1. Brake System Diagnosis and Repair
Chapter 72 - Part Two

2. Disc Brake Service
A typical major disc brake service involves four basic operations:
Replacing worn brake pads
Rebuilding/replacing the calipers
Machining the brake rotors
Flushing the brake fluid

3. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
1. Loosen the wheel lug nuts

4. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
2. Raise and secure the vehicle, remove the wheels

5. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
3. Push the caliper pistons back into the caliper

6. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
4. Unbolt and remove calipers (With brake hose still attached)

7. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
5. Hang calipers by a piece of wire (or bungee cord)

8. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
6. Remove old brake pads from calipers

9. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
7. Install anti-rattle clips on new pads

10. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
8. Install the new pads into the calipers

11. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
9. Clean, lube, and slide the caliper assemblies over the brake discs

12. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
10. Assemble the caliper mounting hardware (reverse order of disassembly)

13. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
11. Torque all bolts properly

14. Disc Brake Service
The twelve steps for replacing worn disc brake pads are:
12. Install wheel and torque the lug nuts

15. Disc Brake Service - Caliper Parts

16. Disc Brake Service - Caliper
Caution! You can crush your finger when using compressed air to remove a caliper piston during rebuilding.

17. Disc Brake Service - Caliper
You should use only brake cleaner or brake fluid to clean brake caliper parts! Coating the brake caliper piston with brake fluid before installation helps to make reassembly go easier.

18. Disc Brake Service - Caliper
You should use a pointed hook tool to remove the caliper piston seal.

19. Disc Brake Service – Disc/Rotor
The two most important precision measurements that need to be made on a brake disc/rotor are the disc thickness and the disc runout .
Measuring disc thickness
Measuring disc runout

20. Disc Brake Service – Disc/Rotor
The minimum disc thickness is measured across the two friction surfaces in several different places.
The maximum disc runout is the amount of side-to-side movement measured near the outer edge of the brake disc’s friction surface.
Measuring disc thickness
Measuring disc runout

21. Disc Brake Service – Disc/Rotor
The warpage or brake disc runout typically should not exceed 0.004”

22. Disc Brake Service – Disc/Rotor
Brake Lathe for machining Disc/Rotors off the vehicle

23. Disc Brake Service – Disc/Rotor
On-the-Car Brake Lathe for machining Disc/Rotors on the vehicle. (You don’t have to remove the disc to machine it!)

24. Disc Brake Service – Disc/Rotor
When machining a disc, you must do all the following:
1. Measure the disc before machining
2. Measure the disc after machining
3. Document the measurements on the repair order
Brake discs should be inspected for all of the following defects:
1. Hot Spots
2. Cracks
3. Warpage

25. Drum Brake Service
A typical Drum Brake Service includes these seven operations:
Remove parts from the backing plate
Clean and inspect the parts
Replace the brake shoes
Replace or rebuild the wheel cylinders
Turn the brake drums
Lubricate and reassemble the brake parts
Pre-adjust, bleed, and test the brakes

26. Drum Brake Service - Tools
Drum Micrometer Brake Cylinder Hone Spring Depressor Pressure Bleeder
Micrometer Bleeder Wrench Brake Spring Pliers Dial Indicator

27. Drum Brake Service
Gently hammering on the brake drum can help loosen it.
Springs on drum brakes can be different colors.
Leaking wheel cylinders will affect brake operation.
Working on drum brakes requires many special tools.
When honing the wheel cylinder it is never a good idea to pull the hone out of the cylinder while it is spinning or you may cause damage to yourself, the hone, or the wheel cylinder!

28. Drum Brake Service - Parts

29. Drum Brake Service - Tips
Some good methods of remembering how the rear drum brake parts go together: Taking a digital picture Taking only one side apart at a time Making a drawing
If a brake drum’s inside diameter is too big the drum must be replaced.
The preparation of the brake drum’s inner surface is called machining, turning, or resurfacing

30. Drum Brake Service - Tips
Brake shoe linings are fastened to the brake shoe by rivets, glue, or both.
Lubricating of the backing plate should be done with high temp grease, sparingly.
Parking brakes should never be adjusted too tight.
Parking brakes that are adjusted too tight can overheat, drag, or cause pulling.

31. QUESTIONS?
Check in the Duffy textbook Chapter 72