I am so excited that Mike is looking for a Caterham. I will finally
have someone to comiserate with (or get excited with as the case may
be).
The deDion rear on the Caterham is a English Ford Sierra unit. The
differential from an independent suspension is mounted in the frame
where you would expect it. As mentioned previously the third
member is now sprung weight, reducing the unsprung weight, a good thing.
The original solid rear axle was located fore and aft by two trailing
links. These were two parallel rods going from in front of the wheel
arch to the axle. The side to side location of the original axle
was controlled by an "A" frame where the legs of the A were mounted
to the frame, one leg each in front of the wheel arch and the top of
the A mounted to the bottom of the differential housing. Very strange
but very light. Typical mode of failure was the axle tubes would
wrap and twist, hence a reinforcing plate the length of the axle,
and the differential housing would crack where the A mounted.
The deDion suspension has the differential mounted to the frame, has
traditional half shafts with U joints running out to the wheels,
and has any number of ways to mount the coils and shocks. You pick
your favorite. The Caterham has coil overs at the outboard end.
Now the trick. The fore and aft location is still the trailing links,
the lateral location is still the A arm, and there is a tube running
from the left wheel to the right wheel. This makes sure that the
wheel can travel up and down but will always be absolutely vertical
to the road. The tube will weigh less than the differntial and carrier
and hence reduces unsprung weight. Why they kept the A arm is
a mystery.
The end result is that this version of suspension is more reliable
a good thing on a Seven, but slower. The added weight is the
problem. There is a special racing class in England for Caterhams
and the deDion is slower...
Michael
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