TheSamba.com :: View topic - Install Power Steering from a Prius...Less than $100

Mon Oct 09, 2017 12:27 am

I recently installed the electronic power steering unit from a Prius into my 73 Squareback.
It cost me less than $100 and took about 20 hours' work.
It might've taken less time, if I knew what I was doing...! :P

Don't know if there's still interest in this, but here goes anyway.

Selecting the EPS unit.
These four short YouTube clips explain the whole selection process.

https://youtu.be/f4TYQ_KJSpc
https://youtu.be/cERfqzKfoAk
https://youtu.be/JAE1D70MHgk
https://youtu.be/IDGjRSHUj1g

To summarize, I chose the Prius unit, for several reasons. I had bought a Saturn unit and it just didn’t fit. The motor stuck out to the bottom left instead of the bottom right, which interfered with the wiring and relays mounted to the wheel well. The piggyback SCU (Steering Control Unit) makes the Saturn unit much larger, too…the ability to mount the SCU elsewhere is an advantage. And the amount of steering “boost” is plenty, without having to buy an extra dial control. Finally, I am able to buy all the Prius EPS units I want for $50 at the local pick-a-part. Include the Borgeson output coupling (see below) for 20 bucks, and the mounting hardware, and you’re still well under 100 bucks.

If you pick the unit yourself, here’s a couple of hints. Try to find a wreck where most of the dash is gone over the steering wheel; the SCU (steering control unit ) is above and to the left of the wheel. Also, make sure you get all the plugs that go into the unit, with as much wire as possible still attached; at least 6 to 12 inches.

TEST THE UNIT – PUT 12V across the main power leads of the ECU and 12V+ to the keyed input wire. Grab the output and input shafts. I used the sliding input shaft and the u-joint on the output shaft bent over to 90 degrees. You can use vice-grips or pliers, but make sure you don’t damage the splines on either shaft. Hold the output shaft steady and twist the input shaft. The motor should turn in the opposite direction.

Mon Oct 09, 2017 12:29 am

2. The fundamentals: The point in this exercise is to cut out the middle of your steering tube and steering shaft, and replace them with the EPS unit. This involves the cutting, fitting and connecting of four basic pieces; the input shaft, the output shaft, and the top and bottom steering tubes.

But of course there is more to it than that, so here is the terminology I’ll be using, in pictures:
Top VW shaft, bottom VW shaft, top VW tube, bottom VW tube, EPS tube,
EPS fixed input shaft, EPS sliding input shaft, EPS output shaft, EPS main mount.

Jack up the front of the car and put it on jackstands to make the lower steering coupling as accessible as possible. Remove the left front wheel. Remove the steering column.

GENERAL NOTATIONS: The measurements that you will be taking are important, but not critical. When the EPS unit is finally mounted, you will be able to adjust the upper tube, upper shaft, and lower shaft at least ½”. We will be measuring and cutting everything around the center of adjustment. When you take measurements, If you’re a quarter inch off, plus or minus, you should be fine. Everything else will be adjusted to fit.

Three shaft ends need to be cut perfectly square…they butt up against each other and provide alignment of the shafts to each other. You will need to figure out how to square these using whatever resources are available to you. I don’t have a lathe, so I cut these with a hacksaw, and then had a friend square them on a lathe.

Oh yes, that friend….credit where credit is due, my friend Spider is nearly 90, spry as can be, and ran an airplane fix-it shop for 40 years; he is a wealth of information and experience. (And some really cool old tools, too!) Many of the ideas in this conversion, and most of the machine work, came from him. Thank you, Spider!

Mon Oct 09, 2017 12:33 am

Now we’re going to make a jig to hold the EPS unit in place, so you can easily take measurements.

Get a 2” wooden dowel from the hardware store, and two hose clamps that fit around it.
Cut it to 7-8” long. Drill a 5/8” hole in the center of one end of the dowel,
and put one of your hose clamps about an inch from that end,
to prevent the wood from splitting.

