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Discussion Starter · #1 ·
My '71 Demon exhibits an alarming handling quirk. The E body 489 axle is three inches wider than an A body axle. To stop tires from hitting the fender lip, I mounted air shocks to raise the body.The shocks are plumbed In parallel, so that one or the other share common pressure, and transfer pressure to each other, depending on road surface. Front tires are 215-55-17, the rears are 235-55-17, The idler arm, ball joints, pitman arm and gear box check to be in excellent condition.
Driving on any crowned surface or un-even surface makes the front end squirrely by darting left and right to the point of being alarming. What could this be? the alignment was adjusted by a good shop about 2000 miles ago, and the rear axle checked to be at 0.27 degrees out of alignment.
Will narrowing the axle by three inches solve this problem? Is this and new springs and normal shocks the answer?
Thanks for any suggestions!
Ron.
 

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Have you checked the wheelbearings for being too loose? Grab the top of the front tire and push and pull from the side, see what happens and can be checked without jacking the front end up. Having air shocks to jack the rear end up to clear the wheel wells probably isn't helping either, he leveling feature may also be working against you. Have you tried looking at offset rims to get the tires inside the wheel wells, even though three inches is quite a bit of extra sticking out, would this be an option compared to finding an A body 8.75 or narrowing the rear end?
 

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Discussion Starter · #3 ·
Thanks Dana. I have the max wheel offset available from Coys Wheels each side is 1.5 inches further out than an A body axle. I did check wheel bearings, while under the car and on jacks. I'm tending to agree that the air shocks are the culprit. They must change rear camber enough to steer the car somewhat. Guess it's swap axles or narrow this one, and normal shocks as well. New springs might raise the rear enough to negate the need for air shocks, too, a less costly fix. Got some thinking to do!
Again, thanks very much for the valuable insight.
Ron
 

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There is no camber issue to deal with on the rear axle. However, you have increased the ride height which adds a little to the problem but you have classic example of front end alignment issues. Raising the rear changes the caster dramatically and it looks like the suspension has lost it's positive desire to self center.
 

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Discussion Starter · #5 ·
Your input is appreciated. The problem exists regardless of how high I raise the rear. If anything, it seems worse with the rear down around normal height. The shocks air pressure being higher may negate some of the transfer of pressure from side to side.
I just might give a new alignment investment a try, though.
Thanks much.
ron
 

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Remember anytime you change the ride height of a vehicle; it will throw off the alignment numbers, even on an 'Old School' RWD car with a straight (not IRS) rear axle. In other words; if your Demon was aligned with the rear end x number of inches up and you drop or raise it more than about one inch either way, you will upset the static (vehicle sitting still) camber/caster/toe angles up front.

Too; even if the rear end height height is 'dead nuts' to the last time you had your A body aligned, you could still have worn out lower control arm bushings (the ones in line with the Torsion bars) which WILL cause all sorts of nasty steering problems.
 

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Excessive camber on the front could cause this feeling.

So could caster, especially if you've raised the rear enough to create a positive caster situation, rather than negative.

Furthermore, the setup you've chosen acts not only as a shock, but as a sway bar. It is possible that the rear of the car is too stiff. If the rear of the car cannot roll effectively, more of the pitch in the road surface will be transferred to the frame, and this could (and probably will) cause weight to shift at the front, unloading one wheel while planting the other. If the load is unbalanced at the front, and the car passes over another pitch in the road, the car could dart to one side or the other. (Due to amount of grip, suspension geometry/compression, etc.)

It could also just be that the road is that bad that the car finds it easier to follow the ruts than to ride over them.

Porsches use wider rear tracks than front tracks, so you may research this issue in relation to their cars for some other clues.
 

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Jerry Simcik said:
Excessive camber on the front could cause this feeling.

So could caster, especially if you've raised the rear enough to create a positive caster situation, rather than negative.

Furthermore, the setup you've chosen acts not only as a shock, but as a sway bar. It is possible that the rear of the car is too stiff. If the rear of the car cannot roll effectively, more of the pitch in the road surface will be transferred to the frame, and this could (and probably will) cause weight to shift at the front, unloading one wheel while planting the other. If the load is unbalanced at the front, and the car passes over another pitch in the road, the car could dart to one side or the other. (Due to amount of grip, suspension geometry/compression, etc.)

