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What’s the best oil for a PRM 120 (mechanical) Gearbox?


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For years I have been using standard engine oil in our PRM 120 mechanical gearbox. But it was recently brought to my attention that PRM now recommend Automatic Transmission Fluid (ATF) Dextron II or III.

 

Well I get out there and find there are all sorts of ATFs available, with ‘overlapping’ standards: some for Dextron II and IID, others for Dextron II & III plus a lot of other standards, some for Dextron II, III & VI, etc.

 

The easiest ATF to buy off the shelf here is Comma brand -- and there is a mineral ATF called ‘AQM, a semi-synthetic ATF called ‘AQ3’, and a fully synthetic ATF called ‘MVATF PLUS'. My instinct is to go for the MINERAL AQM version.

 

Any thoughts or insights?

Edited by Jim Batty
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When I looked a few moths ago I found they were all stated to be backwards compatible. A mechanical gear box in no way stresses the oil like a vehicle auto-box will so I would use the cheapest. Dexron 2 if I recalls as being the most readily available. I think your instincts are correct.

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I checked with PRM years ago what I should put in my 120 and they said "whatever you put in your engine". That is what I have done for 14 years now without problems. However, I do see the latest manual advises to use ATF so I don't know why this advice has changed.

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I checked with PRM years ago what I should put in my 120 and they said "whatever you put in your engine". That is what I have done for 14 years now without problems. However, I do see the latest manual advises to use ATF so I don't know why this advice has changed.

 

I understand that there may have been instances of problems with the clutches when using engine oil but have no further details.

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We were told by the previous owner that our PRM500 has always had Morris 10/40 in.

 

Yes - spot on. Exactly right for a plate clutch PRM gearbox

 

The 80 and 120 are cone clutch gearboxes, which is why they use ATF

 

Richard

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  • 1 year later...
On ‎07‎/‎02‎/‎2016 at 13:26, RLWP said:

 

Yes - spot on. Exactly right for a plate clutch PRM gearbox

 

The 80 and 120 are cone clutch gearboxes, which is why they use ATF

 

Richard

Hi Richard,

Was going to post but had forgotten that I'd already asked the question. Anyway, tempis fugis v memory and my local chandler said Morris 15-40 is right for it which is what I bought some time ago. Only 1400hrs on the 3L2 and I know the previous owner changed the PRM 500 oil maybe at around 1000hrs some 3 years ago. The oil looks clear and clean, is it really worth changing? UPDATE: changing now to 15/40 as verified by PRM.

Edited by Markinaboat
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