Measuring the free arc on a leaf spring

[Gene M.]

Re: Measuring the free arc on a leaf spring

Guys as I stated the proof is installed in the car and seated with a short ride where does the car sit. All the measurements in the world will prove nothing. Not every spring (especially replacements) is spring tempered as the originals. Some are good results others fit like crap. But measure away if that's your bag.

[Ron G.]

Re: Measuring the free arc on a leaf spring

Just my 2 cents. I am not an expert on measuring a rear springs arc, but I can tell you that the 63 -64 rear springs are different in their arc compared to later mid years and C3's. Like you said Ed, the proof is in the way the car sits when it is all done.

[Duke W.]

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

The only real purpose of that bolt and nut is to hold the spring together during shipping and handling. Once installed on the axle it's redundant. You can use vise grips to hold the bolt head. Since it's not visible when installed "tool marks" are inconsequential. Just make the nut is "tight" and use blue Loktite if you want insurance.

Duke

[Gene M.]

Re: Measuring the free arc on a leaf spring

The only real purpose of that bolt and nut is to hold the spring together during shipping and handling. Once installed on the axle it's redundant. You can use vise grips to hold the bolt head. Since it's not visible when installed "tool marks" are inconsequential. Just make the nut is "tight" and use blue Loktite if you want insurance.

Duke

The bolt head does serve to center locate the spring in the hole of the rear end cover. It also keeps the side to side lateral position leaf to leaf in place.

[Duke W.]

Re: Measuring the free arc on a leaf spring

...agree with your first point, but there's no way that little bolt could keep the leaves aligned in any type of use. It's the big plate and four big bolts that provide high clamping force through a lever arm that keeps the leaves aligned in normal road service or racing.

[Gene M.]

Re: Measuring the free arc on a leaf spring

...agree with your first point, but there's no way that little bolt could keep the leaves aligned in any type of use. It's the big plate and four big bolts that provide high clamping force through a lever arm that keeps the leaves aligned in normal road service or racing.

Your comparing the clamping friction force to a shear force on the bolt. Ya gotta be kidding that bolt don't align the leafs end for end.

Without the bolt the leafs would be all over the place. Just not logical.

[Richard M.]

Re: Measuring the free arc on a leaf spring

Ed,

I had a similar issue with a 1967 F41 Rear Spring. The lower leaf was compromised when I took it apart and found a large rusty divot hidden by the next upper leaf. I acquired a replacement lower leaf from Eaton. I was concerned that the assembled spring would be out of spec but fortunately it was fine on the final result after installation.

As you can see the arc of the original and replacement were very close.

Original(painted light grey on right), Eaton replacement darker dull grey on left). There was a noticeable kink on each end of the original.


Also below is a reference photo sequence of my rebuild process. It shows the clamps to hold the leaves together before tightening the center bolt. Also shown is the "wrong" length bolt head, which I had to grind to fit. I suspect you already know this, but to avoid differential case damage ensure the full weight of the car is set after a roll-out to stabilize the suspension before you torque the 4 spring bolts.

Rich

[Ed S.]

Re: Measuring the free arc on a leaf spring

Richard,

Thank you - your post is very informative, a great how-to. Among other things one can see that all leafs are arced in an F41 spring vs the last 3 being flat for the standard spring. I am sure many will benefit from your posting in the future.

BTW - re torquing the 4 bolts that hold the spring & plate. I am very aware of that important detail. Not only that but..... I believe you don' torque them down until the car is at the correct ride height as well. And.....from carefully reviewing the AIM I also learned that a number of fasteners associated with the rear suspension are not to be torqued until the full weight of the car is on the suspension. It is just not the 4 spring bolts. Of course this only applies if you went beyond removing & replacing the rear leaf spring. I did that and one additional fastener that comes to mind that must be torqued with the weight on the car on it is the front trailing arm bolt - the one that secures it to the chassis. Thanks again for the great pics.

[Duke W.]

Re: Measuring the free arc on a leaf spring

Your comparing the clamping friction force to a shear force on the bolt. Ya gotta be kidding that bolt don't align the leafs end for end. Without the bolt the leafs would be all over the place. Just not logical.

If you had ever studied mechanical design you would have learned that you never, ever allow a bolt to be loaded in shear. If the static friction from the applied clamping force is less than applied shear load, the bolt will likely break. The retainer plate and four large bolts provide more than enough clamping force to overcome any tendency for the leafs to move either fore-aft or side to side.

[Gene M.]

Re: Measuring the free arc on a leaf spring

If you had ever studied mechanical design you would have learned that you never, ever allow a bolt to be loaded in shear. If the static friction from the applied clamping force is less than applied shear load, the bolt will likely break. The retainer plate and four large bolts provide more than enough clamping force to overcome any tendency for the leafs to move either fore-aft or side to side.

Yes I have an engineering design background and you are making assumptions in static and dynamic system and overlooking the initial assembly that positions all the leafs in proper position prior to initial loading the spring prior to final tightening the four 9/16" bolts with the full loading of the car. It is not the shearing of the bolt that concerns me but the initial position of all the leafs prior to completed assembly procedure. Also your assumption of my mechanical background is flawed also. Thought prior to statements is essential.

[Duke W.]

Re: Measuring the free arc on a leaf spring

Yes I have an engineering design background... and overlooking the initial assembly that positions all the leafs in proper position prior to initial loading the spring prior to final tightening the four 9/16" bolts with the full loading of the car.

...doesn't sound like it to me... where did you study mechanical design? I did mine at the U. of Washington ME Department. Like I said earlier I agree with your first premise that the small center bolt helps locate the spring laterally. However, once the four big bolts that secure the spring to the carrier cover are tightened, you could drill a hole in the plate, remove the small nut, and this would have absolutely no effect on spring security.

[Gene M.]

Re: Measuring the free arc on a leaf spring

...doesn't sound like it to me... where did you study mechanical design? I did mine at the U. of Washington ME Department. Like I said earlier I agree with your first premise that the small center bolt helps locate the spring laterally. However, once the four big bolts that secure the spring to the carrier cover are tightened, you could drill a hole in the plate, remove the small nut, and this would have absolutely no effect on spring security.

Your slander of my background holds no merit with me. And I could care LESS of your educational claims. Again not impressed. My design back ground is none of your business. Being I have no need to impress nor satisfy any ego. I choose not to submit especially with your losing argument. End of discussion.

[Alan D.]

Re: Measuring the free arc on a leaf spring

Another picture for reference, may help? Mar 64 original spring, taken around 2000 (It was cleaned, not blasted, and then painted with Ionokland)