Power steering shudders when turning steering wheel when not moving. Three replacement reman racks and two known good pumps have been tried.Correct fluid is usedbeen flushed and bled many times,alignment set to specs.Put front wheels on turntables,turn back and forth full lock to lock effortlessly. Problem disappears if idle is raised slightly,no problem at all when moving along.I inherited this problem from another shop.Have cheched the rack mounts,subframe,steering column u-joint,replaced high pressure hos,checked return hose for restrictions,strut upper bearings/tierods/ball joints for binding,am running out of things to check!

steering rack or gear . 2X2 - 4X4 engine . Depends on steering system .
When you turn the steering wheel, the steering gear rotates the pitman arm which forces the relay rod to one side. The tie rods connect to the relay rod with the ball studs. The tie rods transfer the steering force to the wheels. Use the tie rods in toe adjustments. The tie rods are adjustable. The pitman arm support the relay rod. The idler arm pivots on a support attached to the frame rail and the ball stud attaches to the relay rod.
The 2 tie rod are threaded into the tube and secured with jam nuts. Right and left hand threads are used in order to permit the adjustment of toe.

Binding linkage , steering gear worn etc....

Power Steering System Description and Operation (w/o Electro-Hydraulic Steering)
The hydraulic power steering pump is a constant displacement vane-type pump that provides hydraulic pressure and flow for the power steering gear. The hydraulic power steering pumps are either belt-driven or direct-drive, cam-driven.
The power steering fluid reservoir holds the power steering fluid and may be integral with the power steering pump or remotely located. The following locations are typical locations for the remote reservoir:
• Mounted to the front of the dash panel
• Mounted to the inner fender
• Mounted to a bracket on the engine
The 2 basic types of power steering gears are listed below:
• A recirculating ball system
• A rack and pinion system
In the recirculating ball system, a worm gear converts steering wheel movement to movement of a sector shaft. A pitman arm attached to the bottom of the sector shaft actually moves one tie rod and an intermediate rod move the other tie rod.
In the rack and pinion system, the rack and the pinion are the 2 components that convert steering wheel rotation to lateral movement. The steering shaft is attached to the pinion in the steering gear. The pinion rotates with the steering wheel. Gear teeth on the pinion mesh with the gear teeth on the rack. The rotating pinion moves the rack from side to side. The lateral action of the rack pushes and pulls the tie rods in order to change the direction of the vehicle's front wheels.
The power steering pressure hose connects the power steering pump union fitting to the power steering gear and allows pressurized power steering fluid to flow from the pump to the gear.
The power steering return hose returns fluid from the power steering gear back to the power steering fluid reservoir. The power steering return line may contain an integral fin-type or line-type power steering fluid cooler.
In a typical power steering system, a pump generates hydraulic pressure, causing fluid to flow, via the pressure hose, to the steering gear valve assembly. The steering gear valve assembly regulates the incoming fluid to the right and left chambers in order to assist in right and left turns.
Turning the steering wheel activates the valve assembly, which applies greater fluid pressure and flow to 1 side of the steering gear piston, and lower pressure and flow to the other side of the piston. The pressure assists the movement of the gear piston. Tie rods transfer this force to the front wheels, which turn the vehicle right or left.


Your best bet , take it to a qualified repair shop.

If the steering wheel is turned to full lock position, the power steering system is being exposed to thousands of PSI for a brief moment until the pressure relief valve kicks in and allows pressure to bleed off. Which is the hissing/groaning noise you may have heard before. That brief moment of extreme pressures is the most common causes of failures in power steering pumps along side dry steering while not moving. If you have shudder going both ways, you will need a new power steering pump because it is worn out. If you get a shudder in one direction and not the other, then you will need a power steering "Rack and Pinion" assembly. If it was my car, I would do both at the same time so you don't have to worry about the other component going out later on and starting the whole process over again. I hope this info helps!

Dave, the knocking noise may end up being unrelated. As for the shutter/hesitation, depending on the vehicle, it may be a filter/in-line valve. Check the pressure hoses and the outlet of the pump. Certain pump designs will have, what seems to be an extension coming off of them, a pressure valve/limiter..

I'm going to agree with the rack conclusion. Keep in mind I can't see it for myself.
If you take the load off the front wheels, you should be able to turn the steering wheel without effort.
If the effort changes while turning the wheel, the only things affected would be the rack and the column.
If you notice it turns ok with the engine off but not with the engine running, it could be something with the pump or one of the lines, or still something with the rack.

If the pump is ok then the problem lies in the power rack and pinion unit. This is a common problem, and is caused by internal "O" ring seal leakage due to a scored piston bore inside the rack and pinion. You can try having the system fluid flushed clean and adding a of bottle LUCUS brand power steering fluid conditioner, I have seen this correct the problem. I have personally used the product and it works, not all the time but it is worth a try, the replacement of the steering rack is about a $900.00 job parts and labor.

lift the front wheel off the ground and fill the pump resovoir to the max, then slowly turn the wheels from full lock right and then to full lock left, recheck the fluid level and top off as ness, repeat until the air is gone, then let stand and allow the remaning air bubbles to migrate to the pump, then recheck in after everything is cold.

the steering Rack and Pinion unit is defective, no other part causes this problem.. here is the part number, these are good units.

A-1 CARDONE Part # 221000 {[Rack & Pinion] Complete Unit; Reman.}
Reman.; Hydraulic Power Steering; RWD; Includes Inner Tie Rods $207.00

To find out witch it is,pump or rack and pinion,break loose the presure line on the power steering pump with a wench.Start the car and turn the steering wheel back and forth,you may need to loosen the nut on the power steering hose two or three turns to get the fluid to shoot out.It should come out pretty forceful.If it doesn`t,then replace the pump.If it does come out really powerful,replace the rack and pinion.

try taking the vehicle out in the parking lot and cut the wheel to hard lock, apply light throttle and do circles to the left, stop cut the wheel to hard lock on the other side and repeat this three or four times, also you can apply throttle while in park and rotate steering wheel lock to lock many times, the explorers are known for having air trapped in lines,try this and let me know.

Hi! The pulley could be worn or the belt is not properly adjusted.Causing the belt not to grip the pulley but slide on it,creating a friction.