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Final Drive Fluid, fill by measured volume or fill to level hole?

Anyname

Anyname

Active member
I've always filled the final drive on my 86 R80 monoshock until the level reached the overflow hole. This past weekend I tried using the 350cc volume the manual recommends. That turned out to be way more than needed to reach the overflow hole. So what do you all think? Is the measured volume correct or should I stick with the overflow hole?
 
Because the grease is quite viscous, you will find that running it a few miles will settle the grease and your fill will be low. You can warm the grease first to help it settle but you want to get that 350cc in there.
 
For me, I fill to the bottom of the filler threaded hole threads. When I pop it open thousands of miles later it is sitting right there at the bottom of those threads. I do measure the amount of fluid in the engine; but the trans and rear end get the "thread" measurement technique. Now, the driveshaft, that's a different animal altogether........
 
DennisDarrow said:
For me, I fill to the bottom of the filler threaded hole threads. When I pop it open thousands of miles later it is sitting right there at the bottom of those threads.
Click to expand...

I was going to say the same thing but our experience is with the pre monoshock rear drives. :) My Haynes suggests that fluid is poured in from the very top and you want the gear oil to be seeping out the inspection hole.
 
20774 said:
I was going to say the same thing but our experience is with the pre monoshock rear drives. :) My Haynes suggests that fluid is poured in from the very top and you want the gear oil to be seeping out the inspection hole.
Click to expand...

:clap :rocker :thumb
 
I attended the BMW Service School in 1974 and they said to the threads on the rear drive filler hole. This is not a critical measure. As long as there is at least 90% of the required volume of gear oil, and you don't over fill, you'll be fine.
 
Over the years I’ve seen too many cases of stripped threads on the FD check plug on the bikes with the check plug screwed directly into the back side of the FD, and I continue to see them showing up at Tech Day. BMW used a small-diameter fine-threaded steel plug screwed directly into an aluminum housing with a crush washer for sealing, making it all too easy to strip those threads. And a proper repair in that area requires disassembly of the FD to assure no swarf is left behind. So for bikes equipped with that rear-mounted check plug, I drain the gear oil HOT, install the correct amount of gear oil through the filler hole, and button it up. Absent any visible leaks or excess gear lube showing up in the driveshaft tunnel, I don’t see a need to ever disturb that check plug.

Best,
DeVern
 
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Greg -

I think what you learned in service school was overtaken by events in later years. I agree that the filler plug at the 9:00 o'clock position when looking at the drive from the right side of the bike makes sense for refilling as you say. As DeVern says, that location had a change in later years to where it was a "check plug" not the filler plug. The filler location was located at the 12 o'clock position IIRC.
 
20774 said:
Greg -

I think what you learned in service school was overtaken by events in later years. I agree that the filler plug at the 9:00 o'clock position when looking at the drive from the right side of the bike makes sense for refilling as you say. As DeVern says, that location had a change in later years to where it was a "check plug" not the filler plug. The filler location was located at the 12 o'clock position IIRC.
Click to expand...

They took a perfectly good system in use for 50 years and "improved" it to a system that is flakey and fragile.
 
This thread reminded me of an old BMW rider I met in Detroit when I started riding BMWs in the early seventies. Fill to the bottom of the threads... The same was true of the /5, 6 and 7 transmissions. This guy would lay his bike over on it's side to get more oil into the trans. He figured if a little's good, a lot's better. Just glad I didn't take up his school of thought. I agree with using the prescribed, measured amounts. Never had a failure as a result.
 
20774 said:
Greg -

I think what you learned in service school was overtaken by events in later years. I agree that the filler plug at the 9:00 o'clock position when looking at the drive from the right side of the bike makes sense for refilling as you say. As DeVern says, that location had a change in later years to where it was a "check plug" not the filler plug. The filler location was located at the 12 o'clock position IIRC.
Click to expand...