It doesn’t quite fit into the firewall hole, so using a sander or grinder,
shave one end of it a little, till it fits into the firewall hole an inch or two.
It doesn't have to fit tightly.

FITMENT - Push the dowel onto the EPS output shaft.
It will be a tight fit; you will probably need a hammer to get it on.
You can pry it back off with a couple of flat screwdrivers.

Put the other hose clamp loosely on the dowel.
Move the EPS unit into place in the car, and put the dowel in the firewall hole.

If you wish, you can suspend the steering wheel end with a piece of wire between the two steering column mounting bolts. Slide the EPS unit forward or back and rotate it until you figure out how it best fits under your dash. Think about how you’re going to attach the main mount to the car. For me, the motor was sticking up under the dash at about 45 degrees; I’ll show you later how I chose to secure the EPS unit in place. The motor could just as easily stick straight out to the right, without interfering with your pedals. Depends mostly on what’s behind your dash. The more the motor points upwards, the closer your EPS main mount will be to the dashboard, for easier mounting.

When the unit is where you want it forever, mark the top of the firewall tube on your dowel.
I put the second big hose clamp there, to fix the position.

Measure the distance between the bottom of the EPS tube and the middle of the two VW steering tube mounting bolts,
and write it down.
This is your “Top Tube Length.”

Remove the EPS unit from the car.

PREPARING THE FIXED EPS INPUT SHAFT – when I started cutting, metal chips got onto the plastic coating on the input shaft spline. The sliding input shaft would no longer “slide;” I ended up having to torch and wirebrush off the coating, and then of course, the spline was a little bit loose. So my advice to you is to leave the sliding shaft on the fixed shaft before cutting the EPS tube. Do not remove it until all cutting has been done, and all metal chips removed. Even a little distortion of the plastic coating will cause it to not slide easily.

TOP TUBE – Cut the VW steering tube to the “Top Tube length” you measured above.
Measure from the middle of the elongated mounting bolt holes.

Amazingly, the VW steering column tube fits perfectly over the EPS steering tube.
BUT…There is a weld on the VW tube just below the (2) mounting bolts
that will prevent the cut VW tube from sliding all the way down the EPS tube.

Remove the plastic slide collar and sticker from the EPS tube.
Make sure the sliding shaft is on the fixed shaft, to keep metal chips from getting into the spline,
and even pack some rags or oily paper towels between the EPS tube and sliding shaft, below where you will be cutting.

Cut the EPS tube just short of the weld on the VW tube.
Save the cut EPS tube. We will be using it later.

Slide the VW steering tube onto the EPS tube. It should bottom out.

Mon Oct 09, 2017 12:50 am

PREPARING THE SLIDING EPS INPUT SHAFT – Blow off any metal chips with compressed air, if you have it, before you remove the shaft. Pull out any packing you put in there. Hold it upside-down and remove the sliding EPS input shaft from the fixed shaft.
Again, be careful not to get any metal chips on the plastic spline coating…sorry to be redundant, but this is really important!

Cut off the end of the sliding EPS input shaft; the end with the steering wheel nut thread and splines.
There’s a shoulder right above the taper that the Prius upper bearing butts against; I cut it right at that shoulder.

Make sure the cut is perfectly square.
Tap a ¾” thread into the hole, all the way through where the shaft tapers outward.
Again, make sure that no metal chips get into the sliding shaft spline.

Mon Oct 09, 2017 12:56 am

TOP OF VW STEERING SHAFT – Put the VW shaft into the cut VW steering tube. Make sure the steering lock collar on the VW steering shaft butts against the upper bearing in the top of the VW steering tube. Make sure your anti-rattle bearing spacer is in place.
Mark the shaft where it exits the cut steering tube.

MAKING THE UPPER SHAFT ASSEMBLY - Cut 1¾” of ¾” threaded rod, and make sure the end threads are not boogered. Then thread it into the top of the sliding shaft enough to raise the sliding shaft ¼” or so. This will be what you use to adjust end play.

Now measure the distance from the bottom of the EPS tube to the top of the EPS sliding shaft. Measure that distance upwards from the mark you made on the VW shaft. Cut the VW upper shaft to the correct length. The end of the VW shaft needs to be perfectly square.

