C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

leaf spring info.

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Old Nov 18, 2013 | 10:59 PM
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Default leaf spring info.

I am looking for some help with c4 leaf springs.
They have 3 letters engraved on them (BMB,HMJ,HKX,ect.)
My question is the spring rate of these are all different.
Are the larger numbered spring rates stiffer springs or softer.
Thanks for your help.
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Old Nov 18, 2013 | 11:51 PM
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Originally Posted by c4guyjmh
My question is the spring rate of these are all different.
Yes , in most cases

Originally Posted by c4guyjmh
Are the larger numbered spring rates stiffer springs or softer.
Thanks for your help.
No relevance.
the rate varies by year and what suspension pkg it was installed with

Put up what you have and someone will tell you the rate
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Old Nov 19, 2013 | 05:40 AM
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Here's a chart with the spring rates for various years. Unfortunately it doesn't have the "secret code" letters for the springs. My recollection is that mine has a small metal tag with the letters stamped on it.:

http://corvetteactioncenter.com/tech...l#.Uos_aqX5Frc
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Old Nov 19, 2013 | 05:52 AM
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Originally Posted by c4guyjmh
Are the larger numbered spring rates stiffer springs or softer.
Thanks for your help.
Yes larger numerical numbers would be "considered" what you call "stiffer" - Is that correct terminology? Not quite but it works for most.
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Old Nov 19, 2013 | 06:19 AM
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Originally Posted by Cliff Harris
Here's a chart with the spring rates for various years.
Unfortunately it doesn't have the "secret code" letters for the springs. ]
You needs WVZR-1's C4 parts manual to see what code spring was installed in which year in order to cross reference that chart


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Old Nov 19, 2013 | 09:36 AM
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aligned/w this thread,would there be negative consequences to installing a stiffer front spring than the FE1 softride spring originally installed on the front of an '89?

Or is there a benefit to the consumer hoping for a better sporting ride? In conjunction/w new Bilsteins,bushes,and ball joints?
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Old Nov 19, 2013 | 09:52 AM
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Thanks to all that replied.
My problem is the 86-87 FE1 suspension that came with the kit
did not come with leaf springs, so i am trying to find some that
will not be real stiff like some vette's i have been in.
The car will weigh about 1800 lbs and be mostly street driven.
(a little road course driving)
Thanks for the help.
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Old Nov 19, 2013 | 09:56 AM
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Originally Posted by DucXL
aligned/w this thread,would there be negative consequences to installing a stiffer front spring than the FE1 softride spring originally installed on the front of an '89?

Or is there a benefit to the consumer hoping for a better sporting ride? In conjunction/w new Bilsteins,bushes,and ball joints?
If a person wasn't willing to do "both ends" of the car along with the appropriate sway-bars I think it might be a foolish venture. If you have a "broken or failed" front spring already that might change the conversation. A negative consequence - likely not but maybe not economical or practical "just to do"!

You really need to check the spring code of what you have. In '89 I believe the only thing that changed the front spring was FX3, FE1 & FE7 were the same. Quite sure. Now an after-market "sport" option could be considered and the game changes. There's even an adjustable one for the front.
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Old Nov 19, 2013 | 10:06 AM
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I will be doing both front and rear.
I found a adjustable rear leaf,but it is expensive,
not sure if i should go that direction.
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Old Nov 19, 2013 | 10:16 AM
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Originally Posted by c4guyjmh
Thanks to all that replied.
My problem is the 86-87 FE1 suspension that came with the kit
did not come with leaf springs, so i am trying to find some that
will not be real stiff like some vette's i have been in.
The car will weigh about 1800 lbs and be mostly street driven.
(a little road course driving)
Thanks for the help.
You never mentioned that the "build" isn't a C4 but only the IFS/IRS were used. That changes dramatically your approach I'd think. Have the springs that you have or can get easily "measured" and install them, if you're unhappy with the build you now have your "known" weights and can buy a spring with a rate that you might prefer. Sometimes it's wise to mention your intentions.

What is the build? Many times the C4 control arms, rack etc are used but there's no provision for using the C4 leaf. The '87 and earlier requires more parts than the later to use the leaf. What exactly I guess do you have?
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Old Nov 19, 2013 | 10:43 AM
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As I said, I do not have the springs so i can not measure them.
I have the front suspension (minus the springs) Welded to a tube chassis(jig built)
and a rear end(minus springs) that mounts to the chassis.
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Old Nov 19, 2013 | 11:21 AM
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Originally Posted by c4guyjmh
As I said, I do not have the springs so i can not measure them.
I have the front suspension (minus the springs) Welded to a tube chassis(jig built)
and a rear end(minus springs) that mounts to the chassis.
I mentioned or "get easily" BUT - the softest springs that you could get for an '87 or earlier chassis would be the HKX or HMP. Both are for "soft ride" coupes. You can NOT use a spring from an '88 or newer on the front. Find one of those springs as inexpensively as you can and do the build with it if you want to maintain the transverse spring. Before installing have it measured, it's several years old and then you'll know the "spring rate" of what you have. If you're unhappy with that build your options would be to have a spring fabricated with a lesser "spring rate" or do maybe "coil-overs". Measured I mean "spring rate" NOT dimensionally.

On the rear of the build you can use any year C4 spring - '84 - '96!
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Old Nov 19, 2013 | 11:48 AM
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Since your looking for the lowest matched spring rates front and rear. you will want to get as close to the 96 non z51 coupe c4 spring rate specs as possible as they are known for their good ride with 26mm front sway bar and 24mm rear sway bar. the 96 spring rate is 60nm front and 26nm rear. Since you have a 87 and earlier front suspension what you will need to go for is the 54.4nm HMN code front spring available on 86,87 convertibles. If this spring cant be found the 54.0 nm HKX used on some 85 base suspension coupes. Next is the lightest spring rate its 51.8nm HMP used on 85-87 base suspension coupes. In the rear you will want the 26nm RHZ used from 94-96. If your running the lowest spring front rate listed maybe run a larger front swaybar and you will be very close to how a 96 drives.
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Old Nov 19, 2013 | 11:56 AM
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Thank you all,GREAT INFO!!!!
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Old Nov 19, 2013 | 03:27 PM
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You mentioned coil over shocks,if I went this
way will i need the leaf springs?
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Old Nov 19, 2013 | 03:43 PM
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Originally Posted by c4guyjmh
You mentioned coil over shocks,if I went this
way will i need the leaf springs?
No ! The suspension would be completely adjustable wheel to wheel. You might maybe mention your build a little more completely. Snapshots?
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Old Nov 19, 2013 | 03:58 PM
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I will take some shots of the suspension and chassis.
I hope i can down load them on this site.
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