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Starting a build, have spring questions

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Stormin

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I am helping my friend build his 79 stepside. The ultimate goal is 42" tires with little or no suspension lift and obviously a lot of sawzall work. We are still trying to decide on spring choice and location and I had a few questions.

the front:
We are considering swapping the rear 52" springs to the front. I have read the tech article but I had some questions. I understand that putting in a longer spring requires moving the spring hangers but I don't understand why in the tech article both of the hangers were moved forward and the longer swing shackle was used. Looking at the final picture it seems to me that moving just the front mount and using the stock length shackle would result in the spring being in the same location with the swing shackle in a vertical orientation. Is there a reason why the shackle should slant toward the spring?
Also there will be a bit less weight in the front as we are moving the battery and radiator to the back and losing all the creature comfort type stuff (ac, heater, etc). Should we remove some of the springs from the pack to gain more flex?

the rear:
In the rear we will be losing the outer fenders on the stepside bed, cutting two feet out of the length, and shortening the width so the bed sits inside the frame. We are considering moving the axle forward a foot to a foot and half. This will provide a wheelbase the same as a stock blazer or a couple inches shorter. We haven't yet decided what springs to use in the rear. We are considering buying a set of fiberglass springs. Has anybody had any experience with them?
My last question has to do with locating the axle after you move it. If we move the axle forward does the pinion angle need to remain the same as stock or must it be adjusted? Also, when we move the rear springs are there any geometry rules we need to consider with spring mounting? For instance does the relationship in height between the front and rear mounts matter, or the orientation of the center pin of the spring to the frame of the truck?

This is my first complete build involving a lot of fabrication, so I'd appreciate any advice anybody has. I'll be sure to get some pictures taken and post em up as we go!
 
I have a K5 52s up front shackle flip in the rear 2in body and tons of cutting and I rub a tad on the firewall. Granted I have no bumbstops, soon to come though. Thats where Im at. Good Luck -Ryan
 
Yeah I am expecting to have contact with the firewall. We are gutting the interior and I am hoping we can get away with tubbing the firewall a bit on either side for a little more clearance. When you did your 52" swap did you move both brackets? Still a bit confused on this issue and I'd like to see some different ways of doing it.
 
People move the rear bracket to get a better shackle angle. This nets both a better ride and more flex. If you tried to use the shackle bracket in the stock location you would have very little down travel.

I have 52's in the front of my truck with basically no lift. I can only have ~1" of uptravel because:

a) the spring is very close to the pitman arm (I am still running crossover) and the draglink is close to the engine crossmember.

b) the springs sit flat at ride height so any uptravel makes the springs inverted which kills springs in a hurry.

I use bumpstops to limit uptravel and I am running the top 4 leaves out of an old 52" spring pack, so I'm sure they sit lower than a new spring pack.

As for wheelbase on a truck with 42" tires, I would shoot for 110-120"
 
how to set up swing shackle angle

Okay I have been trying to wrap my brain around shackle angles all day and I've read a lot of posts about it. Nothing I read was really spelled out completely and I'm still feeling a little :confused:. Here is what I think I understand please try to make sense of this if you dare and correct me if I'm wrong

When one side of the suspension is being compressed while climbing over an obstacle the other side of the suspension will droop due to the inherent nature of a solid axle. This is why the shackle angle must point in allowing the suspension to droop so the "downhill" tire stays in contact with the ground.

Assuming that I'm correct in this statement it seems to me that the best way to locate spring mounts is as follows.

The front mounts should be set first according to where the axle needs to be located. Then a point should be found on the frame as measured from the front (fixed) spring mount that is equal to the actual length of the spring itself. This point represents where the spring would contact the frame if it were compressed until it is flat (essentially the limit of the compressive action of the suspension). Call this point A.

Then a second point should be determined, (point B), that is the location of the rear spring eye of an uncompressed spring while the other spring is compressed to point A. This is basically the point where the spring is at at full droop. There is no reason for this point to be any lower because the spring cannot droop more without the other side compressing more.

So now that I have the two points it seems to me that the frame end of the swing shackle should be mounted on a vertical line from point B. This way the shackle will be vertical when the suspension is at full droop. And it should be mounted at a point equal distances from point A and point B. With this setup the shackle angle will always point inward at normal ride height, although how much inward it points would depend on the weight of the vehicle.

Okay, does everything I've said make sense or have I got it all wrong?
 
The idea of the shackle angle is this:

Since leaf springs generally have a lot more droop than compression (and this is especially evident with a low ride height) you want to set the shackle angle accordingly. In this case you would want the steepest shackle angle that

a) prevents the spring from hitting the frame
b) doesn't limit uptravel

If you are going to use 52's at roughly stock height you will have practically no uptravel anyway.

Here is a picture I drew to kinda illustrate what the shackle would do ideally:

springs.jpg



In the real world the spring rate of the spring won't let it droop as much as the third picture but having a steep shackle angle will ensure that the rate of the spring is limiting your flex and not the shackles.

The overall idea is to ensure that the shackles don't limit your flex in any way.

With my current rear springs (just lift springs with a couple leaves removed, no shackle slip) the short and vertical shackle is what limits flex. A shackle flip with the correct shackle angle would flex a lot more.
 
You will find as you build that occasionally not everything comes out as neat as on paper, Shackle angles effect wheel travel greatly. As has been explained. In order for one side to droop the other side doesn't need to go up(to a point). This sounds a bit weird but after putting bump stops on several rigs you don't limit the droop very much if at all. With 42s and a stock heigth you will have to limit your uptravel somewhat, so that really should be a non issue. I personally like to have the shackle laid back like this \ at about a 15* angle.

