Gearbox Oil

[alexander]

Hi All
I see in the handbook that the gearbox oil is the same as engine oil, I drained the gearbox to work on the selectors and the oil smell’s very much like hypoy oil. What is the recommend gearbox oil in 2021.
Thanks
Dave

[Keith Clements]

I use 20/50 with molyslip although there is some discussion on modern oils attacking the bronze bearings in the box.
On some of our Jowetts I use classic straight 30 with molyslip. The molyslip is there because Jowett boxes are frequently run low on oil as most users do not check every 200 miles.
The hypoy oil might have been used to hide a noise when selling a car. Much used in addition to sawdust pre MOT.
This might explain your selection issues. Flush out and put in SAE30.
Check the oil you took out for steel, brass and bronze debris.

[Nick Webster]

The issue with using an EP gearbox oil stems from the Sulphur based additives that may attack the bronze. Going back some 50 years to before low Sulphur North Sea crude feedstock, the lubricating base oils had a fair bit of sulphur in them naturally. Apart from some reports of damage ( ! ) this was shown to be beneficial in some respects for most gearboxes and so it is now included as an additive. Control of Sulphur content is now rather more precise and manufacturers will play down the risk of damage. However it is fair to say that modern gearboxes comtain much less bronze and hence there will surely be less reports of problems. If you do decide to go for a specific gearbox oil then do not use one marked GL5 but go for GL4 or even lower if you can get it. There are more additives in GL5. These days there are some classic gearbox oils on the market, including some that don't have a GL rating at all. I have not really looked into this but I would point out that some of the specialist oils are for vintage gearboxes with straight cut gears. You could use this in lieu of the motor oil option (see below) but being specialist it might be expensive. You might be able to hunt down a low sulphur EP oil suitable for for a Javelin with helical gears. Of course without any additives at all it wouldn't actually be an EP oil so it is a bit of a balancing act.

On the question of using engine oil in gearboxes, I suspect that quite a lot of manufacturers specified this because they were a bit suspicious of EP oils. Turns out that perhaps they were right. However if you use a multigrade there is every chance that it will contain detergent in some degree or another - even if it is marketed as a classic oil. Using a detergent oil in a classic engine is fine, providing it is modern enough to include a disposable filter element in the oil circuit. In the gearbox the detergent may tend to wash out the synchromesh baulk rings and smooth changing will suffer. A straight SAE 30 or SAE 40 classic oil is unlikely to have a detergent additive and is a much better bet and honestly, the one I would favour in general.

To conclude then, use either an EP oil with a very low GL number or a non detergent straight motor oil. Changing any oil more frequently than specified is always beneficial.

Nick

[alexander]

Thanks both i’ve used a 30 oil after changing the selector bars for a better pair but after many hours/days of trying to get a smooth change I’m still having problems.
Will open a new topic once I’m clear what’s happening.
Dave

[Mike Allfrey]

Hello Alexander,

My Jupiter gearbox has been filled with Penrite 80 Manual Transmission oil for what it is worth. It appears to work well and, has been used for over twenty years, even on a hot day (at 42 degrees C), the gear change remains smooth and easy.

I have no experience of using additives, so cannot comment there.

All the best,

Mike A.