WATCHPOINT:To determine whether you have an LT77 or R380 box fitted to your vehicle use this rule. LT77 gearboxes have reverse gear selected to the left of 1st Gear whereas R380 Boxes have reverse gear selected on the right below 5th Gear.
WATCHPOINT: Never, ever undo a drain plug until you have undone the corresponding filler plug FIRST. That way you are absolutely sure to be able to refill with fresh lubricant after you have drained all the old oil out!
Locate the main manual gearbox filler plug and loosen it using a 1/2” AF spanner (LT77 Gearbox) or T55 torx bit (R380 Gearbox) and position a Drip Tray and Oil Drain Pan beneath it. In the picture below, showing an LT77 box, the square filler plug is numbered 1.
Remove the filler plug but watch out for a possible dribble of oil.
WATCHPOINT:Note that the filler plug is in a very awkward locationand it will be impossible to get any oil into the box without a flexible tube.
Locate the main gearbox drain plug in the side of the gearbox roughly below the filler plug. In the picture above it is the large hexagonal plug numbered 2.
Using a 32mm Wrench (there isn't room for a socket to be fitted) Loosen the main gearbox drain plug but do not remove it yet. Reposition the drip tray and drain pan under the drain plug but bear in mind that when you remove the drain plug the gear oil will first shoot out horizontally before gradually falling back to drain out directly beneath the drain hole. Usually it runs down onto the chassis cross member and then spreads out to drip off quite a wide area so you really do need a wide drip tray and drain pan.
When you have your drain pan in place unscrew the loosened drain plug by hand BUT keep the plug pressed firmly against the gear case at all times as you unscrew it. When you are satisfied that there is no more thread, just your hand pressure holding it in place, then double check your drain pan is in position and whip away the drain plug as fast as you can so that your arm is not covered with oil as it gushes out.
While the oil is draining wipe any debris off the drain
plug. It is magnetic and usually it acquires a little ‘hedgehog’
of iron filings. This is quite normal and nothing to worry about, however
if any large chips of metal or gear teeth are present on the plug or in
the drained oil this indicates some internal damage has occurred in the
box.
A ‘hedgehog’ of iron filings such as can be seen on the left hand drain plug is normal and not cause for concern. Larger lumps or chips in the drained oil might require further investigation. On the right can be seen the same drain plug after the filings have been wiped off.
Once all the oil has drained out replace the drain plug (preferably using a new copper washer) and tighten. The correct torque is 50NM but since a socket and torque wrench can't be used you should tighten carefully by hand. It may be useful to apply a torque of 50NM to a spare nut and bolt so you can gauge what this torque feels like before applying a 32mm spanner to tighten the drain plug.
If you have an earlier LT77 box you now need to reposition the drain pan underneath the extension case drain plug, its hole drains out vertically so the bowl can be positioned directly underneath it. Note: Later R380 boxes do not have this second drain plug.
Wipe off any debris from the drain plug and once all the oil has drained out replace the filter and plug (preferably) using a new copper washer. The plug should be tightened to a torque of 50NM.
The gearbox can now be refilled through the filler plug.
Fill the gearbox until oil starts to run back out of the filler hole, it should take around 2.7 litres before this happens. Wipe any debris off the filler plug and refit it, tightening to a torque of 25NM. (DO NOT OVERTIGHTEN since the plug thread is a taper variety and will damage the gear case if too much torque is applied).Never, ever undo a drain plug until you have undone the corresponding filler plug FIRST. That way you are absolutely sure to be able to refill with fresh lubricant after you have drained all the old oil out!
When you have your drain pan in place unscrew the loosened drain plug by hand BUT keep the plug pressed firmly against the gearcase at all times as you unscrew it. When you are satisfied that there is no more thread, just your hand pressure holding it in place, then double check your drain pan is in position and whip away the drain plug as fast as you can so that your arm is not covered with oil as it gushes out.
While the oil is draining wipe any debris off the drain plug. If any large chips of metal or gear teeth are present on the plug or in the drained oil this indicates some internal damage has occurred in the box.Once all the oil has drained out replace the drain plug (preferably using a new copper washer) and tighten to a torque of 30NM.
The gearbox can now be refilled through the filler plug.
WATCHPOINT: Note that the filler plug is in a very awkward location and it will be impossible to get any oil into the box without a flexible tube.
Fill the gearbox until oil starts to run back out of the filler hole, it should take between 2.3 and 2.8 litres before this happens. Wipe any debris off the filler plug and refit it, tightening to a torque of 25NM. (DO NOT OVERTIGHTEN since the plug thread is a taper variety and will damage the gear case if too much torque is applied).