Thread: 73 Lt95 Gearbox Oil

Originally Posted by Meccles

So, back to what to put in, 20W-50 GTX engine oil works just fine. As it did for 12 years when I used it previously Yes other oils may work, but bang for buck hard to go past this
If anyone here has worked on mini's with common sump engine/gearbox, that also runs engine oil...

Agreed, I use this in then engine and bix on mine - cheap, and you only have to carry one too up container.

Originally Posted by Blknight.aus

it was LR's first pressure lube fed gearbox. I recall reading somewhere that it was originally triald on hydraulic oils but with a shorter service interval it was found that the engine oil of the day was up to the task and having a single oil for multiple components made it easier to maintain in the field.

Gear oil was quickly eliminated initially due to the loss of flow rate through the pump strainer and then because of the loading it put on the pump that either chewed out the teeth or the square drive of the pump.

Im halfway tempted to trial the box on someting like a hyspin 48 hyd oil but I dont have a run up bench or the gauges to monitor the pressures and flow rates in the box.

That would pretty much be it in a nutshell - i.e. serviceablity and availability versus cost.

But don't forget, vehicle manufacturers do not want their products to last forever...

So the use of an engine oil in a gearbox was purely a commercial decision, which found itself substantiated by a design fault in the pump, which meant that it couldn't handle high-viscosity hypoid gear oils.

So consequently, there should be nothing wrong with a dedicated low-viscosity gear oil, provided it remained stable throughout the operating temp range (which really is not hard to do, when you consider the original oil was mineral 20-50...)

The biggest issue I see, is that so many people do not adhere to the service intervals for gearbox and diff oils.... why? because they don't get dirty looking like engine oil does, so they think it's still OK.

My absolute worst case change interval is every 12 months on diffs. I do 15K intervals on all my auto gearboxes (which is about half the recommended 'extreme hard use' guideline) and since owning the RRC, swivels and engine get 5000km services, trans has had one service interval, and will be due in 6000km time for it's next, BW has had 2 changes (every 5,000) but now it has Neo in it, I will simply monitor it. I have been assured it can go the lifetime of the transfer case without worry, but I'll get it analysed at 30,000 for peace of mind.

Insofar as using mineral hydraulic oils- hyspin46 would work, but you would also have to consider service intervals, and perhaps initially have the oil analysed after 100hrs, to see if there was any breakdown. Like all things 'untested', it's only proven to work after it has been 'tested' and tested in the real world (i.e. until failure). My only question is whether hyspin actually has the correct properties for pressure fed gear applications, and not specifically hydraulic ram applications

It would be OK if someone had a spare LT95 and a willingness to test.

If it was my LT, and I wanted to remain loyal to the engine oil recommendation, I'd be looking at 10-40 synthetic motorcycle oil and checking it at the first drain interval, to see if the oil was suffering breakdown.

If I wasn't concerned about adhereing to spec, then something like Castrol Syntrans 50E would be my choice if I wanted a straight grade oil.

Oil companies are great at providing PDF BS, so one really needs to look past the press advertorial junk and look deep into the specs and independednt lab test results if they wish to be certain of facts.

Given that the current modern 20-50 engine oils are totally different to the prehistoric 20-50 oils once used and which were once suitable, I would have my doubts about using a modern engine oil. Especially when they are high in surfactants, low in anti-friction compounds, and full of marketing BS.

but if I didn't care, I'd just buy the cheapest crap out there, chuck it in and hope it worked, and if it didn't and the box lunched all it's gears, then oh well, just get another gearbox......

Interesting post with many valid observations. Will have to think about it and digest. Hadn't really thought that long and hard about oil for gearbox as LT95 has been such a reliable unit in past with GTX. It seemed a no brainer to keep using it. But, it was 18 years ago when I last used GTX in an LT95 and as you correctly point out, oils ain't oils anymore.

It's been proved that the 15/40 engine oils are a recommended and excellent choice for these boxes so why not use it? Castrol Syntrans appears to be another that works well especially with a tight box. I wouldn't bother using hydraulic or atf oils. I have stretched box oil changes out to 50k without any problems.

I change mine every 2 engine services - that seems to coincide with Castrol GTX coming on special at Autobarn.

I ran this question past Bearman. He said any good quality 20W-50 oil. But was very specific, said not to use any ATF/ Hydraulic type oils. I figure as he rebuilds them he should know.

This was response from Penrite Tech department:

Range Rover, 3.5 Litre V8 Eng., 4-Spd. Man./ Auto., 4x4 (1974-1984)

Manual gearbox > On our website we actually suggest a mineral oil equivalent to a straight 30 (but really SAE 20W-60)--- HPR 30. Service fill is listed at 2.6L, but a dry fill will be more, of course.

From the product information:

...............HPR 30 is suitable for use in motorcycles with wet clutch assemblies and is also suitable for use in gearboxes requiring a SAE 30 non friction modified engine oil. It is suitable for use in vehicles with a combined engine / transmission application such as BMC Minis, especially those used in competition conditions...............


Regards,
Alan Jeffery
Technical Support

This looks pretty decent oil for both engine and trans so might have to give it a go.

The service book recommends SAE 20W/50 API SE oil (Penrite HPR 30). The ADF documentation recommends SAE 40 (Penrite HPR 40).