Mooser: Any other changes like where the spacers were for each spring? Were both springs flat up against the diff? Thanks for all the great information.

 

Spacers for both were as supplied. The TRW style one has a thicker stack of stuff on the top but also has a set of steel side-plates to prevent you from over-tightening the glass spring. then a fiber/plastic material spacer that goes between the metal plate and the diff




That top stack is about 1" total. The fiber spacer has the "dink" that locates the mount into the rear, but maybe you could remove it and mickey mouse something up and raise the spring up 3/8" which I believe would be a straight 3/8 at the wheel well


The Van Steel one (shown) has only a plastic spacer at the top and a larger spacer at the bottom to make up the total thickness



So interesting enough, it's probably 3/4" or better higher at the differential that the TRW

One thing I did notice is that the TRW spring moves quite easily for the first couple of inches and then stiffens right up while the VanSteel moves only a fraction before stiffening up. That shows when you look at the difference in free-arch of probably 2~3 inches vs installed or 1- 1 1/2"
M

 

Nice setup! Flat half-shafts, almost flat spring, and short bolts!

Would you remember which spring it was you used? Was it a low arch version or just a std VBP? Anyone ever measure the arch before you put it on?

 

It's a standard VBP spring. Their softest; I believe a 315 lbs? I don't remember measuring the arch but it was much less than the TRW style I had before.

 

Someone sent me an arch measurement of 4.5" for a 360lb VBP spring. That sounds like a low arch one to me.

The sprung weight in the back of a 71 Vette should be about 1420lbs. That 360lb spring would straighten out (compress) 3.9 " to hold it up.(1420/360) Leaving only 0.5" arch left after it's installed.

The springs that need 10" bolts still have 1-2" of arch left after they are intsalled.

My guess is the "too high" TRW spring starts with an arch that is at least 1" too high, like around 5."-6"

A softer spring like the 196lb 9 leaf stock ones, would have to compress 7.25" to hold the same weight. So it probably starts around 7.75"

You know I have a stiff 7 leaf out in the garage. It's not OEM it's by Triangle spring. I should go measure it.

 

Stolen from another post:

Eaton Rear Steel Spring Information.

The most popular rear leaf springs used were 2 different versions of a 9 leaf springs and a 7 leaf spring. A 10 leaf spring was used very sparingly. The differences between the springs were their rates. The down and dirty description of rate is it is the amount of weight required to deflect a spring one inch. The higher the rate, the stiffer the spring. The 7 leaf spring has a rate of 305 lbs. The 9 leaf spring which all 9 leaves are curved has a rate of 196 lbs. The 9 leaf spring which the 1st 6 leaves are curved and the shortest 3 leaves are straight is a 2 stage or variable rate spring. It's rate starts at 140 lbs and increases to 196 lbs when all the leaves are touching.

The loads they were designed to carry are all pretty much the same. The 7 leaf has a design load of 1,325 lbs. Both 9 leaf springs have a design load of 1,360 lbs. All 3 springs are designed to have a 3/8 reverse arch when at their design load. In order to accomplish the same spring height when under load with the spring having different spring rates, the free arch of each spring is different. The free arch of the 7 leaf spring is 5-7/8 inches. The 9 leaf spring is 7-1/2 inches and the 6/3 spring is 8-11/16 inches. The correct way to measure the free arch is for the spring to be off the vehicle. Place a straight edge across the ends of the spring and measure down to the main plate next to the center bolt.

While we use the correct type of steel, SAE 5160 High Alloy Spring Steel, the thickness's have been adjusted to sizes the steel mills now produce. Way back when the mills would produce quantities as low as 5 tons of a size. Today 22 tons is the bare minimum of one size they will produce. And that is a lot of Corvette springs. While the overall thickness of the springs have slightly increased, the fit, feel and performance of the springs are unchanged. However the free arches have been lowered from the original factory specs in order to maintain stock ride height.

 

So if the stock steel springs were 140, 196 or 305 lbs per inch of deflection, then it might make sense that putting composite springs with 300, 330, 360, or 400 lbs (assuming they are measured the same way) would not deflect as much and would require much less arch for us to end up close to the stock heights on our cars.

 

I was glad to see some Eaton information. I was currently compiling some of this data on my own. Thought by sharing data between us we could all help each other.
Does anyone have any "Free arch" measurements for any type of rear spring they could share? Please mention what kind & rate of spring.