A couple of points that I have learned. You really don't know what full droop is unless you can lift the opposite tires ( i.e. right front left rear) you can estimate pretty close though. I have used sandbags to simulate engine weight and other compononts too. You ususally end up doing all the spring mounts when everything is out of the way so using sandbags to simulate will help get the final product closer to what you want than not.

Don't be afraid to cut stuff off and start over again either, a little extra time getting it just right will pay off big in the end. That extra 10 minutes is usually the difference between " Thats a nice rig" and one where poeples jaws drop when they see it in action.
 
Oh yeah, I forgot to address one more thing:

The downtravel of one side has nothing to do with how much the other side goes up. As I said before, I only have ~1" of uptravel but I bet I have 12" of downtravel (at the spring, just guessing).

IMO using bumpstops actually creates leverage that forces the dropping side down.
 
Okay so I was off base with the droop being limited by compression. Thanks for pointing that out. So I understand now how a steeper shackle angle allows for more droop. What is the magic number to shoot for as far as angle? I've heard some people say they like to see 30 degrees, blazinzuk said he likes 15. Are there any tradeoffs in ride quality or elsewhere as you go to a steeper angle?

I do understand that sometimes a little trial and error is the best route, but I'd just like to better understand the mechanics of how leaf springs move. Thanks for the input and for putting up with all the questions.
 
The longer your springs are the less angle you need I have 60" springs in front. I have a different opinion than alot of poeple on here. I like to have a ton of uptravel as well as downtravel so the 15 degree angle works well for me. With as low as this truck you are building is going to be I would say go closer to 20 to 25 I think 30 is too much but once again this is my own personal prefrences. I know a couple of guys who are running their shackle angles at closer to 50 to 60, they all have very little uptravel.

One thing to remember although its been done many times and is proven to work well the 52s aren't the only springs out there Ford springs can work the 56s from one tons and burbs, I have a set of rear springs from a full size waggy that would work sweet in a front application for a chevy, I am using Dodge springs. Mixing and matching can work really well too.
 
blazinzuk said:
The longer your springs are the less angle you need I have 60" springs in front. I have a different opinion than alot of poeple on here. I like to have a ton of uptravel as well as downtravel so the 15 degree angle works well for me. With as low as this truck you are building is going to be I would say go closer to 20 to 25 I think 30 is too much but once again this is my own personal prefrences. I know a couple of guys who are running their shackle angles at closer to 50 to 60, they all have very little uptravel.
Click to expand...

For me, more uptravel would be better but it simply isn't an option with crossover steering and leaf springs in front (remember that I'm basically running at stock height). My shackles are ~7" long and are probably at a 60 deg angle (from vertical, i.e. the shackles sit more horizontal than vertical).

The low ride height is well worth it to me and the solution to allowing more uptravel is to go to full hydro steering along with a link suspension in the front.
 
I hadn't really thought about the crossover until you mentioned it, which is something that we definitely are going to be doing on this build. Should I take that into consideration when I mount the springs? Would I be better off to do the crossover first? The axle will probably be a dana 60 (which I've heard is easier to convert to crossover).

Speaking of axles, we're going to look at some for sale this weekend. What do you guys think about $1700 for a front D60, spooled and a 14B rear, gov-bomb both with 5.38s? I know the 5.38s aren't super low for the 42s but a Stak transfer case with crawly gears is in the distant future.
 
Stormin said:
I hadn't really thought about the crossover until you mentioned it, which is something that we definitely are going to be doing on this build. Should I take that into consideration when I mount the springs? Would I be better off to do the crossover first? The axle will probably be a dana 60 (which I've heard is easier to convert to crossover).

Speaking of axles, we're going to look at some for sale this weekend. What do you guys think about $1700 for a front D60, spooled and a 14B rear, gov-bomb both with 5.38s? I know the 5.38s aren't super low for the 42s but a Stak transfer case with crawly gears is in the distant future.
Click to expand...

If this is a trail only (trailered) rig then go with full hydro. If it will have to drive to trails you will need crossover and bumpstops (if you are around stock height).

5.38's are pretty low, I only have 4.56's. If you want low gears for the trail you should be changing things in the t-case (which you would with the Stak).

$1700 is too much IMO, I'd say their worth closer to $1400.
 
I'll chime in only because I'm running 52" springs and 42" tires. Here's my shackle angle for the front
2186902_242_full.jpg


I will be setting my bump stops to stop the axle when the springs flatten out. You don't want the springs to "negative" arch. That wears out springs fast. Also with the low lift and big tires I'm goint to be eating my fenders, so I will cut a lot of it out of the way.
Also I moved the front axle forward 2.5"s here's a pic with the tires mounted, but I have yet to trim the fenders.
2186902_348_full.jpg
 
muddermilitia said:
I'll chime in only because I'm running 52" springs and 42" tires. Here's my shackle angle for the front
2186902_242_full.jpg


I will be setting my bump stops to stop the axle when the springs flatten out. You don't want the springs to "negative" arch. That wears out springs fast. Also with the low lift and big tires I'm goint to be eating my fenders, so I will cut a lot of it out of the way.
Also I moved the front axle forward 2.5"s here's a pic with the tires mounted, but I have yet to trim the fenders.
2186902_348_full.jpg
Click to expand...

What does the front hanger look like. I was thinking about moving mine forward also.
 
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