A power steering box is another option.

Electric steering does not feel nice. Make sure all the steering joints are good and the steering should feel fine

Some have managed to use power steering boxes from the 164

It's interesting. I bought my 1800E in 2019. Had owned an S back in the day and never noticed any steering issues, however I found the E steering really heavy. Maybe because in between all my cars (Merc 280se 3.5, Jensen, Merc 280SL) had power steering.

I now I have EZ power steering and it is superb. I wish I had fitted it myself, however, as I have had to fiddle with it quite a bit afterwards. Wish I'd done it myself.

That said, EZ will fit it for you. Anytime I have spoken to the UK rep, he's been extremely responsive.

Plus I now have a lovely wood rimmed Nardi steering wheel!

Recommended.

I fitted a EPS column unit from a 2008 Nissan Versa on my 1971 142. At present, it is operating in the fail safe mode because I don't have a CAN bus speed signal. In the fail safe mode assist is fixed. With my 185/65 tires it is perhaps a nudge on the heavy side for parking; but, a huge improvement compared to the stock non assisted steering, particularly since I have a smallish Moto Lita steering wheel. Works out perfectly for around town urban driving. The assist makes the car sensitive to steering input on the highway. If you can't hold your arms steady then you are likely going to be wandering. If you retain the original Volvo hoola hoop sized steering wheel you definitely are not going to like the fixed assist while driving on the highway.

When I installed the EPS I completely ditched the lower portion of the 140 steering column with the rubber mounted break away section. In its place I used the splined collapsing column from the Versa. The splined collapsing column from the Versa eliminated all the torsional flex that existed in the rubber mounted break away section on the Volvo. That further increases the directness of the steering which some people may not like at highway speeds.

The 140 comes with 0 deg to a tiny amount of positive caster which means that there is very little self alignment in the steering system at speed. Volvo minimized the caster to reduce steering effort at low speed. I have been experimenting with increasing the positive caster to the 1+ degree range which has increased the self aligning in the steering geometry. Between that and my small steering wheel I have not been particularly motivated to experiment with generating a CAN bus speed signal to further reduce assist at high speeds.

I picked the Versa EPS column unit because the way the drive motor was mounted on the column worked better on a LHD 140. I expect that on a RHD 140 or 1800 there might be an interference problem with the drive motor. The Prius EPS might be a better fit on an RHD car.

I think my all-in cost was around $600 Cdn with me doing all the design, procurement and installation.

I believe the EZ use a Corsa C electrical unit.

Yeah, the steering does feel fine. Just that I do a LOT of manoeuvring at essentially zero speed and it’s a bit of a pain. I’ve heard people say that EPS can ruin the feel when driving which I don’t want to do, also that it can put undue stress on the steering box as it’s not designed to be assisted, not sure how true that can be really.

I find feel is fine is fine at speed, as assistance reduces.

I heard about the steering box strain thing as well, but so long as you're not whizzing the steering from lock-to-lock at standstill, I don't see how it can do any harm.

This is the cue for someone who knows more than me to prove me wrong/missguided!

Why don't you give Mike Waters at EZ a call? V helpful and approachable. No hard sale- took me 8 months to decide!

Ho much is the EZ system installed?

If you swap to the EZ or similar system you will add stress to the steering box.
And this boxes aren't really strong.

To swap a 164 power steering box is possible and not done in 1 day!!
You have to weld a lot and modify the frame rail heavily. I did it several times. I got faster now and will still need a few days.
The 164 won't fit into the 140 too. The mounting holes are at a different place. The pitman arm is different too.
I have a 140 LHD and a 164 LHD power steering box in Stock and maybe I'm able to do pics.

The Amazon and P1800 are good to drive if adjusted very well. They are without caster, and you will need caster with power steering. I do modify the front axle heavily too. Gaining camber (-1.0° - 1.5°) and caster ( 2.5° - 4°, depends on condition the car will be used.

Wide tyres and rims are not helpfully at original cars if for your feelings the steering is too heavily.

Good luck, Kay

Setting aside friction in the steering mechanism, stress on the steering box is caused by the friction at the tire contact patch, specifically the resistance to rotation around the vertical axis at the contact patch. When the car is not moving or moving slowly the faster you rotate the input shaft to the steering box the greater the torque applied to the input shaft with the potential for higher wear. A column mount EPS does not alter the source of the stress or the maximum stress on the box. If you have big arms and a hoola hoop sized steering wheel you can generate just as much input torque to the steering box as a wimp with a 14" steering wheel and column EPS.

If the EPS facilitates endlessly rotating the steering wheel back and forth quickly while you are sitting in the parking lot, perhaps it will contribute to wear in the steering box. If the EPS facilitates driving the car with a persistent tendonitis resulting from too many botched slice serves on the tennis court I don't think accelerated wear is going to be a material issue. As noted, if you are concerned about steering box wear avoidance of the 205/60R15 tires would be the hot ticket.

Recognizing the inevitable ageing of the original steering box, perhaps my next project is looking for a front steering rack for the 140 that addresses the box wear and friction problems and does not create new steering problems.