Imbizo - Sharing Knowledge - Brakes

TECHNICAL FACTS & FAQ

BRAKE PEDAL

  1. Too much brake pedal play will reduce driver reaction time.
  2. Service pedal if vehicle is 7 years or older.
  3. Areas to check:
    1. Brake pedal bushes.
    2. The clevis. The pin or clevis could have worn.
    3. C. Brake pedal rubber-replacement if worn or broken.

BOOSTER

  1. A booster allows the driver to have control over the braking system under light pedal effort.
  2. Booster needs vacuum to operate.
  3. Vacuum comes from the intake manifold on petrol engines.
  4. On older diesel engines there is a vacuum pump situated on the back of the alternator. These pumps leak oil and can contaminate the booster diaphragm.
  5. On more modern vehicles with diesel engines there is an electric vacuum pump in the engine compartment.
  6. Boost ratio is determined by the size of the booster.
  7. The booster diaphragm is kept still in the booster because of equal vacuum on both sides of the diaphragm. This is made possible by a valve in the booster.

BRAKE MASTER CYLINDER

  1. The brake master cylinder transfers applied pressure of the brake pedal and booster to the calipers and wheel cylinders of the hydraulic system.
  2. “toe-board clearance” is the free-play at the brake pedal. This clearance is between the booster pin and the brake master cylinder. This free-play allows the master cylinder to return to its rest position, ensuring that the compensating ports are left open and thus ensuring that the expanding brake fluid is allowed to return to the brake fluid reservoir.
  3. When replacing master cylinders, measure the depth of the hole of the piston. The new master cylinder must be the same. If too shallow, there will be no “toe-board clearance”. You will have difficulty bleeding the brakes and the brakes will bind.
  4. When reconditioning brake master cylinders, remember to measure the piston with the spring attachment and record the data. This screw is not screwed in till tight, it is screwed in to the specific length that the piston must be in order to allow the other piston to be in the correct position. Remember the compensating ports must be open!

BRAKE FLUID

  1. Properties
  2. Glycol based
  3. Incompressible
  4. Chemically stable
  5. It’s a lubricant
  6. High boiling point 260°c minimum (should be marked on bottle)
  7. Does not freeze
  8. Paint remover
  9. Hygroscopic: ie it absorbs condensation

If brake fluid comes out of the reservoir when replacing brake pads, it is because the brake fluid has been manually topped up when the handbrake light came on. Always suck out excess brake fluid from the reservoir before pushing caliper pistons back as this excess brake fluid will fall onto the suspension components and damage the suspension rubbers resulting in unnecessary repairs.

Always test brake fluid when you open the bottle. Record the date and boiling point on the bottle for future use.

BLEEDING BRAKES

  1. Invest in a brake bleeding kit. This will simplify and shorten the task of bleeding brakes. There are many versions and types available with Textar also having bleeding devices and kits available.
  2. Do not pump the brakes when bleeding as it will cause any bubbles to break up into thousands of tiny bubbles which becomes difficult to bleed out. These bubbles get caught in the ABS pump and ultimately will cause the ABS light to switch on.
  3. Know which circuit to bleed first: e.g. Citi golf, Ford Fiesta Bantam Bakkie-rb-lf-lb-rf, Hyundai Getz-rb-lb-rf-lf, Toyota Hilux D-4D-rb-lb-lf-rf. Always bleed the longest circuit first. Know what braking system the vehicle has.
  4. Avoid spilling brake fluid and do not wash spilt brake fluid off with water as the water can penetrate through the breather hole on the reservoir cap.

BRAKE PIPES

  1. Do not leave callipers hanging on flexible rubber brake pipes. This practice will cause the pipes to stretch and break the nylon braiding, ultimately causing the pipe to burst under pressure.
  2. Do not weld steel brake pipes. Rather replace.
  3. Invest in a set of brake pipe spanners.

