REFERENCE · LIVE

A3 U-Joint & CV Joint Reference

Inspection spec, failure modes, working angles, and the noise/feel signatures that identify each. The difference between a $30 U-joint job and a $700 axle replacement starts here.

U-Joint — Inspection Spec

Radial play (cap-to-yoke)

By hand under shaft

0 in (no play)

Operating angle (driveshaft)

2° - 4° typical

Max operating angle

≤ 8°

Front-vs-rear angle delta

Must cancel for smooth rotation

≤ 1° difference

Grease interval (serviceable)

15-30k miles

U-Joint — Failure Signatures

Clunk on engagement (P→D, accel)

Worn cap or trunion

Replace U-joint

Vibration at speed (40-60 mph)

U-joint binding or imbalance

Inspect + balance shaft

Squeak that stops above 30 mph

Dry needle bearings

Rust dust around joint

Seal failed, replace soon

Visible needle bearing damage

Replace immediately

CV Joint — Inspection Spec

Boot condition

First-line inspection

No cracks / no grease loss

Outer CV operating angle

≤ 47° (steering lock)

Inner CV operating angle

≤ 18°

Cup-to-housing axial play

< 0.5mm

Boot grease type

Moly EP — never grease gun

CV Joint — Failure Signatures

Click during turn under accel

Worn outer CV ball cage

Replace axle

Vibration under accel (straight)

Inner tripod or worn rollers

Replace inner CV or axle

Clunk on accel/decel transition

Worn axle splines or tripod

Grease splatter on inner fender

Boot torn, may be salvageable

Grease loss + visible rust at cage

Replace axle — contamination irreversible

BAY-FLOOR RULES

Decision tree

Clicking in turns → outer CV. Almost always an axle replacement.
Vibration straight-line → inner CV or driveshaft U-joint. Test which by isolation.
Boot torn + caught within 200 miles → reboot, clean, repack with moly EP, save the axle.
Boot torn + driven for months → axle. Grit destroys CV ball cage permanently.
Driveshaft U-joint clunk → both joints same shaft. Replace as a pair.
Operating angles out of spec → suspension ride height or lift kit. Address cause before replacing parts.