Lee Hunter pioneered this conversion in his Marlin Cabrio, and I have unashamedly copied his idea to make up my own Sierra EPAS column . Here are some photos I thought I would share with anyone interested.
If you would like to see bigger photos of the examples below, my flickr site is:
http://www.flickr.com/photos/mikes_bmw_marlin_cabrio/
Standard Adjustable Sierra Steering Column
Corsa C EPAS Fixed Steering Column - there are two types, the other option has adjustable rake, but will push the steering wheel further into the driver by around 25mm
A special Torxx socket is required to remove the centre column stud
The Corsa column can be dismantled to this stage by pulling apart friction joints only: it requires quite a bit of effort, but these joints are only friction fit!
Removing the upper shaft section from the outer casing is more difficult - I cut it away with a slitting disc on a small angle grinder - the case is not required.
The Corsa has a lower link with two u/js: it connects via a set of splines. I cut this short section off.
I then shortened both the inner and outer bottom section of the Sierra column, to maintain the adjustable reach of the Sierra, and welded it to the splined section. This is one of only two specialist welding operations required. Any decent machine shop should be able to put this in a lathe and weld it up to ensure its centre runs true. This is the bottom end complete. If you are happy with a fixed steering column, for reach and rake, then just weld the inner triangular sectio to the splined boss. This will undoubtedly be far easier to intall later, as the motor fixing can be made rigid, as opposed to having to slide with the adjustment of the the Sierra's column.
The top section can then be made as follows:
Cut the Sierra column 15mm below the welded on collar which retains the spring and column bearing alignment.
This fits snugly over the EPAS shaft and internal collar .
The Corsa upper column shaft starts at the same outer diameter as the Sierra's inner diameter, but then widens. This section has to be turned down in a lathe.
And this is the final arrangement of the Sierra EPAS column shaft
The standard Sierra outer column can then be assembled on to this shaft, along with standard switch gear, cowling, and the adjustable reach and rake fixing. It is undoubtedly easier to install a fixed length and rake EPAS Sierra column, as the Corsa's Motor will require reasonably significant torque resistant fixing: making this reach and rake adjustable will require more ingenuity.
The electrics are fairly straight forward. The motor requires a live feed direct from the battery which requires a hefty fuse. The Corsa C system comes with its own ECU attached. It requires two signal inputs from engine and road speed. There are now well tested kits available on the net which provide the hefty fuse link, and a dummy signal source plus an On/Off switch.
Electronic wizzards will doubtless be able to hook up their own sensor system to create their own graduated power steering.
As I am not fitting this until I have achieved IVA approval the installation will have to be dealt with later!