Isuzu gearbox oil

**c.h.i.e.f** · 6th December 2012, 11:46 PM

Thanks rick you input is very helpful for all of us

I to am in Justin's boat as I have an lt85 that has 400k on it without a rebuild and that's been running castrol GTX oil but it has been changed every 5k wether or not it made a difference changing it that often i don't know or wether it was appropriate gear changes all its life...my observation of using VMX80 in my puma box it made it much quieter than the previous oil...

**rick130** · 7th December 2012, 05:47 AM

Originally Posted by c.h.i.e.f

Thanks rick you input is very helpful for all of us

I to am in Justin's boat as I have an lt85 that has 400k on it without a rebuild and that's been running castrol GTX oil but it has been changed every 5k wether or not it made a difference changing it that often i don't know or wether it was appropriate gear changes all its life...my observation of using VMX80 in my puma box it made it much quieter than the previous oil...

I wouldn't have guessed that.
The oil used in the Puma 'box is a 75W-90, full synthetic, VMX-80 is a 75W-80 mineral oil, so you've gone a lot thinner than what was in there.
I've gone the other way with my R380, using a (gasp) 75W-90.

Much less gear rattle when hot and shifts just fine without beating the 3rd gear synchro on the upchange as I used to occasionally get with Syntrans.

I've tried VMX-80 in the R380 and didn't like it at all, (I was using it during and after a flush after using an ester based cleaner/seal sweller) but R380's can be idiosyncratic too.
Interestingly the shift quality was vastly improved by adding the cleaner when I used it in the cleaning/seal swelling stage.

**rick130** · 7th December 2012, 05:49 AM

Originally Posted by justinc

Thanks Rick,

Gets a bit exxy using Sytrans to fill a Road Ranger

I might give the Valvoline Duragear 75w85 a try, Redline MT90 or the Penrite SIN75.

I'll report back then

JC

But they go 400,000km on one oil change with the exxy stuff, and there's no need to re-race at around that distance anymore either (but that might be down to better materials/build quality too)

**c.h.i.e.f** · 7th December 2012, 10:42 AM

Originally Posted by rick130

I wouldn't have guessed that.
The oil used in the Puma 'box is a 75W-90, full synthetic, VMX-80 is a 75W-80 mineral oil, so you've gone a lot thinner than what was in there.
I've gone the other way with my R380, using a (gasp) 75W-90.

Much less gear rattle when hot and shifts just fine without beating the 3rd gear synchro on the upchange as I used to occasionally get with Syntrans.

I've tried VMX-80 in the R380 and didn't like it at all, (I was using it during and after a flush after using an ester based cleaner/seal sweller) but R380's can be idiosyncratic too.
Interestingly the shift quality was vastly improved by adding the cleaner when I used it in the cleaning/seal swelling stage.

Thanks again rick....
I tried to get the original oil for the puma (BOT130M) which is supposedly castrol but castrol will not sell it as its under license to landrover so I asked for an equivalent which they also wouldn't tell me so I decided to choose vmx thinking that would be suitable as said before I have no idea about oils

Running this oil made gear chatter almost non existent compared to before..
I was told to run valvoline hydro trans in the puma and r380 but I am very sceptical on that idea...

**1103.9TDI** · 7th December 2012, 12:07 PM

I'm thinking of giving Motul Motylgear 75W90 a go for the diffs, gearbox and transfer, for the sake of standardisation. Seems to get some really good reports, got any input on this one Rick?

**c.h.i.e.f** · 7th December 2012, 04:02 PM

Originally Posted by 1103.9TDI

I'm thinking of giving Motul Motylgear 75W90 a go for the diffs, gearbox and transfer, for the sake of standardisation. Seems to get some really good reports, got any input on this one Rick?

I also would be interested in this idea for the county

**Bush65** · 8th December 2012, 09:40 AM

Originally Posted by Dougal

Which Syntrans do you use John? I know they make several, I'm using VMX80 because Rick130 suggested it based on the viscosity match.

I'm wondering if something a little thicker than VMX80 might have some noise reduction properties.

FWIW, my original MSA-5P box specified 15w40 engine oil. My current MSA-5G box specifies 5w30. My MSA-5P didn't exhibit the low rpm high torque rumble that my 5G does. It wasn't taking the same torque, but it wasn't that far off.

Syntrans 75w85

Originally Posted by justinc

John,

I am after some clarification about the engine oil vs MTF questions you have raised.

In my limited opinion ( Compared to others more informed about oil choices on this site) I would think that when LR designed the LT95 and specified engine oils, the oils on offer back then were 'suitable' for an archaic design such as this transmission. Modern 15w40 oils are far better surely?

True the torque us Isuzu owners push through these gearboxes will well exceed the little 3.5 V8 so, maybe that is good enough reason to change to an MTF?

However I have been using the 15w40 for 150K now, in both box and transfer, ( Taper rollers for 100K after the thrusts almost caught fire

) and to date no noticeable wear and certainly no failures have occurred.

HOWEVER;
I am always open to trying a better product, if it wasn't for the price (6 litres @ $30/l !) I would be using the Syntrans 75w85 option, for sure.

JC

The LT95 would have been designed over 42 years ago. Back then they had a limited choice of suitable lubricants, but by no means does that mean what they recommended then was ideal. Nor does it mean the recommended oil from back then is the best compromise today.

My main concern is gear wear and IMHO engine oil is not as good as MTF for the high contact pressure between heavily loaded gear teeth. Engine oil is not designed for gearboxes.

Rolling contact between gear teeth only occurs close to the pitch line, and tooth contact is mostly sliding. Wear accelerates rapidly when wear particles accumulate in the lubricant, so whatever we do to prevent this helps greatly.

Onset of gearbox whine is caused by loss of conjugate action due to uneven wear of the tooth flank - both contact pressure and the sliding velocity both vary as teeth contact point changes between the tip and root. As bearings wear and tooth loads increase, gear alignment is adversely affected and the situation becomes worse.

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