technically, I don't think so, but I doubt half the cops on the road would know what a 4 link was, let alone if it was factory on your rig.
I bet you could drive around for your entire life and not be bothered about it.
EDIT: Technically a 4 link is legal as can be. A lot of Wranglers use it front and rear, I'm pretty sure most if not all Dodge Rams had it (or at least my cousin's 97 Ram has a 4 link) until they went to IFS.
The thing that makes it illegal is if it is on a vehicle that did not come from the factory with a 4 link setup.
Technically, if it is "bolt on", then they can't give you any hassle for it. If you welded the brackets to the frame or axle, then they CAN find something to ticket you for, not that anybody ever will. Rolledranger's SAS comes to mind as a fully "bolt on" kit made by a major manufacturer, even though it wasn't neccesarily designed for a ranger, the link brackets bolt to the frame, and everything about the install looks the same as the TJ it was meant for. Basically, the more homebrew and "scary" it looks, the more they're likely to hassle you.
The only LAW that I know of pertaining to this subject would be the washington lift laws, which state anything done to the suspension has to be made by a recognized lift kit manufacturer. If someone else want's to dig up that info to be more precise, be my guest.
Theres no reason it shouldnt be, tons of cars come factory with them. As long as you meet lift laws and your tired dont stick out it doesnt matter what suspension disgine you have. Im sure if its gonna be linked it wont meet ride hight but who gives a $h1t, mine isnt and its leaf sprung. go ahead and link it, when I get another DD mines getting linked.
I'm sure you'll find plenty of reasons here to make it illegal. Pretty much all of us on here are illegal in some way. Notice the no coil spacers line.....
The following laws pertain to suspension and lifts:
Revised Code of Washington (RCW) 46.37.375 which states in part “…(5) Suspension condition. Ball joint seals shall not be cut or cracked. Structural parts shall not be bent or damaged. Stabilizer bars shall be connected. Springs shall not be broken, or extended by spacers. Shock absorber mountings, shackles, and U-bolts shall be securely attached. Rubber bushings shall not be cracked, or extruded out or missing from suspension joints. Radius rods shall not be missing or damaged…”
Washington Administrative Code (WAC) 204-10-036 “Suspension”
“A motor vehicle must be capable of stable, controlled operation while traversing a slalom-type path passing alternately to the left and right of at least four cones or markers arranged in a straight line and spaced sixty feet apart at a minimum speed of 25 mph.
Body lifts are permitted provided that they are manufactured by an aftermarket manufacturer, designed for the make and model vehicle on which they are installed, and installed according to the manufacturer's recommendations. Body lifts may not use more than a three-inch spacer and may not raise the body more than four inches above the frame when all components are installed.
A motor vehicle must:
(1) Have a minimum ground clearance to allow the vehicle to be in motion on its four rims on a flat surface with no other parts of the vehicle touching that surface and a maximum ground clearance determined based on the table contained in WAC 204-10-022 (6)(f) bumpers.
(2) Have spring mounts and shackles properly aligned and of sufficient strength so as to support the gross weight of the vehicle and provide free travel in an up and down movement under all conditions of operation.
(3) Incorporate antisway devices to control lateral movement in rear coil spring suspension systems.
(4) Have a suspension system that allows movement between the unsprung axles and wheels and the chassis body.
(5) Be equipped with a damping device at each wheel location. The dampening device must stop vertical body motion within two cycles when any corner of the vehicle is depressed and released.
(6) Be capable of providing a minimum relative motion of plus and minus two inches.
(7) Not use heating or welding for coil springs, leaf springs, or torsion bars.
(8) Not be constructed or loaded so that the weight on the wheels of any axle is less than thirty percent of the gross weight of the vehicle.
(9) Not raise or lower the height of a motor vehicle while the motor vehicle is traveling more than 15 mph on a public roadway with a posted speed limit of 25 mph or less. Except when lawfully participating in a parade permitted by local jurisdiction.
(10) At no time have any portion of any tire of such motor vehicle leave the surface of the roadway.
(11) Not have any portion of the vehicle or component of the hydraulic system used to raise or lower the vehicle cause or emit sparks.
Nothing in this section shall prohibit a county or city from enacting stricter regulations for aftermarket vehicle hydraulics on a public roadway.”
In addition to the above regulations regarding suspension specifically you will also want to make sure that the height of your bumpers, lights and all other safety equipment is within the legal limit and that you have the proper tire covers.
Revised Code of Washington (RCW) 46.37.500 states in part, ". . . no person may operate any motor vehicle, trailer, or semitrailer that is not equipped with fenders, covers, flaps, or splash aprons adequate for minimizing the spray or splash of water or mud from the roadway to the rear of the vehicle. All such devices shall be as wide as the tires behind which they are mounted and extend downward at least to the center of the axle. . . ."
Washington Administrative Code (WAC) 204-10-022 states in part, “(6) Bumpers: A motor vehicle must be equipped with a bumper on both the front and rear of the vehicle with the exception of motor vehicles where the original or predominant body configuration, provided by a recognized manufacturer, did not include such bumper or bumpers in the design of the vehicle. For the relevant model year, bumpers must accommodate recognized manufacturer impact absorption systems pursuant to applicable SAE Bumper Standards or equivalent standards.
Bumpers are optional equipment on vehicles defined as street rods and kit vehicles by the Washington state patrol vehicle inspectors.
(a) Be at least four and one-half inches in vertical height.
(b) Be centered on the vehicle's centerline.
(c) Extend no less than the width of the respective wheel track distances.
(d) Be attached to the vehicle in a manner equivalent to the original manufacturer's installation.
(e) Be horizontal load bearing and attach to the vehicle frame to effectively transfer energy when impacted.
(f) Be mounted at a maximum height based on the original gross vehicle weight rating (GVWR) of the vehicle, measured from a level surface to the highest point on the bottom of the bumper. For vehicles exempted from the bumper requirement for the reasons stated above, a maximum frame elevation measurement must be made to the bottom of the frame rail. Maximum heights are as follows:
22 Inches - Front
22 Inches - Back
4,500 lbs. and under GVWR
24 Inches - Front
26 Inches - Back
4,501 lbs. to 7,500 lbs. GVWR
27 Inches - Front
29 Inches - Back
7,501 lbs. and over GVWR
28 Inches - Front
30 Inches - Back
A blocker beam or additional bumper may not be used to meet the above requirements.
(g) If an existing bumper from a recognized manufacturer is not used and a special bumper is fabricated, it must be certified as meeting the bumper standards set under 49 CFR 581."
My buddy had a 4runner he built a while back that had a 4-link rear that we fabbed up.
We drove that thing everywhere and never got a bit of grief from the fuzz. Sure was fun seeing some of the looks we got from drivers on the road though, that thing was Insane. lol