Mk 4 Pull-A-Part EPAS

[mike223]

First - planning ahead - why not find a place to get an EPAS system out of the weather?


The only gauges I'm aware of that are going to fit in the same area are Speedhut (due to 1.1" depth).


Also bear in mind - you need to plan ahead and build the dash to be reasonably easily removed with the body on the car - you need this so you (somebody) can later service your wiring + gauges (sooner or later somebody will have to get in there, regardless).

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[mike223]

First required item:

Go to Pull-A-Part (~$65) or Ebay (~$150) and obtain an EPAS unit from one of the following:

Saturn Vue - from 2002 to 2007
Chevy Chevrolet Equinox - from 2005 to 2007
Pontiac Torrent
Saturn Ion - from 2003 to 2006 - only in steering column with metal ECU case.


Also get all the wiring harness.

Also get about 6" of tubing on the driver's side- this will require a hacksaw or tubing cutter at Pull-A-Part, or you'll end up bring home the whole steering column home for ~$125.

No need for the OEM u-joints, you're not going to have room for them on this project.

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[mike223]

The second required part (~$50):

Bruno's Black Box on ebay


How it works:

The Saturn Vue / Chevy Equinox EPAS will not do anything powered up by itself - in this condition, the added drag from the EPAS is negligible - feels just like your original manual steering, no power assist.


From what I've read on the internet - there are seven different maps in this particular EPAS computer (silver metal box), the computer has to receive a message on the serial bus telling it which model car it is in (out of seven), and a speed reference.

This is what Bruno's black box provides - the potentiometer he provides tells his black box what speed reference to provide to the EPAS computer - and therefore determines how much power assist the EPAS unit will provide - high speed reference = lower assist / low speed reference = higher assist).

[mike223]

Third part - u-joint.

This (or something like it) *MIGHT* work - probably not - major diameter too close to 2 x 2. http://www.epowersteering.com/purcha...mooth-u-joint/


When I started working on this project 2 years ago the only thing I could find to properly fit the output shaft of this EPAS unit was a 17mm-36 spline coupling from Woodward Precision Steering, here: http://www.woodwardsteering.com/PDF/...d%20Shafts.pdf

#114 .669/17 mm diameter; 36 teeth

I welded the coupling to an Ebay steering u-joint (3/4"dd).

As you can see from the images, you probably have to have the length of the smaller diameter coupling to clear the front edge of the 2 x 2 tubing.

With maybe a 1/4" to spare...

No - you probably won't be making a functional tilt wheel out of it without further modification.


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[mike223]

Fourth part - mount.


First you'll have to cut the pad for mounting the steering shaft bearing closest to the driver off the 2" x 2" tube above the driver's knees in your Mk4 - go ahead and clean it up and paint over it, make the 2 x 2 look like the bearing mount was never there (scary, I know, but you could always weld one back in).

Now you build a bracket to mount the EPAS on the 2 x 2 tubing as pictured (or come up with a better way).

It's handy if you also get the bolt that the OEM tilt mounted with - this is the cross bolt I'm using.

You're going to have to prototype this piece (maybe repeatedly) because the location is critical - front / back / up / down / tilt / sideways - everything is critical because you don't have much room to work in.

It's all critical to getting the u-joint to fit on the other side without being in a bind.

DO NOT PUT ANYTHING IN A BIND!!!

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[JJ in Cbus]

First off, Nice Work!

Did you have to shorten the input shaft on the power unit, and how did you attach the steering wheel hub?
Also is there still room for the Russ Thompson Turn Signal?

I want to add this mod just not sure how I want to tackle it yet. I would have to completely redo my dash to do it this way, but this is a really clean install.

jj

[mike223]

Fifth - mount computer.

By now you will find that the silver computer will not fit in there in the OEM mounting location.

The computer can mount most anywhere, Bruno says you'd better solder your wires if you cut / lengthen them - these wires are for a torque sensor that measures the deflection in the shaft to determine how hard the operator is turning the wheel - feedback loop - very important.

I chose to fabricate a bracket mounted to where the computer used to be, and mounting the computer to said bracket (new mounting angle).

I do not recall if the torque sensor wires "had" to be cut for this modification - I made up several spare computers with quick connectors (the good gold plated stuff) so I could swap and test as needed (tested some - but never "needed" - works perfect).


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[mike223]

First off, Nice Work!

Did you have to shorten the input shaft on the power unit, and how did you attach the steering wheel hub?
Also is there still room for the Russ Thompson Turn Signal?

I want to add this mod just not sure how I want to tackle it yet. I would have to completely redo my dash to do it this way, but this is a really clean install.

jj

1- Thanks!

2- Getting to that shortly.

3- If the RT turn signal mounts entirely outside the dash panel (toward driver) I see no reason you couldn't add that on - running pretty short on room between dash + EPAS right there.

[mike223]

Six - Wrapping it up.


I made my own dash out of thicker aluminum in the first place - so it mounts solidly enough to locate the "tilt" swing of the EPAS unit.

I'm using a short piece of the OEM steering column and a carefully located hole in the dash to locate that up + down.

It has to be secured up + down to keep the 1/4" clearance between the u-joint / coupling and the front of the 2 x 2 member.


