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One of the
easiest tasks to perform on your BMW is to change the transmission and
differential fluid. The differential and transmission both use the same
lubricating fluid. It’s very important that the fluid in your transmission
is at the proper level, or your transmission will experience significant
wear. The synchro rings and sliders depend on a slick surface to match
speeds when shifting. If your transmission is low on oil, the wear on these
components will accelerate significantly and shifting the car will be more
difficult. If your BMW is having problems shifting, check the level of the
transmission oil. In addition, keeping the differential and its associated
gears well lubricated should help increase your fuel mileage.
The transmission oil also keeps temperatures down
inside the transmission. The engine is a primary source of heat for the
transmission, as the heat conducts and radiates through and around the
points where the engine and transmission are mounted. The transmission
creates heat itself as the gears and synchros turn within its case. Keeping
the transmission fluid at its proper level helps to mitigate heat problems.
Note that on some higher-performance BMW transmissions, there is an external
transmission cooler that operates similarly to the engine cooler.
Change the transmission fluid every 30,000 miles or
about once every two years. Check your owner’s manual for more details on
the scheduled requirements for your BMW. This number is a rough estimate,
and may vary depending upon the use of your 3 Series (track vs. street).
There are many moving parts in the transmission, and they tend to drop
microscopic metal particles into the tranny oil. Specifically, the synchro
rings wear down each time you shift. While transmission bearings are not as
sensitive as engine bearings, they can exhibit wear from these particles in
The 3 Series manual transmission has two plugs for
filling and emptying the transmission oil, located on the side and bottom of
the transmission case. To check the level of the transmission oil, remove
the top filler plug on the side of the transmission (where you usually add
fluid). When you have the plug removed, stick your finger inside the hole,
angle it toward the ground, and see if you can feel any fluid. Do this when
the car is cold and parked on level ground. If you can feel the fluid level
with your finger, your fluid level is about right, or perhaps will need only
a little topping off.
If you cannot feel the fluid level, add transmission
oil to the case. If you plan to change the oil, remove the small plug on the
bottom of the transmission case. Empty the transmission oil when the car is
still warm, as it will drain easier. For this task, have a drain pan capable
of handling at least 5 quarts of transmission oil. As you go, check the
fluid in the pan for any unusual metal pieces or grit in the oil.
While the fluid is emptying, clean out the drain plugs.
Using a cotton swab or a paper towel, carefully clean out any black debris
and particles present.
Replace the bottom plug on the transmission, but don’t
tighten it too much (50 N-m or 37 ft-lbs maximum). Fortunately, this plug
does not tend to leak (transmission oil is thicker than engine oil). If the
plug does leak later on, however, you can always tighten it a little more.
Now, add transmission oil to the case with a hand-operated oil pump. These
pumps are available from most auto parts stores, and attach to the top of
the plastic transmission-oil bottle. They work similarly to liquid soap
dispensers. Pump the transmission case full of fluid until it just starts to
run out the filler hole. It should take a little more than 1 quart to fill.
Replace the filler plug and clean up the few drips that might have come out
of the hole. Tighten the filler plug in a similar manner to the drain plug.
Replacement of the differential fluid is nearly
identical, except you will need a 14-millimeter Allen wrench for the plugs.
If you have one of those semi-rare, four-wheel-drive 3 Series cars (like the
325ix), don’t forget to change the fluid in the forward differential and
center transfer case as well.
In many cases, generic transmission gear oil will
suffice. However, for those BMW 3 Series owners wishing to have the best of
everything for their cars, there is Swepco 201 multipurpose gear lube. This
gear oil is excellent for transmissions, and many of our loyal Pelican Parts
BMW and Porsche customers swear by it. Rumor has it that adding Swepco 201
will prolong transmission life and help to postpone a costly rebuild. While
this can hardly be proven, a lot of our customers agree that Swepco 201
creates a difference they can feel while shifting.
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