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Leaf spring replacement

 
Old 03-12-2019, 11:40 AM
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MikeP84
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Default Leaf spring replacement

Hello all, I am considering replacing my leaf springs on my 84 with newer ones as im sure they have never been replaced before and most likely need it. I have done some weight reduction with aluminum heads and new/lighter intake so im considering replacing my springs with the lighter lbs rated springs. I also would like to soften up the ride a little as I dont autox often and frankly, I think they are to stiff for even that!
My 3 concerns are
1. Is my ride rough because they are old and worn out or should I consider the softer lbs springs.
2. Where can I buy the softer springs? While researching awhile ago I was able to find them for sale, but now I cant seem to find anyone who sells the softer spring.
3. I have read that you need the heavier duty springs in order to lower the front of the car. My thought is that sense I have removed weighed, the softer springs would be the same as if I had the heavy duty springs and more weight.

Any ideas would be appreciated. Thank you!
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Old 03-13-2019, 09:42 AM
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MatthewMiller
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If the springs in your car look okay, with no cracks or other obvious signs of wear, then they are probably functioning just fine. The 84 springs were the stiffest ever used on any C4 from the factory, and if you've significantly lightened the car it will effectively increase the stiffness even more. So you could possibly soften the ride with later springs from an 86 or 87 C4 (the front spring from an 88+ C4 won't fit your car). There are probably people who would be happy to trade you straight up for your stiffer springs, as most of us are looking to increase performance and therefore want the higher spring rates. As for any aftermarket supply, the biggest source of new springs was VB&P and they are now out of business. So it's getting harder to find new ones. I believe Hyperco still sells some, but I don't know what rates or fitments they still make.

As far as lowering goes, you don't have to have stiffer springs to achieve a lower ride height. You just need to cut down the pads on the ends of the front spring, and use longer bolts for the rear spring. However, as you lower the car you take away some suspension travel in compression, so even at the same spring rate it becomes easier to hit the bump stops. That's why most people will say you should have a stiffer spring rate, so that the same bump or acceleration force causes less compression travel and you can stay off the stops. In your case, you may just be trying to get the car back to original ride height. If that's the case, you should be fine. Basically you'd be trying to set your car up like an 86-87 C4 came from the factory.
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Old 03-13-2019, 09:52 AM
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MikeP84
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Thank you for the reply! I thought I had read somewhere that the 84 had the stiffest springs out of all but that was awhile ago. Do you know what they are rated at? I have seen the hyperco springs you are taking about but was concerned that they would be the same as what I have now. The hyperco are rated at something like 380 and the softer springs that I have seen where 290. Lbs are not accurate but they were sometbing like that. If they are softer then ill just get them and call it a day. I wouldn't say I have significant reduced the weighed, but a good 60-70 pounds. My goal is to lighten up the suspension some and if needed, reduce ride height. I may not need to reduce ride height with softer springs, but I may if it's still sky high. Thank you!

Edit: I know I dont need stiffer springs to lower, but the common lowering blocks you can buy are recommended for use with the hyperco "heavy duty" springs if I recall correctly.

Last edited by MikeP84; 03-13-2019 at 10:03 AM.
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Old 03-13-2019, 10:07 AM
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Originally Posted by MikeP84 View Post
Thank you for the reply! I thought I had read somewhere that the 84 had the stiffest springs out of all but that was awhile ago. Do you know what they are rated at? I have seen the hyperco springs you are taking about but was concerned that they would be the same as what I have now. If they are softer then ill just get them and call it a day. I wouldn't say I have significant reduced the weighed, but a good 60-70 pounds id say. My goal is to lighten up the suspension some and if needed, reduce ride height. I may not need to reduce ride height with softer springs, but I may if it's still sky high. Thank you!
According to the famous Hib Halverson chart, the 84 front spring on the base car was 363lb/in, and the Z51 spring was 583lb/in. In 1985, that base spring became the Z51 (stiff) option. So really, the 84 Z51 was the one with the sky-high rates. The 86-87 base suspensions came with 296lb/in front springs. So if you have a base 84, then going to a later base front spring will be about 23% softer. But if your car is a Z51 then going to a later base front spring will cut the spring rate nearly in half. If you hve a front Z51 spring in there now, I am sure you can trade it to someone. That would be a sought-after front spring.

BTW, I forgot to mention this, but I don't think going to a softer front spring is a good way to lower the car. First of all, as previously noted, you don't want softer spring rates when you take away suspension travel. But more importantly, with the OE springs, the softer the spring rate the more arch they built into it. That way, regardless of the spring rate the car had a similar ride height. The point being: if you put a softer factory spring up front it probably won't ride any lower. You need to cut down the spring pads on the ends of the front spring to lower it.

Out of curiosity, how much weight have you removed?
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Old 03-13-2019, 12:01 PM
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MikeP84
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Is there an easy way to identify if I have a z51 or not? I have not seen any markings on the lower A arms that say z51 so I don't think I do. I have replaced my 84 hood with one off an 86 so it does not have the ram air tunnels in the hood, heads with aluminum heads and replace x fire with an edelbrock pro flo which was about 10lbs lighter. Im not sure of overall weight.

