2Diagnosis 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.)
3Brake Pedal CheckMake sure the car doesn’t pull left or right dip the front or rear – might indicate a brake problemShould be about an inch of free pedal at the topShould not be any pulsation in the pedalPut light pressure on the pedal (engine off) if the pedal sinks, it indicates an internal leak in the master cylinderShould be about two inches of reserve pedal at the bottom of the brake travel
4Master 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 cylinderCheck 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 orInlet portCompensating PortCheck Fluid level
6ContinuedCheck 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 areblocked 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.
7Power Brake CheckWith 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.
8Brake Switch TestPush the pedal and have a partner check for light operation* if all lights don’t work check the fuse first before changing out the switchThe switch has two wires—one in (12 volts) and one out (should also be 12 volts is switch is o.k.)
9Road 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.
10Brake 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.
11Brake System Checks Disc Brakes Disk Pad Thickness Comparison Drum BrakesDrum Brake Lining Thickness Comparison
13Items to Check (disk) Check the caliper and mount for Tightness– check for leakageCheck Lines forChecks, Chaffs,and BulgingCheck the rotorFor warpage, cracks,and roughnessCheck bearingsFor loosenessCheck the condition of the lug studs---- and axle nut for tightness
16Measure Rotor Thickness With a Micrometer Rotor Micrometer
17Fluid ServiceCheck fluid with a multimeter--- no more than .3 volts— replace fluidCheck 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.
19Bleeding Types of bleeding Manual Pressure Vacuum Gravity Use dielectric grease for a good sealTry to catch the fluid.Remember it is harsh on paint.
20Master 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.
21Master 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 purgedThese adapters come with most new cylinders
25Wheel 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 backingplate with two bolts fromthe back side.Any leaks=Replacement
27Caliper 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 mustbe replaced each time the line is off( 2 of them per)Any leakage= Replacement
28Measuring the Rotor or Drum This is important to do right because it will determine if these parts can be resurfaced or if they need replacementRemember it is illegal not to mention dangerous to knowingly ignore these readings.
29Resurfacing Rotors and Drums Follow the directions next to the brake lathe only if the rotor/drum has 25 thousandths to work with.Example Max (drum specification)Your measurementExample .850 Min (rotor spec)Your Measurement .880Don’t forget to crosshatch a finish
33Vacuum 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.
34Brake Assignments Inspection of system and components Turn rotors and drums, measure run-out, diameter, thickness of pads discs and rotors.Adjust parking brakeWheel bearing work (possibly)Cleaning brakesBleedingComponent R+R
35Your Job.Complete chapter Questions 1-10 (review) and 1-10 (ASE-style). Page 760Write 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.