Hypoid oil? …why?

[Tapio]

Service manual states that the gearbox and end gear requires hypoid oil.

The difference between a regular bevel gear and a hypoid gear is that in the hypoid gear, the center of the pinion is offset from the center of the crown wheel.
See pic: http://en.wikipedia.org/wiki/Hypoid
This requires special oil, due to the contact point twisting as it’s rolling along the cogs.
But the end gear is not a hypoid gear! And the gearbox doesn’t even have a bevel gear (obviously, since the crankshaft is longitudinally mounted) in there!

So why does BMW say that that the gears require hypoid oil?

Must add: it’s not that I’m losing any sleep over this matter, I’m just wondering if anybody has any info on this.

//T

[Corvus]

Service manual states that the gearbox and end gear requires hypoid oil.

The difference between a regular bevel gear and a hypoid gear is that in the hypoid gear, the center of the pinion is offset from the center of the crown wheel.
See pic: http://en.wikipedia.org/wiki/Hypoid
This requires special oil, due to the contact point twisting as it’s rolling along the cogs.
But the end gear is not a hypoid gear! And the gearbox doesn’t even have a bevel gear (obviously, since the crankshaft is longitudinally mounted) in there!

So why does BMW say that that the gears require hypoid oil?

Must add: it’s not that I’m losing any sleep over this matter, I’m just wondering if anybody has any info on this.

//T

I wondered the same. In fact I'm wondering now, over a beer and not going to be losing sleep either!

I believe a hypoid gear has a degree of sliding, similar to a worm gear, whereas a helical gear, spur gear, bevel gear and I think also a spiral bevel gear all have a rolling action on a constant pitch circle.

If I've got that right will there be more oil shearing in a hypoid, requiring a different oil? Still, that doesn't explain why bmw need it in their gearboxes and final drives!

The gearbox has a torsional ramp action shock absorber. Would this need a hypoid gear oil? Not sure what is in the final drive which needs it. The spline?

At the end of the day maybe they found that they can increase tooth loads (pressure) by using this type of oil, thereby able to use smaller gears?

Just speculation though.

[timbox2]

This probably goes back a few years when you could buy Hypoid or Non Hypoid gear oil, I believe since GL4 or GL5 gear oils came about there is no need to worry as those API's will do for both. Think BMW were just trying to get people to put decent oil in.

What I will tell you is dont worry about the FD, stick std 80/90 whatever.

But when it comes to the Trans, do yourself and the box a favour, put Mobile 1 75/140 full synth in that, makes a huge difference. takes a leap of faith mind as its like water in the bottle.

[Dog Tyred]

Never ceases to amaze me just how knowledgeable the Trixter community is!
It seems that no matter what the question there is always someone out there that knows the answer.

Keep up the good work chaps (although makes me realise just how thick I am )

DT

[Corvus]

This probably goes back a few years when you could buy Hypoid or Non Hypoid gear oil, I believe since GL4 or GL5 gear oils came about there is no need to worry as those API's will do for both. Think BMW were just trying to get people to put decent oil in.

What I will tell you is dont worry about the FD, stick std 80/90 whatever.

But when it comes to the Trans, do yourself and the box a favour, put Mobile 1 75/140 full synth in that, makes a huge difference. takes a leap of faith mind as its like water in the bottle.

As I interpret things, using an API GL4 in a hypoid transmission would be wrong. Shouldn't it be GL5?

But doesn't that still bring us back to the original question posed by tapio?

By extrapolation, shouldn't an old requirement for a specific hypoid gear oil these days default to a GL5 rating? In that case shouldn't we owners of older boxers be looking to put GL5 in? That in turn brings us back to the original question. Why? There are no hypoid gears anywhere in the transmission, are there?

Maybe they did specify it just steer us towards better "quality" oils, but to me that smacks of a slightly cavalier approach for a German engineer! You have a certain design requirement, you specify the gear oil to satisfy it, surely?

[eyore]

I haven't a clue about the technical ins and outs, but use Castrol Axle EPX 80w-90 API-GL-5 in my FD which from the contributions above seems to be the right oil.

[Merecat]

We need a tribologist!

[eyore]

We need a tribologist!

Err um..................if you say so.

[Corvus]

We need a tribologist!

Ha ha. We do!

I owe an apology. Having checked my facts on tinternet it seems GL4 is suitable for a hypoid with a small offset. (I've been called worse).

That shouldn't get in the way of the original question though....

[Merecat]

Looking back at my notes from years ago. Hypoid gear oil has a greater resistance to shear.

[conkerman]

Indeed.

Shear and pressure resistance is the key in transmissions, especially with helically cut gears.

The loads on the oil in a gearbox are significant. Think of the pressure exerted on the oil film when driving the bike. The additives required to do this are full of sulphur, this is why gearbox oil stinks.

The fully synthetic 75/140 oils seem to get lots of recommendations.

[sandbar]

Castrol Axle EPX 80w-90 API-GL-5 in my FD

Just to add a note of confusion, it would appear that BMW have reduced the amount required for the FD on the 1200s to 180 ml.

I would guess that this has more to do with addressing the ongoing issues with seals etc. How it will affect the wear and performance of the FD is, I suspect, in the lap of the Gods!!

One - perhaps unintended - consequence is that you can get an oil change for both the gearbox and FD out of a 1 litre bottle. The same oil is recommended for both on the HP2 Sport

sandbar

[Tapio]

I believe a hypoid gear has a degree of sliding, similar to a worm gear, whereas a helical gear, spur gear, bevel gear and I think also a spiral bevel gear all have a rolling action on a constant pitch circle.

A bit of hair-splitting maybe, but no, teeth faces are not sliding against one another, but rather turning. If you think of the teeth faces as segments of a cylinder, you get that the cylinder segments are not only rolling, but also turning with respect to each other. This is with involute design:
http://en.wikipedia.org/wiki/Involute_gear
Hope that made sense.

//T

[Tapio]

This probably goes back a few years when you could buy Hypoid or Non Hypoid gear oil, I believe since GL4 or GL5 gear oils came about there is no need to worry as those API's will do for both. Think BMW were just trying to get people to put decent oil in.

What I will tell you is dont worry about the FD, stick std 80/90 whatever.

But when it comes to the Trans, do yourself and the box a favour, put Mobile 1 75/140 full synth in that, makes a huge difference. takes a leap of faith mind as its like water in the bottle.

You may be right. I brought this issue up at my local dealer. He was stumped. He showed me the oil they sell. Label said: differential oil, recommended by BMW. It didn’t say it was hypoid oil. Not all car differentials are hypoid gears. Those with gearbox bolted to the rear axle (Volvo/Daf 343, Alfa Romeo Alfetta, Porsche 944) are not.

In what way does the Mobil 1 oil make a difference? Smoother shifts? Quicker shifts?

//T

[boxerscott]

On subject of transmission case fluid changes, on the 11s drain plug is there meant to be a crush washer? I ask cos I bought a crush washer service pack for my bike from motoworks. It contained 6 washers but no large diameter one for the drain plug. Can not remember if one was on when I drained it weeks ago. I know it has a higher torque value (55nm) than other fill/drain plugs (23nm) with crush washers so perhaps it is a metal to metal friction job?

BTW I use Halfords GL4. Much cheapness when using my trade card