Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Unit 500 gearbox outer cover

hello! I can't get the outer gearbox cover off 1966 5TA. I did get it off (easily) to replace the springs and check the plungers in the foot change mechanism. Cleaned everything up and reassembled with new springs but found I could only select first, neutral and second so decided to pull the outer cover off again to check except now it won't budge more than a few mm laterally. I suspect the plungers have jammed into the quadrant some how. Is there a fix to get if off? I saw an earlier post from 2005 talking about it "locking like a safe without a key". but there was nothing in that post to help should such a situation occur! Thanks in anticipation. H

You're probably correct. One of the plunger securing pins (hardly both) is worn and has let the plunger come so far out that it has jammed into one of the holes in the quadrant. The fix is to bend a strip of flat metal to a shape that allows it to reach the top of the plunger and depress it. It usually takes some trial and error, a lot of patience, and a few well chosen swear words, but I've managed to do it on two occasions. I suppose you could drill through the cover and push it down with a suitable prong, but you would want to know exactly where to drill so you don't end up with a Swiss cheese cover. If it happens again, that's what I'd do, but then I don't mind a plug there, something with a domed head maybe.
I've been super careful with the coice of pin material on my boxes afterwards, the original split pins are way too soft.

SR

Hi Hedgemonkey,
Yes I remember that quite vividly. I did manage to do it in the end but it took a while. By using plastic or nylon wedges try and optimise the opening at the top of the outer gearbox. I then used a modified bent dental pick but other objects could be fashioned to enter the open gap and with the aid of a torch and used to push through the protruding plunger(s) to release the outer cover. Sounds simple but it is a time consuming fiddle. However, it is possible with perseverance.
It is most important to use split pins of the correct size which is an odd imperial size which I believe is 5/64". using anything less will cause the same thing to happen. When fitting the split pin, make sure ther is no slack and pull the pin through fully before bending the legs and rotate the pin so that it doesnt impact the pawl on the split. It is a terrible design and I got some roll pins which are much stronger but unfortunately did not allow the pawls to protrude sufficiently without grinding some of the pawl away so I went back to split pins. If you can't get hold of the right size I might be able to find a couple if you are stuck.
Good luck and keep at it until you succeed.
Best wishes,
Mike
(Twinspin)