Coil Spring Isolator

What sits at the end of a coil spring

A coil spring does not rest directly on steel. At the top, and often at the bottom, a molded rubber or polyurethane isolator cushions the spring end, stops it from clunking as it unloads and spins slightly on bumps, and keeps metal from grinding against the spring seat. The factory pieces harden and crack over the years, and lifted Jeeps often lose them during a spring swap. When a coil sprung Jeep develops a clunk or a squeak over speed bumps with nothing else loose, worn isolators are a common cause. The parts here are the replacements, plus several related pieces that live at the same spot: trim packers, spring retainers, weld-on spring cups and slider inserts for coilover springs.

Isolators: rubber or urethane

Factory-style rubber isolators, sold by Crown Automotive, Jeep and Omix-Ada by position, give the quietest result and the original ride. Energy Suspension and Prothane polyurethane isolators last longer in oil, salt and heat and will not crumble, and some Energy Suspension sets are thick enough to add a modest lift, from three-quarters of an inch to 2.5 inches depending on the application. Urethane can squeak against a dry spring end, so use the supplied grease. Isolators are specific to spring diameter and position, upper or lower, front or rear, and a JK upper isolator does not fit a TJ.

Trim packers for leveling

Many lifted Jeeps and Land Rovers sit a little lower on one side, usually the driver side, because of fuel tank placement and driver weight. A trim packer is a thin steel or polyurethane spacer, typically 5 to 10 mm, placed under one coil to level the vehicle left to right. The Old Man Emu packers from ARB for the JL and Discovery are sold per spring, and the rule is one packer per spring only; stacking them lets the spring seat move and is unsafe. Packers are for small trim corrections, not for lift. If you need more than about half an inch, the answer is a different spring rate.

Retainers, cups and slider inserts

• Spring retainers: zinc plated clips, like the TeraFlex set for the JK and JKU, that hold the coil in its seat at full droop so a long travel Jeep does not drop a spring on the trail. Cheap insurance after a lift.
• Spring cups: weld-on 3/16 inch steel cups from Rubicon Express that replace a rusted or torn factory lower spring seat on a TJ axle. Welding and paint required, and they are sold by position, for example front lower right.
• Slider inserts: plastic rings that fit the dual rate spring dividers on Walker Evans and FOA 2.0 and 2.5 inch coilovers, so the upper and lower springs do not bind or squeak against the divider. Match the shock body diameter.

Installation notes

Replacing an isolator means unloading the spring. On a Jeep with the axle supported on a jack and the frame on stands, disconnect the shock and sway bar links, lower the axle until the spring is loose, and lift the spring out; a spring compressor is rarely needed on a stock height Jeep but may be on a lifted one. Seat the new isolator so its locating tab engages the spring seat, and check that the spring end sits in the pocket of the isolator before reloading. Torque the shock and link hardware to spec with the suspension at ride height, and bounce the vehicle to check for the clunk you started with. Work on coil springs carefully; a loaded spring stores a great deal of energy.