In-between the transmission output shaft and the driveshaft, there is a
flexible coupler that joins the two together. This rubber, reinforced
coupler isolates vibration from the rest of the drivetrain, while
transferring power from the engine and transmission to the rear differential
and wheels. As the car ages, and is exposed to the elements, these
discs (or guibos, as they are sometimes called) develop cracks and begin to
disintegrate. The rubber shell is reinforced with rope cords on the
inside, and it is not uncommon to see one completely fall apart with the
cords flying everywhere. I recommend inspecting this rubber joint
about every 10,000 miles or so (about once a year) to make sure that it
still looks okay. If it fails, it does have the potential to leave you
Replacement is not too difficult, but it does require that you take a few
things apart to reach the flex disc. Begin by raising the car off of
the ground and supporting it on jack stands. See the
Pelican Technical Article on
Jacking Up for more information. The next step is to remove the
muffler and catalytic converter. I have found that it is best to
disconnect the entire rear exhaust system from the forward flange and drop
it as a single unit. This actually sounds a lot harder than it really
is - disconnecting the exhaust is really quite easy. See the
Technical Article on Muffler Replacement for more details. Begin
by unfastening the small exhaust retainer clamp from the bottom of the
Figure 1 shows the underside of
the car with the small exhaust retainer bracket disconnected from the
Figure 2 shows a close up of the
disconnected clamp. Then, remove the six bolts from the exhaust
flanges near the front of the transmission (Figure 3).
You may want to use some WD-40 or other penetrant on the bolts before you
attempt to remove them. If you have a later-model BMW, disconnect any
oxygen sensor wires that may be attached to the exhaust pipes. Now you
should be able to undo the rear muffler clamps and drop the entire
muffler/catalytic converter assembly. Be aware though - this
whole assembly weighs about 50 lbs, so exercise caution as you loosen clamps
and bolts, and drop the entire system down.
With the exhaust
removed and out of the way, remove the light heat shield that covers and
protects the underside of the car. This heat shield is made out of an
aluminum-foil type of material and can be easily unfastened from the
underside of the chassis. Although not 100% necessary, I recommend
removing the lower transmission support bar at this stage - it will make
access to the flex disc a lot easier (Figure 4).
Technical Article on Replacing your Transmission Mounts for more
details. By the way, it's also a great time to replace your
transmission mounts while you have easy access to this area.
Using some paint
or white-out, mark the transmission output flange and the driveshaft to
clearly indicate which flanges connect to each other when you reassemble the
unit. Place a mark at the point indicated by the arrow in
Figure 5, and also another mark in the same place on
the opposite side of the flex disc. This will help you align the
driveshaft with the transmission output flange later on. Also in
Figure 5, you can begin to see the flex disc start to
fail - small surface cracks have appeared in the rubber. Now, remove
the bolts from the flex disc (Figure 6). There
should be six total, and they all might not be very easy to get to.
You will need a deep socket and open-ended wrench in order to get to them.
You will also need to rotate and lock the driveshaft as you work.
Release the parking brake and take the transmission out of gear, then use
your hand to rotate the driveshaft so that you can reach the bolts and their
corresponding nuts, and then re-engage the parking brake. You will
have to rotate the driveshaft three or four times in order to remove all of
Now, turn your
attention to the rear end of the tunnel. Remove the small cross-brace
that spans the driveshaft tunnel (Figure 7 and
Figure 8). This will allow you to drop down the
driveshaft and remove it from the transmission flange. Turn your
attention to the rear driveshaft bearing (Figure 9).
Remove the two nuts that secure the bearing to the chassis (Figure
10), while holding up the driveshaft with one hand. When the nuts
are removed, you should be able to drop down the driveshaft and remove the
shaft from the transmission output flange. Support the driveshaft
using a jack stand. On some cars, you may need to completely
disconnect the center driveshaft in order to remove the flex disc. If
you can't seem to get enough clearance to remove the flex disc, then follow
the procedures in our
Technical Article: Rear Driveshaft Bearing Replacement.
Figure 11 shows the transmission output flange with
the flex disc removed.
Now that you have
access to the flex disc, completely remove it from the driveshaft.
Figure 12 shows a flex disc that is getting very
close to failure. Since you have access to this area, now would be an
excellent time to replace and replenish your shift bushings, or to install a
short shift kit.
Figure 13 shows a brand new flex disc along with new
mounting hardware. For important parts like these, I always try to use
new hardware. BMW recommends replacing the self-locking nuts, but I
also like to replace the bolts if they happen to look like they have become
slightly corroded. Take your new flex disc and attach it onto the
driveshaft. If you look closely at
you will see that the flex disc has an arrow that is cast into the side of
the rubber disc. This arrow points towards where the flanges are to be
mounted. In other words, the transmission or driveshaft flange will
mate against the surface shown with the yellow arrow. The rule of
thumb is that the arrow shows which way the mounting bolts are pushed
through the flex disc.
Torque the bolts
onto the driveshaft first, but only if you have enough clearance to get the
entire assembly back into the transmission output flange. Then, move
the rubber disc back up to the transmission flange and insert the remaining
three bolts, as shown in
Figure 15. Be sure to
align the white mark you made on the driveshaft back up with the matching
mark you made on the transmission output flange. This figure also
shows the arrow on the rubber flex disc, in this case clearly pointing
towards the transmission output flange. With the flex disc bolts
loosely connected, reattach the rear driveshaft bearing. Push it
towards the front of the car as you tighten it down - you want the bearing
to have no slack on the rearward side (Figure 16).
When the bearing is reattached, then tighten up the bolts on the flex disc.
To complete the
job, reattach the heat shield, the exhaust system, and any oxygen sensor
connectors you may have disconnected.
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||35 ft-lb (48
||47 ft-lb (64
||60 ft-lb (81
||74 ft-lb (100
|M3 - M12
||85 ft-lb (115
||16 ft-lb (21
||16 ft-lb (21
||22 ft-lb (30
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