My overall goal would be to soften the ride if possible and restore the ride height. Sense the softer springs are nearly impossible to find im pretty much stuck with the hyperco z51 springs. So by your math I would be going about 23% softer with them correct?
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Old 03-13-2019, 12:26 PM
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Originally Posted by MikeP84 View Post
Is there an easy way to identify if I have a z51 or not? I have not seen any markings on the lower A arms that say z51 so I don't think I do. I have replaced my 84 hood with one off an 86 so it does not have the ram air tunnels in the hood, heads with aluminum heads and replace x fire with an edelbrock pro flo which was about 10lbs lighter. Im not sure of overall weight.

My overall goal would be to soften the ride if possible and restore the ride height. Sense the softer springs are nearly impossible to find im pretty much stuck with the hyperco z51 springs. So by your math I would be going about 23% softer with them correct?
For an 84, the front spring should have the code "BMB" if it's a Z51, or "HMZ" if it's a base model. You would also be able to see the Z51 code on the RPO label if you can find that (the sticker that shows all the option codes for the car). Other softer front springs include codes HMN and FJY. Supposedly, according to one source at least, there are even softer springs coded HKX and HMP, but that doesn't square with the Halverson chart, so I'm not sure. You could post a "Want To Buy" ad in the C4 Parts Classified forum.

Looking at Hypercoil's own site, I don't even see any front springs for a C4. Hmmm. I do see some options on Van Steel's site, the softest of which appears to be HCO12410VSE. They rate that at 343lb/in.

I don't think you've dropped more than ~70lbs off your nose, so that shouldn't be causing massive differences in ride height. Bottom line is that if your car has the Z51 spring in it now, you can make a big change to go softer. But if it's a base spring, you can only go about 23% softer with later OE base springs. It seems like the Van Steel (or Hypercoil or whatever they are) spring will be equivalent to an 85-87 Z51 spring. In terms of changing your ride height, you really need to focus on the pads at the ends of the springs. If you want a softer ride and you only have the base spring in the car now, then you may get a better improvement in ride quality by changing shocks (depending on what's in there now). Dampers tend to have a bigger effect on ride quality.
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Old 03-13-2019, 12:42 PM
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Thank you! I'll take a look at the code later this afternoon. I just found a good forum called "comparing spring rates 84-96 Z51" which seems to go into good detail about the codes and their respective rates.

I agree, I dont think its much more that 70lbs so it probably hasnt raised the nose enough to be noticeable, but it just seems high to me. Non the less you have answered my question. If I have a base, 23% decrease in spring lbs would probably be exactly what im looking for. If I have a z then ill look for something that is a little less than 50% decrease. I think that might be too much. Either way I'll be able to soften the ride a little which is exactly what I am looking to do. Thank you!!

Edit: my shocks are new so id rather not replace them again but ill keep it in mind if new springs dont make a difference or if I do just have a base model.

Last edited by MikeP84; 03-13-2019 at 12:46 PM.
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Old 03-17-2019, 09:52 PM
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Matthew, so I checked my springs today and the front has a code of BMA and the rear has BMF. Do you know what the lbs are on these? Thank you
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Old 03-17-2019, 10:07 PM
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Originally Posted by MikeP84 View Post
Matthew, so I checked my springs today and the front has a code of BMA and the rear has BMF. Do you know what the lbs are on these? Thank you
I don't see the BMF code on the published charts. However, according to at least one post on this forum, your spring codes both indicate the base suspension and not the stiffer Z51. So it looks like your front rate would be 362lb/in and the rear spring is definitely 411lb/in.
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Old 03-17-2019, 10:42 PM
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Thank you! I can't imagine what the car would be like if it had the stiffer suspension. It'd probably break even my young back! Thank you
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Old 03-18-2019, 08:40 AM
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1984 c4 was know for rough ride having firm springs even on base car. The 84-87 share springs and suspension. Chevrolet started softening the ride in the base cars to address harsh ride complaints. All the rear springs interchange and there are different rates. Rear spring is fairly easy to replace. In 1988 front suspension changed so 88+ suspension parts won't fit your car. Finding used softer spring is easy and thrifty, any rear spring for an 85 or later. The front spring is more involved to change; if you decide to change it also.
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Old 03-18-2019, 03:52 PM
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I originally had planned on replacing both with new equipment but I can't find new front springs anymore. Thinking about only replacing the rear with the z51 326lbs. It should make a bit of a difference if the current one is 411lbs. That should give me a good balance front and rear and soften things up a bit. I would be afraid to go softer and have the car feel tight up front and lose in the rear.
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Old 03-19-2019, 12:06 AM
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if u had z51 id trade you straight across for my 86 base springs. excellent cruising and daily springs. im building a track car with it and need stiffer springs.
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