Truck & Jeep Shock Rebuild

A truck shock rebuild at MST Motorsports includes full disassembly, shaft and body inspection, new seals and bearings, fresh shock oil, bladder or IFP inspection, re-valving when the damping needs to change, and a nitrogen recharge. A rebuild restores the damping the shock was built to deliver and gives it a service life again.

• Disassembly and inspection. The shock comes apart and we check the shaft, body, piston and eyelet bushings for scoring, pitting and bend.
• Seal and bearing replacement. New seal head components go in. A weeping shock is most often a worn seal and a scored shaft.
• Internal component evaluation. We measure shim stacks, pistons and needles against spec and against the vehicle's weight and use.
• Fresh oil at a viscosity chosen for heat and load. Shock oil that has been cycled through heat breaks down, and degraded oil aerates more readily. Once it foams, the damping goes with it. We replace it rather than top it up.
• Bladder or IFP inspection. Internal floating pistons and bladders keep the oil and the nitrogen separated. When that separation breaks down the oil aerates and the damping goes soft, which is what a shock fading partway down a washboard road often is.
• Reassembly and nitrogen charge. We charge to spec with nitrogen, which is dry and inert. Shop air carries moisture into the shock, and moisture corrodes internals and emulsifies the oil.

Serviceability varies within a brand as much as between brands — some units are built to come apart and some are sealed at the factory. We confirm which type a shock is on inspection.

MST Motorsports rebuilds and re-valves Bilstein, Icon Vehicle Dynamics, Carli, Cognito, Fox and King shocks for trucks and Jeeps in house in Washington, Utah.

On the truck and Jeep side that usually means Bilstein and Icon Vehicle Dynamics on half-tons, Broncos and Wranglers; Carli on Ford Super Duty and Ram 2500 and 3500; Cognito on GM heavy-duty trucks; and Fox and King on lifted builds running coilovers or remote-reservoir shocks. We also install and service suspension components from Rough Country, ReadyLift, TeraFlex, Rock Krawler, Rubicon Express and EVO Manufacturing.

Elka and Walker Evans shocks are rebuilt on the same bench on the powersports side.

Truck shocks in Southern Utah wear from heat and load rather than mileage. A shock turns suspension movement into heat and has to shed that heat into the air around it, and four conditions in Washington County make that harder:

• Sustained summer ground temperatures. Shock oil that runs hot for hours thins out, and thin oil moves through the valving too easily. That is heat fade, and it shows up as reduced control late in a long drive.
• Washboard dirt. The roads out toward Warner Valley and Sand Hollow cycle a shock continuously at small amplitude, mile after mile. That is the hardest duty cycle a shock sees, and it is the main reason two identical trucks can need service at completely different points in their lives.
• Towing. Tongue weight sits on the rear suspension for every mile of a tow, and the rear shocks control that added mass over every bump. Trucks that tow regularly tend to show rear shock wear first.
• Dust. Fine grit works into the shaft seal and scores the shaft, and the scoring is what makes a shock weep. Rinsing the shock bodies after a dusty weekend extends seal life — grit that never reaches the seal cannot score the shaft.

A lift kit changes the suspension's travel range, and a shock that was correct at stock ride height is usually wrong after the lift. Two failure modes show up in the shop repeatedly.

Too short. The shock tops out before the suspension reaches full droop. The shock becomes the travel limiter, and the eyelet, mount or shaft takes the load.

Too long. The shock bottoms internally before the bump stop makes contact, and that impact goes into the piston and the shock body.

Valving matters as much as length. Damping valved for a stock half-ton is well short of what the truck needs once it carries a steel bumper, a winch, 37-inch tires and a bed rack — the springs are carrying more, and the shock is controlling more mass over the same bumps. Re-valving during a rebuild is how the damping gets matched to the vehicle's current weight and use.

A Power Stroke, Cummins or Duramax front end carries several hundred pounds more than the gas version of the same truck, and that weight sits high and far forward, over the front axle. The front shocks on a heavy-duty diesel control more mass over the same bumps. Diesel trucks therefore come in for front shock service on a shorter interval than their gas counterparts. On a lifted diesel running a long-travel system from Carli or Cognito, the shock is also controlling more travel, and the valving has to account for both.

A truck or Jeep shock needs service when it is weeping oil, when the vehicle keeps moving after a dip instead of settling in one motion, or when the tires show cupped wear.

• Oil film, wet streaks, or dust caked to a wet shock body
• The truck continuing to move after a dip instead of settling in one motion
• Nose dive under braking or squat under acceleration that was not there before
• Cupped or scalloped tire wear, which can mean the tire is not being held consistently against the road
• The rear of the truck moving sideways over washboard
• Damping that feels fine in the first hour and vague by the third

For a serviceable shock from Bilstein, Icon Vehicle Dynamics, Carli, Cognito, Fox or King, a rebuild brings the damping back and is the usual answer. The case for replacement is a bent shaft, a cracked or dented body, a damaged mount, or a shock that is the wrong length or valving for the vehicle's current setup. Inspection confirms which of the two applies.

Any suspension work that changes a truck's ride height needs an alignment afterward, because ride height moves the suspension geometry with it — caster on a solid front axle, and camber, caster and toe on an independent front end. On a lifted solid-axle truck or Jeep that can also mean caster correction and track bar adjustment. Alignments are performed in our Washington, Utah shop on top-of-the-line Hunter HawkEye Elite alignment equipment.