Hyraulics (power steering) question

I am trying to buy parts to convert my newly acquired 1995 Toyota Tercel from std. to power steering. Went to the junk yard and found a power
steering rack and pinion. Didn't buy it yet. Looks identical to my manual steering r&p except it has hydraulic cylinder in the middle with two fittings and hoses. Question: What actuates the cylinder? Is there a switch in the steering wheel? Is the gear box different? (they look identical) Is the cylinder simply actuated by my turning the wheel? Is there some valving within the cylinder? Any enlightenment would be greatly appreciated.
BTW, if it's as simple as I think, I could just purchase a two way cylinder with sufficient stroke and mount it in a push-pull position?????
Thanks,
Ivan Vegvary
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Ivan Vegvary wrote:

Ivan,
Dare I say this? I will anyway! You are over your head here if you gotta ask! :-)
It's NOT as simple as you think. The rack with the actuator is only half the system (maybe less). You need the pump, too. The system is a hydraulic pump and an actuator, usually with the valve that operates the cylinder built into the actuator housing. You are also going to need the pump, pulleys and belts, any associated idlers and mount brackets, pressure and return hoses and possibly different engine mounts, depending on the differences between the power steering equipped and armstrong steering models. Chances are good that the accessory layout is different between A/C equipped and not, as well.
While I do not claim experience on that particular model, my experiences in keeping my small fleet of nearly expired vehicles going, leads me to say that it is only sometimes as straightforward as finding a donor with the equipment you want and adding it to your own car. Such interesting features as totally different alternators being used depending on the equipage of the car, different mounts , different pulleys and idler setups. It is also worth checking to see if it uses the same steering linkage components as well.
Good luck! It may actually work out that it IS as easy as swapping in what you want, but you will have to do a bit of research to find out.
Cheers Trevor Jones
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Thanks Trevor, I am trying to do the research here, on line. Yes, I know I need the pump, pulleys etc. Donor car has all of that. The main reason I asked the question is because I cannot believe that it's all that simple. What I am calling a hydraulic cylinder (built into the middle of the rack and pinion) is possibly what you are calling an actuator? Am I right? If that's the case then I only need to scrounge the parts previously mentioned. (e.g., rack & pinion, pump, hoses, reservoir, pulleys and belts). What am I missing? Yes, since I do not know how it all works, I still cannot figure out what triggers the power cylinder? Is there something in the cylinder that senses the motion of the steering wheel and then, in turn, it decides to assist? Please explain if you know.
BTW, I'm not a total dummy. Have a 1948 and 1952 Pontiac for which I have fabricated many brackets and modified many pulleys in order to hang accessories not originally available. Yet, I never worked on power steering.
Thanks, Ivan
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ignoring the issue of installation, the power steering works basically as follows:
1. the pump produces pressure and has a pressure relief valve so it doesn't destroy itself 2. the steering wheel connects to a servovalve, rotating the wheel ports fluid to the left or right cylinder. 3. as the wheels turn, there is a mechanical negative feedback - when the wheels have turned far enough the valve is no longer porting fluid and the power assist stops doing anything. 4. htere are over travel stops so if you loose power you can still steer the vehicle, but the steering will be sloppy.

--
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Ivan Vegvary wrote:

Yup! The actuator is the same cylinder. The valving that causes the pressure to push the steering is built into the power steering rack assy. Turn the steering and the valves actuate. They are pretty reliable, but occasionally they just die. Better trained guys than me can fix them, but I just look for a rebuilt part when I have to.
I am surprised that you have not done any PS work yet. Just a pump, two hoses, and the actuator/rack assy, in most systems. It's the details that get in the way of it being simple, like getting the parts to fit in the engine compartment. Less of a problem with that in the older cars than most of the new ones.
Cheers Trevor Jones
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Ivan Vegvary wrote:

Since no one else actually answered your question , yes , the valving that actuates the hydraulics is *usually* built into the rack and pinion or steering gear box . The movement of the steering wheel moves a spool valve before the rack actually moves , which ports hyd fluid to the proper side of the ram while also relieving pressure on the other side .
--

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'76 FLH "Bag Lady"
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Thank you so much for your answer. I couldn't figure it out. This answers my question.
Ivan Vegvary
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[...]