Alternatively, a mounting plate attached to the back side of the 3/4" crossbow tubing could work nicely, used instead of / or in addition to the OEM steel column tubing.


For the steering wheel I'm using a Longacre 56605 quick release. IIRC, I had to bore the inside of the quick release hub to fit the input shaft.

I secured the hub to the input shaft using two flat headed allen screws, drilled through the hub (countersunk), tapped to the input shaft, with loktite - I would not recommend welding to this sort of equipment.

Cut the input shaft to match the length of the QR hub (wherever you want it).

I had to make adapters for the steering wheel to quick release.


I mounted the potentiometer inside the glovebox (above the hour meter, lol).


When I started this I did not expect to be satisfied with it - 1.5 years + 1500 miles later - operationally it has been "flawless".

The only issue I have found is that the voltage sag from starting the engine will cause the unit to not work (until rebooted) - so it needs to be powered up after the engine has been started (delay).

I wired the power to Bruno's black box with power to the fuel pump (switched) - Prior to starting the engine I run the fuel pump + turn it off, then start the engine, then turn the fuel pump back on.

I don't have a problem remembering to do it that way because the lack of power steering reminds me to cut the fuel pump back on.

This could be accomplished in a number of different ways - it just needs a delay of some sort.


Good luck.


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[JJ in Cbus]

Whoops, sorry I didn't mean to interrupt. Still, Nice work.

[BadAsp427]

Hello, I really like this install. I have a two questions

- do you use a Manual or Power rack with this modification?

- would you use a Manual or Power alignment specs?

[mike223]

You use a manual rack and align it for power steering.

[FlyingCobra]

You use a manual rack and align it for power steering.

Is there any reason in your mind why you couldn’t use a power rack (obviously without the hydraulics hooked up) with this? My thought being the lowest turns lock to lock I’ve seen for a manual rack is 3.5 vs 2.5 for power. I like as few turns as possible.

[mike223]

Funny you should ask that.

I enjoy autocross and have found that if I get boxed into a tight 90 (it happens), it takes me a full turn of the wheel to get into the 90, and then that full turn of the wheel has to come back out before I can get too far back in the throttle.

Which is a hot mess of hand over hand work with the steering wheel.

The pull-a-part epas described above will pull 315mm slicks with the 15:1 rack - parked on concrete - using one finger on the steering wheel if turned to max assist (potentiometer).


This year I added a 2:1 steering quickener between the epas and the 15:1 rack and that's the best mod I've done to the car.

With the steering limiters required to keep the tires off the LCAs / sheet metal - effectively, I am about 360 degrees on the steering wheel lock to lock.

Probably too quick for most people (think F1 / Indy car steering).


The only catch is that the epas will not pull the 2:1 quickener + 15:1 rack (or a 1.5:1 quickener) parked on asphalt - it works fine once you're rolling.


So my winter project may be to move the epas to the rear of the SN95 pedal box and put the 2:1 quickener on the driver's side of the epas.

Still trying to decide if the benefit of that modification would be worth all the prototyping.


Another option would be to leave the 2:1 where it is, ditch the epas, and install conventional power steering.


So I quess I'm hinting that the pull-a-part epas may not pull a depowered rack unless you're rolling - but it will pull the 15:1 rack with one finger, parked, if you like.


Just to be clear - the computer on the epas is smart enough to detect when the load is too much, so it doesn't destroy itself trying to pull against the stops (or when the load is too high). Just like hydraulic PS and the pressure relief spring.

[Big Blocker]

Thank you for confirming that an EPAS unit will fit under the dash if a little bit of pre-planning and thought go in to the process . . . I've been wanting to add EPAS to my MKII for a few years now and this just might be the [visual] push I needed to get started.
Excellent documentation and the pics make it look really easy.

FWIW, I'm running a manual 4 turn lock-to-lock Flaming River in my car pushing 275x40x17's up front. The low ratio of the FR rack makes it pretty easy to steer but PS has always been on my mind to allow me to ad caster for tracking. Being a MKII, I don't have the bearing saddle/bearing issues of the later MKIV's and there's a good amount of room in that position.

Doc

[FlyingCobra]

Thanks for the details, Mike. Food for thought. I’ll start with the EPAS and go from there.

[toadster]

what's the main difference on alignment between the manual rack and power steering rack?

assuming the EPAS makes it 'power' steering - wouldn't it be similar to the PS rack setup?

also, does the unit make any noise? not that you'd hear it with the exhaust, but for low speed (parking lot) is there any noticeable sound?

[mike223]

what's the main difference on alignment between the manual rack and power steering rack?

assuming the EPAS makes it 'power' steering - wouldn't it be similar to the PS rack setup?

also, does the unit make any noise? not that you'd hear it with the exhaust, but for low speed (parking lot) is there any noticeable sound?

Align it as power steering.

Operation is silent.

[swwebb]

FYI, http://www.epowersteering.com/ sells an electric power steering kit for the FFR Mark IV for $650 - you need to contact them because it is not listed on their web site. I bought a kit and will be installing it shortly. If you have power steering, you add more caster, which will make the car track better in a straight line.