4 Link Rear Suspension

 

   
 
 

4 Link Rear Suspension - Page 3

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With the links in place I turned my attention to the brake lines.  due to the amount of droop this suspension is capable of, the lines need to be mounted on the links.  A soft line at each end of the link will take care of the little bit of motion present when the axle articulates.

How does it work?

After two trips I can give some driving impressions.  I'll update this page in a couple weeks as I try more types of terrain.  

The rear suspension is neutral when accelerating, no lift of squat from the back end which is what I was aiming for.  On the road the biggest thing you notice is the body lean.

  This setup is much more plush than my previous leaf spring setup and I feel it is a little too soft to be a daily driver.  A sway bar may cut down the body roll enough to make it a viable road handler, or you could go with  stiffer springs (say a 125/150 lb combo).  I estimated the rear suspension was supporting 1000lbs of unsprung weight and gave that figure to Dave at Polyperformance to calculate the required spring rates. I actually think the unsprung weight is well under 1000lbs since I cut off the back end, it's very easy to lift the rear end several inches by myself. Anyway, I still think I got the spring rates nearly perfect for off road use, more on that below. 

Off road on two track dirt roads the suspension really soaks up the bumps.  A good example is driving off of ledges, with the new setup the rig just smoothly comes off the ledge and the springs absorb the impact so you hardly notice it.  With my leaf springs the impact was pretty jarring and could be felt throughout the entire rig.

  It really forced you to slow down to a crawl.  The one fly in the ointment comes when trying to climb loose inclines like seen in the picture above.  In 2wd there just isn't enough weight over the rear suspension to push the tires into the ground and provide traction.  4 high solves that problem but I decided to experiment by moving some more weight over the rear axles. 

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I had welded some tabs to the rear frame before I painted it with this scenario in mind.  Using some .5" x .06 wall tubing and some 3/4" conduit, I fabricated a small rack that sits above the rear axle in the dead space behind my flat storage deck.  The rack will snugly hold 4 of the medium sized ammo boxes, 3 of them shown in the picture above.  Behind the ammo boxes is a small recesse where I strapped my spare front axle shafts and spare front drive shaft.  All total I estimate that puts about an additional 60 lbs over the rear axle between the axles, tools and spare parts stored in the boxes. I'll know the results of this experiment shortly.

Update - Moving some more weight over the rear axle helped traction a little when in 2wd.  It also made the rig a little more stable when driving down dirt roads.  Before the change the rear end would swing out in nearly every sharp curve, now it only does it if I apply too much throttle or turn too sharply.  After mounting the rack and moving my boxes back I had to adjust the pre-load on the coil springs to level out the back.  I screwed the coil retainers down another half inch and it cut the body roll quite a bit.  I also noticed the rig didn't feel so "floaty" at high speeds.

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Update 5-04-03

I believe I have the rear coilovers tweaked so the body roll is almost eliminated. I have been adjusting the preload nut a little bit before each trip and then evaluating it's effect.  These adjustments combined with some stiffer front springs seems to have done the trick.  After a day of driving roads and 4 trails out in the Florence Junction area I can say the sway when steering is gone, also high speed driving on dirt roads feels as stable as my old leaf spring setup.

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After bending a brand new front leaf spring last weekend, I took my springs to Valley Spring here in Phoenix and had them make me two new main leafs w/ a military wrap second leaf.  They used the remaining leafs from my stock YJ rear pack (5 leaf).  This pack is a little stiffer than the original (it's not broken in yet), but the extra stiffness helped reduce body roll and doesn't seem to have affected ride quality.  It's still nice and smooth on bumpy roads.

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I also added a limit strap to the rear axle.  I welded a block in between my link mount tower and the link mounts so it will act as a brace and relieve some of the stress the tubing is seeing.  The block was then tapped in three places so I would have a little adjustment for strap length.  I also added a rib to the rear of the housing to distribute the forces over a bigger area instead of just at the top of the housing.

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One thing about the stiffer front springs, they don't stuff as well as the old ones as you can see in the picture above.  I suspect as I break them in they will flex better.  This is one tradeoff that should be considered.  They still stuff into the wheel well when the other tire is forced into the something, in the picture above the passenger side front tire is hanging in air.

Update 6-01-03

After more testing I have determined that a 120/150 spring rate makes a pretty good compromise between off road flex and on road stability.  I have the coilovers set so the upper springs can compress about 3 inches. These setting combined with my limit strap set so there is no slack with the suspension at rest has made the rig nice and stable at speed while turning.  Out of curiosity I moved the limit strap so there was about an inch of slack and boy what a difference.  In corners the there was enough body roll to allow the back end to break loose on corners very easily. It was scary enough that I moved the limit strap back to being tight before we headed back to the trailers.  I think the last test I am going to do is try running the 100lb coils with the 150's and see how it responds.

The Weak Link