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Should my springs have an arc?
https://www.slantsix.org/forum/viewtopic.php?t=5769		 Page 1 of 1
Author:  Travis Bickle [ Thu May 15, 2003 9:00 am ]
Post subject:  Should my springs have an arc?
I have a 68 Dart, with slightly wider tires than stock. When I hit a pothole (mostly on the right rear), or corner with a back seat passenger, the tire sounds like it bottoms out in the well.

[Originally it had a set of 4 leaf springs, with coilover shocks that were in pretty bad shape. I could not find replacements for the coilovers, so I had a friend put on a set of used 5 or 6 leaf springs, (i forget) :) and new monroe shocks.]

I notice that when the car is on the ground now, the leaf springs run in a straight line. Is this normal?

I need to find a solution, one suggestion I've had is to put air shocks on, but transfering the weight to the shock mounts just sounds like a bad idea.

Any Suggestions?
Author:  Eric W [ Thu May 15, 2003 12:56 pm ]
Post subject: 
If I remember right, the shop manual says that the springs are supposed to be like that. By being flat, it helps side stability and ride. It also says a littel reverse arch is also normal. My Satellite is like this and rides nice and firm with HD gas shocks. My friends stock '68 RoadRunner and Coronet are the same way. So for stock springs, I'd say your OK.
Author:  bud L. [ Fri May 16, 2003 5:55 pm ]
Post subject:  4wd
I have had a coupla Dodge 4WD's and the frt leafsprings are reverse arched. They ride like crap, so I always wondered if the springs were arched 'normally', would it ride any better?
Author:  Matt Cramer [ Fri May 16, 2003 6:36 pm ]
Post subject: 
Travis: The springs should normally be flat like yours. In your case, the wider tires permit less travel. You could cure this by raising the rear and adding more travel, or increasing the stiffness so it doesn't bottom out. I prefer stock or slightly lower ride height, so I would increase the stiffness - either by adding more leaves, or a set of clamp-on "add-a-leaf" helper springs.

Bud: You'll have to give a more precise definition of "ride like crap." If the ride is simply too stiff and harsh, a higher spring arch alone will not cure it. Raising the ride height while decreasing the spring stiffness may work. If it more along the lines of a twitchy handling that will dart this way and that over potholes, you have a more complicated suspension geometry problem. Changing the spring arch may affect this, but you <i>really</i> have to know what you're doing if you want to cure a suspension geometry issue.
Author:  bud L. [ Fri May 16, 2003 8:31 pm ]
Post subject:  more
It doesn't handle strange, there is just no compliance. In the regular rear leaf, it is obvious where the jounces go. They're absorbed in the rear half of the leaf, and the deflection of the rear shackle. But in my frt leafs, it 'looks' as though they're already 'jounced' and there is nothing left to absorb a jounce. Hey, I am no professional engineer, it just looks like that to me. I don't think it is worn out or anything, because I've owned it since 40K(it's always been that way), , and I've seen other brand 4WD's that look exactly the same. Maybe they are trying to limit the 'spring lengthening' to avoid steering geometry problems. Any more frt leaf 4WD's out there? You know what I am talking about?
Author:  Matt Cramer [ Mon May 19, 2003 7:39 pm ]
Post subject:  Upside down leaves
A leaf spring will bend until either it breaks or something stops it, so the amount of arch has almost no effect on ths spring rate. Although springs that are higher at the ends are the most common, there is no trouble with designing a leaf spring to work "upside-down." The limit on how much travel in jounce it can absorb is determined by the distance to the bump stop (or whatever else it might hit if the bump stop has rotted away).

BTW, the front (or frame-mounted) half of the leaf spring absorbes some of the impacts too, but on most Mopars it's not as much as the rear (or shackle-mounted) section. IIRC most four live axle setups put the shackle at the front suspension on the front end.
Author:  Travis Bickle [ Tue May 20, 2003 11:24 am ]
Post subject:  tire damage
Update: I've lifted the car, and noticed that the tires are actually hitting the the fenders. There are no scuff marks in the wells, but there is damage to the lettering on the sidewalls. How much is the rear supposed to sway? I'm guessing my only option is to replace the rims with something that has a shallower dish. $$$$ :( I can barely get my fingers between the fender and tire when parked, havent tried it running yet :lol:
Author:  Dart270 [ Tue May 20, 2003 4:44 pm ]
Post subject: 
With stock bushings and geometry, the wheels will move back and forth 1/4-1/2" or so. Polyurethane spring bushings will reduce this to 1/4" or less. You are right that narrower tires, or less dish on the rims is the only sure fire way around this, but the poly bushings may get you where you want to be.

Wear good running shoes, and watch those fingers on your second test... :lol:

Cheers,

Lou
Author:  Travis Bickle [ Wed May 21, 2003 12:56 pm ]
Post subject: 
Poly urethane bushings!!! great idea.

I started looking into the kits, and I think I'd like to do the front end as well. looks like I have my summer project!!

:D
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