 

That's great. Here is the link to the Eaton website with all kinds of information about steel springs.

https://www.eatondetroitspring.com/leaf-springs/

And a written out podcast with more than you ever could want to know about the early days of C1-C3 steel springs.

https://www.eatondetroitspring.com/f...e-suspensions/

 

I have been struggling with the high rear end on my 73 since I frame off rebuilt it quite a few years ago. This winter I finally decided to take a more serious attempt and bought Global West Tubular A Arms and Viking Coil Overs. Really dropped the front. In the rear I replaced the 9 leaf which was new when installed and I had to use 8" bolts to get it lower but still way high. This time I bought a TRW fiberglass spring. It came with 8" bolts and it was just as high as the 9 leaf with the 8" bolts. My rear end has a 78-79 cover on it so it uses a 2 1/2" wide spring. (20 years ago when old rear covers failed, we used 78-79 because they were heavy duty.) The guys at Eaton Detroit were really very helpful. With all the variables in my set-up, I shipped them my old spring because it was a known value and they took about 2 1/2" out of the arch. I just put it back in and this finally got the rear down!!! FINALLY!! I haven't rolled it but I am down 13/4" at the rear fender lip. I am confident it will settle some more. I really can't say enough about the great help William at Eaton Detroit gave me and helped me finally solve this problem. My spring came back looking better than a new one. I will try to get a picture tomorrow. My free spring arch before was 7 1/2" and came back at 5 1/4". Front end is now 26 1/2" and rear is 27 1/2". Spring is almost flat and half shafts are almost parallel to ground.

 

Great information. That is one good thing about steel springs...a spring shop can re-arch them. I have had that done on 4x4's in the past (higher not lower).

 

That's the way we lowered race cars back in the day. It can be done with a steel spring, but not a composite one.

 

I'm not either so we can end that part of right there. I am pretty positive that I said earlier that I sell multiple springs and I would take that one back. All the other comments were based of stuff you said.

 

In an effort to get this back on track.....Do you have any info on spring heights?
Any free arch measurements?

 

Sayfoo,
I get what you are saying now, I just went back and re-read what you had said earlier. My apologies
I'll say this, I was still in the Marine Corps when it hit he fan between him and Zip. I know when I started here that Zip was coming up with all of their own kits and writing instructions for them. He states on his website this was all BS but there were plenty of Corvettes here getting vac lines pulled out and measured and drawn. We still own one of the ones that was used, if anyone sees us in Carlisle it is our 70 LT1 that has 58000 miles on it. There were some mistakes in the GM manuals and Dr. Rebuild had also admitted to creating some mistakes as well. I think the one that you are referring to would be the blue line on the back of the headlight switch. It was a hectic time since we were the largest customer of Dr. Rebuild at the time and all of sudden we were completely cut off from him.

 

JAbbott? Anything positive to contribute about springs?

 

I just did a lot of research into this for my car, and yours and others as well. Your picture shows a spring arch loaded of 3.25" That's just way too high. (Stock GM is -.37" with a 6.5" spring bolts).
You would need 10.1" long bolts to lower it back to stock. And as others have said the 10" bolts are just not safe with a 15" wheel because they go below the rim.

Your TRW 340# spring probably has about a 7.25" free arch, it's just too much. And it can not be changed once made.

I just got off the phone with VanSteel. The Van Steel low-arch springs have a 4.25" free arch and should get you where you want to be with a 7.5 to 8.0" spring bolt, much safer. Probably the same thing I'll get. If you have a mild engine and want it to ride well their EZ-ride is an exact duplicate of the 81 spring, made on the original factory molds.



I am going to move the rest of my spring info to a new thread.

 

Sooooo, I reached AIM wheel arch height of 27.9 inches, down from 29.5 and my half shafts are level.

To achieve this I had to place the spacer under the spring and I had to use 10-inch bolts with the nut run all the way down to the end of the bolt.






This probably will settle a little. For the moment it’s hanging a bit low for my comfort.

 

Looks to me like the recipe for a flat...……..
Try jacking the front of the car up so as to cause some rear squat and look at how close the spring end gets to the tire sidewall. Then imagine a pothole in the road jouncing the car waaay more.

 

Yikes! I wouldn't drive a car with a spring that close to the tires.