, grind rivet off flush with the arm. Don't grind away the entire dimple in the center, you'll need this later. Don't forget eye protection.
8. Install the special tool with C-clamps, vise-grips, what have you, making sure that the point of the screw engages the dimple in the bottom of the stud.
9. Tighten the screw to press the stud out of the arm.
10. Clean up the end of the stud with a file and chamfer the edge a bit.
11. Drill and very carefully tap the stud. To keep everything metric, I used an metric 4.0 x 0.7 tap, predrilled with a 1/8" drill. Thread the screw all the way into the stud to ensure that the threads are deep enough. I used an M4x10 screw.
12. Check the ball stud for nicks, clean up with a file if needed.
13. Once again check that the shift knob hasn't moved and that the selector arm is still in the forward position. Move the cable over toward the driver's side until there is just a small clearance between the cable boot and the linkage as shown. (This is the closest the boot gets. It gets farther away in Neutral and the even numbered gears.) Mark the new position for the stud on the arm by eye.
14. Centerpunch the mark, then predrill and drill the new hole. Be aware that the drill will tend to catch and shoot through the hole when it breaks through, so keep a piece of wood under the arm to protect the transmission. Pick up the cuttings with a magnet as you go.
15. Chamfer the hole on top and use the Dremel to deburr the hole on the bottom side.
16. Check the fit of the stud in the hole, adjust if needed. A tight fit is ok.
17. Install the stud and put the screw in and tighten. Check that the stud pulls down flat on the arm.
18. Pop the end of the cable onto the ball.
19. Remove the tape on the shifter knob, run through all of the gears, and smile. You can measure the gear positions again to see how they compare. Third gear:
20. Clean up the area, then replace the weight, air intake, and splash shield.
The third-fourth stroke was reduced from 4-1/16" to 3-3/16", which is a reduction of about 22%, though it feels like more. It's a bit notchy, but nice overall.
