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 My gearbox tunnel is out and I am repairing the starter. This gives me easy access to the gearbox  dipstick. What is the best oil for an overdrive box on a 3A. The gearbox is in very good condition and has been overhauled recently.

I have just checked the oil dip stick and there is nothing showing. I have Comma EP90 GL5 in the box at present, bought from Moss who now only have Dynolite How often does the oil need to be fully changed and not just topped up. The nearest oil I can find is Comma gear oil high performance SX75w-90 GL5. 

What does GL5 mean and is it better that GL4 semi synthetic

Thanks  Richard & B

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Hi Richard,

           firstly DO NOT use GL5 oil.  These traditionally have a high sulphur content and can damage any brass or bronze components.

You MUST only use a GL4 oil.

There is great debate about exactly the best oil for a GB with O/D. 

I use a gearbox oil. In particular Penrite GB40 GL4. It is designed specifically for gearboxes and does not harm the yellow metal.

You will get answers recommending EP90 etc these work well but do ensure it is a GL4.

DO NOT use an engine oil such as 25/50 as this may contain a detergent for cleaning the engine. This could cause frothing etc.

 

Tin hat on and cowering behind a wall

 

Roger

Edited by RogerH
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No good hiding Roger, we know you are there !

I used to us a cheap 20/50 (as recommended by my box re-builders - Hardy Engineering,) but I have now seen the light, & my box now contains Penrite GB40

Bob.

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I’m no expert, so all I can contribute is that my 3a ( tr6 box with A type od) was purchased  in 2016 after a recent previous owner gearbox rebuild and had used EP80/90.

i use (and abuse) my car in club sprints etc. And on the road for leisure drives club runs.

At the beginning of 2018 I had to do some remedial work on the box due to leaks that let me do the 2018 season and continued with the EP80/90.

at the end of 2018 I had the box and od professionally rebuilt (not due to the EP oil I don’t think)  and upgraded for competition and the builder supplied dynolite Gear 40 oil.

This has been used for 6 months and 2 sprint competition and works well, no slippage etc.

as Roger said I have been advised to stay away from GL5 version as it is not good for yellow metals.

h

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Hi Hamish,

 unless I missed something in the shop I have noticed that the Dynolite oil does not specify any GL rating.

I'm sure it is very good but a simply GL number would calm nerves.

 

Roger

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1 hour ago, RogerH said:

Hi Hamish,

 unless I missed something in the shop I have noticed that the Dynolite oil does not specify any GL rating.

I'm sure it is very good but a simply GL number would calm nerves.

 

Roger

Roger 

I understand the concern ( having just paid for a rebuild and upgrade) but the builder recommended it and Moss says the following in their listing description. Sometimes you can only go on faith from reputable sources.

This multigrade oil replace the SAE40 & EP90 commonly used in gearboxes. It is compatible with straight-cut and synchromesh gears, and safe for use in overdrive units. It does not contain any EP type additive that would destroy yellow metals such as bronze, copper or brass. This oil does not contain any friction modifier additives which can cause slipping in overdrive clutches and preselector gearboxes, such as Cotal or Wilson.[P]Replaces oils originally specified as EP90, SAE40.”

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Penrite GB40 as recommended by the gearbox rebuilder 3 years ago.......who seems to vary depending upon what Moss are promoting! Clearly favouring a.n.other brand now:-)

Iain

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Here in the 'States SAE 30W non-detergent motor oil has been thoroughly proven. I must have done over 100K miles with my Webered TR250 O/D transmission using the stuff.

There should be a detectable, if slight increase in fuel economy with this over the gear oils, giving less viscous drag.

Similarly, I noticed several more miles between fill ups using a synthetic oil in the differential ( poured like water, almost ).

 

Cheers,

Tom

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