Yes, I was referring to the earlier rear drive design with the filler at the 9:00 o'clock position. Anything newer is a heresy and not a real BMW. :hide
 
GREGFEELER said:
Yes, I was referring to the earlier rear drive design with the filler at the 9:00 o'clock position. Anything newer is a heresy and not a real BMW. :hide
Click to expand...

They had two young engineers and one old guy. The young fellows thought they needed something to do. The old guy suggested side stand design. They didn't like that. They wanted to do power train work. They decided to work on final drive design. The old guy said "No". The final drives were just fine.

Then the old guy retired and the young fellows got promoted. Now they could redesign final drives. Their first act was the Airhead drives. After they "improved" the drain and fill for the Airheads they moved on to the Oilhead and later drives. They designed the drives for the K1200LT and the Oilheads. After those drives failed a lot they then designed the ventless, lifetime filled drives. Then they redesigned these to have a vent and a drain.

Then they moved on to designing and specifying the camshaft and rocker arm designs for the R1200 series bikes.

They are now senior engineers in charge of quality control and we are all in trouble. The end.
 
My point is that filling to the bottom of the threads is correct *IF* the grease has really settled in the drive unit which, if it is cool and the grease is thick, it often times will not do. Therefore, measuring out the correct amount and pouring it into the drive unit will indicate whether the grease has really settled and the unit really is filled to the bottom thread.
 
ebeeby -

I assume your "grease" equals "GL5 gear oil". Gear oil will flow slowly...grease not so much! :wave

What I do...and it probably doesn't make much difference...is after pour the gear oil into the fill hole on my /7, I spin the rear tire to see what happens to the level of oil. If needed, I can add a little bit. To be honest, as long as there's a reasonable amount of oil such that the crown gear is running through the oil, it's being slung all around for beneficial effect.
 
ebeeby said:
My point is that filling to the bottom of the threads is correct *IF* the grease has really settled in the drive unit which, if it is cool and the grease is thick, it often times will not do. Therefore, measuring out the correct amount and pouring it into the drive unit will indicate whether the grease has really settled and the unit really is filled to the bottom thread.
Click to expand...

My manual specifies 80-90 Gear oil. It's thick but by no means a grease.
 
Another GREASE Thread

yep.....suth earn as it gets.....that suff you get when you fry bacon.....yep, thats bacon 🥓 grease, that white yunk that you spread on your 5 year old chest when they have a cold...Vasoline, and that gunk you dip your fingers in and get a fistful to spread on wheel bearings.....GREASE....
:dunno :whistle
For this ol boy raised in Gotebo, Oklahoma, spent 6 months in mechanic school before getting out of Army in San Antonio, and now for the last 27 years in Rural Georgia.....NOW THAT IS suth earn......Grease is that stuff in a can that you get out of the can by the spoon, hand, ladle, or just melt in the can.........


We finally get another oil thread and now I guess we can have it called, A GREASE THREAD.......:laugh :laugh
 
Final Drive Refill Difference

Per recent experience, it requires about 300cc to refill till oil comes out the side hole. Need to reinstall the side plug in order to add the last 40-50cc. So, I'd say either way is OK, since 50cc is not gonna make or break. On the other hand, the extra 50cc adds to the margin of safety if the fill level is not monitored properly.
 
jhall said:
Per recent experience, it requires about 300cc to refill till oil comes out the side hole. Need to reinstall the side plug in order to add the last 40-50cc. So, I'd say either way is OK, since 50cc is not gonna make or break. On the other hand, the extra 50cc adds to the margin of safety if the fill level is not monitored properly.
Click to expand...

If we are talking about the later rear drives with the level check plug at the 9:00 o'clock position, then the point of that hole it to indicate the correct amount of fluid - to the hole - not more or less. If you bike is losing rear drive lube enough that the level needs to be checked you will see on the rear wheel in most cases.
 
If you use the check hole, understand you must fit a new washer, not reuse the existing crush washer.

Given the really small size of this screw and the fact that the housing is aluminum, the risk of stripping the threads is high. You'll need your little bitty torque wrench for sure.

I always avoided all this by just filling with the specified amount.
 
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