front spring narrowing calculations ???

I am about to take the '38 Ford front spring I have in to have it narrowed as I need to move it behind the axle and I'm splitting the bones. With the whole suspension on the ground the spring shackles were level and the eye to eye centres were about 996mm apart.

After I removed the spring from the suspension it curled a bit more to it's "relaxed" position and the eye to eye centre measurement shrunk to about 945mm (that's with 3rd and 4th leaf from bottom broken in the middle).

I calculated the new eye to eye centre measurement to be between 795mm and 800mm in the new position, but that's with the shackles at about 45 degrees downwards towards the spring. In the end I want this new measurement to be the "final" width after the engine's weight has been placed on it.

How wide do I specify to the spring shop to make it???

I'm also going to ask them to reverse the eyes for that extra bit of lowering effect.

 

bttt

 

Remember that the spring was designed to be mounted under tension on the Fords. I would guess the best way to "guesstimate" this would be to use the spread original eye to eye width and "relaxed" original eye to eye width measurements and figure the percentage of reduction to your new perch measurements. Transfer this reduction percentage to the spring and see how things work out.

 

I don't know about calculations, but if the original lower spring is "s****" then cut it down the middle, cut sections out and bolt it back up with a large G clamp until its the right length to use. Then you'll know for certain the proper length to ask for when having one made.

 

I thought about this but wasn't sure if there was a more accurate / scientific way.

Thanks for the replies.

 

Based on the Speedway catalog, and my experience installing a Posies front on a Model A, here's what worked for me: Measure the eye to eye center distance where the shackles will attach to the bones. If you are using shackles that are 1-1/2" long (not wide), subtract 3" from the above measurement. That should be your spring eye to eye (centerline) width. The idea is to install the spring with the shackles horizontal and very little tension on the spring when there is no weight on it. When the weight of the car is applied the shackles should go to the 45 degree position ***uming the spring pack is correct for the weight of the load.

 

Thatnks Bob. That work for me.