HISTORY OF BRAKES AND LAWS

 

 

·        1925 MODEL T

·        1929 MODEL A

·        steel rod going to each wheel, apply brakes manually

·        hydraulic system, started with one master cylinder for all 4 wheels and

             if something broke, all braking was lost

·        1967 – New Law, must have a dual reservoir or tandem brakes which would insure that there would be ˝ the system if a hose broke.

                                                                                                                                      

FMVSS#                    - FEDERAL MOTOR VEHICLE SAFETY STANDARD

 

·        “Brake Bias” – because of weight transfer, favoring one set of brakes over another

·        To minimize rear wheel lockup

·        Problem with just having front brakes

·        Past bias was more like 60/40, now might be more like 80/20 or even 90/10 with the shorter wheel base cars,  These systems are really like having two master cylinders, one part for half of the system and one for the other half

·        Diagonal split,   4 lines from master cylinder,  if a rubber brake hose broke, you would still have one front and one rear wheel braking which gives even more controlled braking.  minimize rear wheel lockup lock up brakes in rear, you lose control

 

 

 

Diagonal Split – one goes out, will still have one in front, one in back

 

Base brakes/Foundation brakes –

 

Anti-Lock Brakes –

 

Ways to minimize rear wheel lock up?  (to change to proper brake bias)

 

1.  Size of calipers or cylinders

2.  Size of Friction material

3.  Hydraulic Valving

4.  Brake design – disc/duo servo/non servo (servo =less braking)

5.  Size of the drum – bigger drum = more leverage

 

Duo Servo – has a wheel adjuster (opposite of cylinder), will float a little; has cylinder and pivot at top with star wheel at opposite side – servo action in forward or reverse

 

Non Servo  - a wheel adjuster next to cylinder, block at bottom; cylinder and anchor block at opposite end – star wheel is next to cylinder

 

Duo Servo

 

 

Servo – applies pressure to something else

Servo action - .030” clearance between drum and shoe, force of one shoe pushes on the star wheel adjuster to the other shoe

     Example:  primary shoe – provides some braking but also forces secondary shoe to brake

 

Self energizing – the rotation of the drum improves the friction

     Example:  wedging action tries to pull itself in making it more effective (pg.90)

 

Move out at top, away from anchor pin

 

 

 

 

 

 

 

 


How does self-adjuster work?  When you are in reverse and stop, why don’t they keep adjusting?

 

Non Servo –Leading/Trailing

·        Less efficient than duo server

·        Has leading (front) – trailing (back)

·        Chances are sizes are identical

·        Shoes must come back to anchor pin – IF NOT, SOMETHING IS WRONG!

·        Strut rod on wrong, parking brake not releasing

·        This can cause lock-up on that wheel, it gets a “head start” on braking

 

 

 

 

 

 

 

 

 

 

 

 

 


Hydro boost –Brake power assist that runs off power steering pump

·        Hydraulic lines from power steering to unit behind the master cylinder

 

 

 

 

 

 

 

Duo Servo

I.D.

Primary

Secondary

Edge brand: PRI

SEC brand

Smaller

Larger

Front of vehicle

To rear of car

Lighter in color

Darker in color

Less coefficient of friction

Higher COF

 

If you get these backwards; will still work, but will make a difference in inches.

 

Hubless Drum

 

1.  Centering cone on spring, aligning cup in lathe

2.  Put hub on

3.  Another aligning cup

4.  Spacer – to equalize pressure

5.  Nut/spacer combo

6.  Machine tight together, less vibration

7.  Push rod back in corner of hub

8.  Put equalizer on top, turn knob in and out a little

9.  Vibration dampener on hub

10.  Step, stop lathe

 

Rough cut – 20 speed

·        Scratch test, bit makes contact with drum -  if constant noise, OK

·        If on/off noise – turn 1/2, moves in 1/2 inch

·        If 2 scratches are side by side – drum has high/low spot

- preferred scenario

·        If in opposite sides – our mounting is wrong

 

Take off at least .005” – each line is .002” = 2 1/2 lines

 

