4 Link Front Daily Driver Help.

9724VF350

9724VF350

Tractor Guy
Joined
Mar 2, 2010
Messages
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I'm in need of some suggestions on building a 4 link front suspension for a currently leaf sprung Excursion.

I know that I could just throw in a radius arm superduty axle, and buy the 4 link conversion for it, but my leaf spring axle is 100% rebuilt. Sandblasted, painted, seals, ball joints, unit bearings, brakes, bearings, u joints, ect with 0 miles on it. I really hate to do that all over again on a different axle.

I'm just looking for a better handling and riding street setup, with a tighter turning radius. Offroading will not happen, and I would prefer to lower it a couple inches.

I have my own CAD program to design brackets with, and good connections on having them laser cut and CNC bent. I would prefer to design it 100% bolt on. I mainly need educated on the magic behind the 4 link bars themselves. Placement on the axle and frame, length, ect.
 
Search over at pirate4x4 as some of those guys could build a 4 link in their sleep. I'm leaning over there as I'm going to build one on my mud truck.
 
There are 3 and 4 link calculators out there that you use in Excel to see how it will work and how things change through travel. If you're doing a parallel 4-link, use the 3-link calculator. It is designed to use a panhard bar. The 4-link calculator is made for triangulated 4-links, and will give you a few numbers that are wonky. But still gives a good visual representation of it all.
 
Been thinking of going radius arm over 4 link just because of how expensive rod ends are. Plasma cutting and bushings are cheap!
 
This is a doc I wrote for guys in exactly your position, who really just need a starting point. Its several years old, and is off-road performance oriented, but it might help a little bit.

Link Suspension Basics

In my experience….

Design

Keep your lower links as low on the axle as possible. Most people are happy with mounting the bottom of your link end flush with the bottom of the axle tube so they don’t catch on rocks or other trail obstacles.

Keep your upper links as high on the axle as possible. The average is about 8” of vertical separation between the lower link mounting point and the upper link mounting point if the lowers are mounted slightly below axle centerline. The farther you mount the lower links below axle centerline the lower your can mount your upper links, and the less separation you will need. The higher your mount your lower links, the greater torque your engine/drive train exerts, the larger the tire diameter, the greater your vertical separation needs to be.

Get as much angularity between your upper and lower links as possible when viewed from above the chassis to decrease the loads seen by the links and link ends. Keep your links as far out (toward the knuckle) on the axle as possible.

Make your lower links as long as possible and make your upper no less than 75% the length of your lowers. Rule of Thumb: Make your lowers about 75 to 90% of your desired tire diameter.

Mount your panhard as high on the chassis as possible even if it means making a tall mount off the axle.

Make the panhard as long as possible and make it as horizontal as possible, but sacrifice this to ensure it’s the same approximate length and angle as your drag link if you have standard crossover steering. A high panhard will keep your roll center as high as possible to decrease body roll. Your roll center on a panhard suspension is at the middle of the panhard when viewed from the front. A horizontal panhard will help keep the axle from moving side too side too much, as will having a long panhard. Having the panhard match the drag link will help prevent or eliminate bump steer with crossover steering.

Parallel 3 links and Wristed radius arm suspensions should have the double arm/radius arm on the pinion side. If possible mount the upper to the top of the diff to counteract axle torque. Keep the arms as long as possible

Try to mount your coils so the center of the spring is the same height as your roll center.




Materials

For most rigs a 9/16” grade 8 bolt is enough for the link ends, but the standard is to use a ¾” heim joint with a 5/8” bolt hole. For those that wish to drive with no consideration of link end damage, I suggest a ¾ to 1” grade 8 bolt and 1-1/4 heims.

1.5” schedule 80 A53a pipe is a good starting point for links less than 40” long on rigs that weigh 4500 or less, you may bend one your first trip out, but you may never bend one if you don’t thrash your rig over rocks or logs. I have used this material on the rear of my 6000 lb buggy for 4 years and have yet to bend a link. I used this on the front of the same buggy and bent one a year over the last 3 years. I now use 1/8” wall rectangular tube with 3/16 and ¼ bottom and top caps.

Today’s standard for lower link material is 2” .250 wall DOM tubing. Heavy rigs or even lighter rigs driven with a heavy right foot often use 2” .375 wall or heavier. Upper links can typically be constructed 60-75% lighter depending on application and suspension design.

Link brackets should be fabricated from no less than 3/16” A36 mild steel plate, and should be gusseted with no less than 1/8. Heavy rigs, or rigs that will be driven hard on hard terrain should be ok using no more than 3/8” link brackets. I typically fabricate my upper link brackets out of 3/16 and my lowers out of ¼ with 1/8 to 3/16” thick washers welded around the bolt holes to increase the fasteners load bearing surface.


Brook
 
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Lots of good info offered here.

A friend of mine has me 90% convinced to swap axles. Bigger brakes, bigger ball joints, improved trac bar, ect. He also swears up and down that the factory radius arm suspension is better than the 4 link conversions for pavement only ride and handling.

Torn on this one.
 
9724VF350 said:
Lots of good info offered here.

A friend of mine has me 90% convinced to swap axles. Bigger brakes, bigger ball joints, improved trac bar, ect. He also swears up and down that the factory radius arm suspension is better than the 4 link conversions for pavement only ride and handling.

Torn on this one.
Click to expand...

I am in similar disarray as well but I have my 95 which I don't want to fool with the unit bearings and metric front axle.
 
9724VF350 said:
Lots of good info offered here.

A friend of mine has me 90% convinced to swap axles. Bigger brakes, bigger ball joints, improved trac bar, ect. He also swears up and down that the factory radius arm suspension is better than the 4 link conversions for pavement only ride and handling.

Torn on this one.
Click to expand...

If your sticking on the pavement, I would probably agree with that. Radius arms also turn the whole axle into a sway bar which helps stabilize the vehicle.
 
not enoughsmoke said:
I am in similar disarray as well but I have my 95 which I don't want to fool with the unit bearings and metric front axle.
Click to expand...

Put the obs spindles and hubs on the coil sprung axle. I think I've seen a conversion kit somewhere.
 
9724VF350 said:
Lots of good info offered here.

A friend of mine has me 90% convinced to swap axles. Bigger brakes, bigger ball joints, improved trac bar, ect. He also swears up and down that the factory radius arm suspension is better than the 4 link conversions for pavement only ride and handling.

Torn on this one.
Click to expand...

That's what I would do.
 
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