Front Suspension Confusion

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domdart

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I have a 68 Dart with the 340 k-frame from a 72 Duster. It has 73 disc brakes. The 68 ride height is 2 1/8", 72 height is 1 5/8", and 73 is 1 7/8". My new front wheels (cragar 15x6 -6mm offset) and tires (BFG 225/60-15) stick out too far. To keep them from rubbing, I raised the front with the torsion bars. When the local old school suspension guy did my alignment, he wasn't comfortable with the results. He told me to bring it back up to him if I lower the ride height. The car drifts sideways when driving it, so I want to get the height, caster, and camber right. The car also has all new front suspension parts (ball joints, tie rods, bushings etc..). I put some 185's on it and lowered the height. I'm going to take it back up to the guy and I would like to have it set at the right height. What is the correct height? Does the 73 disc set-up stick out further? I found some cragars with a +6mm offset. I don't think the 12mm difference is enough.
 
The ride height measurement I get is 1 1/4". Her are some pics from this morning.
 

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strange - the disk brakes set up might be slightly wider but not enough to notice - I think the "problem" was the 225 60 15's and wheels.. you'd be surprised what a few mm's will do for tire clearance...
 
The '73 disk set up does stick out significantly further, the difference is close to a 1/2".

And a 12mm difference between a -6 and a +6 offset is also significant, that's also almost a 1/2" per side.

I ran 225/60/15's on my duster with 15x7" police rims, which have a +6 offset (4.25" backspace). The car was lowered from the stock height and had no issues with rubbing, although that's about as wide a tire as you can go with that backspacing.

As you know, the ride height also changes the alignment pretty substantially. Being raised up that far can make it impossible to get the correct alignment.

Also, is your alignment guy using the stock alignment specs? Because if you're running radial tires, the stock specs are wrong. Stock alignment specs are for bias ply's, which require alignment numbers almost opposite from radials. You should be looking for -.25* to -.5* camber, as much positive caster as you can get (usually +3* or so with the stock suspension parts), and about 1/16" toe in.

The car still looks like it's ride height is too high to me, but stock was pretty high and none of my cars are at the stock ride height so that may be part of the problem. And those 185's look like a pretty short tire.
 
After blu
The only thing I can add is that if you are set on those first wheels,you may have to install the Moog Problem Solvers to get the camber straightened up.And you may also have to trim the fenders for turning clearance.Setting the ride height for a wrong-way wheel-offset issue is not the best idea. Actually, that's being kind. The camber is best controlled when the lower control arm pivot points are parallel to the ground. You will experience the least amount of camber change, at this setting, with the wheel moving up and down over bumps and through dips. If/when the camber moves around, the car has a tendency to self-steer.That is to say wander and drift. In a turn, depending on the severity of the turn, you might not notice, cuz the outer wheel is taking all the load. However, when traveling in a straight line at 30 plus mph, if the road is not dead-flat or if there's a cross-wind blowing, this wander requires constant correction. At hiway speed this is just plain not safe.
Your alignment guy is in the best position to set the ride height, cuz he can see on the instruments, exactly what is going on. It will take him some extra time to get it right, so ask him to check the camber change from one inch down from LCA-level to 1.5 inchs up from LCA-level, and set the ride height where ever there is the least amount of camber change, in that range.If when in this position, the aforementioned .25* to .5* camber cannot be achieved or the caster goes negative, then the Problem Solvers will be needed.
After you get the car back, measure and record the exact position of the LCA, so that you can return the car to it if the T-bars sag. And Do Not change the ride height thereafter. If you change the ride-height, you will mess up the toe,mess up the on-center steering, and the car will quite likely eat front-tires.
So make the wheels fit the ride-height or buy new proper-fitting wheels.And if/when you do that, tuck them in as far as possible, to minimize wander due to a possible/quite likely, non-factory scrub-radius, which also causes wander.
Yeah I know, another long-winded post by AJ. I used to spend a lot of time rolling on the hiway miles. I hated that wander, however slight. Since I worked in an alighment shop and had unlimited use of the shop and equipment;one summer I decided to get after it. I will not tell you how many alignments I put on my 68 Barracuda.You might think me crazy. The above is some of what I learned.

You get it here for free!
 
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