How are Springs measured?

I'm posting this over here in 'Early' CJ5 since the springs seem to run from '55-'75, but I'm trying to replace the front springs on my '73.
I'm trying to determine the distance Eye to Eye of the front and rear leaf springs.
And an arc (offset?) measurement would be nice also.

I see 'length' shown (39.75") in the tech manuals but I can not for the life of me determine if that measured eye to eye or overall.
I may be assuming incorrectly but I like to know the dimension as the spring is laying flat on the ground (after tipping & smashing one's toe...)
no load just free state.
I'm going off of the Section_12 portion of the 1972 TSM over at oljeep. (I think, maybe, kinda, perhaps... )

My mind has gone numb with all the searches and the conflicting information I've found out there.

Thanks,
_Dan

 

IIRC the Alcan site has a good diagram - http://www.alcanspring.com/faqs.htm

If anybody has an idea what the convention is, they will.

 

Its measured along the inside curved surface, not a straight line eye to eye

 

Thanks Tim, they did. I missed that section in all my searching this morning. I am sure getting burned out with all this searching.
I'd rather have a ratchet in my hand than a mouse ...

It appears that the importers are doing this. Gives them a great deal of leeway in regards to tolerance.
They don't have to worry about getting the springs in correct form just so long as the curved surface is at 'X' dimension.
The sketch below shows this exaggerated, but the point is that you can achieve the curved surface dimension but your eye-to-eye dimension
would be incorrect and would have to be taken up by the movement in the shackles. And the arc dimension to the center line between the eyes
would produce lift or lowering depending on what it came out to be.
It is not the proper way to dimension a manufactured piece part or assy and if you were tasked with having to design the tooling to fabricate it
you would not have enough data to fabricate the tooling. And nowhere in the TSMs, that I have seen, do they show a 'curve surface' dimension.

 

The spring shop that did my springs told me that was the correct way to measure. I measured original factory springs the same way and it was the correct length. Not 100% sure

http://www.eatondetroitspring.com/how-to-measure-leaf-springs/

 

Thanks, that is one more link to add to the reference page I'm building.
But the method outlined still leaves me scratching my head. I have only run across one page that even shows the spring arch dimension.
General spring shows the surface dimension & spring pack dimension but no dimension for the arc.
None of the TSM's or charts I've seen for our CJ5's shows arc or arch. And I can't see how without that you can properly determine your mount points.
Realistically you could have 36" between the eyes and still have the surface dimension held and a rather big arc.
That wouldn't be easy to mount.

_Dan

 

Another reference

 

See ! We're all right

 

hehe, right would be - being able to afford to send it to a shop and saying "Make it Right!"
I really, really didn't think two weeks ago that I would be expending this much energy on leaf springs.

Thanks eveyone for the effort in this quest. It's going to make for one heck of a "Tech Thread" maybe even a short story.
But then what else is new in regards to this affliction?

_Dan

 

and now straight from the 1972 TSM, Section 12, Page 12-5 (from oljeep site) we present an extra 1/8" for everyone's enjoyment:
(not to mention completely different method of specifying spring rates...) (1974 section 11 is the same dimension - 39-3/4")

 

Here's a neat bit of tech info from Eaton's Site back in 03-2000 -=-LINK-=- (courtesy of The Wayback Machine and Archive.org)

Eaton's How-to from 2000 (07/99) -=-LINK-=- (courtesy of the Wayback Machine and Archive.org)
Pretty much the same as above, just in an engineer's form.
(edit: or as I just noticed, the same as the "Download Leaf Spring Measuring Form" Link on the current page...)

Learning more & more with each passing minute - wonder if I'll ever get the Jeep® ready for the road....