Hi!
The gamepad I used got identified directly in the Pi as a HID device. So connected the left thumbstick works for analog directional movement, IF the game/system supports it and when the analog button is activated on the pad.
For the "hack" (which I found how to do on this wert forum) I used a 10k potentiometer and de-soldered the thumb pot for left and righ (there is two, also up/down pot)
There is 3 solder points to de-solder per pot.
But best is to removed the thumb PCB completely which I did. So you have to de-solder 12 poings: 3x2 points + 2 for the button micro switch and also additional 4 soldered legs just to make it sturdy. (slow and steady and you will get there)
Then I reattached the secondary pot or else it will send max UP value without it. Connect it to a PC and configure via "USB Game Devises" to see
The 10k pot then should be fixed in position with only the turning point - centered, and inserted in the back end of the steering shaft. If this make any sense?
If you want to I can show this in pictures.
Cheers