I'm headed out for the evening, but will move my other car and take a closer look at the thickness of my spring tomorrow. With Alan's advice, I'm questioning my casual measurement.

FWIW, when I changed my spring, I fastened all four spring/diff case bolts BEFORE securing the ends. Tackling it any other way (sequence) scares the bejesus out of me. There's a huge load on the spring when the ends are drawn up/in. BE VERY, VERY CAREFUL. You can find other's experience in installing the spring by searching this forum. As for me, I have a hydraulic jack as part off my four post lift. I jacked the spring ends into position, one at a time, using the jack's rubber disk shaped feet near the end of leaf #1. The rubber feet kept the jack from slipping. I'd hate to be around if the jack slipped.

Again, if you end up using different length bolts or a different thickness spring vs what came out of the car, be sure to avoid burying the bolt past the hole's bottom and breaking the diff casting. I recommend you install a bolt without the spring, measuring the maximum depth of thread engagement available. Add to that the thickness of your spring assembly plus the washer and the retaining plate to determine how long a bolt you can use. Make sense as typed?

 

Don (red roadster). Thanks for the spring and bolt advice. I'm with you 100% on the spring loading and bolt length advice. I had already planned on premeasuring the blind holes.. I'm definitely going to return the spring I have and see if they can get me the Eaton, if they can't I see where the Eaton unit is available from Zip for a few bucks more.

Happy New Year!

Thabks again.

 

Like Alan said, here's a pic of the liners. The edges are trimmed on each side along the center region to allow the bolts to pass because the shaft of the bolts rides up tight against the metal leafs.
I don't know about removing liners 1-2 as GM designed it that way.

 

Hi

It looks like your spring leafs are not tight against each other. May be they settle if you put some weight on and can start the bolts then.

Happy new year. Günther

 

Hi a,
Happy New Year!
Be sure to heed Don's warning!…. if the 2 bolts used in the forward locations of the spring mounting plate are too LONG…. they WILL damage/crack the case. They are in BLIND holes.
Regards,
Alan

 

Your installation issue does look that the center leaf bolt is not firmly tighten.
An original 9 leaf spring measures just shy of 2 ¼ firmly tighten.

Regarding your rear height issue. I have tried several venders to find most sell the JRS brand spring they have all been consistently higher than original stock height. I like and bought my current spring from Eaton although 7 not a 9 leaf, they build/manufacture them. When I spoke to Eaton I request spring to be lowered -1” per my previous experiences. He said his are built to spec and he question the necessity of that and also mentioned that something regarding the suspension rebuild/installation could be wrong. In my own opinion it is pretty straight forward not sure what could be done wrong, regardless when I installed the new lower -1” (using std 6” outer spring mount bolts) it still sat too high (28 ½ at wheel well) so I sent it back to have them lower it another -1” (totaling now minus 2”) After install again that additional -1 equated in only another ½ inch drop.

Using longer outer spring bolts will lower your height issue but I consider their use a Band-Aid fix and question its effect on the spring rate and geometry.

If you decided to purchase from Eaton keep this in mind or you may still end up with that 4x4 look.

Keep us updated.

 

Thanks guys. Pretty sure I'm going to return the JRS and contact Eaton. I was thinking since I already have 8" outer bolts I'd just go with standard arch. I am considering the 7 leaf though seeing as I've been riding on a composite 355 # for 6 years (and adjustable Konis) and as a previous member commented the 9 leaf may not match the front springs that were likely matched when the rear suspension was set up. It also has an aftermarket rear sway bar.

Thanks again to all and the excellent photos and knowledge. You guys are awesome.

Andy.

 

Hi Andy,
You might find this info from Eaton useful.
Regards,
Alan

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. But we will not talk about it.

The diferences 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 305lbs.

The 9 leaf spring which all 9 leaves are curved has a rate of 196lbs.

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 140lbs and increases to 196lbs 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 centerbolt.

Whle 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 form the original factory specs in order to maintain stock ride height.

 

Hi

Thanks for this info.
Interesting, the difference between the 7 and 9 leaf spring.
How soft must a a 9 leaf Vette be in the back having nearly only 1/2 the rate of a 7 leaf Vette ? I'm driving the 7 leaf and find it by far not too hard.

Rgds Günther

 

If you decide to go with the 9 leaf, here's how my Eaton was delivered.
I cut the clamps off, disassembled the leafs, painted them dove gray installed new cups and a grade 8 center bolt.
I did go to longer end bolts and the ride height is perfect on my car as I don't run a spare.
The Eaton while not an exact copy, is close enough for me.

 

Hello there,
I have a 1968 Big Block Corvette convertible with the four speed.
After having a dealer rebuild my Posi my car was returned to me looking like yours does. My car looked like it was jacked up and the half shafts were at being overworked due to the angles involved.
I spent over a year trying to figure out why it was like that. After replacing all the have shaft U-joints twice I decided that I had to solve this.
Vette Brakes sold me a set of bolts that put my car back down where it was supposed to be. It turned out that the dealer put shorter bolts on the outer part of the spring mount. After changing the bolts my car's ride felt so much smoother and I don't see the back of the car in the mirror any more.
Call Vette Brakes (VBP) and talk to them about the situation.

 

Hi ctm,
I'm curious about these "shorter bolts" the dealer installed.
What was their length and why do you think they did that?
Was this a Chevrolet dealer?
Regards,
Alan

 

Hey all, thanks for all the great photos and advice. I ended up taking the 9 leaf back to Full Throttle Vette and exchanged it for a 7 leaf that measure 2.5" in the center. After pulling apart to paint and reassembling, it bolted right up the way it should have using the 3.5" bolts that were used with the composite spring setup. After a quick drive in the neighborhood it looks like the space between tire and wheel opening lip is just under 2", much better than the 3" with the composite and 8" outer bolts, and the half shafts are sitting at almost level. I will advise for those replacing their steel springs, the JRS springs are definitely thicker, the 9 leaf read 3" in the center... they say they can't buy the thin steel that was used previously to produce the originals. After looking at their website, it looks like trucks, jeeps and 4x4's are much more the norm. Also, from an aesthetics standpoint, the liners were a mess, the edges were "boogered up" and pinched and cut where they banded the springs, at the clamps that everyone removes, and were generally (the liners) in pretty rough shape. Again, nothing an offroader customer would complain about, but not really what a Corvette guy wants under his ride. From the Eaton photos that were shown, I'd advise going that way, looks like they were about $75 more than what I paid for the JRS. Thanks to all once again. Here's a shot of the spring in the car.

 

Hi Andy,
Looks like this worked out for you! Good!
For clarification…. just which spring did you buy from FTV, and what length t-arm bolts did you use?
Regards,
Alan

 

The spring is JRS' 7 leaf, 3.5" bolts for anchor plate and 8" trailing arm bolts I had purchased previously. I'm not sure if any shorter than the 3.5" anchor plate bolts would have worked.

Andy.