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Old 01-07-2021, 02:01 PM   #1
Hyper
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Join Date: Feb 2002
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1999 WRB GM6
2.34 LR destroker

Default EPAS conversion

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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Last edited by Hyper; 01-07-2021 at 02:22 PM.
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Old 01-07-2021, 02:01 PM   #2
Hyper
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Join Date: Feb 2002
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1999 WRB GM6
2.34 LR destroker

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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

Last edited by Hyper; 01-07-2021 at 02:21 PM.
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Old 01-07-2021, 02:02 PM   #3
Hyper
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reserved2
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Old 01-08-2021, 12:06 PM   #4
Wayne Suhrbier
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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
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Old 01-08-2021, 05:40 PM   #5
ether947
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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.
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Old 01-09-2021, 02:40 PM   #6
Hyper
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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
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Old 01-10-2021, 04:43 PM   #7
20wrx09
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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?
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Old 01-10-2021, 05:49 PM   #8
ether947
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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.
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Old 01-13-2021, 11:01 PM   #9
Homemade WRX
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Much subscription.
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Old 04-01-2021, 07:50 PM   #10
ether947
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EJ207 version 8

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Any updates?

I have my column physically bolted up so I can drive my car. I am loving the extra legroom. I have the controller, but I need to find a wiring harness from a BRZ/FRS so I can run it at least in failsafe mode.

I also have a 15 STi rack on the way.

And I still need to figure out a clock spring solution.
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Old 04-01-2021, 07:58 PM   #11
Hyper
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the machine shop I dropped it off at hasn't even started
its hard to find good help
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Old 04-02-2021, 09:59 AM   #12
Bud le savoyard
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so nice
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Old 04-08-2021, 08:55 AM   #13
Homemade WRX
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Quote:
Originally Posted by Hyper View Post
the machine shop I dropped it off at hasn't even started
its hard to find good help
You have the worst luck with machine shops, and I'm sorry for you. I'll follow up on What'sApp. Grievances that need not be aired on here.
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Old 04-26-2021, 07:32 PM   #14
ether947
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So, a quick update. I wired up the BRZ p/s motor controller (everything except canbus) and it works. I haven't driven it yet but I've depowered my VA STi rack and now I am waiting on a few odds and ends to install everything.
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Old 04-28-2021, 07:22 AM   #15
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Quote:
Originally Posted by ether947 View Post
So, a quick update. I wired up the BRZ p/s motor controller (everything except canbus) and it works. I haven't driven it yet but I've depowered my VA STi rack and now I am waiting on a few odds and ends to install everything.
So I'm assuming you went ahead with the AGT controller?

Also your pics up above are gone now. I'm on my computer and not on my phone btw.
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Old 04-28-2021, 10:44 AM   #16
ether947
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Quote:
Originally Posted by Homemade WRX View Post
So I'm assuming you went ahead with the AGT controller?

Also your pics up above are gone now. I'm on my computer and not on my phone btw.
I am just using the BRZ/FRS controller in "failsafe" mode.



I will relink the images. I'm having issues uploading images to the Nasioc host so I link images from my blog instead. I wasn't sure if I had a bandwidth cap.
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Old 04-28-2021, 04:28 PM   #17
Homemade WRX
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Ah, right on!! Thanks for following up so quickly.
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Old 05-07-2021, 02:01 PM   #18
danscomp
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As a quick comment, that part that's glued together may be the portion that collapses during an accident, so you don't take a steering wheel to the chest.
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Old 06-03-2021, 07:23 PM   #19
ether947
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EJ207 version 8

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So here is my final parts list.
  • GR Upper Steering Column (swap over ignition switch, etc...)
  • BRZ/FRZ Power Steering Motor w/Controller
  • BRZ/FRS Steering Linkage
  • Depowered VA STi Rack and Pinion





I haven't put too many miles on this setup but everything seems to be in working order. On occasion, the p/s assist will cut out in parking lots (ex. very low speed, clutch in; or cold starts). I'm not sure what the issue is there. Might be an alternator voltage thing. I am thinking about doing the diode mod and/or the 3-wire mod as well.

I haven't taken the car to the Dragon yet, and my usual testing roads have been busy as hell for some reason. But so far, I like the level of assist that the "failsafe" mode provides.

I have a blog where I go into more details, but I am thinking about starting a build thread just to go over the highlights.
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Old 06-03-2021, 07:46 PM   #20
snow_bound26
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Very interested. Subscribed
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Old 06-05-2021, 03:35 PM   #21
Homemade WRX
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Please do share!!
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Old 07-19-2021, 12:43 AM   #22
ether947
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EJ207 version 8

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A quick update.

A couple of weeks ago I took it through the Dragon for a trip to NC. The steering was a little on the heavy side but nothing unmanageable. I also have 265 summers over 245 all-seasons and a 13:1 rack over a 16.5:1 rack now. It cut out on me a couple of times but I haven't figured out the pattern yet. For most of my 2-3hr drive through the mountains, it was fine.

Other than those issues, the system works great. I hear the click of the control module when I turn the key on that reminds me that it is still there.

Recently, as in yesterday, I retorqued my suspension rotating points (top hats, ball joints, etc) and the steering is considerably lighter. I guess I did a good ole gutentight method before. My car has long had an issue where the steering did not want to return to center. I have replaced every steering component on this car and I was disappointed to still have the issue. It returns to center easier but I still have to help it. I'm not sure what the issue is there.

I started a build thread but I have been having issues uploading images to the Nasioc host. But I am slowing adding more info.
https://forums.nasioc.com/forums/sho....php?t=2937433

Oh, and I found this $50 controller for the BRZ EPAS on eBay. However, it is Portugal.
https://www.ebay.com/itm/144032280559

I also found these connectors that look like the BRZ connectors so you might be able to make your own power harnesses.
https://www.ebay.com/itm/265072946013
https://www.ebay.com/itm/265072955344

I have a few odds and ends to fix but I'm kinda focused on my tall boi shifter now.
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Old 07-19-2021, 03:01 AM   #23
Hyper
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from what I have read, with EPAS self-centering relies mostly on the caster

that cutting out is a big issue imho, I would imagine the EPAS has some torque sensors that communicate through CAN with the controller, waiting for some inputs which they are not getting - just a guess
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Old 07-19-2021, 06:47 PM   #24
ether947
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EJ207 version 8

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I have around 5 degrees of caster before the EPAS swap, but now that I think about it, I need to check the tension adjuster torque specs on the rack.

The cutting out doesn't happen often when driving. It does it on cold starts, but as soon as I blip the throttle to back out of the garage it starts working. I'm thinking it is either a voltage issue or a torque sensor issue. I am going to try the diode mod to see if that helps.
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Old 07-20-2021, 12:42 AM   #25
T-37
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King Pin Inclination along with caster will help with return to center. There's a great motoiq article that covers it in detail.

https://motoiq.com/the-ultimate-hand...n-and-scrub/3/
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