DavieB said:
Im a truck mechanic to trade, but dont have a clue where to start with bikes. Without a doubt I could strip it to bits and rebuild it. but I dont have a clue how to adjust Gears. This is the only bit im unsure of everything else I could figure out (I think)
A man of your means will have no bother. Gear adjusting is easy. If you were to take the cable off the derailleur it has an internal spring that moves it the mechanism the way to the end stop. You adjust the end stop so the chain meshes on the smallest gear and doesn't drop off.
If you then reconnect the cable and take up the slack, each click of the shifter pulls in (I think) 1.2mm of cable. The actual figure isn't important, all you need to know is it's the same for each click, which it is, inside the shifter, and this is why you *don't* mess with what's inside the shifter. The rear derailleur mech is set up so that for every 1.2mm of cable it moves *exactly* the distance between 2 gears. The gears are each equally spaced so every click pulls 1.2mm and pulls the mech one gear to the inside of the wheel. You can't change this, it's a function of the shape of the thing and the way it operates. You are pulling the mech onto the bigger gears, against the spring, and going smaller you are releasing cable and letting the spring work the mech back.
If you keep clicking the shifter the shifter pulls in 1.2 mm per click, this moves the mech, one gear per click, until you get to the biggest gear. You then adjust the end stop that controls this gear to stop the mech going too far and dumping the chain into the spokes.
That's it. So to set up your gears click it all the way to the smallest gear at the back. Keep clicking and if it dumps the chain adjust the outer end stop (small screw, Pozi). Then go one click bigger, it should shift one gear. If it doesn't then adjust the *cable* till it shifts up one gear. Remember you are *pulling* the cable inner so shortening it, but the adjuster works on the *outer* so you need to make it longer to "shorten" the inner cable and vice versa. Once you havce got this to work, each extra click will give you one gear more. You may have to add a turn or so to the adjuster but not much once it's about there. Go all the way up to the biggest gear, only adjust the end stop if it goes too far or not far enough. That's you.
The front gears are the same but there are only 3 of them (or2). Again al you need to know is that with the cable unhooked the springf will pull it to the smallest gear, and you re using the shifter to pull *measured amounts* of cable through, each pull moves the mech the amount required to shift one gear.
You're a mechanic, have a play with it and now you know the basic mechanism it will become clear how to set it up. If you can do a handbrake cable on a car a bike's gears are very similar.