simple transverse spring mount question

I did several searches on this subject, but none I read had a simple, straight foward answer. What is the best way to determine the distance between the spring brackets on transverse mounting brackets? Does Posies front spring thoughts apply to the rear also ? I have a 8 leaf spring of unknown make which measures 36" eye to eye, and speedway SS shackle kit, i'll make my own axle brackets, how much to add to the 36" + shackles? Some suggest some preload, others don't. I really don't want to have to do this but once!

 

I faced the same problem with a swap meet spring and a ford 9 inch.
I went ahead and preloaded the spring then measured it and located my brackets where the shackles would be at mid travel like Posies suggests. Turns out I was off by about an inch and the springs were compressed too much.
Rather than cutting and moving the mounts, I re-arched the spring to get the shackles back to mid travel. Re-arching the spring was pretty easy. There is a tech post in the archives on making a little fixture to re-arch springs.
There is probably an easier way but I always like to do things the hard way...

 

If your spring is 36" at the eye centers then it is probably around a 1940 or so. I have one in the attic that I can measure later today and get back to you. At least that way you'll know what you have. I also have a 40 axle and can tell you what the hole distance is on that to help you determine what you need.

 

Any help on this would be appraicated Mike, I would have thought more guys would have some input on this as a bunch of rides on here run 'em. Also, it may or may not be a '40, thought it seems to have more arch in it than the more flat profile of a '40 spring

 

You might just give Posies as call -- tell them you have their front spring and just had a quick question. They are typically good on the phone.

Dale

 

When I did mine on the T I added a half inch per side of preload since I'm not running a panhard bar. I just measured the spring eye to eye added up the shackel length at horizontal and added the half inch per side.
With the car on the ground and loaded the shackels are pretty close to the 45 degrees you'd like to see. In this picture the car is sitting on my sloped lawn.

 

How about putting a picture up so everyone can see it and maybe identify it.
What kind of car are you working on and what type of rearend are you putting in.

Also, normally you pick a ride height and work from there. The 36" spring eye to eye sounds short, although if it were a front spring that would mean the shackles were somewhere a little over 40" as the spring will probably deflect at least 3" if it were to carry about 600lbs. If that were the case the shackle brackets would be around 43" center to center.
If you have a spring shop close, I would take them the spring along with information on what you are trying to do and have them tell you what the Load Rate is.............this should give you the amount of deflection and you are home free.

But again, you need to determine ride height first, then work from there or you will be doing this again either moving the brackets or making a new main leaf.

The right way to do this is to reload the spring with the amount of weight you will be running.................then take the measure, you can't determine how much the spring is going to deflect unless you know the Load Rate.

Or.............give Eaton Spring a call and talk with them.

The picture of the bare frame shows that the shackles are not under load, or less than 50lbs.................the second shows about 250lb or half of the Load Rate of the spring.............with fuel tank and other full interior it will be another 250lbs which will be the shackles to 45 degrees................anything less that 45 degress will not let the shackles work and could cause bind and a harsh ride.

IMHO

 

Thanks for all the input, I've got the spring apart right now cleaning it up and tapering the leaves, so a pic is not possible. The frame back half is not built yet, I'm building the frame to suit the ride height of the spring/wheel/tire combo in relation to the front ride height

 

I agree with the other gentleman, that a 36" eye to eye length sure sounds like a front spring to me. Before you spend a bunch of time on it - you should insure that it is a rear spring. You don't want to be setting up your rear suspension to use a front spring -- you'll never get the ride you want.

 

BobbyD,

What kind of frame/car are you working on and what rearend are you putting in it?????????????
Is the spring going to be behind the axle or on top??????????????

Bored&Stroked is correct, the front and rear springs of early cars have vastly different Load Ratings.

The first picture of unprimed body shows actual "loaded" ride height, and the second in primer shows "unloaded" ride height.................there is a difference of at least 2/3" in the rear. It is very important to know what the load rating of the spring is and have the correct length main leaf..............or you will be starting over again.

IMHO