I just had to do it. I was getting fed up of the original broken one. I broke it when I lost reverse gear. Snapped the knob clean off the shaft one day trying to get reverse.
So because of this I took the housing off and had a look at the assembly. I could clearly see what turned out to be an adjuster, so now I have either reverse and 1-4 forward gears, or 1-5 forward gears and no reverse.
I celebrated by buying this new knob which set me back €20 but it was a necessity. Hope you like it much as I do 🙂
(Typed on an Acer Aspire 8930. Probably the worst laptop I have ever owned or used.)