STI Disassembly. Don't do it.
Rear mech cable broke in the shifter in the worst place possible, underneath the mechanism. No amount of cajolling was going to get the cable and barrel end out from there. The change mechanism was stuck solid. So, after a couple of hours of watching you tube videos I figured I had nothing to lose by taking it apart. I knew the odds were against me. Taking everything apart and remembering where the components go was not a problem. It's a Tiagra shifter about 10 years old. There are two main issues with the rebuild. The first can be solved for £2. There is a part which is needed to get the return spring on the shifter in to the correct position. Searching on line solved this. SJS Cycles stock this shimano part. It's a very small metal tube. See video by RJ The Bike Guy on you tube for how it is used. The second issue is more difficult. There is a spring which is under tension on the front of the shifter which uncoils on disassembly. Trying to retension it is proving incredibly difficult. It must have been put on by machine. If I can't solve it, it will be a second hand shifter from E-bay for about £20. So, my advice would be. Make sure you replace your mech cables on a regular basis. If you break a cable inside the shifter, it is possible to remove it in most cases. If it gets trapped under the mechanism and the gears wont move then you have a problem. I have also learnt that the earlier shifters were much easier to take apart and reassemble. I wonder if Shimano have now made it much more difficult so that you have to buy new ones. Incidently, I am led to believe that newer shifters have a plastic part directly under the shifter which can be removed by taking a screw out to gain access to stuck cable end under the mechanism.