It could also just be that the road is that bad that the car finds it easier to follow the ruts than to ride over them.

Porsches use wider rear tracks than front tracks, so you may research this issue in relation to their cars for some other clues.
Lifting the rear of a vehicle will drop, not 'raise' caster. In other words; the imaginary line(s) between the upper and lower balljoints will tilt forward at the top. '\' is positive caster, '|' is zero (0) caster and '/' is negative caster if viewed on the RH side of a vehicle, reverse those images if looking at the LH side. :)
 

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How is going from a negative measurement to a positive one a drop??? We're saying the same things, but I disagree with your terminology.

(BTW, I said "raised the rear.")
 

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A positive caster causes the car to lift (ever so slightly) when the car is turned and that is what causes the steering wheel to want to return to center. (both tire/wheels want to get back to the lowest point) "0" gives no direction to the tire/wheel and therefore they can go whatever way the bump suggests.
Camber usually is set to have the top slightly out from the bottom so that the tire/wheel wants to turn outward causing any slack in the tie rods to be compressed making for a positive action to the steering.
Also the angle between the upper ball joints and the centerline of the tire assembly is set to be usually slightly inside of the middle of the tire causing the tire to also want to turn outwards complementing the camber setting. Having the two angles meeting near the center of the tire lessens the affect of bumps making the steering wheel jump and turning easier at all speeds.
Each setting causes an effect that reacts with other settings.
Any one of these not being correct can upset the balance of the steering and cause the steering to wander or even go to a death wobble.
 

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Discussion Starter · #12 ·
Info overload! Many many thanks, gents. For your consideration, the whole front end component catalog is near new (3700 miles), including rubbers. The LCA 's are "B" body ,as part of the disc brake conversion from MP Brakes. The air shocks allow the rear end to compress the axle on one side and extend the other when parked on an un-even surface. I'm thinking that this is occurring while driving on crowned surfaces, where the problem exists. Today I'm going to check the strut rods for proper tension.
 

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Jerry Simcik said:
How is going from a negative measurement to a positive one a drop??? We're saying the same things, but I disagree with your terminology.

(BTW, I said "raised the rear.")
As I stated: lifting the rear of a vehicle will drop AKA make the caster more negative since the upper balljoint effectively goes 'forward' vis a vis the lower balljoint.
 

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Wow - yep, my bad. Totally had my negative and positive quadrants mixed up. (I was thinking "/" was negative for some reason...) Sorry!
 

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Bearhawke said:
As I stated: lifting the rear of a vehicle will drop AKA make the caster more negative since the upper balljoint effectively goes 'forward' vis a vis the lower balljoint.
And changing a car designed to have positive camber to a negative camber will totally erase the self centering action causing the steering to want to wander.

No two engineers agree on how to have the best suspension but both can achieve good results using a different direction getting to the same end. Understanding which direction they used is the key to making it work right.
 

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Jerry Simcik said:
Wow - yep, my bad. Totally had my negative and positive quadrants mixed up. (I was thinking "/" was negative for some reason...) Sorry!
It's all good :)
68RT said:
And changing a car designed to have positive camber to a negative camber will totally erase the self centering action causing the steering to want to wander.

No two engineers agree on how to have the best suspension but both can achieve good results using a different direction getting to the same end. Understanding which direction they used is the key to making it work right.
Camber? I think you meant to say caster? :runaway:
 

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Discussion Starter · #17 ·
I'm leaning toward caster being the cause. I'm going to inflate the shocks to full extension and test drive on a crowned road. This may point to the fix. If the wandering changes, the shocks are toast, and new springs and shocks go in .
 

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Discussion Starter · #18 ·
Eureka! The fully extended shocks have effected about a ninety percent cure to the squirrely handling. Most of you geniuses pointed to caster as the problem. It appears that caster is the issue. By inflating the shocks to max height, I have effectively moved the upper control arm center ahead of the lower. now, the steering does not return to center like it did. Could be my bad for over tightening the free play adjuster. Easy fix.Now, so many thanks for the help and patience. You guys are the best. I only hope I can offer some more useful advice as well.
 
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