Thursday, March 29, 2012
Guibo
Pelican Technical Article:
Difficulty Level: 5
Difficulty scale: Adding air to your tires is level one Rebuilding a BMW Motor is level ten |
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This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series.
The book contains 272 pages of full color projects detailing everything
from performance mods to timing the camshafts. With more than 650+
full-color glossy photos accompanying extensive step-by-step procedures,
this book is required reading in any 3 Series owner's collection. The
book was released in August 2006, and is available for ordering now. See
The Official Book Website for more details.
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 stranded.
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 Pelican Technical Article on Muffler Replacement for more details. Begin by unfastening the small exhaust retainer clamp from the bottom of the transmission. Figure 1 shows the underside of the car with the small exhaust retainer bracket disconnected from the transmission. 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). See the Pelican 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 the bolts.
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 Pelican 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 Figure 14,
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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