So that you never loose any performance, we’ve designed our geometry, both in length and angle, with the unique advantage of maintaining the vehicle’s caster throughout the full range of wheel-travel. The result is consistent handling regardless of terrain when combined with our specialty tuned Radflo coilovers.



The end result is a soft ride over small high speed sections, larger hits are soaked up with unbelievable control and yet the vehicle still responds crisp and nimble with little body lean for street driving. If you think a coilover’d rock buggy suspension has to be a slinky sloppy mess, then you’ve never experienced what tuned coilovers can truly do.



The Summit Machine Large Flex Joint is our most popular size of joint we make. A rebuildable spherical joint for the builder looking for quality. These joints meet or exceed expectations in performance, reliability and durability. Many success stories of this joint lasting 75,000 and even 100,000 miles or more! See below for full description…

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Before I purchased the 3-Link system for my 88’ 4Runner, I scoured the interwebs researching what makes an ideal link setup. 4Wheel Underground seemed to be the only company that mentions ‘road manners’ when talking about their suspension. This characteristic was most important to me when looking at link kits for the front since I drive my truck as a daily driver as well as to and from the trails. While I haven’t been able to get to some trails yet(life in the city), driving on the road is stable and very
predictable, I’m amazed that an SFA can perform this well on-road. Clearly, the R&D that has gone into this product is driven by passion and not profits, which becomes apparent when I needed to get technical support over the phone. The forums available for these kits are a welcoming community that gives the user wealth of information. The impressive craftsmanship that goes into each kit is complemented by the stellar customer support that I received on multiple occasions. There is only one problem I have found with the 3-Link front kit so far: They make the rear leafs feel inadequate and will soon be replaced by the 4-Link rear setup. I would highly recommend a 4Wheel Underground 3-Link kit to anyone looking to upgrade their existing
SFA or SASing their truck.

RBx, March 24, 2014

I am amazed at the performance of this link kit, super stable and rides nice on road, ridiculously smooth offroad at speed, and it is very predictable on the rocks and it's very predictable at speed or on rocks and better in off camber situations than any of my buddies home linked kits or any leaf sprung vehicle. Not enough can be said about the precision of the brackets as well. The bumpstops always hit the pads dead center, no matter how the suspension is being compressed.

Peacesells, March 25, 2012

Just wanted to give everyone a heads up on the front suspension!!! It is a kick ass set-up I have went on a few runs with it now. It has better handling then leafs (night and day) I have air mailed it so many times and just beat the hell out of it and have yet to have a single problem!!!! This set-up is everything i was looking for, the quality is A+. I can say as soon as i get into my own place the truck will be getting the rear 4 link from 4WheelUnderground as Brian has had better service and quality then any other company out there. leafs can not even come close to competing with coilovers and overall strength. I highly recommend 4WheelUnderGround to anyone that does mild to wild wheeling!

Scott, May 3, 2012

I finally finished everything, limiting straps, brake lines, etc...and did a test drive on a fire road and a bunch of street testing. All said and done, the three link setup works very well. On the trail I was able to go faster than I was with leaf springs. This does not mean I am a baja racer, it is still a 20 year old truck with a solid axle, but where I was going 10 to 20mph before I am going 30 to 40 now. As for the on road performance, the three link works well and I suspect that anybody running crappy Rancho or a RUF would probably crap themselves with joy after this three link was done. I even had a fabricator/mechanic friend of mine comment that this was the best looking three link he has seen on a 4runner and that he was surprised at how well it drove going down the road. I am happy and hope that anybody sitting on the fence pulls the trigger, links their rig, and shoots me an e-mail so we can go wheeling when it is all said and done.

Noahrod, June 12, 2011

So not real happy with this setup. It makes it too easy and there's no challenge going on runs with my Jeep buddies. Do still enjoy watching them struggle on crap I can effortlessly walk up though.

Subpilot, August 20, 2011

Installed shortly after i got it. Wheeled it all last summer and been driving it a fair bit on the roads lately. Flex is awesome and drives great. It’s running around on 39.5 Iroks. I will probably order from you again in the near future. It just pops up obstacles. Very happy! You built a great product.

Matt Wehrly, April 5, 2012
Phone: (+1) 818.402.6945
Prescott Valley, Arizona