Shad Laws

Hello-

I got to thinking... a common complaint about the FD design is that there is too much power steering assist. It'd be nice if the feel was a little more direct and a little heavier... not necessarily as much as a manual rack, but definately less than the factory gave us.

Has anyone ever tried to do anything about this?

It seems like it'd be a not-too-complicated fab job. What you need to do is increase the stiffness of the torsion bar in the valve on the rack. This can be done by decreasing its effective length and/or increasing its effective diameter. It seems like welding some small strips along ~1/2 of its length to increase the stiffness to that of the larger part of the bar should decrease the power steering assist by about 1/2 and decrease the "slop" felt on the wheel by about 1/2 (all power steering systems have "slop" - you need to twist the bar to open the valve!). It seems like this would make everything nice and happy...

The alternative solution is to think about some way of limiting the pressure from the pump. However, doing this will decrease the assist but INCREASE the slop. This is because you have to apply more manual steering torque before, but through the shaft with the same low stiffness, so more slop...

Any thoughts?

Take care,
Shad

adam c

iTrader: (2)

I like my power steering as is. No slop!

Shad Laws

Hello-

Maybe I should clarify... I should say "compliance" or "springiness," not "slop." Yes, there should be no backlash or freeplay... that'd be bad :-). But, ALL power steering systems have a very notable amount of compliance in them. This leads to a lack of feeling "direct." You'd like every little twitch of your hands to translate onto the road, but it doesn't because you are twisting through a very flexible shaft.

To give you an idea of how flimsy this is, all of your manual steering torque goes through a flexible shaft about 3-4" long and only about 3/16" in diameter. I'm not 100% positive of these numbers as I haven't yet pulled apart an FD rack, but have done a few other cars (including magnasteer setups... neat concept!). It should be somewhere about that size... a tiny 3/16" shaft. Every time you apply torque, it has to twist before the wheels can move. Fun, eh? People that remove the PS pump and loop the PS lines have this effect show up a lot, as now they have to apply a bunch more manual steering torque at the steering wheel through this same tiny shaft.

The angle of twist of the shaft dictates how much power steering assist you get. The design idea is that the more torque you apply, the more it twists, and the more help PS gives you. So, if we make the shaft a bit more rigid, it twists less and PS gives you less assist.

It's not a no-brainer modification - it does need a machine shop. But it might be nice :-).

Take care,
Shad

maxcooper

I have not heard of that upgrade idea before, but it sounds interesting.

I have noticed that installing a shock tower bar sharpens the steering feel by a noticeable amount.

I am not sure if this has any effect, but perhaps an underdrive main pulley would reduce the assist a bit. I had an underdrive pulley on my car for a while, but I never really noticed any difference in the steering. I wasn't expecting anything, though, so I wasn't looking for a change. I would guess that the change is minor (since I never noticed) if it changes it at all. But it might offer some reduction of the power assist.

-Max

SPOautos

Just pulling the ps off the car, looping it, and draining out some fluid works for me....and its easy haha

rotorbrain

stephen. . . would it be too much for me to ask to drive your car around the parking lot when you get it back up. . . i wanna know what that feels like.

paul

Shad Laws

Yes indeed.

Steering "feel" can really be thought of as two things. One is a static effect - weight. It deals with what you feel when you hold the wheel at a certain point. The other is a dynamic effect - crispness. It deals with what you feel when you are moving the steering wheel. If you want to be more technical about this definition, you could be... I am waving my hands a bit here... but it gets the point across :-).

Adding a shock tower bar helps to eliminate some compliance in the system, making the dynamic crispness much nicer. A similar, but more powerful, effect would be felt if you could get rid of that less-than-pencil-thin torsion bar you have to turn through. That tiny bar is a prime example of compliance... it's like turning through rubber.

It won't do anything except at very low RPM. The power steering pump is designed to give nearly maximum pressure at idle speed. That way, you can turn in parking lots. When your RPM goes up, a bypass valve opens in the pump to modulate the pressure as needed... it's a pressure-relief sort of thing. The pump itself is a simple, positive-displacement, rotary vane pump... inefficient, but capable of pretty high pressures. If you underdrive it, then you are just increasing the RPM necessary to get max assist. You *might* notice that assist at idle in a parking lot goes down, but that's it.

Now, we could simply change the pressure relief setting, and/or add another pressure relief bypass valve. This would lower the pressure and decrease the assist. This gives us the desired weight we want - we can get the correct static effect. However, the dynamic effect is worse. Now, instead of using a little bit of manual steering torque to twist the torsion bar, we're using a lot more... this means that more compliance will be felt and the crispness will go down.

The ultimate limit of this type of modification is when you set the assist pressure to zero - you get rid of the pump and loop the lines. This gives lots of static weight, but will give you LOTS of compliance. The dynamic effect will feel yucky - you are turning through rubber. I've driven cars like this and cars with a real manual steering rack... let me tell you, there's no comparison. The manual steering rack feels a lot more direct and crisp.

I'm highly considering buying a spare FD rack and making the modification to test it out. I think that the FD needs power steering to remain a true daily driver, but as-is, there's just too much of it. This whole "looping the lines" thing is a poor solution at best. Converting to a FC manual rack is a good way to go, but you get a slower steering ratio and you make the car less friendly to the daily driver. I'm convinced that there's another way...

Take care,
Shad

Shad Laws

Hello-

Have you driven a similar car with a truly manual steering rack? If so, you've probably noticed a distinct difference in the crispness of your steering commands... you'll feel a lot of compliance in your looped-line setup if you have to put all the steering torque through the tiny-*** torsion bar. If you've taken a rack apart before, you know what I mean.

Now, there's another solution that works just as well. You can make a truly manual FD rack. The advantage over an FC rack is the quicker steering ratio... well, whether its an advantage or not depends on your vehicle usage. Anyway, here's how. First, get rid of all the pumps and lines and stuff like normal. Then, take apart the rack. Get the pinion shaft assembly out and take it apart into the outer part and the inner (torsion bar) part. Your goal is to put these pieces together into one. Clean them up and take them to a good welder. He should be able to weld them together, making the compliance essentially nil.

Also, you don't really need to loop the lines. Drain all the fluid out of the thing, then put some filtered breathers on the two inlets in the rack. They can be had from McMaster for $1 or so.

Take care,
Shad

DamonB

If you want a heavier wheel crank in all the caster you can.

DaleClark

iTrader: (55)

I dunno if there's something equivalent on the FD, but I found a Japanese FC site once that showed an adjustment on the power steering pump. It was a set screw with a jam nut, and from what I could gather you could raise or lower the hydraulic pressure with this, changing the amount of assist. Never had a chance to mess with it on an FC. Does make sense, though.

Dunno if that would give you what you're looking for, though. Personally, I love the FD's power steering .

Dale