Steering effort: Modification for steering rack / PAS Pump

[HJ2]

Hello all,


A dear friend of mine who loves his M100 more than anything has developed severe chronical pain in one arm/ shoulder / half of the neck.
As a result it gets harder and harder to take the Elan for a spin

To slow the process I would like to modify the steering so that it takes less effort to turn the wheel. He has an S2 now, so I could change the steering rack for an SE one, as this turns lighter.
Is this due to different internal orifices in the steering rack itself? Would it be possible to make an alternative set of orifices so the steering is a tad lighter?

I have also thought of mounting a smaller pulley to the PAS pump (+ a shorter aux. belt obviously), but I am not sure if this gives the desired result.


Does anyone have experience with this or would like to share some thoughts here please?

[Jamie N]

Just go the monumentally easier route and fit a larger steering wheel for him , couple that with that skinny tyres as well....sorted .

[Dave Eds]

Skinny tyres or slightly higher pressures in the current ones ......

[dapinky]

This is a project that I will follow with interest.

A while ago I was looking at the viability of fitting an electrically assisted PAS in the steering column (as per Vauxhall Corsa/Astra), coupled with a steering rack from a non-PAS Elan...... but the rack proved pretty impossible to source.

I have considered fitting a Vauxhall rack (with modified mounting points for the Elan), but never really got past the "can it be done?" stage.

As with any such project, there are always a number of ways to achieve the result, but some are always far simpler than others - so I'll watch with interest.

[Saltire]

There’s a company called Easysteer in the UK that does a retrofit electric power steering kit. I’ve no idea if it could be made to fit the M100 or not, though.

Interestingly, I see that Allon White (Lotus and Morgan dealers) are now offering an EPS kit for Morgans. Might be worth asking them if it can be modified to fit the Elan.

[HJ2]

My starting point: why buy new when you can modify the stuff you allready have.
Does anyone know for a fact where the steering difference between SE and S2 come from?

[dapinky]

My starting point: why buy new when you can modify the stuff you allready have.
Does anyone know for a fact where the steering difference between SE and S2 come from?

Now, I could be well wrong here (so, what's new?) as I'm going from a faded memory of something I heard/read many years ago......

.... something in my brain is saying that there is a difference in 'turns' of the steering wheel from lock-to-lock ......

.... to me, that would suggest a difference in the gearing rack/pinion as opposed to the actual hydraulics of the PAS.

(But even if the memory is correct, it doesn't mean that the science is!)

[HJ2]

It sure smells like you’re right then on the science dept.

[Jamie N]

The big question is though.... Would it really be worth the effort swapping them?, My S2 feels like there is virtually no discernible difference between it and the SE's I've had, and Mrs has driven
both with no comments on heavier steering on one or the other, ( she's very pernickety about heavy steering ). Might be an idea to try and get him a shot in an SE to see if it would be worth doing
before going for it, imagine it turned out he felt very little difference after going to all that bother.

[dapinky]

Another thought,

Have you (or he) checked the condition of the lower UJ on the column? When my old one finally seized up (in one plane) and I swapped it out for a new one, I really felt the difference from what had been gradually getting worse over many years.

A £20 replacement part may be all that is required (for now).

[HJ2]

When I think about it:

The rack&pinion relation is responsible for the unassisted power effort necessary to turn the wheel, assuming that all mechanical components are up to specification.
The Power assist is fluid based, so perhaps i should dig a little deeper in the steering rack orifices story here?

I will check all the mechanical components, but the car in question is meticulously well maintained so i dont expect any anomalies in the uni joint, ball joints ec.

[Simon_P]

HJ,
The PAS works by maintaining constant pressure on both sides of the hydraulic system in the rack. The steering column connects to a shaft in the rack which is a torsion bar it is surrounded by the valve body. When the steering load is high the torsion bar twists uncovering the valve port and increases the pressure on the appropriate side of the rack and hence providing assistance until the torsion bar is relaxed.
There’s a much clearer description and diagram in the mamual.
In essence a less stiff torsion bar will provide greater assistance.
The torsion bar makes the assistance proportional to the load hence less assistance is provided at high speed - so consider this if you go down that route.

I'm guessing that the pump has a bypass and so produces a constant pressure - If it does reducing the bypass will increase the pressure and hence assistance - but everything will be working harder.

It may be possible to get the rack rebuilt with lower gearing - more turns less effort, but unless you change the torsion bar this will result in less assistance and the same driver effort.

Retro fit ePAS works on the column and is programmable.

A bigger steering wheel is simple and effective.

[Saltire]

Very informative; I never knew that!

[HJ2]

Thanks Simon, that was very informative and helpful
Even I can (almost!) understand how it works now

Doesn't an increase in pressure in the system influence the compensate rate of the system, thus increasing assistance?
Or is the flow rate limited by an orifice / choke in the mentioned bypass that might open up possibilities here?

[Simon_P]

I've reread the manual and my earlier guess was wrong - the flow goes through the rack and the pressure reduces as the speed of the pump increases, so you'd need to know how the pump works in order to alter its output.

Also mixed up the high speed bit - the output of the pump reduces as engine its speed increases so less assistance as revs increase.

[HJ2]

I've reread the manual and my earlier guess was wrong - the flow goes through the rack and the pressure reduces as the speed of the pump increases, so you'd need to know how the pump works in order to alter its output.

Also mixed up the high speed bit - the output of the pump reduces as engine its speed increases so less assistance as revs increase.

I only know its a vane pump...
I will disassemble one to see what engineering trick was used to make it speed dependent.
But now that we know this... could I then just use a larger pulley in stead of the expected smaller one? Hmmmzzz.. I wonder...