Not always. I was working on one car, a bellcrank setup. It had a heavily ported steering box and servo, just like the one jr4x posted photos of earlier. I could make it a depowered box by pulling off the end cap, removing the piston nut, and threading in a set screw into the lower vein hole. This would free flow the piston and isolate the two ports from each other.
with it driving both the box piston, and a ram (2.5x1.5x9) it worked perfectly. Paired with a psc1400 tc pump, 6” pulley, it could go lock to lock in 2 seconds, 3.5 turns, (~45 cu in displacement) and idled the motor around 900 rpm. When letting off the throttle, going into a corner, at race speed. It was still limited by flow. However, after every race, the box was toast. From stretching some part of the case(loose sector shaft to piston) breaking teeth, or destroying the servo in the box.
with it setup to not send pressurized fluid to the box piston. The steering was much faster. Still 3.5 turns obviously, but no lag. Lock to lock as fast as you could move you hands. Downside- it chattered the wheels. Not always. Was real bad when paired with a Howe TT pump. Switched out to a 4.5 gpm pump (5.5 inch pulley) and it was better. Custom made 7 inch pulley, not much change. settled on 6” pulley. Theory here was too much flow, causes the de cylinder to out run the linkages.
At this time, it would turn left to right great, and from right to about 2’0clock, great, chatter from 2 till 12, then fine till left lock. Changed torsion rods. From .185 to .205 to .235 , all without much change, .250 it was getting near no powersteering at all. Tried sweet/psc/Howe servos paired with the magic quick ratio manual box psc sold. No serious changes where had. Time for diving deep into the problem after the race season was up.
hydrodynamic this is when we tried a steering rack setup. First placed down, along side the trans, under driver, pushing a linkage to bell crank on the axle. This reduced the shaking in the spot it did by 1/2. This convinced me at the point of two things. It wasn’t steering box related. It was linkage related.
reducing the weight of the dynamic parts between the servo and the knuckle was key to solving this. and second, you could use nearly anything mechanical, as long as it could transfer the 28inlb that it takes to fully open the servo.
next step was a rack mounted to the axle,servo in the dash, 90degree box beside lower links,shaft to the rack, parallel to the hydro ram. No need for it to be one in the same unit. As the chassis had 3 degrees of roll steer in the links, flexing it out, we could have the shaft going to the rack input 3.5 degrees opposite steering input. Based again off 3.5 turns. Solved the steering chatter issues. But. 3.5 turns lock to lock, yuck. Reviewing the most successful setups that used this, they mostly use just a draglink to the knuckle from the box(three links fronts)
from there, it was a simple change to just chassis mount a rack, and use a cable. Downside, if the pump goes out, your going to have to stop and fix it, rather then push through to the end of the race.
Conjecture time. Ever compare a hydro steering valve with a Saginaw servo? The difference in operation is it uses a small displacement motor, to open the valve, instead of a steering linkage. But what if you could use both?
I think there is possibility, you could combine hydro valve, attached directly to a rack, and use a cable to the ram clevis (linear movement) and have ‘feel’, non-drifting wheel, and redundancy. if a cable breaks, it is just full hydro.
why didn’t you just do that?
