A shimmy through the wheel or pedal under braking is usually discs, but confirm before spending.
Causes, in order:
- Uneven pad deposits / warped discs — the classic, and often just uneven pad-material transfer, which hard bedding or new discs cure.
- Worn front control-arm bushings (Front Control Arms) letting the arm walk under braking — reads as a shimmy.
- A worn front wheel bearing (Wheel Bearings).
- A sticking caliper slider heating one disc.
Diagnose:
- Measure disc run-out and thickness variation with a dial gauge before condemning them.
- Judder only under braking points at discs; judder all the time at speed points at bearings, tyres or balance.
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