Trouble-shooting of an automobile brake system

1.18. Trouble-shooting of an automobile brake system

The main defects and that’s caused in the braking system of automobiles are discussed here. The remedies for these defects are also given.

1.18.1. Trouble: - Waste of braking effort or power:

(a) The brake fluid may have leaked and entered the brake drum and soaked the brake lining. The lining has to be replaced in such a case and the source of leak repaired.

(b) The presence of air in the system which has to be bled. Also, the source of air entry should be detected and repaired.

(c) The brake lining may have worn smooth. This has to be replaced.

(d) Operating linkage of the brake system may be out of adjustment or disconnected/which may be adjusted or reconnected.

(e) Automatic brake adjuster may have stopped functioning which may be inspected and repaired or replaced as required, after which brake shoes may be adjusted.

(f) Brake shoes may be distorted, which may be replaced.

(g) Brake drum may be too thin or cracked. In either case it has to be replaced.

(h) The master cylinder may be defective, which may be overhauled.

(i) In case of disc brakes, apart from the relevant causes out of the above, the rubber seal ring may be defective, which has to be replaced.

(j) Broken lines, which may be detected and replaced or rectified.

(k) Defective brake valve, which should he inspected and suitably readjusted or if necessary, replaced.

(l) The oil soaked brake linings which have to be replaced.

1.18.2. Trouble: - Brake fade:

"Brake fade": is a condition caused by overheating in which braking effectiveness reduces, and may be lost. It may occur for many reasons. Vaporization of the hydraulic fluid, thermal distortion is under extremes temperature, resulting in a reduction in braking capability that requires replacement of the affected parts.

(l) Brake fluid may have deteriorated with use. The same may be flushed out, fresh fluid of correct specifications filled in and the system bled.

(m) Poor contact between brake lining and the drum. The shoes may be ground to correct radius and/or adjusted.

(n) The brakes may be dragging. In such a case, the appropriate cause of defect has to be investigated and remedy provided. For details see the relevant portion of this very article.

(o) The brakes may have been excessively used. If so, reduce speed/load and use lower gears. This may help to cool down the brakes.

(p) The driver may be in the habit of riding the brake pedal, which causes the brakes to drag and thus became excessively hot leading to brake fade. The driver should not keep his foot on the brake pedal unless specifically required.

1.18.3. Trouble: - Brakes binding:

In case of mechanical brakes, the binding or dragging may be caused by the following reasons:

(q) The brake shoe retracting springs or the pedal return spring may be weak or broken, which should be replaced.

(r) The brake shoes may be jammed over the anchor pins, which should be lubricated.

(s) Parking brake may be too tight which may be adjusted.

(t) Parking brake may not get released. The brake linkage may be cleaned, lubricated and adjusted.

In case of hydraulic brakes, apart from the above reasons the defect may be due to following more causes:

(c) Incorrect free pedal play to allow piston in the master cylinder to uncover by-pass port. To remove the defect the pedal free play should be adjusted as given in the shop manual of the particular vehicle.

(d) By-pass port in the master cylinder might have been blocked, which may be cleaned with alcohol and compressed air, filled with fresh brake fluid and bled. Wire or drill should never be used for this purpose.

(e) Piston cup in master cylinder or wheel cylinder might have swollen up possibly due to the addition of mineral oil in the braking system. The only remedy in this case is the replacement of the rubber cup.

(f) The fluid level in the master cylinder may be excessive which may be rectified or the vent hole in the cover of master cylinder may be clogged which may be cleaned.

If however, only one brake is binding or dragging, it may be due to:

(a) Brake shoes on that particular wheel may be out of adjustment, which may be readjusted.

(b) The retractor spring on the wheel may have grown weak or may be broken. In either case only remedy is the replacement.

(c) The wheel cylinder may be defective, which may be repaired or replaced as required.

1.18.4. Trouble: - Brakes overheating:

The overheating of the brakes is most likely due to the same reasons for brakes binding/fade. Apart from these, they may occur also after a prolonged use of brakes while descending a hill. In case of disc brakes apart from the above, the piston in the caliper may be seized. To remedy this, caliper has to be rebored and the piston should be replaced.

