Measuring the free arc on a leaf spring

[Ed S.]

When measuring the free arc on a leaf spring (in this case a 64 standard suspension) does the spring have to be assembled (the 9 leafs plus liners secured together with the center bolt & nut torques to spec) or can the large spring be measured independently?

My spring is out of the car and apart. I ran a string through the center holes of the large leaf, distance from string to top of arch is 8.5 inches, should be 10 inches but.... is it 10 inches assembled or disassembled? Trying to determine if this original spring is usable.

[Ed S.]

Re: Measuring the free arc on a leaf spring

Called Eaton, got the answer - measure assembled with liners & center bolt torqued to spec. Good stuff to know.

[Gene M.]

Re: Measuring the free arc on a leaf spring

A free measurement sitting on the floor is not going to guarantee the car will sit at correct ride height and perform as intended. One needs to install and seat the spring with use then make height measurements of car. Only then are measurements of the car are meaningful to have the spring tweeted if necessary.

[Ed S.]

Re: Measuring the free arc on a leaf spring

Gene, I would have to agree with you. Ideally, the best way would be to have each spring or the entire assembly tested in some type of a device or jig that measures resistance at various degrees of deflection. Absent that capability, the next best option is trial & error. FYI - I reassembled the spring, came up with 9.75 inches of arc, thickness of each spring and all springs assembled with liners are within thousands of an inch of design. No way of telling if this spring is going to work without installing it. Next step - media blast and carefully inspect for hair line cracks. If I get a GO on that step then, paint, assemble, install and pray. Thanks for your advice.

[Joe R.]

Re: Measuring the free arc on a leaf spring

Hi Ed,

Scroll down to page 2 of this newsletter for an article on how to measure and re-arch your leaf springs off the car:

http://www.stlouisncrs.org/news_files/St_LouisNCRS_ChapterNewsletter2ndQuarter2012.pdf

Joe

[Ed S.]

Re: Measuring the free arc on a leaf spring

Joe - thanks for the reference, quite an interesting tech article and approach. As it turns out, I will install a new main leaf to replace the original that is pitted and scaled enough to question it's integrity. Secondary leafs are good. I am proceeding with this course of action after consulting with one of the best (perhaps the best) authorities on leaf springs in the NCRS. For those that might be interested, another article on Compression Ratios, authored by Duke Williams in the referenced newsletter is quite interesting as well. Thanks again for your assistance.

[Joe R.]

Re: Measuring the free arc on a leaf spring

Hi Ed,

I'm glad you enjoyed the newsletter! We are very fortunate to have guys like Frank and Duke contributing to the hobby!!!

Joe

[Ed S.]

Re: Measuring the free arc on a leaf spring

Joe,
I really did enjoy the articles, both were very informative and helpful. I wish there was a way to catalog, archive and search all newsletter tech articles. There is so much great stuff being done by members, it is unfortunate that it can't be easily shared and benefit a larger audience. Thanks again to Frank, Duke and all that submit tech articles.

[John L.]

Re: Measuring the free arc on a leaf spring

What is the torque spec for the center bolt and is there a special tool used to hold the round shaped bolt head in place when taking off the nut, or just use pliers? thanks

[Ed S.]

Re: Measuring the free arc on a leaf spring

John,

I checked the AIM for a torque spec on the center bolt. It is not listed. My guess is that it is not listed because the spring was delivered to the Corvette assembly factory in an assembled configuration. It was already assembled and torqued and not an assembly line function. By coincidence I called Eaton Spring a few minutes ago to order a new main spring. I also ordered a new center bolt because the Eaton bolts have the correct head height, 1 quarter inch - so it does not have to be ground down to fit inside the hole in the diff (carrier). I asked the sales tech rep what the Eaton recommended torque value is for that bolt. She said - "we don't have a torque spec for that bolt, only have values for U bolts (for straight axle applications). She recommended to clamp the spring as tight as possible then tighten the bolt as best you can. The objective is to have the bolt tight enough to preclude any movement between the leafs where they are in contact with each other.

I have learned from other threads that the best way to install the bold is to use an old bolt or a drift pin to ensure alignment of the leafs, then squeeze the leafs together with a two large C clams that are positioned on each side of the center bold but far enough from the bolt so you can get a wrench on the nut. Tighten the two C clamps as much as possible, - the leafs should be seated - then install the new bold and tighten it - tight! If the head of the bolt rotates hold it with a pair of pliers or vice grips - it should not take a lot of force to keep it from rotating as you tighten the nut with a deep well socket and ratchet. If anyone with experience in this process has more specific guidance, please advise.

[Joe R.]

Re: Measuring the free arc on a leaf spring

Hi Ed,

That is a great idea to get all the newsletter tech articles in one place. I'm not sure how to do that. But for starters, here is our newsletter page:

http://www.stlouisncrs.org/news.htm

Enjoy!
Joe

[Gerald C.]

Re: Measuring the free arc on a leaf spring

My "free arc" measures about 10 1/2". Does that seem reasonable???

Jerry

[Ed S.]

Re: Measuring the free arc on a leaf spring

Jerry,

I think 10.5 is too much arc. This pic is not my spring being measured - but it illustrates how it should be done - but ..... I think the string in this pic is not in the right place - it is not "at the top" of the hole - it looks like it is at the 3 o clock position - should be at the 12 o clock. The measurement will be off if the bolt is not tight and the spring is not compressed. Hope this helps. BTW - I am not an expert at this. I recently did a lot of research and am passing on what I learned - right or wrong.

[Gerald C.]

Re: Measuring the free arc on a leaf spring

Ed,

I used your string method and placed my string at the top of the hole and I get 10", so I think the spring should be in good shape.

Jerry

[Ed S.]

Re: Measuring the free arc on a leaf spring

The experts say 10 inches is correct. I think the tolerance is + or - .187 inches or somewhere in that range. Send my your e mail address - I will send you an article on C2 springs that is quite detailed.