Oil Transfers....oil moving someplace other than where it belongs
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oiltransfers.htm
article 49
1. If the REAR DRIVE has more..OR
LESS... oil than it should have, and the driveshaft oil level is
lowering, the seal at the rear drive input may need replacing.
If the top (oil inlet) vent is spewing oil you may simply be in very
cold weather, with a frozen-up breather vent.
This does not apply, of course, to the driveshafts that are run
dry in later models...assuming those driveshafts are not filling with oil from
the transmission or someone has made the choice to put oil in the driveshaft!
It is possible for a clogged vent (the hollow
speedometer cable bolt where the battery negative cable attaches) to allow the
driveshaft housing to both pressurize or have a vacuum with a temperature
change; such effects could allow a 'sucking' of oil forward, past the rear drive's input
seal (or, a pressurized driveshaft housing forcing oil into the rear
drive)....so this is an area to check
first, as checking it is VERY simple, check the hollow bolt. THAT
speedometer hollow bolt vent is NOT the vent being discussed just
below.
Early models (/5 in
particular) had more potential for driveshaft oil to appear to get by the rear
drive input seal and fill the rear drive. On all early models
(I do it on
some later ones too!)....when I fit the pinion gear and nut, I put Permatex non-hardening Form-a-Gasket on the splines for the input gear (and Loctite BLUE
on the threads where the nut tightens). It is possible for oil to get behind the splines of the
input gear, behind the nut, and behind the seal containing outer threaded
ring....and thus those areas have some sort of sealant applied. The oil
travels right along those splined areas getting past the
seal. That nut must be VERY tight, and if it loosens, bad
mechanical
things happen.
The very earliest /5 models did
not have a driveshaft and transmission venting system quite like the 1972+
models, and the rubber accordion could, if quite cold, reduce its size
due to a slight vacuum in the driveshaft housing; and, be
torn up some by the U-joint. A fix is possible.
Now and then I hear of someone having a rear drive that has vented oil to the
outside. This is USUALLY reported in the Wintertime. There can
be several causes.
a. Rear brake drag is overheating the oil and it is
spewing out the vent.
b. If the weather is very cold, the inner gears, etc.,
will throw the very cold oil upwards and tend to plug the breather; or, moisture
has collected and the
breather is frozen closed. It is OK to run the
oil level half an inch or so low, and when the rear drive heats up from normal
riding, the phenomena stops.
c. If the input gear (pinion nut) is loose, not
uncommonly seen, oil can work its way past the input seal, from driveshaft to
rear drive. CHECK the rear
drive oil level now and then.
Normal oil level is at the bottom of the threads of the filler plug on
very early
models. On later models, there is an oil plug
(extreme rear,
centered, small plug). That plug must not be
over-tightened. Proper oil level is such that the oil
barely runs out, if plug is removed.
I think that as little as 50 CC left in the driveshaft
housing would likely be more than enough to lubricate everything,
primarily the spline and gear cup to the rear drive, and it is questionable if anything
much gets INTO
the universal joint. The driveshaft level is hardly
critical.
Some folks simply measure the oil and install the measured amount. I have done it that
way sometimes, preferring to use a tiny screwdriver or a small allen wrench out of the
on-bike tool kit as a measuring stick. Keep in mind what I said about
trying to measure the quantity, if the driveshaft angle is
flatter. BTW, if the oil is put into the filler hole too
rapidly, it will bubble up and overflow. Drizzle it in slowly. For really long tours,
if I am riding a bike known to transfer oil to the transmission
from the driveshaft housing, I keep a
modest sized plastic syringe with a few inches of attached plastic line, in my tool kit...for transferring oil. You can improvise a wedge for the center stand.
I have never seen, nor heard, of any airhead having the
driveshaft run dry from this oil transferring to the transmission. I am not worried about transferring
oil that is molecularly somewhat sheared by transmission gears, back to the driveshaft. Or from any of the three places back to any other of those three.
2. If the transmission level has been lowering, it could be a faulty
transmission output seal. It can
also be the 13 mm headed bolt located in the center
of the top of the transmission. Use a
sealant on the bolt threads and the washer. I use Permatex non-hardening Form-a-Gasket.
Oil is being
sucked up into the
carburetors.
If you are doing an input spline
lubrication, and see the input seal of the transmission leaking at all...fix it
NOW!...it is NOT difficult.
Oil can move forward into the clutch area, due to
that leaking faulty transmission input seal.
Replacing the input seal CAN be done carefully, without doing too much other than removing the
transmission.
The seal that the shift lever goes through, into the
transmission, fails now and then, and you do NOT have to remove
the transmission to fix that.
NOTE that the transmission of the early Paralever models (Paralever models have dry drive-shafts) have an open, not sealed
and too large, V shaped vent hole, located just forward of the transmission output
flange (that's the part on the transmission output shaft that the
U-joint bolts to)...it is...just above, at 12:00 position, of the transmission output seal (that
seal, green, has the open end, spring end, facing rearward on the
Paralever model). Paralever models should have that hole plugged with RTV silicone compound (or something
similar), and a very tiny hole put in it. Later models don't have
it. NOTE what I said about
the greeen seal...the Paralever models have the output seal (no
matter color) put in
REVERSED from the the other models.