The bottom of the VW shaft butts against top of sliding input shaft. The VW steering shaft is actually a tube. You need to thread the bottom of the VW steering shaft with a ¾” thread to connect it to the top of the sliding input shaft. But the VW shaft ID is slightly too small to tap a ¾” thread. So you will need to tap drill it to 21/32, then tap the ¾” thread. A depth of 1-1½” is good.

Thread it onto the threaded rod in the EPS sliding shaft until the two shafts are hand tight with each other. This is what I now call the upper shaft assembly.

If the thread inside is not straight, the two ends will not butt up to each other. If this happens, you can bore the inside of one or both threads to 11/16 …this will loosen the thread enough to fit, without losing adjustment.

Mon Oct 09, 2017 12:57 am

ADJUSTING THE END PLAY: The top of the VW shaft lock collar must butt against the upper VW tube bearing, with just a few thousandths end play. This provides support so the steering shaft and wheel are not loose axially.

Put the upper shaft assembly onto the fixed EPS input shaft. Now put the upper steering tube onto the EPS unit; the VW steering tube should bottom out on the EPS steering tube. Check the steering shaft end play. If it needs adjustment, pull the assembly back apart and adjust the threaded rod by turning it into or out of the sliding shaft. This will raise or lower the sliding shaft on the fixed input shaft.

A little plumber’s putty or rubber cement on the sliding shaft end of the threaded rod will keep it from turning, and losing your adjustment, when you screw the VW shaft back onto it.

When we weld the shafts together, the putty or cement will burn off. We do need to keep the threaded rod from accidentally turning inside the upper shaft assembly once it’s in use, so it doesn’t move during use and change the adjustment, and put too much thrust on the upper bearing. We can do that with a roll pin, or by rosette welding the threaded rod in place.

Do not weld yet. Welding should be almost the last thing we do, when we are sure everything is adjusted properly.

Mon Oct 09, 2017 1:01 am

BOTTOM SHAFT LENGTH – Put the Borgeson 312500 coupling onto the EPS output shaft, and set the set screw in the EPS output shaft notch. Measure the distance between the boss on the EPS unit and the end of the coupling.

Mount the EPS unit with the top shaft and top tube assembly in place in the car, using your 2” dowel and (2) top column mounting bolts. The two bolts should be in the middle of the elongated mounting holes. Make sure the top VW tube is bottomed out on the EPS tube.

You want to know the measurement from the top of the firewall tube to the bottom of the output coupling.
First, measure the amount of dowel that sticks out of the firewall tube.

Then subtract the length that you measured above, from the boss to the end of the Borgeson coupling. Write this number down.

Remove the EPS unit from the car.

Mon Oct 09, 2017 1:05 am

Mount the VW shaft to the steering box coupling. The steering actually has TWO couplings.

First, the flexible urethane one with four bolts in it.

Second, the end of the steering shaft has a clamp with a single bolt in it, that holds the T that goes into the flexible urethane coupling. If this bolt is loosened, the shaft has about ½” of axial adjustment to it.

Make sure the four flexible coupling bolts are tight, and loosen the single axial adjustment bolt. With a paint pen, mark the VW shaft twice where it comes out of the firewall tube; with the adjustment extended, and with the adjustment compressed.

We want the lower VW steering shaft to butt up against the Borgeson coupling shaft.

Now is the time to figure out how you’re going to center the coupling on the lower VW shaft, before you weld it. In my case, Spider turned a small diameter on the lathe, that fit inside the coupling. It's not easy, because you're turning the long end of the shaft; the "crush cage" won't fit through the lathe chuck.

You could also use a lathe to make a little “plug,” with the ID of the lower VW shaft on one end, and the ID of the coupling on the other end.

Or tap 3/4 threads in both sides, like you did with the input shaft assembly above.

