GL4 or GL5 oil in transferbox?

[Kobold]

As I'm preparing to check up the fluids of my 1985 90 I'd look for the right fluid for the transfer box, and here I became somewhat confused.

As my Haynes workshop handbook states it should be filled up with SAE 80-90EP GL4 or higher,

I still have 3 bottles unopened 80W-90 GL5 gearlube universal transmission oil in my garage.

Then I googled on this subject and the answers are somewhat opposite to each other.

The first answer I found that it should not be used as it may be agressive on the brass parts, as the other states

Land Rover currently has commercial arrangement with Texaco/Chevron that leads it to recommend a Texaco/Chevron MTF94 fluid. From the freeback we have received and read on this Forum and elsewhere, we feel it’s a little too viscous (5W30 or 70W80) to give the best results. Nonetheless you should use it in preference to ATF if your choice is limited to the two.

However, there are better alternatives such as the fully synthetic MT75D gear oil however rather than simply plug MT75D I’ll give pointers to what you should look for when seeking alternatives to ATF or MTF94.

Firstly, the lubricant must have the original 5W20 low viscosity of ATF fluids to give minimum gear drag. However, it MUST also be formulated only from fully synthetic base stocks since these will have a much higher lubricant film strength so as not to be squeezed out of those all important high pressure contact areas where wear might occur. This, and the low viscosity, has the added benefit of reducing friction which lowers transmission noise and improves economy.

It must also be highly shear stable and able to maintain its optimum working viscosity over a very wide temperature range. This and a very, very carefully matched coefficient of friction (probably the most critical parameter) will ensure that it dramatically improves gear shifting in LT77 and R380 boxes (especially from cold).

It is the improved shear stability and higher film strength that enables synthetic gear lubricants to outlast their plain mineral counterparts by up to 5 times. However, we err very much on the cautious side and recommend only a doubling of drain intervals.

Note that unlike engine oils, gear oils do not have combustion by-products building up in them, nor do they suffer the higher temperatures of engines, so extending drain intervals is entirely acceptable if the lubricant is of the highest performance and the increase is modest. The exception to this would be if the gear oil were contaminated, perhaps by water or mud during deep wading, though this is unlikely. If the oil is contaminated in this way it MUST be changed immediately, regardless of its formulation.

LT230 Transfer Box (Land Rover 90 & 110, Discovery, Range Rover)

That’s the problems of the LT77 and R380 boxes solved, but what about the LT230 transfer box to which these are commonly mated?

You should NOT use ATF, MTF94 or MT75D in an LT230 TRANSFER box. It must use a thicker gear oil such as EP90 (monograde), EP80W90 (multigrade which is better for cold starting lubrication on winter mornings) or EP75W90 (typically fully synthetic giving the best lubrication of all). This is the same lubricant that you should use in your axles and you should look for an API GL5 specification for best protection.

Borg Warner Chain Drive Transfer Box (Range Rover)

The only transfer box from Land Rover where ATF was originally recommended is the BORG WARNER chain drive box as fitted to Range Rover vehicles from around 1989 onwards. Again, type DIII is the best grade currently available but guess what, these Borg Warner boxes suffer from wear around the chain and sprockets!! Another application for a fully synthetic MT75D type solution, we feel.

LT95 & LT85 (Land Rover 90 & 110, Range Rover)

Very early 90 and 110’s were fitted with either LT95 4-speed (also fitted to early Classic Range Rovers) or LT85 5-speed gearboxes.

These boxes are very robust and when mated to engines in standard tune are relatively unstressed. Consequently, both boxes can be filled with a 15W50 or 20W50 engine oil (API SG/CE or ACEA A2-96/B2-96).

So my question is, is it safe to use the GL5 oil in the transferbox instead of GL4?

[FridgeFreezer]

It's happy with either.

Mods - how about a sticky/tech archive post or something for this subject?