Wheel Alignment 'Caster' is off

pbm

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8,748
Location
New York
A few weeks ago I posted about hitting a 'huge' pothole. I finally got a wheel alignment done and the caster on the right (passenger) side (which is the side I hit) is off. The printout says RF CASTER Min.-1.80, Max.-3.80, Nominal- 2.80, Actual 1.0. All the other numbers are within the range except Cross Camber which is 0.1 and its supposed to be 0.0 and Cross Caster which is 1.3 and should be 0.0. The guy at the shop tells me that this means the right side wheel has moved back slightly. He told me to keep an eye on my tires but theres a good chance all will be OK. What do you guys think? Bent strut? control arm? what else??? Thanks
 
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502
Location
Canada
One thing in your favor is Castor isn't a tire wearing angle, but to say its OK is negligent. Something is bent or at least shifted. It could be something as simple as a shifted subframe or more serious like a bent ball joint that could snap without warning. Does the vehicle pull to the right?
 

pbm

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New York
Thanks Rabbler, I was hoping that a knowledgeable BITOGer would have some ideas/suggestions. I drove it approx. 60 miles this morning and it feels good. There is no noticeable pulling in either direction. When you say 'shifted subframe' what exactly does that mean? I'll keep an eye on the balljoint. Thanks again.
 
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4,872
Location
MN
The caster was off in my Lesabre from a bent control arm. A very similar situation. This made the car wander and pull to one side on certain roads. On my car, with a strut front suspension, it required drilling new holes(or slotting) and moving the top strut location on both sides in order to equal it out. Eventually I just replaced the control arm and then returned the struts to their original location.
 

pbm

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New York
T-Keith: I haven't noticed any wandering but I've only driven about 60 miles since the alignment. If it doesn't cause premature tire wear and isn't dangerous I'm gonna leave it the way it is.
 
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Chicago Area
Probably a bent control arm. When it is replaced, you will need a complete alignment of all specs. BTW, that cross camber spec of 0.0 is really stringent and hard to accomplish.
 
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39,806
Location
Pottstown, PA
Caster won't typically cause a "pull". It's more of a drift. Normally, with an older front end, it's biased. Off hand, I can't recall which way, but I think it was setup to drift to the left. Too much it shimmies (oscillates uncontrollably - like a shopping cart "caster"). It just over corrects and keeps on going ..too little (toward neg-) and it will be all over the place. Cars with manual steering and bias ply tires had neg- or near zero caster.
 
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Honolulu, HI
like Gary said, castor affects steering angle on turning, not left/right it's like the shopping cart or bicycle fork. less castor is more up and down angle on the steering, faster turn in at low speed but less stable at higher speeds (depending on the rest of the susp) High speed cars are set up with more castor, 4 to 5+ deg. they'll sacrifice low speed turning a bit for stability. another effect of increased castor is maintaining more camber when loaded as in hard turns something is shifted or bent. hopefully bent because it's harder to correct a shifted geometry
 
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Canada
 Originally Posted By: pbm
When you say 'shifted subframe' what exactly does that mean? I'll keep an eye on the ball joint. Thanks again.
You don't say what kind of vehicle you have but on most FWD cars the front suspension bolts to a "sub frame" that then bolts to the main vehicle frame. There is usually some slop or clearance to center the sub frame under the main frame or unibody structure. Often in a collision or big pothole the subframe get shifted one way or another. Often nothing is bent just shifted off center. Many time I would just loosen the subframe attaching bolts and it would snap back into position. A good experienced alignment tech should know to check this. Finding a good alignment tech is another story. Castor angle is important for steering stability and proper return to center after a turn. Often techs would reduce Castor on the Left side to offset road crown. I'm very surprised your vehicle doesn't pull right. It's also possible the reading isn't accurate on that side and nothing is wrong.
 
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1,304
Location
Kankakee, IL
Caster will pull to the most negative side. Camber will pull to the most positive side. Toe will not pull just sets steering wheel center. You need to know what SAI and IA are after a reading like that to find out what bent. Most likely you either knocked the lower subframe out of whack or bent the lower control arm. This would move the lower ball joint back causing the negative shift in caster angle (closer to 0). Most of the time a shift like that would cause a definite pull. If both IA angles are the same (or within .5) and SAI is out that says between the pivot points are the OK and something else is bent (strut tower, frame control arm). If you have SAI about the same and IA out of whack you bent something in between the pivot point (Upper strut mount and lower ball joint on most cars). I would most likely expect the SAI to be out in this case sue to that angle be directly related to the Caster (same angle measured from the front instead of the side). So something is bent.
 
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426
Location
NY
Camber will cause a pull to the negative side. Toe will cause a pull just the same. The only difference is caster is a non tire wear angle. U probabaly bent the lower control arm
 
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39,806
Location
Pottstown, PA
With toe it will either plow or wander. Toe in, plow. Toe out, wander. The steering wheel will be where the steering wheel will be. Constant correction, can't get your "line" ..toe out. A somewhat numb band in the center of steering (wherever that might be in steering wheel position), toe in.
 
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