With the “dowel minus output coupling” measurement from above, measure and mark the cutting point of the VW shaft from right between the two marks you just made. Cut the bottom VW shaft to the right length. Make sure you cut it a little longer if you’re going to turn down the end diameter of the shaft to fit inside the coupling like I did. Again, for proper alignment, it needs to be as perfectly square as possible.

Mon Oct 09, 2017 1:12 am

EPS OUTPUT TUBE – BOTTOM TUBE – Remember that piece of EPS tube that you cut off? It just so happens to fit perfectly into the recess around the EPS output shaft, and telescopes into the bottom VW tube.

What I did is to make a bracket of 3/16 steel that bolts to the 3 bottom EPS bolts.
(If anybody wants a PDF of the pattern for the bracket, I'll be glad to send you one. I couldn't figure out how to upload a PDF.)
(Or...tell me how to upload it, and I will!)

The bolts are 8mm x 1.25. The two bolts that hold the bracket are 16mm long; you need two 20mm bolts to compensate for the thickness of the EPS’ native main mounting bracket. You need to “extend” the third casing bolt with some threaded rod and nuts, to hold the bracket flat.

Then I cut a hole in the bracket, the OD of the EPS tube, mounted the tube so it goes into the recess in the bottom of the EPS unit a little bit (to center it perfectly on the output shaft) and welded the EPS tube (on one side only) to the bracket. I think the pictures show this better than I can describe it.

Then I drilled a hole for the set screw to pass through. The set screw goes into the Borgeson coupling, with a little blue thread locker.

Then measure and cut the length of your bottom VW tube.
Drill and tap a couple of 10-32 allen head set screws in the lower steering tubes,
to hold it in place on the steel bracket tube.
Don’t drill and tap the upper tube for set screws yet.

I put a plastic collar/bearing in the end of the VW tube, to help keep everything centered.

The plastic collar would not go over the Borgeson coupling, so I had to put it on the shaft before welding on the coupling.
If you do use a plastic bearing, the lower shaft will not necessarily go right through the exact center of the firewall hole; the lower coupling and plastic bearing will keep the tube where it needs to be.. What’s important is that the output shaft is aligned with the steering box. Rather than using the native VW firewall seal, you can just seal it with silicone.

Mon Oct 09, 2017 1:29 am

CHECKING FIT - Now, before welding, sub-assemble everything together and check that it all fits.

Put the bottom steering shaft onto the EPS output shaft. Put the set screw in.

Then put the EPS and lower shaft assembly into place in the car, and bolt it to the steering box coupling.
Leave the steering shaft coupling adjustment loose.

Slip the upper shaft and tube assembly onto the EPS unit and install the two steering column mounting bolts finger-tight.

Check the fit of everything. Loosen the upper tube mounting bolts and slide the whole assembly forward or back
until your steering box coupling is either fully compressed or fully extended, then tighten the coupling.
The through bolt needs to be against the shaft, to prevent the coupling from "jumping" under heavy pressure.

Compress the whole steering assembly slightly to make sure the top VW tube is still bottomed out on the EPS tube,
and tighten your upper tube mounting bolts. Make sure your upper shaft bearing end play is still correct.
If not, take off the top tube and shaft assembly and adjust the play again.
Now is the time to shorten something if you need to.

When you’re sure it all fits, and your end play is correct, weld your input and output shafts together.
Then reassemble the whole thing in place in the car.
Don't forget to tighten your steering box coupling!

If your end play has changed slightly after welding (mine got looser):

If there's too much end play, you can shave a little metal off the bottom of the VW upper steering tube.

If there's too little end play, you can slide the VW upper steering tube slightly up the EPS tube before you set-screw it in place.

Mon Oct 09, 2017 1:41 am

MOUNTING THE EPS UNDER THE DASHBOARD

I got a piece of 3/8 dowel and cut several pieces about 5” long, with a sharp angle on the end.

Rotate the EPS unit until the dowel touches the firewall above it, with the motor sticking out at the angle you want.
Make sure the top VW tube is still bottomed out on the EPS tube.

