What The 85724 Is
The 85724 is an aftermarket hydraulic shock absorber built for heavy-duty truck suspension service. It damps axle movement so the springs or air bags do not keep cycling after a bump. On a semi tractor or trailer, that means controlling wheel hop, keeping the tire loaded, and stopping the cab and frame from pitching every time the road changes.
A shock is a wear item, not a lifetime part. The piston pushes oil through valving inside the tube, and that oil takes heat every mile. Over time the valving fades, the oil thins, and the seal at the rod lets pressure past. The shock still bolts up and looks fine, but it has stopped doing work.
This unit is offered by World Truck Parts as a direct replacement for the interchange listed. It is an aftermarket part. We are not affiliated with, endorsed by, or authorised by any vehicle or component manufacturer, and any other brand's number here is printed for identification purposes only.
Why These Numbers Cross
85724 and F01991S235 cross because they describe the same physical shock: same extended and collapsed lengths, same end-mount types and orientation, same bushing bore, and damping valving in the same range. Those are the dimensions that decide whether a shock bolts in and works. Change any one of them and the part is a different part, regardless of what the label says.
Cross-reference lists get built from that dimensional and functional match, not from a shared catalogue family. F01991S235 is listed here so you can identify the 85724 against a number stamped on a casting, printed on an old box, or pulled out of a fleet parts system. It is not a claim of common origin or of brand association.
Treat the cross as a starting point, not a guarantee. Trucks get respec'd, suspensions get swapped, and a previous repair may have put a non-original shock on the axle. Confirm fit by VIN, or by measuring and reading the number off the shock you just removed, before you commit the order.
Checks Before You Order
Measure the old shock eye-to-eye fully extended and fully collapsed. Then check the ends: loop/eye, stud, or crossbar, and whether the top and bottom differ. Note bushing inside diameter and the width across the eye. Those five numbers plus the interchange give you a solid identification. Photograph the old unit before it goes in the scrap bin.
Replace shocks in pairs across an axle. A new shock on one side and a faded one on the other gives uneven damping and chews the new unit. While the wheel is off, look at the mounting brackets for elongated holes and cracked welds, and check the bushings on the opposite end of the axle — a shock that fails early usually had help.
85724 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 85724. 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 | F01991S235 |
Frequently asked questions
Is 85724 the same shock as F01991S235?
They cross to the same shock by length, mounting style and damping range, which is why F01991S235 appears in the interchange for 85724. The other number is listed for identification only. Confirm against the number on the shock you removed, or by VIN, before ordering.
How do I tell if the shock is actually bad?
Look for oil wet down the body from the rod seal — that is a failed shock, not road film. Bounce test the corner and watch for more than one rebound. Also check for a hot shock body after a run when the others are cool, and inspect the bushings for cracking, ovaling or play at the mounts.
Do I have to change both sides?
Replace shocks in pairs on the same axle. Damping fades gradually, so the surviving shock is rarely as strong as a new one, and the mismatch loads one side harder and shortens the life of the new unit. If both axles are on the same service interval, plan them together.
Not sure it fits? We check before you pay.
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.
More cross-reference guides
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Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.