Brake Service Chapter 52 Page 732

Diagnosis is Key This will make or “brake” you as a technician. This is really no laughing matter because if we don’t find the problem, mis-diagnose, or don’t properly repair a brake problem it could lead to our harm and/or (on a test drive) the customers life as well if the problem is not found on a test drive. (we don’t test drive after most repairs here at SPHS– it may come up and get us someday; so do it right and let me look at it before you turn the car loose.)

Brake Pedal Check Make sure the car doesn’t pull left or right dip the front or rear – might indicate a brake problem Should be about an inch of free pedal at the top Should not be any pulsation in the pedal Put light pressure on the pedal (engine off) if the pedal sinks, it indicates an internal leak in the master cylinder Should be about two inches of reserve pedal at the bottom of the brake travel

Master Cylinder Inspection Hold pedal down with light pressure for up to a minute, if the pedal sinks and there is no external leakage of the system; it indicates an internal leak of the master cylinder Check for roughly equal fluid levels in the reservoir; if one the front brake chamber is lower it may indicate worn brake pads ( front brakes do more work) or one of the piston areas are leaking over and overflowing the other chamber. Replenishing or Inlet port Compensating Port Check Fluid level

Rear seal Check

Continued Check the compensating ports—( have a partner press the brake pedal down while the cover of the reservoir is off and you should see a small surge coming up in each chamber; if there is a heavy surge, there is air in the system) Brake drag– if the compensator ports are blocked or the brakes pedal is adjusted to tightly, the brakes will be applied all the time. (try rolling the vehicle by hand– it should roll easily. Isolating an air-in-system problem– same as compensating port test; but; pump the pedal 10 times and hold the last pump– then release– note the chamber with the high surge.

Power Brake Check With the engine off, pump the pedal several times as you do you should hear a rushing sound—this checks for a hole in the booster diaphragm which would render it useless. With pressure on the pedal, start the engine and the pedal should sink about an inch.—If yes, it’s a good booster.

Brake Switch Test Push the pedal and have a partner check for light operation * if all lights don’t work check the fuse first before changing out the switch The switch has two wires—one in (12 volts) and one out (should also be 12 volts is switch is o.k.)

Road Test or Customer Complaint Diagnosis Pedal pulsation— Drums out of round, rotors warped. –might need resurfacing or replacement. Grab– grease or oil on the linings, wrong or improperly installed pads.– clean and fix oil/grease problem. Pull– oil on one set of pads (on one side of vehicle), frozen caliper, blocked hose, loose brake parts.-various repairs needed.

Brake Pull cont. If the vehicle pulls to one side while braking– check for a brake not working on the opposite side of the pull. Don’t forget, worn wheel bearings, bad suspension parts, and chassis part all could create a brake pull.

Brake System Checks Disc Brakes Disk Pad Thickness Comparison Drum Brakes Drum Brake Lining Thickness Comparison

Disk Brake Check

Items to Check (disk) Check the caliper and mount for Tightness– check for leakage Check Lines for Checks, Chaffs, and Bulging Check the rotor For warpage, cracks, and roughness Check bearings For looseness Check the condition of the lug studs---- and axle nut for tightness

Use Dial Indicator

Disc Brake R & R

Measure Rotor Thickness With a Micrometer Rotor Micrometer

Fluid Service Check fluid with a multimeter--- no more than .3 volts— replace fluid Check for dirty or clouded fluid– should be clear **DOT 5 has a purple dye added to identify and caution you not to mix DOT 5 with the others.

Bleeding

Bleeding Types of bleeding Manual Pressure Vacuum Gravity Use dielectric grease for a good seal Try to catch the fluid. Remember it is harsh on paint.

Master Cylinder Service Most of this is just replacing the cylinder. You may have to change out the reservoir when you get a new cylinder. Take care not to cross-thread the lines. Always start by hand.

Master Cylinder Service Before installation the master cylinder needs to be bench bled. (you can use the master cylinder installed method seen below) Pump pedal until all air is purged These adapters come with most new cylinders

Drum Brake Check

Items to Check (drum) Check Wheel Cylinder for Leakage Check anchoring clips Check Lining Thickness All springs for “spring”

Drum Parts Adjusting Screw Wheel Cylinder Hardware Backing plate Drum

Wheel Cylinders Replacing this is more common than rebuilding them The bleeder is usually frozen– take some penetrating oil and give it time to work, use a six point socket and try to remove. You might get it; out 50/50 shot at it. Same goes for the lines. It is held to the backing plate with two bolts from the back side. Any leaks=Replacement

Drum Brake R & R

Caliper Service It is more common to replace calipers than to rebuild. The bleeder is usually frozen– take some penetrating oil and give it time to work, use a six point socket and try to remove. You might get it; out 50/50 shot at it. Same goes for the lines. Copper sealing rings at the line must be replaced each time the line is off ( 2 of them per) Any leakage= Replacement

Measuring the Rotor or Drum This is important to do right because it will determine if these parts can be resurfaced or if they need replacement Remember it is illegal not to mention dangerous to knowingly ignore these readings.

Resurfacing Rotors and Drums Follow the directions next to the brake lathe only if the rotor/drum has 25 thousandths to work with. Example 10.030 Max (drum specification) Your measurement 10.005 Example .850 Min (rotor spec) Your Measurement .880 Don’t forget to crosshatch a finish

Adjusting Parking Brake Cable

Adjusting Parking Brake Lever

Adjusting Parking Brake

Vacuum Booster Service The vacuum hose going into the front chamber needs to be in good shape. Gently pry the check valve out and a rush of air into the booster should be heard. The check valve will need to be replaced if the brake work accordingly to the engine RPMs. Check to see if the rear chamber of the master cylinder is up to level- the booster’s seal might be bad and drawing fluid into booster.

Brake Assignments Inspection of system and components Turn rotors and drums, measure run-out, diameter, thickness of pads discs and rotors. Adjust parking brake Wheel bearing work (possibly) Cleaning brakes Bleeding Component R+R

Your Job. Complete chapter Questions 1-10 (review) and 1-10 (ASE-style). Page 760 Write on a separate paper and write out the complete question and your answer. ( do not write the other answer options). Complete the chapter worksheet (I will give it out). You may write on it. File all items in your note book. Notebooks will be graded in the future.