An important thing to watch is the reservoir capacity. Make sure yours is big enough to keep the system cool. If the donor car has the same size everything, the reservoir from it ought to work fine, but after you get it all hooked up, pay attention to the PS fluid for a while to make sure it's not getting burned.
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wrote:

The slave cylinder idea you have is worthless without a spool valve to actuate it. For forklifts and other off-road power equipment, they mount the spool valve at the bottom of the steering column (Ross) and the steering is hydraulic only - no mechanical backup linkage.
That makes the equipment design a whole lot easier since they don't have to route a rigid steering linkage through the entire forklift to get to the rear axle steering box, but if the hydraulics die on you for any reason (stalled engine, blown hose, fluid leak) you have no steering control.
Obviously, you can't have that on regular cars and trucks. There are too many people who deliberately do not keep their cars in good repair ("I can't afford to fix it") and losing all steering control at 70 MPH on the freeway would be a very bad thing...
The parts from the junkyard car should all drop in and bolt up, and the spool valve is built into the power steering rack along with the actuating cylinder. Be sure to get the pump brackets to the engine, and the idler pulleys (and their brackets) if the belt routing is different.
The only wrinkle you have to watch out for is in computer interface - some cars with very small engines (no excess power) have a pressure sender on the high-pressure side of the hydraulics to warn the computer that you are cranking the steering wheel hard over at idle, so the EFI computer can keep the idle steady.
If you have a donor car, you can watch for something like that. The wire is probably there for it on your car to just be hooked up, they don't use separate body wiring harnesses for PS and MS cars. Worst case if you don't install it, the idle droops if you crank on the wheel at idle till the computer notices and bumps it back up.
You might even manage to stall it, but you should figure out what not to do pretty fast (like parallel parking without feathering the gas slightly) - we got along fine for many decades with power steering and without automatic idle speed controls...
--<< Bruce >>--
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On Sat, 21 Oct 2006 06:08:11 -0500, with neither quill nor qualm,

--snip--
Right you are, Snag. Most units I've seen were drop-in replacements. Just add hoses, pump, and pump brackets/belts and you're home free.
Of course, all this differs by models and year of auto/truck, so you have to make sure all the pieces fit if you interchange things.
The wrecking yards have all that interchange info at their fingertips so they can sell more parts. (Use their resources, Ivan.)
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Ivan Vegvary wrote:

Since no one has really discussed it, the power steering on road vehicles is really power-ASSISTED steering. If the engine dies, you still have control, even though the effort seems like a ton. An all-hydraulic design won't have that. The PS gear has all the valving needed along with the actuator(s), all that's needed is to connect up the pump and steering shaft. As others have said, this may be more fun than you want. Another thing to watch for is that you may need other steering parts like tie rod ends or steering knuckles, you might want to do some measuring before committing. The manual gear box may be a different length and may need other bits. If you've got a donor with all the stuff in good condition, you might just luck out with a transplant situation and not have to do a lot of cobbling up of brackets and such. Take a digital camera with you, memory sometimes fails after the 15th bolt or so and you end up with a box of brackets and mixed bolts and no idea what goes where. Snap the donor's build label so you know model year and build month, sometimes really needed when you go for spare parts. Save all the original fasteners you can find, too, very often they're something proprietary and the dealer doesn't even have them. I know that on some vehicles you need special pullers for the PS pump pulley, you can't even get close to removing the pump and bracket without the puller. It's that way on my van. Look for a lever-action tie rod end popper, too, if you need to grab them, a pickle fork just messes them up.
Stan
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