ST1100 final drive oil.

[alphafang]

Here's a question for you all.

If the final drive unit requires hypoid 80 gear oil why doesn't the gear box?

I don't see what the difference is I'm confused, I have had cars which have the gear box within the engine using engine oil for lubrication and cars with separate gear box's using hypoid gear oil. Is it due to temperatures I wonder? as in separate gear boxes, like the final drive unit don't get as hot as gear boxs within the engine.

[STeveo]

Somebody with more pieces of paper than me may know better, but I belive it is to do with the 'shearing' action of final drives and differentials. The pinion teeth of the drive unit 'slide' across the crownwheel teeth and this area is under a great amount of pressure, therefor the oil has to have 'EP' (extreme pressure) additives to do its job. If the same oil was used in the engine/gearbox your clutch would slip and the heavy oil would slow the engine due to drag. The g/box of most bikes use straight cut gears which have a relatively small surface area and in contact for a short time per revoultion compared to a spiral drive of a diff. Units like diffs and car g/boxes cannot get rid of heat as quickly as an engine and need to use heavier oil to compensate. Hope this helps.

 

[Aj1300]

Well said Steveo,

[alphafang]

That's the sort of answer I needed, one I could understand and relate.   

Cheers STeveo brilliant thanks mate.

[Brock]

The gear box on most bikes, is part of the engine cavity as it helps to save weight and space, so it makes sense to use engine oil to lubricate it. I dont recall any car that has an engine and gearbox combined. As cars are heavier the loads imposed on the transmission are higher so they can use an oil that is suitable for the job (XB Falcon used 30/40 oil, same as engine)  Most diffs run 80 to  90 weight as the loads applied are very heavy. Diffs while they do get hot, are usually far cooler than engines, unless the oil has leaked out   

[alphafang]

Most transverse mounted car engines used to be, I'm thinking, Austin Mini, Austin Maxi (Kimberly) and such.
Not sure if any modern cars are though.

[saaz]

The mini definitely did, as the old BP 5000 was specified for it.  The requirements are a conflict though, as the gears require different oil specifcations than the rest of the motor. Gear drives, hydraulic lifters etc all shear the oil to some degree, so I don't think it is the gearbox alone.  My car requires 10,000kms oil changes and it is a 5.7 litre GM motor.  The ST1100 has 12,800 km oil changes specified, and it has a shared gearbox.