|
The
cross member supports the rear differential on two rubber bushings
(white arrows indicate the differential holes)
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|
and
locates the ends of four suspension arms.
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| There
are three changes we would like to make to the rear cross member:
First, we would like to remove the suspension
slop. |
| Second,
we would like to make the cross member lighter. |
| Third,
since we are lowering the car a great deal, we would like to raise
the differential to keep the half shaft angle small for efficiency. |
|
This
would involve cutting most of the top (shaded area) of the cross
member off to fit the diff.
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 |
| While
this would certainly make the cross member lighter, it also would
make it quite a bit weaker. We decide we will end up with a stronger
and lighter cross member by building a new one from scratch. |
| The
first step is to build a jig from the old cross member This is a simple
matter of bolting on bits of angle iron to the points we wish to duplicate
and then welding the angle iron together in a way that will allow
us to remove the old cross member |
 |
| We
take some previously fabricated bushings (left) and use a one inch
hole saw to help get the tubing to fit nicely. |
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|
We
bolt the bushing to the jig and weld a bar in place.
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We
remove the rear bar from the jig and finish the weld. The more of
the weld that can be done in the jig, the more chance it will fit
back in the jig.
The next step is to bolt the rear bar back into the car and try and
decide just where we want the differential. This involves much checking
that the diff is square to the bar and the centerline of the car and
guessing the half shaft angle at ride height. Amazingly the diff's
studs end up in the middle of the bar. It is a fairly simple matter
to drill holes through the back bar and then tack weld bushings in
the holes held in place by the diff. |
|
We
remove the rear bar from the car and finish the welds for the diff
holes (marked with white arrows). Having had a close look at how
the differential will have to sit, we know we need to bend the front
cross member bar to clear the diff. We put a nice bend in each end
and fit it to it's own bushings (front bar highlighted in yellow).
Four cross tubes add stiffness and strength.
|
 |
| Now
we need brackets to hold the lower suspension arms. We are replacing
the old lower suspension arms. The new ones are lighter, adjustable
in length, and use rods ends instead of rubber bushings. |
 |
| We
make the brackets out of rectangular tubing. The brackets are drilled
then cleaned up using a grinding wheel. |
 |
| The
brackets are bolted into the jig and then pipes are fitted to support
the brackets. |
|
Green arrows point to the brackets. |
 |
| After
much cutting and fitting and welding, the new piece is done. It is
15.6 lbs or 8.8 lbs lighter than the original. It is also much stiffer. |
|
Green arrows point to the suspension brackets. White arrows mark the
holes for the differential. Blue arrows mark the bushings that bolt
to the car frame. |
 |
| When
it is all assembled, it looks like this. |
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