Power steering - more feel required!

[jpyke]

Hi all,

I know this is a much discussed topic but I would really like to do something about the lack of feel I get through the steering. I've bought a spare rack and stripped the control valve down to see how it works. From what I can see the torsion bar is pinned to the splined input shaft at the top, and to the pinion shaft at the bottom with hardened steel roll pins. If these pins aren't tight the torsion bar does not turn right away when you begin to turn the steering wheel so what you end up with is power assistance coming in straight away and no physical connection to the pinion. I'm guessing that this is what makes racks get more and more assisted as they wear through use.

My first plan is to try to find slightly oversized roll pins to see if I can tighten up the connections to the torsion bar.

Plan 2 is to approach Adwest (the original manufacturer) to see if they would be interested in working with me to develop something that feels better - perhaps just a stiffer torsion bar. Looking at their products I notice they do a standard rack that looks similar to the Stag one which they claim is a universal offering, I wonder whether anything could be done to make the spool valve from that fit our racks.
Anyway this is all pure conjecture at the moment and I'm not at all sure if they'll be interested (suspect not). However, I think they would be more interested if I was after more than a 1-off, so as a quick gauge of opinion, could you let me know if you'd be interested in a modified spool valve?

Thanks.

P.S. I know that there is a school of thought that reducing pump pressure will help - I'm not sure that it will; you need to change the gain of the system, not the "input voltage" and the torsion bar is what sets this.

[Johnboy]

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Hi, I'd be interested.

I did reduce the pressure on mine, extra shims in the pressure release valve, but it didn't make the difference I expected. So I would definitely go for a mod that will give a bit more feel. (As long as idoesn't cost too much :?)

John

[mad cyclist]

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may be your pump is on the way out as bizarrely they get easier before going pop allegedly.

rgds Nick

[V Mad]

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jpyke wrote:

Hi all,

...........If these pins aren't tight the torsion bar does not turn right away when you begin to turn the steering wheel so what you end up with is power assistance coming in straight away and no physical connection to the pinion. I'm guessing that this is what makes racks get more and more assisted as they wear through use.
No, power assistance is proportional to the twist in the torsion bar. If the pins are loose you just get wasted movement in the steering wheel.

My first plan is to try to find slightly oversized roll pins to see if I can tighten up the connections to the torsion bar. This is one of the common reasons for play in the steering.

Thanks.

P.S. I know that there is a school of thought that reducing pump pressure will help - I'm not sure that it will; you need to change the gain of the system, not the "input voltage" and the torsion bar is what sets this. Correct, this is simple control engineering theory, but changing the pump pressure is like changing the supply voltage not the input voltage. In this kind of control system changing the pump pressure has absolutley no effect on the gain (until system reaches linear limits).

From my experience, the PAS on the Stag varies from abysmal (dead feel) at worst, to acceptable (a reasonable degree of feel). The question is why do some stags have that lack of feel. If you agree that some stags (probably the minority)do have acceptable steering then the system does not need modifying. IMO one reason is that the rack has beenis too tightly adjusted (at the damper), probably an attempt to compensate for wear. Another reason may be a badly worn gear which binds and does not move freely enough. I can only suggest you try another rack on a sale or return basis if you can get it (used or recon).

[singapore stag]

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My steering had a very light feel to it, until.......the washer that holds the top bearing split. After fitting the T Hart modified thingy the steering feels real heavy. Don't like it.

Maybe there is something else wrong:?

[peter f]

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From my experience, everyone'ssteering feel seemsdifferent. Mine has a light feel which I really like.

It needed rebuilding at one point, so I tried a couple of other racks,but preferred my original, so me and a pal rebuilt that one.

People in the SOC Club have have tried it, and also Clive Tate drove it back from Evesham to Wakefield when he fitted the ZF box, and all commented they thought it felt really light.

I've got used to it over the years however, and it suits me fine.

Peter

[Coppo]

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My steering felt tight not long ago, took the rubber caps off of the top of the suspention turrets filled with 3 in 1 oil turned the steering a few times..bingo it was sorted...the thrust washers in the top mounts had dried up.

Give it a try first before you start stripping things out.

Paul.

[singapore stag]

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Gonna try what Coppo suggested, I found that thesimplethings like this always works with the Stag.....

