Small tolerance parts drive big outcomes. Special‑order and custom shims correct fitment gaps, restore engineered geometry, and prevent progressive wear across suspension, driveline, and bearing systems. This post gives a technician‑ready guide to when to use custom shims, how to specify them, and shop practices that turn precision into measurable savings.
Why precision matters
- Match design intent: Accurate shim thickness and geometry restore OEM or application‑specific clearances so bearings, seals, and gearsets share load as designed.
- Prevent cascading failures: Even a fraction of a millimeter off at a shim seat amplifies into uneven wear, heat, and component fatigue down the line.
- Reduce labor and parts cost: A correct custom shim eliminates repetitive stacking, trial‑and‑error repairs, and expensive component replacements.
- Maintain serviceability: Precision parts hold tolerances under load, reducing rework and warranty claims.
Types of special orders and when to use them
- Single‑piece custom shims for high‑compressive or high‑precision locations where stacked plates creep or crush.
- Tapered and wedge shims to restore caster, camber, or steering axis tilt when flat shims cannot achieve the angle.
- Machined spacer blocks with locating features for repaired or modified frames and welded alterations.
- Material‑specific shims (stainless, hardened steel, coated alloys) for corrosive or high‑temperature environments.
- Hybrid shims with load spreaders built in to protect thin sections from point loads.
How to specify a custom shim — technician workflow
- Document baseline: photograph seating surfaces with a ruler inset, record measured stack thickness, alignment numbers, bearing preload, and gear contact patterns.
- Define the requirement: specify exact outer/inner diameters, locating holes, slot geometry, taper degree (if wedge), and tolerance on thickness to the hundredth of a millimeter.
- Select material and finish: choose corrosion‑resistant or hardened alloys and specify plating or coating if exposure demands it.
- Request prototype: order a single prototype for fit, torque, and run‑in verification before full production.
- Verify and document: torque to spec, re‑measure preload/angles, road‑test under representative load, photograph final stack with ruler inset, and save part drawing and measured outcomes to the vehicle record.
Shop best practices to maximize value
- One‑variable‑change rule: change only one shim or dimension between measurements and re‑record results immediately.
- Standardize spec sheets: keep a templated custom‑order form with required drawing fields, material options, and finish choices to speed orders and avoid errors.
- Stock common custom part numbers: for repeat fleet customers, pre‑order or stock frequently used custom shim part numbers to cut lead time.
- Use load‑spreading designs: where thin shims face concentrated loads, always specify integrated spreaders or add plates to prevent crushing.
- Document everything: store ruler‑inset photos, before/after measurements, prototype notes, and final part drawings in the vehicle file for future service and warranty defense.
- Measure ROI: track reduced rework, extended bearing and tire life, and lowered downtime to justify custom part decisions to fleet managers.
Treat special orders and custom shims as engineering solutions, not luxury options. Precise specification, prototyping, and disciplined verification convert a small part into a long‑term reliability gain and clear cost savings for fleets and shops.