Play with the dowel length and angle on the end of the dowel, until the sharp end of it looks just right against the firewall.
I used the flat side of a bench grinder wheel to change the angle on the end of the dowel.
I had grind it about 7 or 8 times to get it just...right...!

Then I put a spot of paint on the end of the dowel, and marked where to drill the firewall.

Remove the unit and drill a ¾” hole through the firewall.
Gradually work the drill to elongate the hole, to about the correct angle for the bolt to go through the EPS’s native bracket.

I used an unthreaded steel spacer to penetrate the firewall, and an unthreaded nylon spacer to go around it and keep it in place.

McMaster number: 9241A479 Steel Unthreaded Spacer, 3/4" OD, 1-1/4" Length, 3/8" Screw Size

McMaster number: 94639A895 Nylon Unthreaded Spacer, 1-1/2" OD, 1-1/2" Length, 3/4" Screw Size
NOTE that the plastic spacer is 1/4" longer than the steel spacer.
This is because you will be shortening it a little, when you cut and grind the angle.
If the nylon spacer ends up a little too short, you can get a 3/4 ID x 1-1/2 OD washer to go around the steel spacer and make up for the shortage.
(Fortunately, McMaster sells the nylon spacer in bags of five, so you can "practice" on a few till you get it just right.)

Also two 3/8 x 1-1/2 fender washers, one 3/8” flat washer, and one 3/8” locknut.

And a 3/8 bolt...In my case, the bolt turned out to be about 3 to 3-1/2” long. You can use the 3/8 dowel to estimate.

Mount the EPS unit back in place.
Prop it up with a stick till the native EPS mounting bracket lines up with the hole in the firewall.
Again, make sure your top VW tube is bottomed out on the EPS tube.

Put a 12" (or so) length of dowel in there to help the stick hold it in place and keep it lined up, while you shape the angled plastic spacer.
Put the steel spacer over the dowel and through the firewall hole.

Cut the plastic at an angle to match the firewall, using your angled 3/8 dowel to get the approximate angle.
You can then grind the angle on the plastic spacer on the flat side of a bench grinder wheel, until it fits just right.
Then grind the angle on the other half of the plastic spacer to match the first one.

Put the two plastic spacers over the steel spacer.
At this stage, you want the ends of the steel spacer about the same as the plastic spacer.
When you sandwich the firewall in there, that will put a little compression on the plastic spacer, which is what you want.
If the steel spacer is significantly longer than the plastic (more than the thickness of a washer) you can either cut it down a little,
or add a 3/4" ID x 1-1/2 OD (or larger) washer between the fender washer and the plastic spacer.

Assembly is a bear; you WILL need an assistant.
First, glue the fender washers to the nylon spacers with a little RTV; otherwise, they keep falling off.
Put the fender washer and outer nylon spacer on the bolt. Then put the steel spacer into the nylon spacer.
Then put that assembly into the firewall. Then have an assistant put the nylon spacer over the steel spacer, INside the firewall.
Then try to get the whole thing lined up with the EPS native mounting bracket and get the bolt in.
Then put on the flat washer and lock nut. Tighten it until the plastic squeezes the firewall pretty solidly.

Now drill and tap a couple of 10-32 allen head set screws in the upper steering tube, to transfer some of the steering torque to the two upper column mounting bolts.

Mon Oct 09, 2017 2:07 am

17. ELECTRICAL – Find a suitable place to mount the SCU (Steering Control Unit.) I had plenty of space under the dash.

There are only three wires to connect… your two main power leads, and the ignition switch lead.
Fuse the main leads with a 40A fuse. In practice, the most I've seen it draw is 28 amps, momentarily, when I turned the wheel really quickly.
Most of the time it draws one or two amps.

That’s it! You’re done! Install your steering wheel and drive!

Note that you may need to take your top tube off once or twice and jump a spline or two on the sliding shaft, to get your steering wheel and cancelling ring where they need to be.

Note also that it takes the SCU 6 seconds to recognize that the Prius PCU is not there,
and go into fail-safe mode, which gives you a fixed amount of steering assist.

