Maggie13 Posted November 22, 2022 Share Posted November 22, 2022 What is the correct oil that is easily got in the UK for spitfire mk3 gearbox. I believe it has the d type overdrive? Am I right in saying i need 2.5 litres. Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted November 22, 2022 Share Posted November 22, 2022 I would think a GL4 spec gear oil in either ep90 or 80w90 viscosity? Quote Link to comment Share on other sites More sharing options...
Maggie13 Posted November 22, 2022 Author Share Posted November 22, 2022 Is this one ok. https://www.commaoil.com/productsguide/view/6/183 Is some gl4 not suitable because of additives or sulphur or something. 1 Quote Link to comment Share on other sites More sharing options...
Clive Posted November 22, 2022 Share Posted November 22, 2022 34 minutes ago, Maggie13 said: Is this one ok. https://www.commaoil.com/productsguide/view/6/183 Is some gl4 not suitable because of additives or sulphur or something. GL5 is a no no in the gearbox. (More to do with it being too slippery for the brass synchros rather than sulphur) The comma oil you linked to is ideal, I used it for many years (now have a 5L can of millers, same spec but it happened to be on offer!) I prefer an 80-90 oil as it helps the gearchange when cold, Quote Link to comment Share on other sites More sharing options...
glang Posted November 23, 2022 Share Posted November 23, 2022 I believe GL5 has additional additives to make it suitable for higher stress uses (racing, high power drives etc) which might make it better for our heavily modified cars but unfortunately some brands have additives which attack copper based metals so to avoid any risk most people stick with GL4... Quote Link to comment Share on other sites More sharing options...
glang Posted November 23, 2022 Share Posted November 23, 2022 and yes my manual says 2.5 pints for OD 3 rail Quote Link to comment Share on other sites More sharing options...
Clive Posted November 23, 2022 Share Posted November 23, 2022 47 minutes ago, glang said: I believe GL5 has additional additives to make it suitable for higher stress uses (racing, high power drives etc) which might make it better for our heavily modified cars but unfortunately some brands have additives which attack copper based metals so to avoid any risk most people stick with GL4... No, even a yellow metal safe GL5 oil must not be used in a gearbox. The GL5 stuff is just too "good" at being an oil, it reduces friction too much. So the synchros do not grip. Change to steel synchros with friction linings and GL5 would be fine. Quote Link to comment Share on other sites More sharing options...
glang Posted November 23, 2022 Share Posted November 23, 2022 Never heard that one and I wonder if your thinking of the low friction additives that you can buy separately and which yes shouldnt be used on OD boxes. Ive used said additives in non OD 3 rail units with no ill effects or noticeable benefits for that matter.... Quote Link to comment Share on other sites More sharing options...
Clive Posted November 23, 2022 Share Posted November 23, 2022 29 minutes ago, glang said: Never heard that one and I wonder if your thinking of the low friction additives that you can buy separately and which yes shouldnt be used on OD boxes. Ive used said additives in non OD 3 rail units with no ill effects or noticeable benefits for that matter.... Nope. Otherwise gearbox builders (eg BGH) would spec a GL5 oil for the type 9 gearbox,. But they specify GL4 oils Many gearboxes produced today from Honda, Toyota not to mention BMW, Rover/MG etc etc specify GL4 or the very similar MTF (or their own oil) which does not meet GL5 spec. Conversley, I would very happily use a yellow metal safe GL5 oil in a diff. Quote Link to comment Share on other sites More sharing options...
glang Posted November 23, 2022 Share Posted November 23, 2022 Think some manufacturers specify a GL4 because their equipment doesnt need GL5 as the gear loads arent sufficiently high so no point using the more expensive oil. Im struggling to find warnings online about synchros slipping with GL5 although of course plenty about the risk to the yellow metal of synchros. In fact I would have thought synthetic gear oil is more likely to cause slipping due to its increased friction reducing properties... Quote Link to comment Share on other sites More sharing options...
Clive Posted November 23, 2022 Share Posted November 23, 2022 Try looking for some of the Honda warnings... I believe that most? GL5 oil is yellow metal safe these days. Besides, the cost of the different spec oils is very very low. So manufacturers recommend teh best oil that wil have teh least number of warranty claims and produce the best efficiency. Synthetic has nothing to do with slipperyness. You can get synthetics is almost all grades, but it is the specification (not just the GL number) that dictates its properties. Quote Link to comment Share on other sites More sharing options...
glang Posted November 23, 2022 Share Posted November 23, 2022 I thought it wasnt recommended to use synthetics for engine run in because theyre too slippery and dont allow proper contact for components to bed in? Apparently to achieve GL5 and be yellow metal safe involves the use of more expensive additives so most use the cheaper ones to keep the price of their product down. If you want a GL5 oil thats compatible its going to be more expensive and although it might not be much these days it'll make a difference to the car manufacturer producing thousands of vehicles... Quote Link to comment Share on other sites More sharing options...
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