Oil Transfers....oil moving someplace other than where it belongs
©
oiltransfers.htm
article 49
1. If the REAR DRIVE has more oil than it should have, and the driveshaft level is lowering,
and/or oil is spewing out the vent...the seal at the rear drive input
may need replacing...or, there is another problem; OR, you may simply be in very
cold weather, with a frozen-up breather vent...OR??......READ ON....
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, bypassing, well, getting past, the
seal. That nut must be VERY tight, and if it loosens, bad
things can happen. Note also, that 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 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 early
models, and the check oil plug (extreme rear, centered, small plug) on later
models. 350 cc.
2. If the transmission level has been lowering, it could be a faulty transmission output seal or the center top bolt threads and under bolt and washer head...in the aircleaner area.... is loose (or needs a sealant such as Permatex non-hardening Form-a-Gasket) and 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, but you have to remove the transmission fully.
Now and then I hear
of oil moving forward into the clutch area, due to a 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 driveshafts) have an open, not sealed,
too large, V shaped vent hole, located just forward of the transmission output
flange...just above, at 12:00 position, of the transmission output seal (that
seal, green, has the open end, spring end, facing rearward). This was
carried over from the non-Paralever models. 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 that the Paralever models have that output seal put in
REVERSED from the the other models....the open end faces INside the
transmission.
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 constantly, or 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 100cc 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, 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. The normal filling,
is 150 CC, except that the early /5, short wheelbase models (that
is, up to roughly middle of 1973) used 100 CC. 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. 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 very thoroughly, insert the proper amount of oil, and 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.
Restating: The rear transmission cover, 12:00 position, at top of the bearing seal area, behind the U-joint flange....has a tiny
V-hole/opening...this allows driveshaft housing oil to be thrown up against that point, and into the
transmission. This is not a fast happening phenomena, it takes some miles, often hundreds to a couple thousand. This is how the oil
magically gets into the transmission on non-Paralever models.
I know of no good cure for this minor problem of oil
transfer...other than to fix the
sagging suspension...IF that is a large contributor in the case at hand. You can just live with the situation. The amount of oil required by the
driveshaft is small. You can plug the hole and use a smaller
hole in the plugging...but this is exceedingly difficult to do with the
transmission in the bike. Fancy venting at the filler plug, etc., do
not seem to work OK.
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 overtighten this bolt, it may fracture. Snip a tiny
section of the battery lug, so you do not have to remove 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. NEVER allow the rubber boot over the speedometer cable
to get old and fail....it is a very good idea to clean the top junction and seal
the boot to the speedometer cable with black RTV cement. Or, pack the
inside of the boot with grease. NEVER spray water
at this area when washing the bike. Water gets into the transmission via
that hollow bolt...or...a
bad speedometer cable boot (even rainfall does that) or nasty spraying during
washing and destroys 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.
80W90 GL5 hypoid differential oil, NON-synthetic, is really best,
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).
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 VERY questionable if anything gets INTO
the universal joint. The normal filling is around 150 CC, except that the early /5, short wheelbase models (that
is, up to roughly middle of 1973) used 100 CC. In any event, only a little oil is needed, and the
driveshaft level is hardly
critical.
Some folks simply measure the oil and install that 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, I keep a
modest sized plastic syringe with a few inches of attached plastic line, in my tool kit...for transferring oil. Probably
not needed. 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.
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