Thread: 73 Lt95 Gearbox Oil

Will try a quality 20/50 in her as a i believe thats what would of been in there before .
Thanks Guys

HPR30 mineral, HPR15 synthetic-------can either of these be used in an LT95 box, and which is better? and why? Thanks for any advice. 110county

Many years ago I tried HPR30 in my 81 RRC which is 60 when hot.

When it got hot I couldn't change gear.

Stick with a 50 grade when hot. It doesn't matter whether it it is 10,15, or 20 when cold . Ie the first W number.
Regards Philip A

Just filled mine up with Castrol GTX 20W-50W which is Castrols recommendation. Figure cant go too wrong with that.

Oil threads are a very topical thing - by that I am inferring that it doesn't matter what is technically correct, there are always conflicting opinions as to what to use.

For myself, I always stick with the manufacturers recommended products, unless there is a specific requirement to change.

I went through several varieties / brands with the getrag transmission on the 16v, and found that the 'best' fluid was actually the genuine bottled MB ATF, which had a quite unique specification for the specific 717.404 (GL275E) manual.

However, after investigating and using several (quite expensive) different brands, I ended up replacing the MB spec'd ATF with Neo Synthetics Hi-vis, which is effectively a 7wt gear oil, full synth, but with an inordinate amount of technology 'inside'.

Without going into too much detail, and starting a war/riot/argument there is a very good reason for using a 'gear' oil in a manual transmission as opposed to engine oil... And that is 'shear'.

A gear oil has much higher shear strength, and this literally translates into the 'film' of oil that covers the gear components and remains 'stuck' if you will...
Motorcycles with wet clutches and gearboxes that share the same oil as the engine also have a much higher quality shear strength than your average engine oil.
It all has to do with the intended function of the oil itself.

So in that respect, if you were wanting the extreme film strength and high molecular shear strengths, then you would use one of the more expensive motorcycle synthetic oils - motul 8100 for example, as your 'gearbox' oil.
But, you still have a change interval to adhere to, and in that respect, a dedicated gear oil has the superior friction modifiers (which do not have to suffer exposure to combustion byproducts) higher film strengths and consequently a slightly higher base viscosity.
Yes, you will need to choose a suitable product which provides the same ideal viscosity as the original specification of oil. So if that is a 20 weight or 50 weight SAE viscosity, then you should choose a product that matches this, as the design of the internal components is such that an excessively thin or overly viscous oil may contribute to starvation of lubrication or damage.

In the case of the borg warner transfer case, I run the hi-vis neo on that as well now, after a year of careful observation in the 16v gearbox.

My actual opinion on the subject is fairly straightforward. Where specified, the synthetic ATF's are OK, as are the super expensive dedicated synthetic gear oils. However I would never run an engine oil in a gearbox (for reasons previously stated) even if the change intervals were the same as the engine oil - there just isn't the same amount of protection afforded in an application which is designed to create a shear characteristic, because gearboxes are not combustion engines, and vice versa.

If you must run an engine oil in a gearbox, then at least do yourself a favour and look to the high quality full ester synthetic 4 stroke motorcycle oils, and change the oil as frequently as you change it in your engine - if you want to afford the best levels of protection.

It's just a consumable, but you can save a lot of money by choosing wisely with a high quality synthetic gear oil designed for the application (and the change intervals can be extended by a huge margin because of the extremely high specification)

Just some food for thought.

There's a good reason for not using gear oil in the LT95 - the little plastic oil pump that apparently likes to break when asked to pump cold 80w-90.

I was using cheap 20w-50 in mine - which was brand new - and then changed to HPR30, which is what's in the engine. The box has been much quieter since. The synchromesh requires double-declutching when cold with either oil, though.

We used Castrol VMX-80 as recommended by LR and the original owner Stage 1 had been driven round Australia and my Son drove it from Kalgoorlie to here with no problems.
Whatever oil you use it needs to be GL4. Most gear oils are GL5 which is not compatible with non-ferrous parts in gearbox, this oil is very thin so will not harm the pump, check out Castrol web-site, Regards Frank.

My actual opinion on the subject is fairly straightforward. Where specified, the synthetic ATF's are OK, as are the super expensive dedicated synthetic gear oils. However I would never run an engine oil in a gearbox (for reasons previously stated)

Your theory is quite valid and in many cases I have used gear oils in gearboxes.

BUT the question remains-

Why did Land Rover recommend to use engine oil in the LT95?

Even back then they would have access to Oil company specific formulations as they seem to now quote the most exotic oils for their gearboxes.

Could it be that their testing indicated that 20W-50 engine oil was ideal for an LT95?

I can recall that I had an LT95 in Saudi that someone had used 80W-90 gear oil and the pump was sheared and the thrust washers destroyed.

Perhaps the width of viscosity difference between hot and cold is incompatible with high sheer strength in gear oils as you rarely see a large difference in viscosity . Although Nulon do make an 85W-140, which I mix with 80W-90 for my transfer case.

Regards Philip A