[jpyke]

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V Mad wrote:

jpyke wrote:

Hi all,

...........If these pins aren't tight the torsion bar does not turn right away when you begin to turn the steering wheel so what you end up with is power assistance coming in straight away and no physical connection to the pinion. I'm guessing that this is what makes racks get more and more assisted as they wear through use.
No, power assistance is proportional to the twist in the torsion bar. If the pins are loose you just get wasted movement in the steering wheel.
Agreed, and I have got wasted movement at the steering wheel - but I've just been looking at the spool valve assembly and in the ROM and the spool sleeve is mounted to the pinion shaft via two well fitting dogs, so movement of the input shaft will result in power assistance being applied and if the roll pins are really loose this will happen before the torsion bar moves very much so I think this would make for an overly light feeling.

My first plan is to try to find slightly oversized roll pins to see if I can tighten up the connections to the torsion bar. This is one of the common reasons for play in the steering. Do you reckon I can tighten this up with larger roll pins?

Thanks.

P.S. I know that there is a school of thought that reducing pump pressure will help - I'm not sure that it will; you need to change the gain of the system, not the "input voltage" and the torsion bar is what sets this. Correct, this is simple control engineering theory, but changing the pump pressure is like changing the supply voltage not the input voltage. In this kind of control system changing the pump pressure has absolutley no effect on the gain (until system reaches linear limits).
Absolutely - sorry, I did mean supply voltage rather than input voltage; I stand corrected! I'm embarassed to admit I'm an electronic engineer having got that wrong! :?

From my experience, the PAS on the Stag varies from abysmal (dead feel) at worst, to acceptable (a reasonable degree of feel). The question is why do some stags have that lack of feel. If you agree that some stags (probably the minority)do have acceptable steering then the system does not need modifying. IMO one reason is that the rack has beenis too tightly adjusted (at the damper), probably an attempt to compensate for wear. Another reason may be a badly worn gear which binds and does not move freely enough. I can only suggest you try another rack on a sale or return basis if you can get it (used or recon).
Yeah I'd say mine was nearer to abysmal than acceptable. I can't detect any looseness in the rack itself and I'm going to hazard a guess that the loose roll pins are the major reason for performance dropping off as time goes by. When I looked at the pinion and the rack on the one I took apart there was virtually no wear on it - but this would make sense if the movement comes predominantly from the power assistance rather than direct mechanical effort

I may be on a hiding to nothing here but the Stag corners rather nicely and it would be great if it was even more fun via some good steering feedback. I'll let you know if I get anywhere!

[V Mad]

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I didntfind the roll pinsaffected the steering feel ie make it light, just annoying to have free play. I found that they had become distorted/worn, and sofitting new ones should take up any slack (I fitted a solid pin though).

Picking up on Coppos point about dry bushes at the top of the suspension struts, these, like any part of the steering system can also affect the feel. Other parts which need checking are suspension ball joints, and track rod ends. I think it is worth jacking up the front, then turn the steering wheel with engine off to see if it feelstight.

[John Wright]

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Maybe what is required is to reduce the effectiveness of the pump as speed increases. This could be done using a bypass that is closed at low speeds and opens progessively as speed increases.A manually operated bypass operated by a bowden cable (e.g. choke cable) could be used to test the idea. Then if this works someone needs to come up with a scheme to operated the valve automatically. Pulses from a small rotating magnet attached to the prop shaft and picked up by a small coil could be used to operate a servo to open and shut the valve. Maybe a servo from a radio controlled car/plane could be used.

Just an idea!

John

[V Mad]

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John Wright wrote:

Maybe what is required is to reduce the effectiveness of the pump as speed increases. This could be done using a bypass that is closed at low speeds and opens progessively as speed increases. a manually operated bypass operaed by a bowden cable could be used to test the idea. Then if this works someone needs to come up with a scheme to operated the valve automatically. Pulses from a small rotating magnet attached to the prop shaft and picked up by a small coil could be used to operate a servo to open and shut the valve. Maybe a servo from a radio controlled car/plane could be used.

Just an idea!

John

Reducing pump output (by any means) does not work.

[jpyke]

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A solid pin sounds like a good idea - may I ask what you used? I'm guessing it would have to be stainless or some form of spring steel to avoid premature wear?

[John Wright]

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Why not? It seems logical that it should.

[Guest]

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What would be really nice, would be somebody making roller bearing top mounts affordable, £120 each is too rich for me, that would take several imponderables out of the equation (ooh err) Martin.