Operation CHARM: Car repair manuals for everyone.

Brake - Judder/Steering Wheel Shimmy: Overview

MODELS: All models

SECTION: Brake

CLASSIFICATION: BR94-003

BULLETIN NO.: IBT94-007

DATE: January 27, 1994

BRAKE JUDDER/STEERING WHEEL SHIMMY

APPLIED MODELS: All Models

GENERAL INFORMATION:

Brake judder/steering wheel shimmy is a condition which may occur in any vehicle when excessive rotor thickness variation is present on one (1) or more of the vehicle's brake rotors.




Rotor Thickness Variation(RTV) is the variation in thickness around the rotor. The RTV can be determined by measuring the rotor thickness with a micrometer at several locations around the circumference of the rotor. The RTV is the difference in thickness between the thickest and thinnest points on the rotor.




Rotor Run-Out is the distance that the rotor surface travels in and out, in relation to the vertical plane of the hub, as the rotor turns with the hub. The distance is measured with a dial indicator.

Note
Rotor Run-Out does not cause brake judder or steering wheel shimmy. However,excessive Rotor Run-Out does lead to rotor thickness variation as the rotor wears. It is the excessive rotor thickness variation that causes judder and/or steering wheel shimmy. This is described in more detail below.

POSSIBLE CAUSE OF BRAKE JUDDER/STEERING WHEEL SHIMMY

A brake judder/steering wheel shimmy incident may develop in any vehicle if the following series of events occur:

* The brake rotor run-out exceeds specification limits.




* As the brake pad rubs against the rotor while driving, the high spots on the brake rotor wear slightly.

* Rotor thickness variation may develop as the high spots on the brake rotor wear. If this thickness variation becomes large enough, brake judder/shimmy may occur.

INFINITI SERVICE PROCEDURE:




Resurfacing the brake rotor using the Ammco On-Car Brake Lathe is the preferred method of correcting excessive rotor run-out and thickness variation. Refer to Infiniti Technical Bulletin ITB92-043 (BR92-001) "Ammco On-Car Brake Lathe Operating Guidelines."




Due to limited clearance, this machine cannot be used on the rear rotors of some vehicles. To resolve this issue, two (2) methods of repair are identified in the illustrated flow chart. Use this chart, as appropriate, when performing brake pad or rotor service.