BMW Luxury Touring Community banner

1 - 18 of 18 Posts

·
Registered
Joined
·
634 Posts
Discussion Starter #1
What is the purpose of the oil passageway/ cutout shown in this picture?
The bearing on the input shaft (and the others as well) are sealed bearings... It is not lubricated by the gear lube and when the bearing is pressed in, the passage way is blocked by the side of the bearing... and also the seal (when properly installed) closes off the passageway... it's basically a passage to nowhere...

seems to be an unneeded passage way...

am I missing something here?
 

Attachments

·
Premium Member
Joined
·
1,490 Posts
They might be there to get a stuck bearing out . Then you could use some tool to pry up with .
 

·
Registered
Joined
·
634 Posts
Discussion Starter #3
the only thing I can think of is, the cutout allows oil to reach the backside of the seal... (the open side...)
maybe the oil keeps the seal flexible... and prevents premature drying or cracking of the oil seal? :confused:
 

·
Registered
1999 LTC
Joined
·
14,456 Posts
johnT said:
the only thing I can think of is, the cutout allows oil to reach the backside of the seal... (the open side...)
maybe the oil keeps the seal flexible... and prevents premature drying or cracking of the oil seal? :confused:
Had a wild thought there for a sec - shear pin locations. Butt, nah - can't be.

Got me, John - hope someone who knows pipes in soon.
 

·
Registered
Joined
·
5,408 Posts
Looks to me like gear oil drain-back slots for tranny oil that gets past the bearings. Given where the bearings seat, the ends of the slots should be just open to the area on the backside of the bearings, permitting drain back.
 

·
Registered
Joined
·
634 Posts
Discussion Starter #6
those bearings are pressed in. you heat the case and tap the cold bearings in.
there is no oil getting behind that bearing. (if the cut out wasn't there.)

since the tranny is apart and I'm waiting for seals...
I have been day dreaming about closing off the cutout on the input shaft...

no more worries of driving the seal in too far / leaks etc.

I mean, a sealed bearing is a sealed bearing.., right?
they are not lubricated by the gear oil...
 

·
Registered
Joined
·
5,408 Posts
johnT said:
those bearings are pressed in. you heat the case and tap the cold bearings in.
there is no oil getting behind that bearing. (if the cut out wasn't there.)
...

I mean, a sealed bearing is a sealed bearing.., right?
they are not lubricated by the gear oil...
In theory, yes. The problem with theory is that theory often does not precisely match reality :D I believe the slots allow any gear lube that does make it through the bearings and condenses behind the bearing to drain away.
 

·
Registered
Joined
·
634 Posts
Discussion Starter #8
mneblett said:
In theory, yes. The problem with theory is that theory often does not precisely match reality :D I believe the slots allow any gear lube that does make it through the bearings and condenses behind the bearing to drain away.
I see your point kinda... I reckon we could argue that point all day... :rotf:
I figure if the oil gets in the bearing... it can get back out... but what do I know...?
I really don't think much oil is getting in. those are sealed bearings and it's not a high pressure situation... just heavy gear oil rolling around in the box...
 

·
Registered
Joined
·
5,408 Posts
johnT said:
I really don't think much oil is getting in. those are sealed bearings and it's not a high pressure situation... just heavy gear oil rolling around in the box...
We agree on this :thumb: I also don't believe there is much actually traversing the bearings.

The slots appear to be there as a preventative measure, to prevent oil build up. BMW/Getrag aren't known waste the cost of machining (they take out costs where ever they can -- witness the mistaken removal of the machined groove in the mid-'80s airhead tranny output shafts -- a significant cost-saving mistake). So there has to be *some* purpose for these slots -- I expect that the slots are there as a result of a "lessoned learned" many years ago. My guess is to cure a weeping of oil past the bearings in the past (maybe back in the days when unsealed bearings were used?).
 

·
Registered
Joined
·
634 Posts
Discussion Starter #11
I forgot to mention one important thing.....
the passageways are on the TOP.... which means they couldn't be drains or reliefs....

I am thinking BMW originally used (or was going to use) open bearings....

here is a pic. of an open trans. case



Uploaded with ImageShack.us

PS:
it's funny how none of the usual know it alls have any comment on this...
sorry to be harsh, but sometimes getting some creative mechanical talk around here is like pulling teeth...
but ask a question that has been answered a 1000 times and you get all kinds of responses...
 

Attachments

·
Registered
Joined
·
130 Posts
It is there for the same reason as the vent on top of the gearbox, the crankcase vent, or the vent on the final drive. If you heat up a sealed chamber the pressure will increase. They could have opened them down, but maybe they wanted 'some' lube to get back there.

My best guess and I'm sticking to it. :D
 

·
Registered
Joined
·
53 Posts
My guess is that when the molds were made for the castings, the thought was to use (or allow for) open ball bearings lubed by the gearbox lube. Oil splashing around would run down those channels, through the bearing, and back into the sump. No telling why they chose to use sealed bearings (I am a little surprised to learn that they do this), but when they did, it wasn't worth changing the mold.
 

·
Registered
Joined
·
634 Posts
Discussion Starter #14
bgerrity said:
My guess is that when the molds were made for the castings, the thought was to use (or allow for) open ball bearings lubed by the gearbox lube. Oil splashing around would run down those channels, through the bearing, and back into the sump. No telling why they chose to use sealed bearings (I am a little surprised to learn that they do this), but when they did, it wasn't worth changing the mold.
I think we have a winner... :thumb:
 

·
Registered
Joined
·
84 Posts
johnT said:
I forgot to mention one important thing.....
the passageways are on the TOP.... which means they couldn't be drains or reliefs....

I am thinking BMW originally used (or was going to use) open bearings....

here is a pic. of an open trans. case



Uploaded with ImageShack.us

PS:
it's funny how none of the usual know it alls have any comment on this...
sorry to be harsh, but sometimes getting some creative mechanical talk around here is like pulling teeth...
but ask a question that has been answered a 1000 times and you get all kinds of responses...
now THAT sounds a little mean spirited(lol)
 

·
Premium Member
Joined
·
7,594 Posts
johnT said:
it's funny how none of the usual know it alls have any comment on this...
sorry to be harsh, but sometimes getting some creative mechanical talk around here is like pulling teeth...
but ask a question that has been answered a 1000 times and you get all kinds of responses...
I think it helps to ask a question that matters. :)
 

·
Registered
Joined
·
634 Posts
Discussion Starter #17
Voyager said:
I think it helps to ask a question that matters. :)
Not quite sure what you mean by that...

but in any case,
Through my own research, I have found the answer as to why the oil passageways are there. 100%


thanks.
 

·
Premium Member
Joined
·
7,594 Posts
johnT said:
Not quite sure what you mean by that...

but in any case,
Through my own research, I have found the answer as to why the oil passageways are there. 100%


thanks.
I simply was addressing your bemoaning of the lack of responses. You asked a question to address your own curiousity, but which had no real import. The transmission will work the same whether you know what those passageways are for or whether you don't. It isn't like someone who has a bike that won't run or brakes that won't work or something important. People here appear to me to be very responsive to questions whose answer gets a bike back on the road. Questions to simply satisfy one person's curiousity just aren't that important and not always worth the time to answer, unless I am really bored and have absolutely nothing else to do.

So, my point was to stop moaning about the lack of responses to a question that doesn't matter. Ask a question that really matters and you likely will get a slew of responses.
 
1 - 18 of 18 Posts
Top