Does your Duster "float" at highway speed?

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AJ/FormS said:
Lotsa of good advice but nobody asked about the width of the rims, the tire pressure and/or the scrub radius. Never mind the shocks.
If the backspace of your non-stock wheels is not the same as the front space, ie; zero offset, like the factory front end was designed for, then the center of the tire's contact patch will not be in the right place relative to the Steering axis inclination; same goes for a tire height that is different from the stockers.
Definitions and Explanations of Suspension Alignment Terms
When this happens, the edges of the tires try to climb up every little rut ,cup or wagontrack in the road. And you perceive it as a constant nervousness. You can mitigate this with lots of tire pressure, but it never really goes away.
You have to fix this or live with the problem.

You can almost make your Duster drive like a SuperCar, you just need to know how. I won't say that my 68 Barracuda drives like a supercar, but it might have followed a newer Corvette for several hours at speeds of on/or about 120mph.

5* castor in an A-body, with zero to .5*neg camber, is very difficult to achieve , even with the Moog offset bushings. My guess is that your tail is a lil low to get that much. If so, then you gotta fix that first. The front has to be a lil down; I set my front ride-height in the center of the best part of the toe-change/bumpsteer pattern, and then adjusted the rear height to be about a half to 3/4inch higher as measured at the extreme ends of the rocker-panels.

Another thing is "bumpsteer" . I had to fix mine which took me hours and hours on an alignment rack. Mine was created by the 5* of castor at zero camber. I eventually dialed it back to [email protected] neg camber. I eventually gave up a lil more camber for street use. which gave me back some castor. But required the bumpsteer to be revisited.
The point is that those angles are ALL inter-related and ALL tied to eachother. And there is no good reason to try to run a race alignment on the street.
BTW
There are a couple of ways to attack/adjust the infamous over-boosted/ numb feedback, of the Chrysler P/S box; and the parts involved are cheep. I now run a very small steering wheel, to make it even faster.Not a faster ratio; just less arm-motion. The factory Barracuda steering wheel is well suited to driving a school-bus; but not at all well suited to driving a street-bomber.
My car is a street-bomber, and a manual-trans; so I steer with the left hand and hang the heck on with the right,lol. I left enough boost in the steering system to make this a pleasant experience.
Click to expand...
Thanks for all the info! Much appreciated! This gives me something to talk to my shop about making my car drive the way I would like.
 
1975 Duster 318 with Power Steering and mostly stock style suspension: I'm currently having this same problem and no help from the alignment shops. Two of them, so far, have sent me home with my wheel turned 90 deg. to the right and said they couldn't fix it (fixed it myself). They could only achieve about 1-2 degrees caster, but also added back rubber behind my strut bar mounts, reducing caster. Mine used to track fine on the freeway at speeds of 80+ with old suspension on old tires. I recently rebuild the front end with .940 bars, new bushings, offset UCA bushings, ball joints, tie rod ends. Adjusting my wheel straight, and therefore centering the range of travel on the steering gear helped a bunch, but it's still not good on the freeway. My next move is adjustable strut bars to maximize caster just short of causing binding in the LCA. I do have one LCA pivot that wollowed out years ago and I had modified a strut bar with threads and jam nuts to compensate. Might just be the key here. Anyway, that's my story - good luck and keep us posted.
 
So much can affect all this INCLUDING REAR SUSPENSION

Decent springs
Decent shocks
Decent tires, not just tread, but tires that will HANDLE Lots of cheap tires don't
Proper alignment. Don't just go changing alignment unless you have reason. The infamous "skosh" chart is a good start
Loose bushings, ANYTHING hardware loose can cause this
 
shittyslant6 said:
Yeah I don't drive mine above 70 becuase It gets a lil tooooo floaty. it's an old car. it's how it is.
Click to expand...

Even when my dart was stock, it never floated, even at 115mph. A slant six car, was never too light in the front.

Dave Huth said:
I had a 68 Charger that floated. The stock steering box had play that couldn’t be adjusted out. Make sure your box is tight.
Click to expand...

This is a biggie as mentioned. Also, bushings are old and, more specifically, these cars are known to break out the location sleeve for the lower control arms.

Modern tires and shocks help a lot, and a full rebuild with better t bars will put it on rails and sacrifice virtually nothing as far as ride.
 
AJ/FormS said:
Lotsa of good advice but nobody asked about the width of the rims, the tire pressure and/or the scrub radius. Never mind the shocks.
If the backspace of your non-stock wheels is not the same as the front space, ie; zero offset, like the factory front end was designed for, then the center of the tire's contact patch will not be in the right place relative to the Steering axis inclination; same goes for a tire height that is different from the stockers.
Definitions and Explanations of Suspension Alignment Terms
When this happens, the edges of the tires try to climb up every little rut ,cup or wagontrack in the road. And you perceive it as a constant nervousness. You can mitigate this with lots of tire pressure, but it never really goes away.
You have to fix this or live with the problem.

You can almost make your Duster drive like a SuperCar, you just need to know how. I won't say that my 68 Barracuda drives like a supercar, but it might have followed a newer Corvette for several hours at speeds of on/or about 120mph.

5* castor in an A-body, with zero to .5*neg camber, is very difficult to achieve , even with the Moog offset bushings. My guess is that your tail is a lil low to get that much. If so, then you gotta fix that first. The front has to be a lil down; I set my front ride-height in the center of the best part of the toe-change/bumpsteer pattern, and then adjusted the rear height to be about a half to 3/4inch higher as measured at the extreme ends of the rocker-panels.

Another thing is "bumpsteer" . I had to fix mine which took me hours and hours on an alignment rack. Mine was created by the 5* of castor at zero camber. I eventually dialed it back to [email protected] neg camber. I eventually gave up a lil more camber for street use. which gave me back some castor. But required the bumpsteer to be revisited.
The point is that those angles are ALL inter-related and ALL tied to eachother. And there is no good reason to try to run a race alignment on the street.
BTW
There are a couple of ways to attack/adjust the infamous over-boosted/ numb feedback, of the Chrysler P/S box; and the parts involved are cheep. I now run a very small steering wheel, to make it even faster.Not a faster ratio; just less arm-motion. The factory Barracuda steering wheel is well suited to driving a school-bus; but not at all well suited to driving a street-bomber.
My car is a street-bomber, and a manual-trans; so I steer with the left hand and hang the heck on with the right,lol. I left enough boost in the steering system to make this a pleasant experience.
Click to expand...
How do you adjust the overboosted steering box?
 
92b said:
Thanks, I'll check that out.
Click to expand...
I have added and subtracted shims ad nauseum, and have come up with some small positive results. (/6 duster) I purchased a new fitting that boasts it does the same thing better. I will get on that swap next week. It may not be this particular one, but similar. Do homework before buying.

Saginaw Power Steering Pressure Reducing Kit | eBay

This is the shim kit that I used with some positive results.

Borgeson Universal 899001 Borgeson Universal Power Steering Pump Pressure-Reducing Kits | Summit Racing
 
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