Steering: Prius Electric Power Steering for my Stude

[Rafe Hollister]

I bought a Prius EPS from the scrap yard last year. They wanted 120.00, but since it didn't have the pump or hydraulics, they sold it to me for 60.00 (true story). So I'm finally getting around to installing it. A larger Ross steering box came in the trunk with my car.

It had just a few inches of double D shaft so I welded up a receiver socket, welded that to a shaft, and welded that to the Prius female splines to mount to the EPS unit. I built a mounting and torque bracket from the EPS up to the cowl just under the hood. Then welded more Prius splines, male and female to a stud of original Stude steering column to mount the wheel. The splines have 2" of telescoping slip, so my wheel is not tilt, but is adjustable in or out, 1.5 in and 1/2 out compared to stock.

I'm installing new radiator, used T5 trans, and a few other things so I won't know if/how it works for awhile. But here are some pictures of how I did it. The main obstacles were where to mount it (heat and limited room in engine bay, conflicts with brake pedal if mounted inside on firewall. So it is located with the steering box on one end and Stude dash bracket on other, with my fabricated bracket keeping it from spinning.

I weighed all the parts and it gained only 15lbs of weight, a chunk of that is in the bigger Ross box. And my Pitman arm is longer and has 1/2 fewer turns, so it should quicken up my steering ratio. Because the new box has the Pitman arm more rearward than original, I gotta lengthen the drag link an inch. It would be cool to make it adjustable if any of you have ideas. Otherwise it's getting cut, sleeved, and welded.

The EPS is collapsible in event of an accident, but I used my carpentry skills to make a zebra wood steering column cover so that's moot.
It was a very fun job, sorta proud of myself. And getting closer to calling myself a bona fide fabricator and hot rodder.
This was only possible since I became a god... when I bought my 1st welder a few years ago. If you have a garage, you need a welder!

Rafe Hollister

Images:
1) original Prius parts (not pictured is computer thingie box)
2) fabbed bracket
3) old and new parts
4) shaft from box to EPS
5) steering wheel mounting, note telescoping splines
6) installed (green steering box))
7) Column cover

[4NStudy]

Rafe:

If you're looking for a way to seal the fire wall opening you may want to consider using a plumbing stack roof vent ( full credit to Jerry Forrester for this idea). I found one that had a 1.5" opening at my local box store, perfect for sealing around the intermediate shaft.

[Rafe Hollister]

Wow, great idea! My original is barely serviceable and I've been wondering what I might do.
Thanks 4NStudy (Oh get it, 'foreign Studebaker')
Rafe Hollister

[PackardV8]

Congrats, Rafe. Update us on how it drives and feels.

The key to your success is probably the larger, heavier Ross steering box. A late Lark Saginaw would also be a contender.

FWIW, do not just graft an EPS onto a worn out small Ross box. Neither the box nor the frame is strong enough to withstand PS.

I was ask to look at one conversion and give an opinion as to why it wasn't working as hoped. The EPS had been spliced onto the OEM pickup Ross box, First, the steering box was so worn the shaft moved vertically so much the seal would not hold lubricant; the box was nearly dry. Then, the owner had installed wider, lower profile car tires with more offset wheels. The tires were grabbing the asphalt and the EPS was trying to force them to move; the frame rail caught in the middle was being twisted at least 1/2".

When I installed GM hydraulic PS on my C-cab, we had to weld the K-member to the frame rails and fabricate a reinforcing mounting plate and weld that to the frame where the PS box mounted.

jack vines

[Rafe Hollister]

Thanks for the insight, PackardV8.
I have been wondering about the increased stresses. I figure the EPS is doing the same job in a parking lot that I do with my 71 year old arms... but doing it faster, so the force must certainly be greater. And with my quicker box and longer Pitman arm, even more so. The K member is what the suspension is bolted to, right? That looks pretty stout on my car?

I am wondering if my EPS mount is enough, been thinking of adding another brace at a 90% angle to the other one. I will definitely be observing flex in the system.

I have been wondering if the EPS is not necessary once up to speed and if it might detract from steering/road feel. I am thinking of installing an on/off switch and then only using it in parking lots... ?

My box appears to be in great shape. I disassembled it, was full of new looking grease, shimmed correctly, and all nice and tight. I cleaned it and replaced grease with John Deere corn head grease (I love saying that... corn head grease). My old box appears in good condition with no noticeable play also.

Rafe Hollister

[4NStudy]

I am wondering if my EPS mount is enough, been thinking of adding another brace at a 90% angle to the other one. I will definitely be observing flex in the system.

I think you're ok with the setup you have. I just used some 3/16 bar stock that I bolted to the cowl and to the EPAS. I haven't notice any flexing or movement.

Regarding the steering movement at speed, I doubt you'll be bothered by the feel.

[clarkwd]

I have a post in the Tech Talk section titled Electric Steering Survey about the EPS unit in my 53. I chose a Corolla EPS unit from a U Pick It lot and am using a rebuilt Ross box. I have grafted the EPS unit into the old column and have retained the old steering wheel. I found room to run the wires down the existing wire track in the old column and made a ring and contact for the horn wire. The top of the unit is attached to the dash with the existing clamp and the bottom of the unit clamps to the box and is what keeps the column from rotating under the rotational load of the EPS unit. As noted in my post, it works, but I'd rather have more centering than I have now. One of this winters projects is to change out the Ross box for a lower ratio Saginaw.

[Rafe Hollister]

That bottom clamp, isn't it in the way of your shift or brake pedals? Wait, that is your steering column support? What keeps your EPS unit from moving? You said, but not sure I get it?
I just read your post in Tech Talk, Thanks. Rafe

[Rafe Hollister]

Some pictures of it all together but not installed. It's gonna be pretty, but will it work? Will my welds hold? Is my garage engineering sufficient?
Rafe Hollister

[clarkwd]

With the setup I have with the Ross 24:1 box, the Corolla EPS and more than 4 degrees of caster, I have almost no centering after a turn. I am looking for a lower ratio box.

[Rafe Hollister]

My car has never centered after a turn (OK maybe just a little bit). I posted here awhile ago about it. As I recall, that is simply the design of our chassis, and was for making the car easier to turn without power steering. Why do you think a different box will help?
By the way, do you know what my old Ross and bigger Ross boxes are ratio wise?

[clarkwd]

The amount of force from the tires or corresponding torque that the pitman arm has to put on the box to turn the worm gear and the EPS unit will change as the friction between the worm and follower changes. The pitman arm torque required to overcome the friction to turn the worm will decrease as the box ratio gets lower, but it will be harder to steer. I think all the 53 on boxes are close to 24:1 with the exception of the Lark power steering box with is 20:1. I'd like to find a late model Lark power steering box, lower ratio and recirculating balls, to make some measurements.

[r1lark]

My car has never centered after a turn (OK maybe just a little bit). I posted here awhile ago about it. As I recall, that is simply the design of our chassis, and was for making the car easier to turn without power steering. Why do you think a different box will help?
By the way, do you know what my old Ross and bigger Ross boxes are ratio wise?

Rafe Hollister
Rafe, I'm not sure who might have told you the steering not returning to center "is simply the design of our chassis", but none of my Studebakers have this problem. All return well to the center after a turn, and I have both manual and power steering models. If your steering didn't return before you started the EPS install, you very well may have a suspension/steering issue on your car.