Brakes - Roughness/Runout Check

9228ford02

Article No. 92-12-4


DATE: 06-03-92


^ BRAKES-ROTOR-REPLACEMENT SERVICE TIPS

^ BRAKES-ROUGHNESS DEVELOPED FROM INCREASE

IN ROTOR RUNOUT

^ WHEELS-LUG NUT TIGHTENING PROCEDURE


FORD:
1986-92 TAURUS 1989-92 THUNDERBIRD 1992 CROWN VICTORIA

LINCOLN-MERCURY:
1986-92 SABLE
1988-92 CONTINENTAL
1989-92 COUGAR
1991-92 TOWN CAR
1992 GRAND MARQUIS


ISSUE:
Brake roughness may occur after the lug nuts are installed and tightened with an impact wrench. The resulting torque difference from stud to stud can be as high as 60 lb.ft (81 N-m). This torque difference stud to stud may cause an increase in rotor runout by as much as .003"-.005"(.076mm-.127mm). The increase in rotor runout may speed up the development of brake roughness.

ACTION:
Tighten the wheel lug nuts in the "final' torque in the sequence described in the Service Manual. Use a torque wrench set to 95 +/- 10 lb.ft (129 +/- l4N-m). When performing brake service work that involves replacing or removing the rotor, refer to the following service procedure which minimizes hub/rotor "stacked" runout, a cause of brake roughness and uneven rotor wear.


HUB/ROTOR "STACKED" RUNOUT CHECK

If the assembled system (new/turned rotor installed on the hub) indicates more then .002" (.05mm) total runout (TIR), it will cause excessive thickness variation in the rotor as mileage accumulates by wearing the high spots off the rotor. Excessive thickness variation in the rotor causes brake pulsation and steering wheel shake.


HIGH SYSTEM RUNOUT

High system runout (TIR) is caused by...

^ Rust/contamination trapped between the hub and rotor mounting surface
^ Rotor or hub (high and low spots) not properly positioned during assembly.

ROTOR REPLACEMENT SERVICE TIPS

1. Completely clean the hub area that will contact the new/turned rotor. Remove rust build up.

2. Install the new/turned rotor on the hub and secure it with at least three (3) lug nuts. Tighten the lug nuts to 20 lb.ft (27 N-m) for testing.

3. Using a dial indicator 4201-C or equivalent, determine the total runout of the system. The total system (rotor and hub) runout must not exceed .002" (.05mm).

4. If the runout exceeds .002" (.05mm), proceed as follows:

a. Remove the rotor and rotate it clockwise until the next hole lines up with a stud.

b. Secure the rotor in the new position, reindexed as described in Step 2.

c. Repeat the checking and rotation (reindexing process) until the system measures .002" (.05mm) or less total runout.


5. If .002" (.05mm) or less runout cannot be reached, the hub should be replaced and Steps 2 through 4 repeated when the new hub/rotor is installed.


NOTE:
IT IS RECOMMENDED THAT NEW BRAKE ROTORS NOT BE MACHINED. NEW OEM REPLACEMENT ROTORS ARE WELL WITHIN THE RUNOUT AND THICKNESS VARIATION SPECIFICATIONS.

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 301000, 306000