Original Hydraulic Seal Destroyed? Identify the Replacement From the Rod, Bore and Groove
A flattened or broken seal can lie to your caliper. The machined gland and piston usually preserve the dimensions that matter for finding a replacement.
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Start with seal function
Before measuring, identify what the component must do: keep oil inside at the rod, separate pressure across the piston, wipe contamination, seal a static joint or guide the piston/rod.
For a rod seal
Measure the actual rod diameter, the gland groove bore/diameter and axial groove width. Inspect the entry chamfer and any separate buffer or secondary seal groove so you do not combine two components into one assumed profile.
For a piston seal
Measure cylinder bore, piston groove diameter and groove width. Note whether the seal is single-acting or double-acting and whether separate wear rings or back-up rings are present.
For a wiper
Measure rod diameter and the wiper housing dimensions. Determine whether it is a snap-in elastomer/TPU style or a metal-cased press-in style; those housing requirements are not interchangeable.
Create a measurement record before ordering
Take photos with the caliper in frame, record dimensions to appropriate precision, note units, and repeat measurements around the circumference. Then use a manufacturer housing table or seal finder rather than trying to reconstruct the free-state size from damaged fragments.
Before you order or reopen the cylinder
Create a sketch that distinguishes rod or bore diameter from groove root diameter and width. Note pressure direction and whether the seal moves with the piston or stays in the gland. Send the sketch with the fragments instead of only three unexplained numbers.
To connect this inspection with the next repair decision, see Hydraulic Seal Sourcing: OEM Kit, Stock Seal or Custom Machined Seal?.
Technical references
Use the exact seal manufacturer and machine service data for final selection.
Need to narrow the fault?
Use the interactive tools after the inspection—not instead of it.
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