Road Test
WARNING: BRAKE FLUID CONTAINS POLYGLYCOL ETHERS AND POLYGLYCOLS. AVOID CONTACT WITH EYES. WASH HANDS THOROUGHLY AFTER HANDLING. IF BRAKE FLUID CONTACTS EYES, FLUSH EYES WITH RUNNING WATER FOR 15 MINUTES. GET MEDICAL ATTENTION IF IRRITATION PERSISTS. IF TAKEN INTERNALLY, DRINK WATER AND INDUCE VOMITING. GET MEDICAL ATTENTION IMMEDIATELY.ROAD TEST CONDITIONS
Perform a road test to compare actual vehicle braking performance with the performance standards expected by the driver. The ability of the test driver to make valid comparisons and detect performance deficiencies will depend on experience.
The driver should have a thorough knowledge of brake system operation and accepted general performance guidelines in order to make good comparisons and detect performance concerns.
An experienced brake technician will always establish a route that will be used for all brake diagnosis road tests. The road selected will be reasonably smooth and level. Gravel or bumpy roads are not suitable because the surface does not allow the tires to grip the road equally. Crowned roads should be avoided because of the large amount of weight shifted to the lowest set of wheels on this type of road. Once the route is established and consistently used, the road surface variable can be eliminated from the test results.
Before a road test, get a complete description of the customer concerns or suspected condition. From this description, the technician's experience will allow the technician to match possible causes with symptoms. Certain components will be tagged as possible suspects while others will be eliminated by the evidence. More importantly, the customer's description can reveal unsafe conditions which should be checked or corrected before the road test. The description will also help form the basic approach to the road test by narrowing the cause to specific components, vehicle speed or conditions.
ROAD TEST
Begin the road test with a general brake performance check. Keeping the description in mind, test the brakes at different vehicle speeds using both light and heavy pedal pressure. To determine if the problem is in the front or rear braking system, first use the service brake pedal, then use the parking brake. If the condition (for example, pull, vibration or pulsation) occurs only with the parking brake, the concern is in the rear system. If the condition occurs when the service brake pedal is applied, the concern is in the front system.
Brakes should only lock up if the ABS is not functioning. (Yellow ABS lamp should be on). If the ABS is not functioning, avoid locking the brakes and sliding the tires. Locked brakes and sliding tires do not indicate brake efficiency. A heavily braked and rotating wheel will stop the vehicle in less distance than a wheel that is locked and skidding. If the condition becomes evident during this check, make sure it fits the description given before the road test. If the condition is not evident, attempt to duplicate the condition using the information from the description.
Customer concerns of brake shudder can often be caused by factors outside of the braking system. Therefore, it is important that the technician adhere as closely as possible to the procedure detailed below so that the causes of the concern can be accurately identified.
NOTE: Brake shudder has been found to be most apparent when braking from speeds around 112 to 120 km/h (70 to 75 mph). Therefore, subject to local road conditions/speed limits, the vehicle should be driven as near to that speed as possible during the road test.
1. Drive the vehicle up to speed.
2. When safe to do so, apply the brake pedal and brake lightly to a stop, noting the speeds at which shudder is apparent. (The shudder can be identified by steering wheel vibration and brake pedal pulsation.)
3. Repeat above steps twice more in order to confirm the critical speed ranges.
NOTE: Allow 1.6 km (1 mile) between each application to allow the brakes to cool.
4. Return to the critical shudder speed, but instead of applying the brake pedal, apply the parking brake lightly with the release button depressed. Check for vibration through the parking brake and/or the steering wheel.
- If vibration is apparent when carrying out the parking brake test, rear brake shudder is present. This must be investigated and eliminated before investigating whether front brake shudder is also present.
- If vibration is only apparent when the brake pedal is applied, it can be assumed the rear brakes are functioning satisfactorily. In these circumstances, continue with the front brake shudder diagnostic sequence.
5. If the road test has established a rear brake shudder condition, the following procedure must be used to isolate the cause:
Remove both the rear wheels, mark the brake drums right or left and remove both brake drums.
NOTE: If any components require replacing or repair, this should be carried out and the vehicle road tested before continuing with the brake shudder procedure.
6. Check the condition of brake components for serviceability (e.g. rear brake shoe and lining condition, loose rear brake backing plate, contaminated rear brake shoe and linings and brake drum condition, etc..). Make sure the rear brake shoe and lining rear brake backing plate contact points and rear brake shoe and lining ends are lightly coated with grease.
7. If no corrective action is necessary turn the brake drum to eliminate any possible runout.
8. Road test the vehicle to confirm the repair. If shudder is still evident, proceed to the front brake shudder test. K - Brake Shudder