3. A problem seen now and then is oil transfer from the wet type driveshaft to the transmission. The common complaint is something
like: "I checked the oil in the transmission and it was overfilled, and the shaft housing was low by the same amount". For some folks this
happens relatively quickly, few miles being needed...and for some
only after longer rides. What you can do is to put a thin
wedge-shaped piece of wood or plastic under the left leg of the
center stand...which cants the bike slightly to the right.
I use a plastic wedge that was intended to help install tire
chains. This wedge is for preventing oil from flowing out
onto the ground. Unscrew the transmission filler/inspection
plug, and remove some oil, I use a very large plastic syringe with
a bit of tubing forced onto the tip. I've seen up to 80 CC needing transfer.
Move
an estimated amount of oil to the driveshaft; remove the wedge
and tilt the bike back slowly, to avoid oil running out.... recheck transmission oil level.
Repeat until level is just at bottom of threads. The situation is not a
serious problem, mostly it is an annoyance. It is almost impossible to fix
this cheaply. Don't think about fancy venting ideas, they likely won't
work.
Primary Causes for this transfer of driveshaft oil TO the transmission:
1. Sagged suspension.
2. Nivomat rear suspension units...which take a very short ride or a few bumps to self-pump up....these were stock items on some RT
models, optional on others. Nivomats after roughly 1982 pump up faster.
3. Plugged breather passages/holes: there are two. The one that sometimes gets plugged is the small diameter hole in the special
hollow bolt
that holds the speedometer cable and battery negative wire. If that hollow bolt
plugs up, you will pressurize the driveshaft housing. If conditions
(heat especially) are bad enough, the accordion rubber will swell up.
See below for description of the other breather hole. NOTE that it
IS possible for that wee hole to be plugged and have a VACUUM appear in the
transmission and driveshaft, and that can suck oil out of the rear drive,
forward.
4. Considerable steep downhill riding, like in the mountains.
5. Heavy load...like 2-up or heavy rider or both
6. Very bumpy roads
7. Overfilled driveshaft housing. The amount of oil needed
is actually quite small, 50 cc is enough for lubrication of the rear drive input
gear, 150 is the typical amount recommended for all after the /5
(use 100cc for it). The oil does not need, nor should it be, filled
to 1/8" above the
'bell' located straight down from the filler hole opening as sometimes
recommended. BMW originally, on early models, said to fill the oil level to, depending on where one finds the information,
'the filler plug'; OR, the
lower threads;...ETC. Do NOT. If you slide a small tiny
screwdriver blade down through the filler port hole,
sideways alongside the internal
bell, and see any oil at the tip when it is removed, you have
enough. But, if the suspension has sacked out
some, that way of measuring is not accurate. So, the best
way to check the level is probably to drain thoroughly, insert the proper amount of oil, and
then fashion
your own measuring tool, for YOUR bike. NOTE that if the rear
suspension is sacked out some, or otherwise you have the driveshaft on a flatter
angle, the oil is much more likely to be transferred to the transmission,
particularly in downhill riding.
8. Combinations of the above 7 items.
9. NOTE: On all models it is IMPORTANT that the hollow bolt
holding the speedometer cable (and battery negative cable) at the right rear of
the transmission, be open...that is, not plugged. This is the ONLY
breather for the transmission and the driveshaft. Clogging is often
only noticed in very hot weather, when the large accordion boot would swell
up. The pressure can force oil out of the boot. Never over-tighten this bolt, it may fracture. Snip a tiny
section of the battery lug, so you do not have to remove, only
loosen, the bolt to disconnect
the battery cable. There is supposed to be a pair of washers on this bolt,
one is flat, one is waverly; be sure you have them, and put the
battery lug between them.
NEVER
allow the rubber boot over the speedometer cable
to get old and fail....it is a very good idea to clean the top
area and junction and seal
that black rubber boot to the speedometer cable with black RTV.
Some will pack the
inside of the boot with grease. I don't.
NEVER
spray water
at this speedometer bolt and boot area when washing the bike. Water
that gets into the transmission via
that hollow bolt...or...a
bad speedometer cable boot (even rainfall does that) or nasty spraying during
washing and it will destroy the transmission bearings! Replacing that boot is
best done with a tapered tool, you can make one from such as a caulking tube
sealing top. The typical leaky place is the actual
top of the rubber boot, where the cable rises upwards....the top
expands. That is why I use RTV at that point. Clean
the cable at that point with acetone, so the RTV sticks really
well.
10.
80W90 GL5 hypoid differential oil, NON-synthetic,
is what BMW specifies...and the
SAME for rear drive, transmission, driveshaft
(non-Paralever).
SOME who use synthetic oils find they have leaks. IF
you have that problem, switch back to petroleum oils, and the seals may fix
themselves, after considerable number of miles. You can also use
75W90, or wider-range 85W140 (probably better for those in super hot weather and
high speeds, etc).
Revisions:
04/21/2003: add .htm title; clarifications (minor)
02/04 and 06/2004: minor clarifications
03/06/2005: incorporate all changes and updates and fix typos
01/21/2010: update, and review entire article