Gearboxes and Fluids

Gearboxes

5-speed LT77 and R380 main gearbox (Land Rover 90 & 110, Discovery, Range Rover)
Firstly, let’s deal with the somewhat notorious LT77 and R380 5-speed main gearbox. These are famed for a poor, notchy gear change, especially from 1st to 2nd gear.
The notchy gear change is due to a combination of a weak synchromesh and the use of a plain mineral ATF fluid.
ATF was originally specified for the LT77 5-speed gearbox and, theoretically, could be used in the later R380 box. Type DIII is the best grade currently available. ATF was originally specified because of the weak synchromesh in the LT77 and R380 boxes (especially second gear).
ATF has a very low viscosity (rated as 5W20 since it falls below normal gear oil viscosity grades) and so it has minimal drag on the gears, enabling the weak synchromesh to do the best of a bad job.
BUT ATF has several drawbacks which is why it is NO LONGER recommended for use in such boxes. These are:
It is generally a plain mineral base stock formulation (even DIII) and this, coupled to its very low viscosity, means that it is poor at preventing metal to metal wear in manual transmissions.
This is compounded by the fact that the viscosity improvers within (thickeners) are more rapidly sheared down in manual transmissions. Again, this reduces the protective film strength of the ATF in those areas of high pressure contact and also increases transmission noise.
ATF thickens as temperatures drop (increasing that drag on the gears) which is why folks notice that gear changes are worst on cold mornings and improve after a few miles motoring when the ATF has warmed up a little.
So, what are the alternatives?
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).
If you choose to use engine oil in your LT95 or LT85 gearbox, we very strongly recommend that you change the oil in the box at the SAME time as you change your engine oil (i.e. no more than 6,000 miles). This is because in manual gearboxes, engine oil provides limited extreme pressure protection and the viscosity improvers within it tend to shear down faster, again reducing protection since the lubricating film thins out.
If you want better protection for these boxes you should opt for 75W90 Fully Synthetic Gear Oil to API GL5 specification.
Be careful though since, generally speaking, GL5 oils are incompatible with the copper alloys found in older generation gearboxes. Certain additives within can cause leaching of the copper and this weakens the component, especially the synchro rings. You should check with your supplier that any GL5 Fully Synthetic Oil you use is FULLY compatible with copper and its alloys and suitable for use in older transmissions.
ZF HP22 4-speed Automatic Gearbox (Land Rover 90 & 110, Discovery, Range Rover)
That’s manual gearboxes covered, but many late vehicles are fitted with the ZF HP22 4-speed automatic box.
In reality, the ZF 4-speed auto box fitted to these vehicles is more than happy with Non Synthetic ATF fluids, and the latest ATF DIII grade is the one to use since it is better suited to the small orifices and electronic control systems in the latest generation of auto boxes. Regular fluid and filter changes will see the box give a very, very long life without the need for Synthetics.
However, if you live in hotter climes, or if the box is being worked extremely hard (say touring the Alps in Summer!), then a Synthetic fluid will significantly reduce the transmission temperature and this is worth the expense alone to avoid an overheated transmission.
So, if you want the best fluid for your ZF auto box then synthetic is the way to go for maximum box life, best economy (such as it is with an auto box!) and lowest transmission temperature. If you want the VERY best fluid then you won’t do better than an MT75D type fluid since it is perfect for ZF 4-speed auto boxes.
Chrysler Torqueflite 3-speed Automatic Gearbox (Range Rover)
Reputedly, this 3-speed auto box offered prior to the ZF 4-speed was about as ‘bullet proof’ as auto boxes could get. It’s a very tough, very simple, long lived unit and runs happily on ATF Type DII or as mentioned earlier, the latest ATF Type DIII type fluid.
Note that not all older generation auto boxes can run on ATF DII or DIII, but the Torqueflite unit factory fitted to Classic Range Rovers is fine with either.

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