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are two studs at one end of the differential that bolt onto the rear
cross member. These hold one end of the differential in position. |
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| The
other end of the diff was originally designed to be bolted to parts
of the car that have now been cut out. Also, we have raised the differential
to keep our flat bottom. This minimizes the angle on the half shafts
(between the differential and the wheels) and minimizes drag by reducing
friction. We spend a fair amount of time measuring parts and trying
them in place. In the end, it works out nicely. We can weld a plate
to our strong battery box/motor housing to support this end of the
differential. |
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The
plate is cut from 3/8 inch mild steel. We clearance where the diff's
drive shaft will sit and drill out some holes to lighten the piece.
We weld it in place and then weld two supports made out of chrome-moly
tubing to the bottom of the plate.
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| We
would like to add two more supports from the engine plate to the top
of the support plate, but these need to be removable. We fabricate
some appropriate size bushings. |
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We
rough cut the angle onto chrome-moly pipes and then use a grinding
tool to round the metal to fit the bushing.
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A tight fit minimizes the welding. |
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The
welding is done with the piece in the car to make sure the fit is
exact.
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With
both supports done, the plate that the diff will bolt to is well
supported.
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There
is about 6 inches between the end of the rear differential and the
motor. We need a short drive shaft to connect them. We decide to
make it out of aluminum because it is easy to machine and light.
We
purchase a chunk of solid round aluminum and cut off the length
we need.
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The
actual machine piece is not too complicated but needs to be exact.
One end must match the flange on the differential with its four
bolt hole pattern. The other end must match the six hole pattern
of the CV joint. The two flanges must be square with each other
and around the same center. The drive shaft should be hollowed out
for lightness.
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Now
we are ready to fit things together. The splined stub axle (see
Electric Imp Work History, February 25, 2002)
goes into the motor. A constant velocity (CV) joint fits over the
part of stub axle that protrudes from the motor. The aluminum drive
shaft bolts on to the CV joint. The other end of the drive shaft
mates with the flange on the end of the differential.
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We
use a level gauge with a bubble to check the tilt of the motor,
the drive shaft, and the differential. The motor and drive shaft
are dead level. We shim the differential to make it level as well.
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If
the whole structure forms a straight line in the horizontal plane,
then the last bolts between the drive shaft and the differential
flange should slide in freely. They do not. We check and determine
that the differential center is slightly higher than the center
of the motor.
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We
have a way to adjust this. We loosen the four bolts that hold the
rear cross member to the car, one turn at a time. A black mark on
each bolt head helps us make each turn exact.
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| When
the bolts connecting the differential flange to the drive shaft slide
in and out without restriction no matter how we spin the connection,
we know the connection between the motor and the diff is true. We
drill the bolt holes to attach the differential's front end to the
support plate. The bolts hold the diff and its shims in place. |
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We measure the gap created by lowering the cross member and make spacers
to fit. |
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| Finally,
we slowly disassemble everything. We look at how hard this will be
to do with the floor attached to the car. Can we remove the differential
without removing the motor? Which way should the head of bolts face
to make them easiest to remove and replace? We discover that lowering
the cross member that little bit has made pulling out the differential
much harder. We must grind a little off its case so it can slide out.
A little work now will make the job at the track that much easier. |
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