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Old 09-25-2006, 05:20 PM
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Coil Over Shocks

I have a pair of used( E Bay specials) Koni coil over shocks on the back of my 28 Model A coupe (2700 lbs) . The problem I have is that it rides rougher than hell. I have 12" 150lb springs on it, the shocks are 15 5/8" extended and 9 3/4" compressed with a 12" ride height. Should I be using 10" springs so I can soften up the ride and if so what rate springs? The Koni coil overs are not adjustable as far as the valving just the ride height.
Thanks - Jerry

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Old 09-25-2006, 06:31 PM
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I would call Koni with the model number to see just exactly what you have..Most likely the shock valving is real stiff so you will get the hard ride no matter what you do with springs..the Koni's I have had anything to do with were rebuildable so the shock valving is changeable..You may also have some very old models of shocks as well...

Sorry..I would have to have them in hand to figure out just what is going on..

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Old 09-25-2006, 06:57 PM
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The difference in spring length alone won't make any difference in the harshness of the ride, and you need the length to make sure you have a few turns of preload on your retaining collar.

How are the shocks mounted now? if they are straight vertical you can angle them and soften them up. Taking a set of vertical shocks and laying them over 20* will make the effective spring rate 88% of the true rating. This would help with a stiff valving also.
If you can't angle the shocks some more then you probably need to change the spring rate to soften it up. Check the speedway catalog, there is a good selection of springs to pick from.

IIRC the 2 1/2 ID springs will work on the Koni shocks. Although they might be a little loose

The chart they provide is kind of confusing as it has no springs with your installed length. If you look up the spring reccomendation by the stroke it says 200# rate for a 1450# rear weight and a 140# for 1250# rear weight.

I think if you have 150# now you would do better with a set of 125#. They have 95# also in a 12" length but that might be a little soft unless you have a bunch of travel.

One More Time may be on to somethin there with the valving, He has probably played with morte of those than me.

Someone may have a better specific reccommendation based on experience.

Later, mikey
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Old 09-26-2006, 02:10 PM
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If your ride height is currently where you want it, then you will need stronger springs if you change from 12" to 10" springs.

I have just gone through changing coil over shocks and springs on the rear of my 1939 Olds (3500 lb total). It had "drag shocks" on it and was very harsh. I installed QA1 adjustable shocks and the ride is much better. But it took me a while to understand the function of springs and shocks, and how they work together and complement each other.

For a comfortable ride you want to use longer shocks and long soft springs. For a stiffer ride and better handling you want to use shorter stiffer springs and you might have to go to shorter shocks to get the right fit and ride height.
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Old 09-28-2006, 02:26 PM
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Spring free height has nothing to do with rate.

Springs just hold up the car, and the shock slows down the springs movement.
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