I am trying to get my head around my diff unit Which amusingly will fit in the axle either way up!)

What is the correct rotation direction for spiral bevel gears?

In the attached example which is the correct rotation direction?

And what happens if you use the diff backwards?
Rescued attachment diff spiral bevel.JPG

If you get it wrong it may be quicker in reverse than forward.

hmmm, i don't know, but blue seems most likely, the other way looks like it could slip off the gears

My thought was blue as well....

Simply because yellow looks very similar to "climb milling" which in the machining world is not a good thing...

But not sure if that logic actually works!

i think if you used it the wrong way around, there would be a lot of slipping on the gears, and therefore a lot more wear

? that spiders got 9 legs!

Can't be spiral bevel ----- Car haven't used spiral bevel gears since WW2 ---- any rwd diff post 1950 or so will be hypoid --- easy to spot the input shaft centre goes inat the bottom of the diff below the axle's centre line -- this keeps the propshaft low to reduce the transmission tunnel height.