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Thread: power steering problems

  1. #1
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    Question power steering problems

    I have a 97 Buick Century that is giving me fits, it seems it only wants to turn freely to the right, but fights like a stubborn mule turning left. I jacked the car up and climbed under for a look, I can find no obvious signs of external damage to anything steering related, and the power steering pump is making no strange noises i had someone help me by turning the wheels lock to lock and didn't see anything obstructing the travel, but it is still difficult to turn. it appears to get worse as the car warms up, because when it was cold it turned with less difficulty. I'm stumped at this point and could use some expert advice, but please, if you don't know what you're talking about and are only guessing, i can do plenty of that on my own. Please reply soonest, I'm going to have to drive this car from Phoenix Arizona to Olympia washington in a week and really don't want to have to "armstrong" it all the way..Thanks
    Last edited by Bear; 06-22-2009 at 01:50 PM. Reason: additional information

  2. #2
    Senior Member Ken's Avatar
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    Quote Originally Posted by Bear View Post
    I have a 97 Buick Century that is giving me fits, it seems it only wants to turn freely to the right, but fights like a stubborn mule turning left. I jacked the car up and climbed under for a look, I can find no obvious signs of external damage to anything steering related, and the power steering pump is making no strange noises i had someone help me by turning the wheels lock to lock and didn't see anything obstructing the travel, but it is still difficult to turn. it appears to get worse as the car warms up, because when it was cold it turned with less difficulty. I'm stumped at this point and could use some expert advice, but please, if you don't know what you're talking about and are only guessing, i can do plenty of that on my own. Please reply soonest, I'm going to have to drive this car from Phoenix Arizona to Olympia washington in a week and really don't want to have to "armstrong" it all the way..Thanks
    Hey, Bear, Power steering is a fairly complex hydraulic/mechanical system and I would recommend getting expert assistance. I've given a simple explanation of a power steering system below which may give you some guidance.

    Hope this helps you, Bear.

    Ken.

    First, here's the quick answer as to how power steering works. A pump, driven by the engine, delivers pressurized hydraulic fluid to either side of the steering mechanism. This pressurized fluid pushing on the steering mechanism helps to steer the car and reduces steering effort. Remember, power steering is actually "power-assisted steering". It is not a drive-by-wire system. The power steering just helps the driver steer.


    Here's the longer answer. There are two main parts to the power steering system: the pump and the steering gear. In most cases, the pump is attached to the front of the engine and driven by the accessory drive belt. The fluid reservoir (where you add fluid) is usually located on the pump. The pump should be sized to deliver sufficient fluid pressure at idle. As the pump spins faster as engine speed increases, a pressure relief valve is used to keep the pressure at the desired levels. In some cases, the engine driven pump may be replaced by an electric pump (therefore there won't be a belt running to the pump).

    The interesting part of the system is the steering gear. There are two major types of steering gears used: rack and pinion, and recirculating ball type (aka worm and sector). Rack and pinion tends to be more prevalent with newer cars, so I'll discuss that type first.
    Here's a cut-away view of a power assist rack and pinion.

    The pinion (2) is attached to the steering shaft which is attached to the steering wheel. Thus, as the steering wheel is turned, the teeth in the pinion mesh with the rack (1) and slides the rack left and right. The rack is attached to the tie rods (3) which in turn attach to the knuckle (not shown) and tire. That's manual steering with a rack and pinion.
    In the power assist system, fluid from the pump (high pressure side) enters the steering gear at (4) and returns (low pressure side) at (5). A valve system inside the gear box directs fluid out at (6) and (7) which re-enters the gearbox at (8) and (9). This pressurized fluid acts on the power piston (10) to assist steering. Thus, if the driver is turning right, additional fluid is directed to the right side of the piston, which helps move the rack and therefore steer the tires.

    Fluid is directed to either the right or left sides by means of a rotary valve and torsion bar. Through this mechanism, the fluid pressure (and thus the amount of "assist") is proportional to the torque due to steering effort, and not the direction that the wheels are turned. In other words, it is possible for the system to help you turn left, even if the steering wheel is right of center. Here is a sketch of the rotary valve. Only one quarter is shown (it's symmetrical).

    The torsion bar (a torsional spring) connects the steering shaft to the pinion. When the steering wheel is turned, resistance is created by the weight of the car and tire-to-road friction, causing a torsion bar in the rotary valve to deflect. This changes the position of the valve spool and sleeve, thereby directing fluid under pressure to the proper end of the power cylinder.

    Here's another sketch of the rotary valve in a hard right turn.

    As you can see, as the torsion bar twists, it changes the alignment between the input shaft and valve sleeve, delivering more pressure to one side, and less to the other.
    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

  3. #3
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    OK, that told me how it works, but not how to fix the problem, I was trying to get away from having to take it to the stealership for service, but it looks like i might have to regroup and think about alternative transportation getting home from here. Thanks Ken..

  4. #4
    Senior Member grouch's Avatar
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    Cool

    Quote Originally Posted by Bear View Post
    OK, that told me how it works, but not how to fix the problem, I was trying to get away from having to take it to the stealership for service, but it looks like i might have to regroup and think about alternative transportation getting home from here. Thanks Ken..


    This sure sounds like a unit I replaced once with a failed internal ressure valve. The one I replaced with a rebuilt unit would turn left but barely right and only with great effort.

    With it being a '97, it sounds even more like a failed power steering rack. You DO NOT need to go to the dealer. This is old enough that they may or may not have anybody who trained on these cars. Often the really good mechanics get tired of getting $15 from the $75 per hour charge and other guging and will open an independent shop.

    Head over to Cartalk.com and look for their part of the site for actual car information. Then look for the "Mechanics files". Then type in the zip code where you're at and all the shops that people have recommended will pop up along with comment from people who used it. My niece blew not one but both heads on her car while 200 miles away. I found a shop there and told her to head over and let them look at it. I ended up getting a tow dolly and hauling it home to rebuild in my shop. However, the shop did a good job of diagnosis.
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  5. #5
    Ridin Dirty dom's Avatar
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    Hi,

    Here is my personal check list/trouble tree:

    • Fluid level is normal
    • Pump works fine
    • No leaks
    • No obstructions
    • Works perfect in one direction and not the other

    If all these are yes.

    Replace the rack!

    "Tutto nello Stato, niente al di fuori dello Stato, nulla contro lo Stato "
    -Mussolini
    All within the state, nothing outside the state, nothing against the state.

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