Kirby G4. Tech drive will not engage forward or backwards. Belt is good. Fo?

I expect you have solved the problem by now, but just in case. I will give you an answer.
It sounds like that fork piece you are referring to has not located on to the lug that is supposed to fit in to it. That lug is ultimately connected to the handle. The fork is connected to the clutches of the transmission. As the force on the handle is applied in a forward direction the linkage applies the corresponding clutch to drive the machine forwards and as the handle is pulled back, the opposite clutch is engaged to drive the machine backwards... Remove the 3 screws under the transmission..... no need to remove the fourth which only holds the drive and neutral lever... lower the transmission an inch or two... then refit it making sure to locate the Lug in to that fork... Its much easier to do with the top cover of the machine removed, but you certainly can do it without removing that cover.
If you do want to remove the top cover for a better look, you need to remove the two screws at the front, easy to see when the head is off and the headlight is raised. Remove the handle ( press button on back of handle ) remove the screw at the bottom of the plastic surround to the handle and on/off switch.. There is a slot about half way up that plastic cover.. stick a flat head screwdriver in that slot and pull upwards and towards the front of the machine to release the plastic. With that removed you will see two more screws which when removed will allow the cover to be removed. You can then clearly see that linkage and can check the free movement of it all.... hope I'm not too late to help you ! Someone just helped me on a car issue on here so I thought I would check to see if there is someone I can help in my field of knowledge !!
I will check back in the next few days to see if anything further has been posted and if I can be of any further assistance.

GJ
June 2011