Electric Power Steering Conversion – Part 2

Continued from Part 1.

With the column completed, I could get it mounted in the car. Woohoo, it fits! And SOMEHOW, the steering wheel spline size is the same for both the GM and stock columns. My quick release bolted right on.

While tiedown straps are nice and simple, they’re not exactly sturdy enough for keeping a steering column in place, so it’s time to break out the cutting and welding tools.

The Miata and GM column mounts are not parallel, so it took a little creativity to get everything lined up correctly. After a little bit of measuring, I realized I could cut the shapes I needed out of a drop of 2″ square tube. Everything looks parallel in the picture, but there’s about a 1/4″ slope on 1 side of each bracket to fix the difference in angle between the stock pickup and the GM mount.

The stock column mounting-plate made a good datum & base to fabricate from. The brackets are bolted to the GM break-away tabs as they would in the donor vehicle, retaining all of the safety features built in to the new column.

I added a couple gussets to stiffen things up, as there will be a fair deal of torque put on this mount during competition.

I hacked the lower mounts off of the sacrificial column, and used the stock firewall mount points as the basis for the new lower mounts. The left-side mount was by far the most difficult. It took quite a bit of jiggery-pokery to get all of the angles correct so that there was ample clearance for the brake pedal.

There was far more room to work with on the right-hand side.

I’d been working with the motor disconnected, as it is big and heavy, and would make things far more difficult in this stage. The time has come to put it back on. Plenty of clearance in the footwell.

Also, check it! I can get about 1″ of tilt on the column (nearly the full stroke in the mounts)! I was fairly convinced that the tilt wouldn’t work with my install, but here we are. Finally, an NA Miata with the oft-advertised but never before actually seen tilting steering column!

The tilting column adjuster handle is VERY much in the way when climbing around the column getting in and out of the car, so that needed to be modified to tuck it out of the way:

I also went ahead and installed a smaller steering wheel. I went from a ~14″ / 350mm wheel to a 11″ / 280mm wheel. This effectively reduces the arc length that the driver’s hands need to travel to put in the same steering angle by about 25%.

With all of the hardware complete, I could get a start on the electrics. I ran and terminated all of the large-gauge wires that carry power to the motor (that are connected directly to the battery with a 60 amp fuse in line), and started modifying the switch panel to accept the potentiometer. I should be able to put the controller in there as well, to keep it out of the box, and tap into a couple of spare pins in the harness going out of the box to run the controller output to the motor, making for a nice, clean install.

Continued on Part 3