Power Steering For A Sierra Column

[Mike]

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!

[GreatOldOne]

As you know, I'm doing the same thing to a BMW column... I'll post up my pics once I'm done.

[denniswpearce]

I,m convinced you boys like building them more than driving them.

[Mike]

Originally Posted by denniswpearce

I,m convinced you boys like building them more than driving them.

........I think you are right!

Mine has taken 7 years so far, and I'm getting worried that I'm running out of mods to make before I go for IVA!

Or that I just keep finding more interesting mods to do than getting on with the final stage of the wiring!

[denniswpearce]

Wow, seven years, thats impressive.

To stay focussed for so long without getting bored with it. Don,t think I could do it.

Fantastic, so bite the bullet, finish the mods, apply for the IVA and have it on show at next years Stoneleigh show. Make that your goal.

Plus of course to emulate Goo and win the prize for best at show.

[GreatOldOne]

Mike - pics as requested:

Corsa Column:





Top of the column after the universal join has been removed, showing the 'cup'



The hinge from the rake adjustment. I'm going to weld this solid in so it's parallel with the rest of the column. It just bolts onto the casting





The left hand side of the diagram below is the amount of outer column I'm leaving on the BMW column after it's mounting bracket, and the amount of inner rod left protruding that will get the plug on the right hand side of the diagram welded on. That piece will be turned to the dimensions shown and will slip in side the cup.



The rest of the corsa outer tube will be removed from the hinge, and the upper portion of the BMW column welded in it's place. Then all I need do is bolt the two sections together, and then put a pin through the transverse holes in the cup and the plug.

I've deliberately made the length dimension on the inner rod slightly short so that there will be some tension on the spring that is on the top of the BMW column, once it's been pushed to and the pin put in.

I'm going to attempt to use the lower Corsa UJ and attach it to a lower stub of the BMW column. As it adjusts for length, I can afford to be a little out on the overall column length measurements as the UJ will slide open along the splines inside it and make up any short fall.

[Patrick]

I really like this idea EPAS avoids all the hydraulic mess and zaps less power from the engine too I've driven the BMW Z4 that has variable electric PAS which is a bit weird at first but very nice when parking. Also sticking in sport mode firms it up nicely (but makes the throttle too sensitive).