Changing Gearbox / Centre Diff Oil and Rear Diff Oil.

Gearbox / Centre and Rear Diff Oil

There are some very good reasons for wanting to change the gearbox and diff oils on these cars, these are: better shifting especially when cold, the oils over a period of time will not provide as much protection as they used to and of course oil technology has improced since the mid eighties when these cars were first made and like with engine oil they do break down after a while and will not protect your gearbox as well.

If you just want to check the level on the box or diff then the procedure is the same. First remove the filler plug and then if oil runs out of the hole then you are ok, if it does not then add a little at atime until it just starts to weep of the hole. Re install the filler plug.

To start with you need to either get a 17mm hex allen key or 17mm drain plug removal tool ( I prefer the 17mm tool as it can take more torque when undoing the plugs). Looking at the gearbox first it is best to warm the oil up by driving the car for 5 to 10 miles to get the oil nice and warm as it drains out better this way. Next you need to jack up and correctly support the car. Underneath you will see on the left hand side of the box about half way up the filler plug, remove this first, why I hear you ask? It's simple if you drain the oil first and then can't the filler out then you got a big problem. Chances are it will be in quite tight, best thing to do is to clean it out first. Next up is to drain the oil out of the centre diff attached to the back of the box, the drain plug is located on the bottom of this, be careful here as the oil does tend to gush out and it won't smell all that great either. Now if you got the time I would leave it an hour or so drain out properly, you won't get it all out but try and leave it as long as possible.

Whilst you are waiting for it drain out now is a good time to clean the plugs as they should have little magnets on them to catch bits of metal. On re filling put the drain plug in and then fill the box with your oil, I have a suction pump for this very purpose which holds 0.5 litre at a time, i have heard of people using turkey basting syringes as well, or you can squeeze it out of the bottle and end up with it running down your arm. Once you are sure you have enough in the box, i.e. it's just dribbling out of the hole then reinstall the filler plug. Whilst you are under this end of the car have a look at the gear linkage that sits on top of the box next to the bellhousing, it's well hidden so maybe a work light will help. Now if you have a spray can of grease sray the linkage well, in particular the part with the ball joint on. This makes a big difference to gear change quality, worth doing anytime you are under this end of the car. The other job well worth doing id lubrcating the centre propshaft bearing, for this you need a grease gun and some patience as it is a bit on the fiddly side, once the grease nipple has been located then attach the grease gun and go for it.

Ok now it's the rear diff's turn, don't forget the tip about taking the filler plug out first, drain and refill the same as you did for the box. Note that the oil for the rear diff is different to the oil for the box. In my experience it's best to cheak the level of the gearbox and rear every 6 months, as low oil kills these very quickly.

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