gearbox/transfer oil


hi iv recently been offroading and the fourtrak had a heavy workout in mud and after a while i could smell hot gearbox oil there are no leakes apart from the one that is already. but the gearbox has had a slight whine for years and years but the whine is now got louder now my dad seems to reckon that the oil in the gearbox/transferbox isnt that special and probably wont cope with too much so im looking to find out what sort of oil i could put in the gearbox and transfer box and also the front and rear diffs so that it will cope with some nasty offroading. by the way its a 2.8td diahatsu fourtrak 1989. any advice welcome cheers


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Its been answered before, in the drivetrain (which is gearbox, diffs) EP90

Full of ideas but no time to do them!!
youtube: Redfourtrack



Replace the gear oils with an EP 90 gear oil to the specification GL4 or higher (GL5) this will ensure the gearbox, transfer case and axles get the correct specification oil. These are all now synthetic oils which are alright with the transmission system, unlike the engines.

It sounds like contamination of one of the oils from heavy off roading, either water or mud, or a combination of the two have entered the gearbox. This will cause internal problems if it is not changed and will lead to premature wear of the transmission internals.
Add an additive such as Slick 50 or Molyslip, this will build up on the internal parts and quiten them down slightly and compensate for wear.

Many people put cheap and often inferior oils into the transmission system, they then forget about it and do not change itas and when it is needed, this is what causes the wear.

To prevent any future damage, check the gearbox and axle breathers, this is located on top of the gearbox, the axle breathers could be located anywhere on the axle.
Replace the gearbox breather rubber pipe and extend it to under the bonnet high on the bulkhead, fit a small fuel filter on the end to stop airborne dirt entering and this will help cure water and dirt ingress.
Move the axle breather pipes to a higher location, the rubber pipes often deteriorate and crack, these are removed and not replaced, any water above the top of the axle then floods in.

EP90 gear oil, not EP 80/90 or EP 75/90 or EP 80; and to GL 4 standards.

thanks assassin

thanks assassin il get on to it i did move all the breather a while ago up to the bulkhead but as you said 1 could have a split in and i was in some pretty deep water and mud. cheers again