Just wondered what determines how much oil goes into a differential or gearbox.
How the manufacturers decide?

For example , why does 70ml have to be removed from the haldex when refilling - why not 60ml or 90ml ? Jules

Well, it depends on how much oil actually needs to be in the gear box.

In some units, they locate the fill hole so that it's lower edge is at exactly the right level so you just fill up until it starts running out and then you're done.

If that's not practical then they put the fill hole where they can, and the only way to get a know quantity is to fill it to the top and then remove X amount.

This is because in a box without a drain you don't know for sure how much oil is left in the bottom after you pump it out. You could measure the removed oil and replace exactly that amount, but if the level was low to begin with you wouldn't have enough.

If the box has a drain at the very bottom of the case, you should be able to simply add the required amount without the fill and remove technique.

Not enough oil, obviously bad, too much would leak out the seals, possibly damaging the seals or whatever is on the other side of the seal. Some boxes have a vent hole which might allow excess fluid to escape harmlessly.

The level has to be at the correct depth so the gears will “splash lubricate” the entire box mechanicals, also it must be below the seals lowest point, at the design stage the gearbox cavity can be changed slightly to enable enough oil to be held so that it will survive service intervals.

Auto boxes are a completely different ball game of course. Regards

David

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Perfect......easier to see than explain  Regards

David

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Dave,

I agree its easier to see what's going on inside the Diff to understand how the level is selected.

Note: What Merlin wrote is technically correct but perhaps a bit too kind to the engineering team. If I were in the meeting and the topic of the front transfer case came up and we were talking about design for serviceability my comments would be far less kind. The team dropped the ball on this one.


For my Diff the first time that I changed the Gear Oil I removed it when it was still hot and it had a lot of air in it.

I basically had a black layer an a brown layer and I though that I might have water contamination but when I checked the oil the next day the brown layer was completely gone, so clearly it was air.

I suspect but I have no proof that the anti foaming additive becomes less effective as the oil is used and air isn't a very good lubricant.

Thanks

Paul

Pretty much regardless of the anti foaming additive a diff (and gearboxes) will aerate the oil to an alarming extent.....even with brand new oil, one of my “jobs” was to film inside engines, g/boxes and diffs (when they were still used separately by us) to monitor oil flow, splash and expansion.

I do miss little challenges like that  Regards

David

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Dave,

That is great information thanks for sharing.

But it does bring up the next question.

What if I switched

From 75W-90 Mobil 1 Delvac

To 80W-140 Mobil 1 Delvac


Would that reduce the foaming?

It is relatively warm where I live so the higher viscosity likely won't be a problem.

I am happy with the 75W-90 so maybe I will just stay with that

Any reccomendations

Thanks

Paul

TBH I’d stay with what is recommended, we would spend months and 100K’s pounds testing for the best results, unless a higher/later specification is available which still meets the requirements of the original engine/gearbox.......go with the manufacturers recommendation. Regards

David

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