After refurbishing the Gear Lever and Linkage I thought i’d change the gearbox oil as I doubt it has been changed since 1991.
Just like the other jobs i’ve completed I simply crawled under the van to do this, it’s a tight squeeze but manageable.
Shopping list:
- Comma 80W90 GL-4 Gear Oil 5L (make sure it is GL-4)
- Oil Drain Pan 6L (this one is rubbish, don’t buy)
- Draper Oil Funnel with Tube
- Gearbox Oil Filler Plug
- Gearbox Oil Magnetic Drain Plug
- Gearbox Fill/Drain Plug Key – 14/17mm
The Drain and Filler plugs are not essential but I wanted to replace with new as the current ones looked corroded and I could damage them during removal.
Before you start, go for a nice drive somewhere to warm up the gearbox as the oil will flow better and make draining easier.
First thing is to remove the Filler Plug, this is the one on the side of the gearbox next to the selector shaft.
Filler Plug
I used the Gearbox Key with a 14mm spanner to remove the Filler Plug. There is enough room to whack the spanner with a rubber hammer to get it out, mine was quite stiff so I gave it a good squirt of Plus Gas Releasing Fluid first.
It important to remove the Filler Plug before the Drain Plug. The Filler Plug may have seized and be impossible to remove, if this is the case you will have no way of refilling the oil if you have drained the gearbox. Follow this handy flowchart:
Drain Plug
The Drain Plug is located underneath the gearbox to the rear.
Mine had quite a bit of corrosion so I cleaned out the inside to ensure the Gearbox Key went all the way in. Position the drain pan underneath and unscrew.
A word of warning: Gearbox oil STINKS. The drain pan I used could not deal with the initial flow of oil so spilled over the side onto the floor and onto me.
The Drain Plug is magnetic to collect any bits of metal floating around in the gearbox and protect your gears in the process. Here is Sir Adventure’s drain plug showing 25 years of gear wear:
Once the oil has finished draining you can replace your cleaned Drain Plug or like me, fit a new one. The plug does not go all the way in, there is some thread still visible when tightened.
Refilling
I used a Draper Oil Funnel with Tube and it was the perfect length to pour the new oil in from the engine bay. The pack also includes a handy screw on funnel for the 5L bottle.
The gearbox takes 3.5L of oil, I poured 1.5L into a separate container then slowly poured the rest into the funnel. Once oil starts to pour out of the filler hole (if the van is level) the gearbox is full. Remove the tube and refit the Filler Plug. Job done!
VW T25 - Sir Adventure 
Very helpful/descriptive advice, thanks very much
William ( 1990 T25 1.6TD JX engine)
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Thanks for the easy to follow advice. I’ve just done mine – hopefully successfully. My gearbox took the full 5L so not sure what’s gone on there.
Craig (1990 T25 1.9TD AAZ engine)
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Hi, have you noticed a better behaviour of the gear shifter by chaining the gearbox oil? Or nothing really?
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Thanks couldn’t find the plug very helpful now off to buy parts
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Just changed the gearbox oil for 1989 1.6TB T25 5 speed hi-top and it took 4.8 l. We took the gear box out completely and had it all levelled up. The manual states 3.5l but that wasn’t enough so topped it up until it just came out of the level plug.
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That’s good to know. I’m not sure if it’s possible to drain the gearbox fully when it’s still on the van so that could account for the difference?
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The gearbox should fully drain even when on the van. I noticed another commentor used 5l but on a different engine size. We removed the gearbox to change the clutch because the gears got stuck intermittently, however, we then discovered the flywheel spigot bearing had disintegrated and that is probably the problem. So changing the clutch anyway today as it has wear, replacing the spigot and also replacing various gear linkage gators. That should all help!
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I have done a complete drain and refill, very much like to describe here. It was about 3 years ago. Here’s the embarrassing bit – I can’t remember if I lifted the van or took a wheel off or what. I want to put some Molyslip in the ‘box because I’ve read good things, but can I work out how to get the filler out?? It’s got to be an age thing (me, not the van – which is an 85 DG with a 4-speed). Thanks.
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