Mon Oct 09, 2017 2:08 am

I put a jam nut on the steering hub nut and tested steering effort with a click-type torque wrench.
With no assist, it maxed out at 20 foot-lbs. With assist, it maxed at 45 inch-lbs, or less than 4 foot-lbs.
This was turning the wheel very slowly while stopped, on a smooth cement shop floor.
Since power = torque / time, you would need to apply more power to turn the steering wheel faster.
Likewise, if the surface had a higher coefficient of friction, like asphalt, turning the wheel would take more power.

IN REAL LIFE: My experience has been that contrary to what is mentioned in the research cited at the beginning of this post, there is little or no “centering” caster feel. However, I don’t find it to be a problem.

Neither is the 6-second delay a problem. The few times that I've taken off slightly too soon, it's been interesting to feel it "kick in."

It is an absolutely amazing feeling to be able to easily parallel park or back into a parking space, like a "normal" car. I had an artificial right shoulder put in last December, and it was a real struggle for awhile. To me, the conversion has been completely worth the time and effort and the petty cost.

Mon Oct 09, 2017 9:13 pm

I am impressed! I never considered that a possibility. Nice work!

Tue Oct 10, 2017 1:04 am

Very cool project!

Tue Oct 10, 2017 2:38 am

Pretty cool. I would normally questions anyone's sanity doing this mod, but I did see the replacement shoulder remark. I also see your car is electric and the wide wheels and bigger than stock tires and I'm assuming heavy front full of batteries doesn't help.

Tue Oct 10, 2017 6:17 am

Wonderful work! Really impressive.

Tue Oct 10, 2017 12:22 pm

Erik G wrote: Pretty cool. I would normally questions anyone's sanity doing this mod, but I did see the replacement shoulder remark. I also see your car is electric and the wide wheels and bigger than stock tires and I'm assuming heavy front full of batteries doesn't help.

Agreed. At first I wondered why someone would that, until I saw the shoulder reference. But combined with all the batteries and running wider tires I could see the need for power steering. Nice conversion, and a very well written write up. Nice job, and I'm glad it worked out well for you. :D

Tue Oct 10, 2017 1:50 pm

Very cool!! Thanks for taking the time to do such a wonderfully complete write-up.

Tue Oct 10, 2017 4:05 pm

Hi, All,
The batteries up front weigh about 480 lbs. That’s like two pretty big guys sitting on the hood, without the dents. To support the extra weight, I just simply put some coil over buggy shocks up there. And I lost the weight of the spare tire and gas tank (and gas, of course.) The electric motor is 115 lbs, and the controller that sits on top of it is 12 lbs., so I actually LOST about 150 lbs. back aft. And the car balances quite a bit better; I am at 47/53. The net net of all this is that the car is at 2240 lbs…about 300 lbs. over stock weight, according to Wikipedia.

Thank you to everyone who complemented my post.
Always a good feeling to know that someone appreciates your efforts.

You know, in researching this project, I have seen other threads attacking the sanity and even the strength and masculinity of people wanting to put power steering in their cars. Some people have gotten downright vicious.

My question is, why? Because it’s not stock anymore? I would venture to guess that a very small percentage of readers of The Samba are “purists” with completely stock vehicles. I understand the motives of “purists…” and I say, God bless ‘em. It is truly a difficult torch to carry.
Anybody who sees my car knows that it left that realm decades ago.

Is it plain old schoolyard machismo? I am wondering what the agenda is of someone who says things like this? To make someone else feel bad?

What if I didn’t have a “valid” medical reason for doing this? Who gets to decide what’s a “need” and what isn’t? What if I just WANT to be able to maneuver my car more easily? Where is the sanity and masculinity of driving a car that’s more difficult to maneuver at slow speed than it has to be?

If a guy wants to do something to his car, and it's moral and legal, and he is willing to pay the price and do the work, who am I to sit in judgment of his reasons? Or lack of reasons? I am going to do what I can to help him figure out how to do it. Whether I agree with his mods or not.
Hey...this is A-MUR-ICA! =D> Can't we all just get along...??!! LOL...

Just a thought…