He now has a 5th gear:) For those who like photos of oily bits, this is how easy it was to cure. Can't quite believe that changing a gear hub was easier than doing the cam belt on this thing
The photos are a mix of the fitted and "spare" gearboxes - basically, you have to do the same on each as far as getting the replacement hub out is concerned - whether or not you also reassemble the spare box is, obviously your choice. I chose not to for now!
Before startng to dismantle things, you need to drain some of the oil from the box. I took out about a litre, which was plenty to keep the "working" area dry, but you may want to take the opportunity to change the oil while you're at it. If you do you'll need 2 litres of 75w/80 EP oil for refilling:
Replace the drain plug before you forget!
Raise the front n/s corner on an axle stand and remove the wheel and the front part of the plastic wheel arch liner. This gives access to the end of the gearbox. Remove the cover by undoing (7x) 11mm bolts and (1x) 19mm filler plug:
The cover has no gasket and is sealed using PU sealant. You may find that it's stuck in place, in which case tapping the edge of it from "behind" (ie: under the engine towards the outside) with a screwdriver and hammer will free it, giving access to 5th gear:
Apologies at this point for the quality of some of the photos - I was using my camera phone and it was very hard to keep oil off the lens as I worked!
You now remove the circlip that holds the selector fork on the detent rod. It's a light clip and can be removed simpply by pusing its end with a screwdriver while using another screwdriver at the other end to stop it spinning:
Also use a suitable punch to remove the detent spring roll-pin. Tap it out towards the back, being careful as you do that you don't lose the spring or the detent ball (see later photo). Put the spring and ball safely to one side:
Now remove the selector shaft roll pin. this is a little awkward with the box in the car, but you can get to its lower end with a bit of fiddling, then tap it out towards the top:
Fifth gear is now disconnected from the selector mechanism. Select 1st gear using the gear lever, then push the 5th gear selectro fork towards the box. This has the effect of engaging 1st and 5th gears at the same time, which locks the box ready for the next step:
Using a 28mm bi-hex (12 pointed) socket and long bar, undo the gear retaining nut. This isn't tight, but it's staked in position after fitting (see later). The long bar should relieve the staking without any problem:
You can now simply pull the 5th gear, hub, syncro unit and selector fork off the end of the box:
This is a (very poor quality) close-up of the inner teeth on the synchro hub. If you look closely you van see that the corners are badly worn - that wear is what forces it out of gear under power:
Here is a (better) photo of the replacement. Notice that the teeth are much better defined and "sharper" at their ends - and that's not just because of the photo!
Reassembly with the replacement hub is essentially the reverse of the above, but with a few points to note.
"Start" the roll pins with the selector out of the box. This is much easier than trying to do it in place. Tap them in so they hold their place but haven't reached the bore, so they won't prevent the fork from going on. This photo also shows the detent ball and spring that was removed earlier:
Fit the hub and selector fork and push them towards the gearbox to lock it in two gears again. Fit the nut and do it up just until it becomes "firm" and doesn't want to tighten any more. I don't have a torque setting available, but it's NOT tight! Stake the edge of the nut firmly into BOTH slots on the shaft (the one shown and one opposite):
Put the car out of gear using the gear lever and move the 5th gear selector fork so that yo can tap the roll pin home. Now fit the detent ball and spring upwards into their bore in the fork. You'll need a rod of suitable size to push on the end of the spring so that you can tap the roll pin in to hold it in place. Once the pin is in far enough to stop the spring dropping out, use a thin screwdriver to press the other edge of the spring up so that the pin can be tapped fully home. Refit the circlip to the end of the detent rod.
Check using the gear lever that all gears can be selected ok, then refit the cover. Before fitting, run a bead of sealant around the cover and spread it to cover the flange:
Hold the cover in place and fit the FILLER PLUG first (but don't tighten it). If you bolt the cover up before fitting the filler there's a good chance that the filler won't want to go in.
Fit the bolts and tighten down evenly using a "diagonal" pattern. Remove the filler plug, top up the oil that you removed as per normal gearbox filling instructions, and refit the plug.
Refit wheel arch liner and wheel, and enjoy an extra gear!
Total time was about 40 minutes, which is an awful lot better than a gearbox change!!!