Why am I changing the gearbox oil so early?

It’s extremely hard to find correct EP90 gear oil in Switzerland, this is my experience at least. It’s also quite hard to ship into the country as most couriers don’t want to carry oils per sae. I was however supplied 1 litre of it by Land Rover at a truly eye watering price some months ago.

As an alternative to EP90 that’s, kind of OK, I have to used SAE 90 oil. It’s the same viscosity as EP90 but offers less protection in the long run. Extreme Pressure (EP) is well suited in gearboxes given the huge amount of force driven across the surface of the teeth.

Oil (in most circumstance) is there to provide physical separation between metal and metal. SAE 90 offers less protection in so much as it lacks the EP properties, doesn’t bond to the gear surfaces and doesn’t reduce wear as well… so that why I’m changing it.

Fortunately  I found I was able to order sufficient quantity of Castrol EP90 for 2 full changes of ALL transmission fluids from Holden Vintage and Classic Cars . This is enough for 6000 miles of motoring.

Both gear boxes, the overdrive, front and rear axles, front axle swivels, steering box and steering relay are specified as oil requiring EP90. Currently only the steering box, steering relay and axles swivels have the correct oil. Time to rectify this…

First we have to drain the oil for the main and transfer boxes.


With a suitable contain below, remove the drain plug from the underside of the gearbox. I’d been out in the car earlier in the day so the oil was nice a warm and trained well.


I later measured what had come out (of both boxes) to check the right amount was in there. It isn’t unheard of for oil to migrate our of the main to the transfer box. Fortunately, both gearboxes had the required volumes.

Drain plug ready for some PTFE treatment to the threads


So the SAE hasn’t done such an good job protecting stuff…. This isn’t even a GL5 oil and its full of bronze

GL 4 and 5 oils are corrosive to yellow metals due to their high content of sulphur and phosphorus. GL 4 is just about OK in a Land Rover gearbox but GL 5 will cause excessive and rapid wear to the bronze (yellow metals) within.

I was quite surprised at the colour of the oil after such a short distance. It could be that as all of the yellow metals are new and set up on the tight side of the workshop manuals tolerances, it’s just things finding their natural “size”.

With the oil drained out, I reinstalled the drain plug and dropped the oil in the transfer box.


A very technical set of tools…


Just as well, as I dropped the adjustable spanner in the container of oil when I refitted the drain plug. Yik.


With the convenient filler plug on the top of the transfer box, 2.5 litres went in easily. 2 full cans plus…


… half a can, and a little bit extra, for luck.

It’s not actually necessary to measure how much oil you put in. If you remove the original filler plug on the side of the casing, the correct level it reached when oil starts to run out of the opening. On LGL, I have a dip-stick assembly and it’s a bit of faff to remove, hence the measuring jug.

No drips… filler plug reinstalled. The overdrive shares the oil of the transfer box. There’s a screw milled into the main-shaft of the overdrive. Using the oil splash inside the transfer case when in motion, oil is thrown onto the screw and draw along it to lubricate the overdrive.


Next comes the task / challenge / opportunity to refill the main gearbox. Oil is filled into the main box by the level plug on the side of the casing. It’s in a tricky location to say the least.

The ex-military Series 3 I had in the UK had a second rubber bung on the gearbox tunnel and a filler cap on the top of the gearbox. Why this wasn’t available to the civilian market I have no idea but I’m definitely keeping a lookout for parts to make these alterations.

My plan was to use this beast of a syringe… advertised as a clean way to inject oil into hard to reach places, I thought it would be the perfect tool.


Problem 1. The oil is very viscous, it was extremely hard to “suck” into the barrel.


I unscrewed the hose and poured the oil in.

Then I set about positioning myself under LGL and threaded the hose into the filler hole. Now I simply push the piston down right. Well, thats the physics of it.

In reality, the piston doesn’t seal well in the barrel. Any change in angle of the shaft sees oil bypassing the double seal running out of the back of the barrel, down the handle, up my arm and into my armpit.

I drained the oil out and put the whole thing in the bin. I’d lost almost 0.5 litres out of this thing, fortunately all in the drip tray so I could reuse it. I’m not sure I got more than 100ml in the gearbox!

Whilst I cleaned myself, workbench, floor and shoes, I mulled over what to do next.

Gravity it my friend in such cases… why didn’t I think of this in the first place…

Bung on the side of the transmission tunnel was removed


…a  length of garden was repurposed and introduced to a funnel.


The hose was poked into the filler hole…


… and oil poured down the funnel from inside the cab. So simple and no mess. I only had to lie on my back to fit the filler plug.

I’ll do the axles at the next opportunity…