Initial Inspection and Diagnostic Overview
Inspection and VerificationPreliminary Checks
NOTE: Always check the fluid level in the brake master cylinder reservoir before carrying out the test procedures. If the fluid level is not at the correct level, fill the reservoir with specified brake fluid. Prior to carrying out any diagnosis, make certain that the brake warning indicator is functional.
A change in brake pedal feel is usually the first indicator of a brake system concern. The change may only be normal ABS function, but is sufficient cause for further investigation. The brake warning indicator in the instrument cluster and the brake fluid level in the brake master cylinder reservoir are also indicators of system concerns.
If a wheel is locked and the vehicle must be moved, open a bleeder screw at the locked wheel to let out enough fluid to relieve the pressure. Close the bleeder screw. This bleeding operation may release the brakes but will not correct the cause of trouble. If this does not relieve the locked wheel condition, repair the locked components before proceeding.
Brake Booster
Inspect all hoses and connections. All unused vacuum connectors should be capped. Hoses and their connections should be correctly secured and in good condition with no holes, soft or collapsed areas.
Road Test
Carry out a road test to compare actual vehicle braking performance with the performance standards expected by the driver. The ability of the test driver to make valid comparisons and detect performance deficiencies will depend on experience.
The driver should have a thorough knowledge of brake system operation and accepted general performance guidelines in order to make good comparisons and detect performance problems.
Select a road that is reasonably smooth and level. Gravel or bumpy roads, except to demonstrate ABS function, are not suitable. The surface does not allow the tires to grip the road equally. Avoid crowned roads.
A key factor in evaluating brake concerns is the deceleration rate. This varies from vehicle to vehicle and with changes in operating conditions. It is evident how well the brakes are working after just a few applications.
Visual Inspection Chart
Vibration When Brakes are Applied
For vibration concerns when the brakes are applied, carry out the following procedure.
1. Verify the concern.
^ Brake vibration concerns are caused by uneven disc wear or lining transfer and should be verified with a test drive since these conditions are difficult to measure with available shop tools.
^ Check Technical Service Bulletin for vehicle specific brake concerns.
2. Remove the wheel and tire assembly.
3. Remove the brake caliper.
4. Inspect the brake linings. Install new pads if the thickness of the lining is below the specification or if cracks in the lining, wide enough to see through down to the backing plate are present.
5. Inspect the brake discs.
^ Install new discs if cracked.
^ Resurface the brake discs if the diagnosis has revealed vibration in the steering wheel, seat, or pedal while braking. Heavily scored brake discs, similar to that caused by linings worn down to the backing plate, should also be resurfaced.
6. Measure the brake disc thickness and record the measurement. For brake discs that require machining, install a new brake disc if the thickness is less than 0.60 mm (0.02 inch) above the minimum thickness specification cast in the brakes disc. This will make sure that the brake disc will be above minimum thickness after machining. Do not machine new brake discs.
7. For vehicles with a two-piece brake disc and hub assembly:
1 Match-mark before disassembly.
2 Remove the brake disc.
3 CAUTION: Do not use an abrasive sanding disc since it will remove paint or other protective finishes from the wheel and metal from the mounting surfaces, adversely affecting corrosion protection and disc lateral runout.
Remove corrosion from the wheel mounting surface, both disc mounting surfaces, and the hub mounting surface. A die grinder with a Scotchbrite surface conditioning disc, or equivalent, is recommended.
4 Align the match-marks and reinstall the brake disc on the hub.
8. CAUTION: Do not use a bench lathe to machine brake discs.
NOTE: Read the entire operating manual and view the video shipped with the lathe before installing, operating, or servicing the lathe.
Machine the brake disc using Rotunda Hub-Mount Brake Lathe/Pro-Cut 201-00002, or equivalent.
1 Install the hub adapter and silencer belt, if necessary.
2 Install the cutting lathe.
3 NOTE: Total indicated reading target is 0.000 mm (0.000 inch), maximum is 0.08 mm (0.003 inch).
Adjust lathe oscillation using a dial indicator.
4 Center the cutting head, adjust cutting bits, and install the clip deflector.
5 NOTE: Depth of the cut should be between 0.10 and 0.20 mm (000.4 and 0.008 inch). Lighter cuts will cause the bit to heat up and wear faster. Heavier cuts will cause poor disc surface finish.
Machine the brake disc.
6 Remove the lathe and, if installed, the silencer belt.
7 Remove the hub adapter.
9. Remove any metal shavings.
10. CAUTION: Do not carry out this step on rear drum-in-hat brake discs.
For vehicles with a two-piece brake disc and hub assembly:
1 Remove the brake disc from the hub.
2 Remove any metal shavings from the hub and disc mounting surfaces and from the ABS sensors.
3 Apply High Temperature Nickel Anti-Seize Lubricant F6AZ-9L494-AA, or equivalent meeting Ford specification ESE-M12A4-A to the hub mounting surface to prevent future corrosion.
4 Using the match-marks, mount the brake disc on the hub.
11. Install the brake pads.
12. Install the wheel and tire assembly.