How does steering gear preload work?

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I have some steering play around center position in my car and I've heard that it's possible to adjust preload to compensate for this. However I've also heard that adjusting the preload on "worn" steering racks is not recommended since the wear is essentially a central wear. This means that once the preload is adjusted in central position, it will become too strong when the car is steered and may result in steering ack binding! Indeed only central pinions are worn but not others. I'd like to know a bit more on how does the preload work. If anybody can explain me in detail what really occurs when the adjustment screw is tightened or give me a picture of the inside of a gear system, this would be nice. I've read that the adjustment screw acts on a thrust spring to preload the system. But does the preload mean that the gear is pressed on the rack? Should I avoid adjusting my steering rack for the reasons I've debated above? Thanks
 
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steering gear preload works like this. you have to gears and you are adjusting the SLACK between the 2 gears. if you have too much slack, you turn 1 gear and the other wont turn untill the slack is taken up. if you set them up with negativve slack where they slightly bind then when you turn 1 gear the other INSTANTLY turns. but there is a downfall, too much preload causes the gears to have friction between. it wont hurt anything, because these are slow moving parts and when i say binding, i mean like slight binding. to give you a real world example my 76 ford elite has worm gear steering with that stupid preload thing. i set the steering preload tight and now when i turn a corner and release the steering wheel the car does not center its self. i have to manually return the steering wheel to the neutral position. then the preload was too lose i could turn the steering wheel left or right real fast while going straight and the car would just keep going straight. you shouldnt rely on any stupid books or anything for adjusting preload. you should adjust it to how YOU like it and not how the manual says to. its not gonna hurt anything to mke it too tight or too lose and test it out. its actually a good way to get to know youre car. personally i like a tight preload to give the car more of a german car feel. (i know its almost a sin to pretend my ford elite is anything close to german) if i am on a long sweeping corner with a high degree of bank and i initate the turn, i can let go of the wheel and the car keeps turning untill the turn ends and the road looses its banking at which point the steering wheel will center its self again. with factory preload setting, or even lose, the car awalys wants to go straight when you let go of the wheel and wont keep turning on a banked turn.
 

kilou

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Yeah this is exactly the same with my car: the steering wheel always want to straighten a lot while cornering and I have this slack around the center position. What I'd like to know is what does the adjusting screw do. How are the 2 gears actually preloaded? I imagine that as the pinions of both the gear and the rack are conical, it is possible to adjust the vertical position of the gear in relation to the rack. This may compensate for slack because by "pressing" the gear on the rack, the contact is made where the pinions are thicker so the slack is compensated. Is this really how it works? I made this little picture to show how I imagine the preload action:  - The pain is that it seems I need to do this adjustment with the rack removed from the car [Frown] This is written in the program that Volvo dealers use in their shop. Indeed I have to measure the actual preload value (the steering torque) after the adjustment and this value must be within 0.6 - 1.4 Nm following manufacturer specifications. The question is do I need to have this value for any position of the steering wheel or only in the central position? Since I need to remove the rack from the car, I must do it things right at the first attempt! [ January 20, 2005, 10:18 AM: Message edited by: kilou ]
 
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kilou, Your diagram is exactly what I was picturing for steering rack preload. Now if I could only get a rough picture of what preload on a steering box is.
 

kilou

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I have no idea of the design of a steering box. Steering rack & pinions are still a mystery for me and I'm not sure of the diagram I made [Smile] Sorry.
 
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quote:
Originally posted by kevm14: kilou, Your diagram is exactly what I was picturing for steering rack preload. Now if I could only get a rough picture of what preload on a steering box is.
a recirculating ball steering box is (oversimplified) a worm and sector setup that uses ball bearings to transmit the force rather than direct contact of the teeth. the freeplay adjustment pushes the steering sector (the part that turns the pitman arm) down against the worm ( the part turned by the steering shaft). not enough freeplay on a recirculating ball can actually cause the sector shaft to fail which leaves you with no steering. hth, Bret
 
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quote:
Originally posted by kilou: Yeah this is exactly the same with my car: the steering wheel always want to straighten a lot while cornering and I have this slack around the center position. What I'd like to know is what does the adjusting screw do. How are the 2 gears actually preloaded?
The ones I have seen, old Triumph TR4, late Honda and GM, there is a spring loaded guide that presses against the smooth side of the rack and shoves it into the pinion gear. I haven't seen another arrangement, but that doesn't mean much. If your arrangement is like that, I don't see any need to take your rack out of the car. For our metrically challanged friends, the torques you give are in the nighborhood of 1 lb-ft. Try this, lift the front end of your car off the ground so the wheels are free. Measure the torque required to turn the wheel. If it's less than about 3 Nm. 1. Back rack sdjustment off several turns. 2. Measure torque, T, required to turn stearing wheel with adjustment full loose. 3. Add 1.4Nm to that number and tighten the adjustment until the torque reads T+1.4. If it's not less than 3 Nm before you start, try disconnecting the tie rods and try again. There is a relationship between rack steering gear torque and preload. For instance, on my Corvette, the procedure is to tighten the adjuster until it lightly bottoms out and back off 1/6 turn. Perhaps someone can supply you with a simmilar number for your Volvo. Normally you set steering gear clearance with the steering centered. If your steering gear is very worn, you should set the clearance with the steering in the tightest spot. Don't overtighten. It increases wear and deadens steering feel.
 