Herringbone pattern – caused by not installing vibration

  Dampener – the leather belt

 

NOTE: 

·        Don’t machine if you don’t have a problem

·        Book recommends only if at least a .015” - .020” groove

 

Machining Drums

 

Cut off as little as possible, but never less than .005”

 

                                                                                                                                                           

                         A = depth of cut     “5 to 20”                                                                 

                    Start at B (on the closed end) and move to C

                    Feed rate – how fast you go from B to C

 

                                                                                          

                   

 

 

Depth

Rate

Optional

Rough Cut

.005”

20 - .020” every rotation

Required

Finish Cut

.005”

  5 - .005”every revolution

 

 

If you cut too small an amount, the bit will float because it can’t dig in and also because the chip of metal will be too small and will not dissipate heat  ______

 

A brake lathe can be radius graduated or diameter graduated.

 

Radius graduated – if turn dial @ .004”, actually cutting .008” off of drum (double)

 

Diameter graduated – if at .004 is .004, what you see is what you get

 

Amoco lathes are all diameter graduated.

 

Some rotors have a cooling groove.                        

 

 

LAB DEMO – HUBBED ROTOR ON LATHE

 

1.  Tapered adapter mounts inside     - duplicates the plane of rotation

2.  Equalizer     and 2 tapered adapters

3.  Nut/spacer combo

4.  Vibration dampener – [vented hub/lead weights]

5.  Uses cutting arm

6.  Make sure you cut right up next to hat

7.  Move knob in until you make contact

·        Adjust sleeve to.0

·        Each line is .002”

8.  Spaces high/low high is for rough-cut, towards machine _________________

9.  Cut .005” off each side to take care of most rotors (slow cut)

·        Minimum is .003” off each side

 

[Can rotate bits 3 times in each side, 6 rotations total]

 

10.  After satisfied with cut, put a non directional finish

·        A Directional finish creates a noise – susceptible to frequency

·        Use sandpaper, move back and forth as it turns

·        DA Sander/ lasts longer, tilt this way                                                             

·        Has a plastic gear – “weak link”

 

11.  When runs to end, there is a brass sleeve will run off end of threads and won’t move anymore; it must jump back on, don’t force

 

LAB DEMO – Free Floating Axle

 

·        94 pre hubbed drum, drum has bearings

 

1.  Take bolts off

2.  Opposite side is lower, lube leaks to other side

3.  If nuts inside come loose, the dual wheels can come out

4.  Bolts – 1 for adjustment, 1 to lock up

 

It is a good  idea to replace  seals anytime you do a brake job  on a floating  rear axle.

·        If it leaks, oil will get on brake shoes.

 

 

Pascal’s Law

 

1.  Cannot compress fluid

2.  Fluid will take shop of the container

3.  Pressure will be exerted in all directions equally

 

   [

Force = P*A    lbs.

Area  = F/P      in2

Pressure = F/A     psi                                                                                                              

 

 

 

 

 

 

 

 

 

 


Strength vs Speed

 

Force = multiplier

Movements = divides

 

·        Pump brake pedal before you move it out of stall

·        Pads must have contact with rotor

 

What provides the small amount of clearance between pad and rotor:

1.  Rotor run out

2.  Action of the square cut seal

 

Lower brake pedal = Loose wheel bearings

 

Disc Brakes:

 

1.  Self cleaning

2.  Less Parts

3.  Self adjusting

4.  Run cooler

5.  Less efficient, require more force

 

How disc brakes are self adjusting?

·        The master cylinder must be able to push piston out farther than the square cut seal can move

 

What can cause a low brake pedal? 

·        Loose wheel bearings

 

Input – master cylinder

·        Having larger area at caliper makes it stronger, but a slower apply

 

 

 

How much force at master cylinder?

·        Hydraulic pressure is constant through whole thing

 

Area of a Circle

.785 x (diameter)2

Must convert to square inches:

   Example = 3” diameter piston 

                     .785 x (3)2 = 7.065 in2

 

Curved piston = to get more surface area.

 

 

 

 

 

 

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