What This Shock Does
A shock absorber on a semi truck does not hold the vehicle up. Springs or air bags do that. The shock controls how fast the suspension moves after it is loaded, damping the spring's rebound so the axle stays planted instead of pogoing down the road. On a loaded tractor that damping force is doing real work on every joint and every mile.
Part 21436086 is a direct replacement damper built for heavy-duty suspension service. It uses a hydraulic valved piston in an oil-filled tube, with a rod, seal and mounting eyes or studs at each end. The mounting style and the extended and collapsed lengths are what determine whether it drops into your bracket, so those are the dimensions to check against the unit you removed.
Shocks work as a set. Replacing one side and leaving a worn unit on the other gives you uneven damping across the axle, which shows up as pull under braking and uneven tire wear. Standard practice is to change them in pairs per axle, and to look at the bushings and mounting hardware while the old unit is off the truck.
Why 21436086 And F03494S235 Cross
F03494S235 is the cross-reference number listed for this shock. It is published here for identification only. PartStop is not affiliated with, endorsed by, or authorised by any original equipment manufacturer, and other manufacturers' numbers appear solely so you can match what is stamped on the part in your hand.
These numbers cross because they describe the same physical damper: same mounting configuration at both ends, same extended and collapsed lengths, same bore and rod diameter, and damping valved for the same heavy-duty duty cycle. Shocks are defined almost entirely by geometry and valving. When those match, the number on the tube is a labelling difference, not a hardware difference.
Treat the cross as a starting point, not a guarantee. Suspension packages get changed mid-production and units get swapped over a truck's life, so the number on the part you pulled off is better evidence than a spec sheet. Confirm by VIN or by reading the number off the old shock before you order.
How These Fail And What To Check
The obvious failure is a blown seal. Oil past the rod seal means the shock is losing hydraulic fluid and damping force. A light film of oil on the tube is normal seepage from rod lubrication. Wet streaks running down to the lower mount, with dirt caked in them, mean the unit is done. Check both sides of the axle before you decide.
Less obvious failures show up as ride and wear symptoms. Cupped or scalloped tire wear, axle hop over broken pavement, cab shudder after a bump, or a trailer that keeps working the fifth wheel long after the truck has settled. Bushings are also a wear point. Grab the shock body and try to move it. Any play at the eye means the bushing is shot even if the damper still works.
Before ordering, measure. Get the extended length pin-to-pin or eye-to-eye, the collapsed length, and note the mount type at each end. Photograph the tag or stamping on the old unit. Those three pieces of information settle the question faster than any cross-reference list will.
21436086 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 21436086. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| OE/Cross-Ref | F03494S235 |
Frequently asked questions
Is 21436086 the same shock as F03494S235?
They cross to the same part by mounting configuration, length and damping specification. F03494S235 is listed for identification only so you can match the number stamped on the unit you removed. It does not indicate any affiliation with the original manufacturer. Confirm by VIN or by the number on the old part before ordering.
Do I have to replace shocks in pairs?
It is the standard approach. Mismatched damping across an axle causes pull under braking and uneven tire wear, and the surviving shock is usually close to the end of its life anyway. Replace per axle and inspect the bushings and mounting hardware while you have access.
How much oil on the tube means the shock is bad?
A thin film is normal, the rod carries a little oil past the seal to stay lubricated. What condemns the unit is wet streaking that runs down toward the lower mount and collects dirt. Wipe the tube clean, drive it, and look again. If it comes back wet, replace it.
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Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
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