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Old 07-30-2020, 05:47 PM
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4 bar setup

Not much room under the car due to a crossmember but thinking about installing a 4 bar setup (not triangle 4 bar). Does anyone have a GOOD feel for the shortest 4 bars that will perform decent for street use? I understand that the longer the bars the longer the arc of swing but (about) where is the tipping point, if there is one?

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Old 07-30-2020, 07:12 PM
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18" before rear steer becomes a real problem.
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Old 07-31-2020, 06:16 PM
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Your shortest setup is going to be leaf springs.
Your going to use the springs to locate the axle and use springs etc as suspension.

You can run full spring.
Half spring with suspension over axle.
Or 3/4 spring with suspension behind axle.

Using a spring allows some flex and also allows for a lower profile as the thing has a arch.

A vertical or horizontal watts link will keep the axle centered.
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Old 08-01-2020, 08:23 AM
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Modify or move the crossmember.
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Old 08-01-2020, 08:45 AM
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4 Bars

Tuff to move the crossmember without taking the body off, putting on the jig, cut and weld. Question was: What is the shortest 4 bar that will work for street?
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Old 08-01-2020, 08:57 AM
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Quote:
Originally Posted by 39 master View Post
Tuff to move the crossmember without taking the body off, putting on the jig, cut and weld. Question was: What is the shortest 4 bar that will work for street?
Understand the question. Trying to help you build the best suspension system, not one that you have to make excuses for.
Alternately, use longer bars, under the crossmember and build a half-circle or a "U" into the bars to clear the crossmember.
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Old 08-01-2020, 10:42 AM
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I think the longest bars or area that the bars would fit in is 27" eye to eye. I think this should give a long enough arc of the rear end as to not deflect it much during suspension travel. This is a backup plan just in case the Corvette rear suspension doesn't work out as planned.
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Old 08-01-2020, 10:46 AM
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Quote:
Originally Posted by 39 master View Post
Tuff to move the crossmember without taking the body off, putting on the jig, cut and weld. Question was: What is the shortest 4 bar that will work for street?
Mount a 2 leaf pack inline with the frame.



Have the hanger at the area where the frame starts to rise on a angle before the axle gusseted so it adds strength to the frame.

Then have a shackle or spring slider mount back where the frame rises behind the axle. Gusseted to add strength to that part of the frame.

Go under the axle if possible.

No issues with clearence at all. You should be able to lay the frame against the grass if you do it right.
Nothing hanging low to catch driving or to high hitting the body when bags dumped. No issues with tires or rims.

The leaf springs and bag position should prevent rotation(hopping).

But installing shocks to accompany the bags in the front/rear of the axle tube in the tradional leaf spring manner will help to eliminate rotation giving up a little clearence(maybe not,).
Shocks may limit how low the frame will lay in the grass if they "bottom out". Make sure when picking shocks you look at how much stroke/travel it has.
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Old 08-01-2020, 11:00 AM
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Take a picture of the back of the frame from the side please.


If that axle is mostly centered in between the angles then you will have no issue going inline.

If it is heavily forward with the tube under the front angle then you may need to have the springs inboard.

Still not a deal killer or anything that will require body removal.
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Old 08-01-2020, 01:17 PM
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Cerial, I have NO idea what you are talking about! Are you saying use parallel leaf springs? Leaf springs with air bags?
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Old 08-01-2020, 01:37 PM
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That happens with him alot lol.

The set up he's talking about is called a half leaf.
The front half of the leaf spring goes from the axle forward or backwards to the frame(the width locates the axle laterally) and the coil spring can be either on top of the axle tube, a little in front or behind the axle tube center line, or even on the leaf spring itself. If it's on the leaf it self, it would called a swing arm.
The leaf is basically just a trailing arm. The width and the bushing bind causes the lateral location.
All work and package a little differently.
If the spring is a little in front, the axle tends to wrap up and load the spring on the throttle and unload off throttle. Mounted behind, it tends to unload the spring on the throttle but also loads off throttle. When the coil spring is on the leaf, the spring isn't effected by axle wrap and remains neutral but aids in traction no matter the terrain.
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Old 08-01-2020, 03:43 PM
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Got any pictures of that rear suspension?
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Old 08-01-2020, 08:24 PM
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Which one?
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Old 08-01-2020, 08:51 PM
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Quote:
Originally Posted by johnsongrass1 View Post
That happens with him alot lol.

The set up he's talking about is called a half leaf.
The front half of the leaf spring goes from the axle forward or backwards to the frame(the width locates the axle laterally) and the coil spring can be either on top of the axle tube, a little in front or behind the axle tube center line, or even on the leaf spring itself. If it's on the leaf it self, it would called a swing arm.
The leaf is basically just a trailing arm. The width and the bushing bind causes the lateral location.
All work and package a little differently.
If the spring is a little in front, the axle tends to wrap up and load the spring on the throttle and unload off throttle. Mounted behind, it tends to unload the spring on the throttle but also loads off throttle. When the coil spring is on the leaf, the spring isn't effected by axle wrap and remains neutral but aids in traction no matter the terrain.
Yes you can go 1/2, 3/4, or full.



I am telling you to go full here.



All the leaf spring is doing is locating the axle. The bags and shocks do all the suspension work.

With a 1/2 and 3/4 setup there is a chance that the axle can wander and you almost need a watts or at the very least panhard bar to counter this.

With a full leaf setup you have 4(6) points holding that axle in place and it acts just like any other leaf suspension. You dont even need shocks if your bags are valved right allowing you to lay frame against the grass. But shocks help lessen the bouncing if this is something you want to do spirited driving with.



All the weight is on those bags(and springs). All the leaf pack is doing is holding that axle in its idle position.

You could use a mono leaf or leafs off of a 3500lb trailer if you accounted for the limited travel. But that is a bit risky in my book. A 2.5" wide 2 leaf pack is a good amount of safety while being easy to find. Most rides you can simply swap out the leaf pack, weld some plates to the axle, and your well on your way to adding bags.




Now looking at your setup I am guessing a 30ish inch spring can be used.

IF your axle is centered between the angular uprights.

If your axle is heavily forward from center then we can use any spring we want because we need to go inside the frame rails. Using a full leaf means that you want the axle to be centered(within a few inches) so that it locates the same each time.
Mounting inside the frame comes with cost.
More body roll, less room for tank/exhaust, additional weight in bracing.

But it gives you a good amount of room that any kind of 4 link will not allow. Even trailing arms are going to be heavier and larger then a full leaf setup.


A full leaf setup is how I like to mount bags.

It is the simpliest, lightest, cheapest, toughest(impacts), gives the most clearence, and in the event of a bag failure or bushing failure leaves still allows for some give that links/heims do not.

Now above you seem I said 4 points with 6 also. That is because the shackles add 2 more points. Now you can use a spring sliders and that eliminates 2 points lessening spring twist whichhelps bushing life. But spring sliders add to maintance. I add a bit of grease every other oil change as a rule.
If I wanted a clean setup I could lay in the grass I would use spring sliders so I would not have a shackle allowing that eye to be hidden and the spring to slide back more.
If the shackles would be hidden and there is room for them to swing then I would use shackles. More if they were already there though. Given the choice between the two in new form that will require some fabrication to install I will pick sliders every time.
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