Black/gold,
Sounds like you may have 'biased' the pawl spring?
If the spring is not set correctly then the gears will shift badly in one direction or not at all.
To correct the problem look at the top photo here:
http://www.oldbritts.com/gearbox_info.html
This shows the ratchet assembly
The cranked leg of the spring should be the lower one.
With the ratchet assembly in the 'neutral' position and ALL THREE PIVOT POINTS EXACTLY LINED UP (what is shown in the photo is the ratchet position as fourth gear is selected) and with the ends of both legs of the pawl spring resting on the plate the legs should either JUST TOUCH or JUST CLEAR the pawl on both sides by EXACTLY the same amount with the pawl resting squarely in position.
The legs of the spring should be bent carefully to adjust it.
The pawl spring can break so it is a good idea to fit a new one occasionally or at least keep one handy as if it does break the gearbox will not select at all.