EPAS conversion

[Hyper]

Ok boys and girls, I can't promise I will go through with this mod, but I will take you as far as I can get

The goal is to convert from PS to EPAS, by retrofitting Toyota Corolla 120 EPAS unit. This unit is basically power assisted steering column.

Its a bit updated, but its cheap, plenty of them available, and what's most important it doesn't the EPAS ECU is not running on CAN, all newer units do which would lead to some electrical challenges later down the road.
The ECU enables power assist with ignition on, and uses VSS signal to modulate steering effort - full assist on low speed (like parking), and less assist during driving.

For this mod to work, EPAS ECU and special Toyota relay are needed, so I sourced all of those for ~ $100

I didn't make a pic of the unit before I started tearing it apart, but it looks like this




The idea is to integrate it into the OEM steering column, create proper brackets and EPAS motor orientation so its not in a way of anything

As is, it would not fit because the brackets are in wrong place, the shaft on the steering wheel side is short, and the splines won't work with Subaru steering wheels.
So I knew I had to try to disassemble it to a level where I could get creative



I cut of the front portion of the tube, and starting shortening the outer tube more and more until I got here:




The shaft consists of different pieces that slide on together, which is perfect - I am going to try to create adapters so that in case the EPAS dies, I can just replace it with another one and reuse all adapters, so this gave me hope.




Notice the U-shaped part, it slides on the shaft for a tight connection between the pieces, that's it! Its not welded or bolted, just like that

The pieces itself has a heptagon shape




I bought a used GC column for the sake of this experiment, here it is next to the EPAS




Next, I had to take the GC column apart, pulled the C-pin out, used rubber mallet to get the shaft to slide out, easy



I was expecting something more solid from a factory part to be honest... but hey, it works and I've never seen them fail



Here it is from the other side, notice the hole - its for the key lock (which I intend to keep)




rear portion that sticks out in the engine bay




and I am out of allowed 10 images... moving to next post

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[Hyper]

front end




I also noticed a strange junction, that seemed to be just a press fit



hard to see on the picture, but there are 2 little holes on the sides with something that reminded me of plastic tabs, so I thought its just plastic glue covering spot welds, so I pulled out my heatgun and starting melting it.... what happened next really shocked me, as that was not plastic, the two pieces were actually GLUED together with some epoxy or resin, the stuff you usually find on hockey sticks when you assemble them




yep, its official, our steering columns are glued together
and those holes are to compensate for extra glue, so that extra compound has a way to escape




Oddly, the shape of the that piece resembled EPAS output shaft





can it be true????....



nope. different sizes


Here is the EPAS with the "toyota" steering wheel adapter, and the "subaru" adapter shaft, showing just how much longer this thing needs to be




My idea is to reuse the Toyota piece that slides on the EPAS output shaft, cut it, do the same with the Subaru part and make a single piece out of it (somehow)




This probably requires a mill and tig, I don't have either so will need to find someone who will be willing to do the coupling for me

but I may not be seeing another solution here, any experienced machinists can chime in?



Next, I need to figure out how to mate the rear part of EPAS with the the "remainder" of subaru column - EPAS uses splined shaft and a steering linkage goes over it, however this won't work because the shaft needs to be expended, another riddle that needs to be solved

[Hyper]

reserved2

[Wayne Suhrbier]

I have no idea how much torque is no the steering shaft, but I don't *think*it would be that much. Check before following the following suggestion. It look slike there is enough metal that you could file a bit off of the outside of the EPAS shaft and a bit off of the inside of the Subie shaft so that they would mate together.

Airplanes are now glued together also

[ether947]

I am curious to see how this all shakes out for you. I am essentially doing the same thing but with the BRZ power steering/GR column (I want the telescoping action).

For connecting the power steering motor to the steering rack (assuming your current setup doesn't work), I would look into the BRZ/FRS steering linkage. If you need spline count/diameter measurements let me know.

For connecting the p/s motor to the column, I got lucky. The GR column matches the spline/diameter of the BRZ motor. So, I just had to trim things down to get the motor to land where I needed it to.

[Hyper]

I'd be curious if BRZ EPAS motor would sit right behind GD dash beam and yet be the same length for the steering wheel to sit at it's normal position

I dropped off all bits at machinist today, who is brave enough to try and help me out once he has time, so this won't be updated until after the end of his month

in the mean time, I will plan the electrical part of this, turns out the EPAS ECU also seeks for RPM input signal to operate only with the engine running

[20wrx09]

This has me interested now that I have already done this setup on an 89 foxbody mustang. We used a quick ratio manual steering rack to keep things simple. The install wasn't that bad since I already had the whole dash out. What was nice about that kit is that it has its own controller and you can set the desired steering output with a dial.
Would love to get rid of the PS pump and clean up the engine bay. What do you plan on doing with the ports for the old hydraulic lines that were connected to the rack?

[ether947]

I am still working on my final placement but this is basically where it lands on my setup. I had to trim some plastics off of the HVAC and wiring harnesses. I also broke my brake light switch so watch out for that.





I probably won't have mine up and running until the summer. I only have one more "free" week before the spring semester starts, and I have a pretty busy one coming up so I can graduate. However, if/when I finish I will post my results.

And just an FYI, here is the motor controller that I am considering.
https://www.agtengineering.com.au/pr...ering-emulator

20wrx09, here is a thread about depowering a steering rack that I found useful.
https://forums.nasioc.com/forums/sho....php?t=2632487

Some people recommend plugging the ports (or looping them together) and welding the quill to get rid of the play in the rack. There is a p/n for a shorter belt as well.

[Homemade WRX]

Much subscription.