PLEASE NOTE THIS IS NOT MY CONTENT

Original source Aggie on the T4Forum (link), I had noticed the images had not been working so wanted to archive these great instructions so they never disappear.

You will need a 3 leg puller and similar 2 leg puller to remove the syncrohub from the mainshaft and to remove the cog from the layshaft. Also recommend an airgun to undo the retaining bolts at the end of each shaft.

Firstly jackup your van on the passenger side and remove the front wheel to get easier access to the end of the gearbox,some T4’s have an undertray which is quite difficult to remove unless the van is on a lift/ramp.
Here’s how to swap the 5th gear cogs!

Clean the gearbox end cover so you can get onto all five securing bolts easier and to ensure no dirt gets into the box.Then undo the five bolts and remove the cover,be ready with a catch container as some oil is sure to spill out.
I changed mine whilst the engine and box were out so the pics are a little different.

The gearbox end cover and five securing bolts easily visible.

Once the cover is of you can clearly see the 5th gears and syncro hub and selector mechanism,mainshaft is much bigger and carries the syncro,layshaft is much more basic.

Next undo the two small torks bolts above and below the syncro hub to free the selector from its pivots then wiggle the selector arm free from its position and place it in the previously removed end cover for safe and clean keeping.
It will then look like this

Now if you havnt already done so then its a good time to take some pics of the syncrohub and the selector slider that slips over it,there are two spring rings(one inside and one out) and three locators (the little rectanglular things)Once youve taken the pics for reference in the reassembly then grab the slider by hand and pull it of the syncro hub and put the bits in a safe clean place again like before.

slider and three locators removed(but only two visible in this poor photo and maybe not so clean and safe)

Now i mentioned airgun earlier here’s when you need it,undo the big 6sided torks bolt in the middle of the mainshaft and the one in the middle of the layshaft while your at it.Then use the 3leg puller to remove the syncrohub and 5th gear cog together from the mainshaft.Inside the cog or on the shaft you will find the needle roller bearing as this cog is not fixed on the mainshaft and its the splined syncro that holds it there along with the torks bolt already removed.

The bolt in the layshaft in this pic is just for the 2leg puller to push against

Next use the 2leg puller to remove the smaller gear on the layshaft

Then you have both the 5th gear cogs removed completely.
Clean everything you have removed (except for the two cogs you are changing) ready to go back in,you need to re-use the syncrohub, slider and locators again.