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Thread: What Causes Caster to be out of specification

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    What Causes Caster to be out of specification

    Hello. I have a 2020 Mirage that was in a total loss accident and the majority of the suspension parts were damaged including control arms and struts. I bought a 2015 Mirage and swapped the parts over. When all this was completed the Caster was still off
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    Now what I had read was that Caster does not affect the treadwear, but the tires are still wearing unevenly on the front. Currently the car has the 15" Mitsubishi wheels on it but am swapping with 14" steel wheels next week.

    What on the car affects the caster, why is it not adjustable, how do I determine what needs to be done to correct Caster, and is the Caster responsible for uneven treadwear?



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    i believe castor is how straight the McPherson strut is. Your lower subframe is maybe bent slightly, shifting the position of the lower control arm thus making the strut not straight. Im sure any alignment issue can cause uneven tire wear. Alternatively if the car was hit in the corner you maybe bent the strut tower top mount.

    The reason its not adjustable is because we have mcPherson strut instead of double wishbone. To adjust caster on McPherson struct you either have to replace the strut if bent. or you have to bend the top strut mount, but this probably requires a frame machine. Or you have an issue/can attempt to adjust or replace the lower control arm and or the subframe it mounts to.

    If you are a patient man you can look at the photo here and attempt to measure your top strut tower mount and see if it is out of alignment: https://mirageforum.com/forum/showth...l=1#post142235

    Best of luck!
    please consider checking out my Mirage related youtube channel: https://www.youtube.com/channel/UC6c...IEViRFw/videos

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    Thank you for this information very helpful, I will check further into these issues, the lower subframe did originally have markings on it from the collision center when it was first totaled. After reading your post it could be the position of the lower control arm on the passenger side, due to the damage on subframe. I never thought anything of it because it looked fine and everything bolted back up pretty easily. I will try and find the originally write up from the collision center.

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    The engine directly attaches to the subframe. If your engine was "out of place" it may have bent the subframe in the process.
    please consider checking out my Mirage related youtube channel: https://www.youtube.com/channel/UC6c...IEViRFw/videos

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    Quote Originally Posted by hkpotts1 View Post
    Hello. I have a 2020 Mirage that was in a total loss accident and the majority of the suspension parts were damaged including control arms and struts. I bought a 2015 Mirage and swapped the parts over. When all this was completed the Caster was still off...


    Now what I had read was that Caster does not affect the treadwear, but the tires are still wearing unevenly on the front. Currently the car has the 15" Mitsubishi wheels on it but am swapping with 14" steel wheels next week.

    What on the car affects the caster, why is it not adjustable, how do I determine what needs to be done to correct Caster, and is the Caster responsible for uneven treadwear?
    Caster is best described by looking at an "easy rider" motor bike. The very far forward front wheel, with the fork at maybe 45° angle is about the max caster you can think of. The more caster, the more the vehicle or wheel will want to go straight ahead. Low caster on the other hand, on a bike with a vertical fork for example, the wheel can be easily made to turn anywhere. It will not have the tendency to want to go straight ahead.

    Unless something is bent, caster should be OK, So have another look at the front axle body to ensure it is not deformed!

    One of your front wheels is too low on caster. Probably because either the top part of the strut is too far foward (improbable) or that lower suspension arm is too far towards the rear. If nothing else seems bent on that car, I would accept it as something you can not change. Just grin and bear it! I would make very sure toe and camber are OK, and rotate the tyres at every oil change.

  6. The Following 2 Users Say Thank You to foama For This Useful Post:

    hkpotts1 (07-12-2022),mohammad (07-12-2022)

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    Quote Originally Posted by foama View Post
    Caster is best described by looking at an "easy rider" motor bike. The very far forward front wheel, with the fork at maybe 45° angle is about the max caster you can think of. The more caster, the more the vehicle or wheel will want to go straight ahead. Low caster on the other hand, on a bike with a vertical fork for example, the wheel can be easily made to turn anywhere. It will not have the tendency to want to go straight ahead.

    Unless something is bent, caster should be OK, So have another look at the front axle body to ensure it is not deformed!

    One of your front wheels is too low on caster. Probably because either the top part of the strut is too far foward (improbable) or that lower suspension arm is too far towards the rear. If nothing else seems bent on that car, I would accept it as something you can not change. Just grin and bear it! I would make very sure toe and camber are OK, and rotate the tyres at every oil change.
    I think you are right that this is the course I'm going to have to take. In the right up from the collision center the sub frame was listed as needing to be replaced, and had markings on the side that caster is off, and could be throwing off the position of the control arm. Messing with the sub frame and the rack and pinion is something I'm not ready to get into, so I think I will just live with it and rotate tires regularly.

    Thank you all for your input!

  8. The Following User Says Thank You to hkpotts1 For This Useful Post:

    mohammad (07-12-2022)

  9. #7
    By subframe are you talking about the suspension crossmember? That's easy to replace. 4 bolts hold it in place. One bolt for the steering shaft, 2 ball joint nuts.
    The engine and transmisson bolt to the body not the subframe as mentioned earlier. Only one dogbone mount attaches to the subframe that stops the engine from rocking.


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