FITTING FRONT BRAKE PADS

  1. Do not use a screwdriver to push back the caliper piston as it may bend the guide pins and damage the guide pins bushes. It may also puncture the caliper piston dust boot which ultimately causes the caliper piston to stick. The result being that the inner brake pad will wear faster than the outer brake pad.
  2. Invest in a caliper retractor tool kit.
  3. When brake pads need changing the calipers need servicing. This is the only time the opportunity arises to do this. Don’t wait for the guide pins to seize.
  4. Invest in a copper based lubricant that can withstand 1100°c and apply to guide pins and caliper anchors when serving calipers.
  5. Transfer any anti-squeal shims from the old pads to the new ones as these are very expensive. Do not throw them away.
  6. Apply a thin layer of copper based lubricant to the anti-squeal shims’ front and back before fitting them onto the new pads.

FITTING REAR BRAKE PADS

  1. When fitting rear brake pads to calipers that have handbrake cables always disconnect the handbrake cable before pushing the caliper piston back.
  2. Service the calipers as the rear pads have lasted twice as long as the front.
  3. When twisting the piston back take care not to damage the caliper piston dust boot. If the boot is twisted, undo it.
  4. Ensure the piston cut outs are in the position so that the pin on the back of the pad can slot into the recess of the piston.
  5. Re-connect the handbrake cable. Do not adjust the handbrake cable. Pump the pedal until there is pressure under foot, then press the pedal hard 7-10 times. This will self-adjust the caliper and handbrake.

SERVICING THE CALIPERS

  1. Wire-brush the anchors where the brake pads seat. Remove any residue brake dust. Remove any anti-rattle clips and wire-brush behind them. Wire-brush the anti-rattle clips as well. If new anti-rattle clips are supplied fit them.
  2. Apply copper based lubricant conservatively in the areas where the brake pads come into contact with the steel parts of the caliper anchor.
  3. Service the guide pins and bushes. Clean and apply copper based lubricant generously in these areas
  4. Inspect the caliper piston dust boot for any cracks or tears and if the boot has gone hard. Overhaul the caliper if any are visible.

BRAKE DISCS & OPTIMUM BRAKE PAD LIFE

  1. For every 1mm skimmed off a disc, the disc runs 100 °c hotter as heat is the number one enemy of friction. This will cause the brake pads to wear faster reducing brake pad life.
  2. For optimum brake pad life new brake discs should be fitted on every brake pad change.
  3. If discs are skimmed the will reduce brake pad life.
  4. Rear brakes should be adjusted every 10 000km and at every front brake pad change.
  5. Wire-brush or sand the wheel hub surface before you fit a new disc. This is to ensure you remove any rust that may have.

REAR BRAKE SHOES

  1. Always check, clean and adjust rear brake shoes when changing front brake pads.
  2. Adjust the handbrake adjustment all the way down before removing the brake drum.
  3. After cleaning, adjust the brake shoes first and then take up the slack on the handbrake cable. This will ensure that the handbrake levers are in the retracted position and that the brake shoes will wear evenly.
  4. Do not use side cutters to remove the brake springs as it will damage the springs ultimately cause breakage.
  5. Service the adjusters and use copper based lubricant to lubricate the threads or mechanisms of the adjusters.

SHOCK ABSORBERS & SUSPENSION COMPONENTS

  1. Check the shock absorbers and suspension components as well. It does not help you if you have a great braking system but you have faulty shocks and suspension components.

Address:
59 Merino Avenue
City Deep
Johannesburg
2049
Postal Address:
P.O. Box 86222
City Deep
Johannesburg
2049
Tel: +27(0)11 627 2500 Fax: +27(0)11 627 2600

 

Information kindly provided by Torre Automotive

Also View:

Brakes/Braking and Road Safety

Safe Braking and Understanding the Brake Components

Imbizo: Know more about Shock Absorbers

Imbizo: Know more about Vehicle Components

Brakes/Braking and Road Safety
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