Apologies for the "no news"...
a recent job change and the usual mundane domestic stuff has kept me busy... but I had the wheel off this weekend to inspect everything in there for the 145's annual dice with Death (aka MOT)
and while I was sitting there in the sunshine with the car jacked up and with my tools out.. I decided to have a go at fitting that 5th gear.
I have some photos which I'll post in a few days... but essentially you just remove the gearbox end-cover and you are presented with the end of the main- and counter-shafts, similar to amfalconer's photo above.
**About 100ml of oil drips out when remove the cover, so you need to catch it.. but it's not a whole gearbox-drain.
1) Ease out the lock tabs. These are a soft part of the big nuts you see on the end of each shaft. Use a metal screwdriver and a mallet to tap out the indents.
2) Undo the nuts. You'll need a 30mm socket and a 2 pence piece. Stuff the 2p into the "v" where the gears meet (2 and 10 o'clock respectively) to stop the shafts rotating. Undo the countershaft nut first (the one on the right) but leave the nut on there.
3) Stick the beast in gear to undo the mainshaft nut (on the left) as it tends to rotate in neutral. This time the 2p has to go into the "v" between the gears at the bottom (4 and 8 o'clocks).
The 2p will get mangled into the gears but will jam them enough to undo the bolts. Make a note which way to turn the brake disc (by hand) to reverse the gears rotation and get the 2p out again. On one of mine, I had to attach the wheel to the hub, to get better leverage. The 2p is killed in action..
4) Now then, now then.. You can remove the nuts. The countershaft gear (on the right) won't come off until you take off the selector fork, hub and sleeve assembly on the mainshaft (so you have to do that first)... otherwise it would be just a "slide it off" job.
5) The mainshaft stuff is where things become waaaaaaaaaay more tricky...
but then you didn't imagine this was going to be too easy did you?
You have to remove this in situ with the selector fork (bronze coloured doodah in the photo), so undo the 10mm screw holding the fork to its shaft. Free it off a bit so it's loose but don't move it at all...
Now.. There is a 3-cornered plate under the nut. Under that is a hub gear which sits inside a sleeve.. and behind that is a synchroniser gear. It would all be a cinch to slide out, if there wasn't 3 springs and rollers in there, just waiting to ping out, if you remove the hub from the sleeve.
So..... hold the 3-corner plate tight against the sleeve. Grab the synchroniser (it's bronze.. behind the sleeve gear) and holding the whole lot pressed together (and one extra hand on the selector fork) sliiiiiiide the whole lot out.
The selector fork is surplus to requirements.. but it's essential not to disturb the set of the sleeve and hub gear. Naturally one is skinnier than the other, so you can't place it down somewhere easily.. but lay it on its front, syncho' up... and DON'T LET ANYONE TOUCH IT..
6) Back to the mainshaft.. Gingerly remove the wafer thin securing washer. It's a skinny thing that fits in a groove and looks more like a metal elastic band. Note which way round it goes, though it may not matter.
7) Slide both the gears off. You're half way there.
8) Fit the new counterhaft and mainshaft gears onto the shafts. Whirl them around and marvel how saucy they look. Stick some gear oil on there to help them on start-up. Put the nut on the countershaft gear, hand tight.
9) Put that skinny metal band/washer on the mainshaft.
10) That sleeve and hub gear and synchro' assembly...
Essentially the outer sleeve has little notches machined inside it that locate 3 rollers ... that sit in slots in the hub gear and are held under tension by 3 small springs. (I'll post a photo).
If the hub moves too much (in/out) inside the sleeve, the springs "pop out" so you have to dismantle the assmbly and spend 2 hours trying to refit everything back together.
I did it ...
by first putting the springs in the holes in the hub gear.... then placing the plate on the front of the hub. Flip it over and put the rollers onto the slots where they will go, resting "on" the springs.
Then align the hub (in/out) with the sleeve, so that the rollers drop into the cut-outs inside the sleeve (you need to make sure the sleeve is fitted to the hub so that the cut-outs line up with the roller slots in the hub gear).
Then use a tiny screwdriver to depress the springs inwards, so that you can squeeze them under the rollers as you ever so slightly move the hub further into the sleeve.
There's three to do and if the sleeve moves too much when you're doing it, the springs of any rollers you have already lined up, will pop out.
It's a teeny bit fiddly and there's a risk of losing a spring or roller, so do this somewhere clear, like the kitchen.
11) Finally fit the synchro ring onto the back and without moving anything (hold tightly in position) offer it to the shaft. You ideally need another hand to locate the selector fork.. and you might now discover you fitted the sleeve back to front..
so take a note of which way round everything goes when you first take it apart.
12) Sliiiiide it gingerly on there. Check that those rollers are still in their slots and that you can see the springs in place too... though you'll feel/hear them "pop" if they jump out.
13) If it all looks good, put that nut on and fit the screw on the selector fork too. You're pretty much done. Just tighten up the 30mm nuts (use what's left of the 2p to lock the gears as before) and then tap in the lock tabs before fitting the cover.
14) Top up the gear oil, Check the gears change okay, refit the wheel arch lower liner and the wheel.
15) Start the car in neutral and check the gears change without noises... if so, you can go for a test drive.
It's not a difficult job and certainly not heavy work. You need a 10mm, 13mm and 30mm sockets.. as well as a small screwdriver.. but no specialist tools or techniques. The only fiddly bit is that mainshaft hub/sleeve gear assembly if (when!) one of the springs pops out... otherwise it's a straight take off/put on job. Worth a punt..
Part no's from your friendly dealer:
Mainshaft gear - 7757956 (31T) Countershaft gear - 7757955 (39T).
The gears themselves are abooot £100 each (obviously I bought one and then had to buy the other to continue what I'd started... ) so maybe a bit dear.... but there it is. Enjoy..