1.18.5. Trouble: - Brake judder:

Brake judder: Brake judder is usually perceived by the driver as minor to severe vibrations transferred through the chassis during braking. The judder phenomenon can be classified into two distinct subgroups: hot (or thermal), or cold judder. Hot judder is usually produced as a result of longer, more moderate braking from high speed where the vehicle does not come to a complete stop.

This may be either due to wrong brake adjustment, which may he corrected, or due to the brake lining rivets being loose, in which case the lining has to be attached again with new rivets, in most cases, the lining also has to be replaced.

1.18.6. Trouble: - Vehicle pulling to one side when brakes applied:

(g) One or more brakes may be incorrectly adjusted, which may be rectified by correct adjustment.

(h) If a compensator is used in the braking system, the same might have become defective, which should be inspected and the defect removed.

(i) The oil or grease might have entered one or more drums, which puts more load on clean linings. The wet linings have to be replaced to remedy the defect.

(j) The cause of the entry of oil into the drum should also be investigated and remedied. The possible causes are defective oil seal, defective wheel cylinders, excessively lubricated or defective wheel bearings, too high level of lubricant in the rear axle, etc.

(k) This defect may also be due to fitting of different linings on different individual shoes. The only remedy is to remove such different linings and replace these by the linings similar to those used on other shoes.

(l) The dust etc. might have entered the brakes plugging some brake line, In which case they may be cleaned.

(m) Uneven tyre pressure may be the cause which may be corrected by inflating all tyres to the specified pressure.

(n) Front end alignment may not be correct, which may be done properly.

(o) Some suspension spring may be weak, sagging or broken which has to be replaced.

(p) Some shock absorber may be weak, which may be replaced.

In case of disc brakes, this defect may arise on account of following reasons:

(u) The brake pads may not he similar on all the wheels; the defective ones will have to be replaced.

(v) Oil or grease might have entered on one of the brake pads. The wet pads have to be replaced and the cause of leakage of oil or grease should also be investigated and remedied.

(w) The piston in any one brake may have seized, which should be remedied by turning the caliper and installing new piston.

1.18.7. Trouble: - Grabbing brakes:

If the brakes are too sensitive or grab, the following may be the reasons:

(q) Brake linings may be greasy or the brake fluid may have leaked on them. The same should be replaced.

(r) Brake shoes may not be properly adjusted which may be done.

(s) Back plate may be loose, which may be tightened.

(t) Brake drum may be scoured which will have to be turned or ground. If already ground to maximum limits, the drum has to be replaced.

(u) Brake lining may be charred. If so, the shoes have to be relined.

(v) Brake lining may be loose on shoes, in which case the same has to be replaced.

(w) Wheel bearings may be loose, which may be adjusted.

(x) Wheel bearings may be defective. If so, the same may be replaced.

(y) Dirt or dust may have entered the brake shoe assembly. The same may be disassembled and cleaned.

(z) Primary and secondary shoes may have been reversed. The same may be reinstalled correctly.

1.18.8. Trouble: - Hand brakes ineffective:

(a) The usual reason for this defect is the stretching of the operating cable, which can be adjusted with the help of the means provided for this purpose.

(b) Generally a nut is provided, at the end of the lever (Hindustan Ambassador).

(c) In case the cable is still slack even after full adjustment as provided, it means the cable is excessively slack and should be replaced.

1.18.9. Trouble: - Excessive loss of brake fluid:

This may be due to:

(a) Leaking of master cylinder or wheel cylinder, which is to be inspected and repaired or replaced as necessary.

(b) Any connection may be loose, which can be tightened properly.

(c) Connecting pipe or hose may be damaged, which has to be replaced.

1.18.10. Trouble: - Presence of air in the braking system

(a) Master cylinder may have some defects causing the leak of air inside. The same may be repaired or replaced if required.

(b) Any connection may be loose, which can be tightened properly.

1.18.11. Trouble: - Brake squeal: 

Sometimes a loud noise or high pitched squeal occurs when the brakes are applied. Check drum linear and disc brake pads for surface roughness. If wrong then maintain it using polish paper.

1.18.12. Trouble: - Brake dust: 

When braking force is applied, the act of abrasive friction between the brake pad and the rotor wears both the rotor and pad away. The "brake dust" that is seen deposited on wheels, calipers and other braking system components consists mostly of rotor material. Brake dust is clean by using compressed air.