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quote:
Originally posted by kilou: I have no idea of the design of a steering box. Steering rack & pinions are still a mystery for me and I'm not sure of the diagram I made [Smile] Sorry.
Put your arrow under the rack so it's pushing up on the rack through a spring and guide (shoe) and you will have a generic steering rack diagram.
 

kilou

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Thanks for all these explanations XS650! Very informative. I'm a little scared to do the adjustment without removing the rack because it's going to be difficult to accurately measure the steering torque at the steering wheel, moreover I don't know how to measure the torque at the steering wheel. Torque values of 0.6-1.4Nm are very small so I need precise tools from Volvo to do it (I can have them for 1 day for free). I understand that the adjustment should be made with the steering centered but in order to avoid any risk of overtightening, should I measure the torque value continuously from full left to full right and see if any spot show a torque value above 1.4Nm once the adjustment has been performed? This would be a safe check but it cannot be accurately done without removing the rack IMHO. I tried to see where the adjustment screw is located but I couldn't find it [Frown] It doesn't seem to be on the lower side of the rack. Below is the procedure from Volvo on how to adjust steering preload:  - I don't understand the story with tightening the screw to 15Nm (maybe this means that I should bottom it out)??? Then I have to move full left and full right several times with the adjustment screw at 15Nm and at last I should unscrew the nut back 1/4 turn (30-60°) and I should be OK. Is this what you understand too? [ January 21, 2005, 06:00 AM: Message edited by: kilou ]
 
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quote:
Originally posted by kilou: Below is the procedure from Volvo on how to adjust steering preload:  - I don't understand the story with tightening the screw to 15Nm (maybe this means that I should bottom it out)??? Then I have to move full left and full right several times with the adjustment screw at 15Nm and at last I should unscrew the nut back 1/4 turn (30-60°) and I should be OK. Is this what you understand too?
It sounds like the 15Nm is to bottom out the adjustment. The 15Nm tells you how hard to bottom it out. The back off 1/4 turn is a pretty common value. My Corvette, completely related has the saem basic instruction except calls for 1/6 turn. If the rack is in the car -and- you can find and adjust the adjustment, you don't need the the special torque wrench. Assuming you can get to the adjustment and it is clear how to adjust it. I don't exactly know how the adjustment is made on your rack, so can't tell you the details. Divide the 0.6 to 1.4 Nm torque by the radius of your steering wheel in metres and apply that calculated force to the steering wheel rim. If your steering wheel radius is 0.2m, then you need a force of 1 / 0.2 = 5 N on the rim of the wheel to generate 1 Nm of torque at the gear box. Back off the adjustment, check the force required to turn the wheel with the adjustment loose. Then adjust the box, and recheck the force required at the steering wheel. It should increase by the calculated amount. You can use a simple spring scale with hook (fish scale) to measure the force required to turn the wheel. You don't need to measure the force or torque in all positions. Just do it with the rack centered, then turn the wheel all the way both ways and see if it has any tight sports. Are you sure the problem is your rack and not something else like tie rods?
 

kilou

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Thanks for all! I'll try to find this adjustment nut this weekend to see if I can reach it without having to remove the rack. I'm pretty sure the slack in the steering comes from the rack but I will soon change both inner and outer tie rod ends to have a completely rebuilt steering [Smile] In any case, I will check that preload to be sure it is correct. I HOPE that Volvo has not put that adjustment screw on the bad side of the rack ie the one that face the crossmember............but I fear this may be the case otherwise Volvo wouldn't have recommended to remove the rack from the car. Thank you very much for all these precious informations [HAIL 2 U!]
 

kilou

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[Bang Head] pffffff the adjustment screw seem to face the crossmember and I'll have to remove the whole rack to access it [Frown] I don't understand the design of this thing because it would have been so much simple to put the screw on the other side [I dont know] Maybe this is made to force people going to their Volvo dealer and pay $$$$ to have the steering adjusted. Anyway, it's going to be one week or more of hard work with less space than when doing the timing belt but I'll do it. I will then be even more happy to have a precise "like-new" steering feel [Big Grin] ..............at least I hope!
 
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