A mechanic works on the brakes on this tank trailer Good brake maintenance is critical to tank fleet safety

Haldex, Bendix offer tips to keep truck and trailer brakes in top condition

Nov. 5, 2015
Brake condition is a focal point in commercial vehicle inspections. Haldex and Bendix recommendations for brake safety.

GOOD brake maintenance plays a critical role in ensuring safe vehicle performance. Not surprisingly, brake condition is a focal point in commercial vehicle inspections conducted by enforcement officials as part of the Federal Motor Carrier Safety Administration’s Compliance, Safety, Accountability (CSA) program.

“Last year’s (2014’s) Brake Safety Week saw about one in 10 vehicles placed out of service for brake adjustment,” says Frank Gilboy, slack adjuster product manager with Bendix Spicer Foundation Brake LLC, a joint venture between Bendix Commercial Vehicle Systems LLC and Dana Commercial Vehicle Products LLC.

He went on to say that drivers play a key role in a solid brake maintenance program. Inside the cab, it’s important to know the vehicle systems’ blinking light fault codes and how to address them.

​Antilock braking systems (ABS) warning lights convey key information on problems with components such as wheel speed sensors. If the vehicle is equipped with traction control and stability control systems, the traction control/stability control lamp will indicate any issues. Blinking light fault codes for both ABS and traction control/stability control systems can be accessed using the dashboard diagnostic switch or a remote diagnostic unit. Using the fault code information in the service data sheet, drivers and technicians can pinpoint and address sensor issues.

Day-to-day, maintaining a clean air system is a priority. Components such as air seals, brake modulating valves, and brake chamber diaphragms are susceptible to premature damage if an air system is contaminated by moisture—and, in particular, oil. Deterioration of seals can cause air system leaks, which are targeted during roadside inspections. Bendix recommends monthly checks for moisture in the air brake system, along with installation and regular replacement of oil-coalescing air dryer cartridges.

Pre-trip inspections

Drivers must conduct effective pre-trip visual inspections, with an eye out for problems such as loose hoses and leaks. At the wheel-ends, visually check that the air chambers are not damaged and hanging loose or with broken push rods. Check foundation drum brakes for lining cracks, linings that may have been oil-saturated due to leaking wheel seals, and broken cam brackets. As long as there are no dust shields, linings can be checked without removing the wheel. And if the vehicle is equipped with air disc brakes, check the rotors for cracks or grooving and make sure the caliper is sliding freely.

More in-depth preparation includes regular, detailed inspection of the brake friction, checking the linings for thickness, cracks, and wear; and measuring the brake stroke. In addition, check the cam bushings and replace if out of specification, as well as lubricate the cam tube until grease purges.

For fleets and drivers operating vehicles equipped with automatic slack adjusters (ASAs), it’s important to remember not to manually adjust the ASA if the brake is beyond the stroke limit. Drivers can incur fines if 25% of a truck’s wheel-ends are beyond the maximum allowable brake stroke (out of adjustment). Simple maintenance, such as greasing the slack, can keep the ASA working smoothly and in proper adjustment. Several factors—including improper lubrication of the camshaft, cam tube, and clevis pins; or excessive wear of the cam head, bushings, and rollers—can cause a brake stroke to exceed the maximum allowable value, but none of these will be fixed by manual readjustment of an automatic slack adjuster.

“Because properly installed and maintained ASAs should never need adjusting after the initial setup, we emphasize the need to learn and address the possible causes of ASA-equipped brakes going out of adjustment, which has a direct impact on brake performance and vehicle safety,” Gilboy says.

Maintenance guidelines

For the maintenance shop, Haldex offers a detailed brake maintenance process. Haldex officials add that mechanics also need to follow specific brake manufacturers’ instructions for brake maintenance.

In conducting a complete brake job, disassembly can impact the assembly portion of the brake job process, all of which affects overall performance of your brakes. During disassembly be sure to carefully inspect every brake part, checking for unusual wear. Part wear patterns can tell a lot about the brake and the entire braking system.

It is important to note that most friction problems can be diagnosed by a close inspection of the old parts. Begin by checking the pushrod stroke.

1.  Check the pushrod stroke per CVSA checking procedures at 90 to 100 psi reservoir pressure. Excessively long or short stroke can alert to problems that need to be addressed during rebuild. Reference Haldex ABA Stroke Adjustment Instructions (L55054) and Haldex ABA Service Manual (L30033) for list of potential problems.

2.  Before pulling the wheels, check each for end play and oil seal leakage. This may indicate seal problems or bearing/cup wear and/or adjustment.

3.  Inspect all brake shoes for even wear. If all brakes are not worn evenly, there may be failed or misadjusted components that will need to be corrected before assembly.

4.  Inspect lining surface for heat checking. If present, this indicates excessive heat due to all wheels not braking evenly, incorrect lining being used for the application, overloading or a combination of these.

5.  Check lining wear across each shoe. An uneven pattern or excessive grooves can indicate the drums need replacing. An uneven pattern can also indicate bent spiders or bellmouth drums, or weak shoe return springs.

6.  Inspect lining surface for grease or oil. Never reuse grease or oil soaked brake shoe. Grease or oil on the friction material will cause the lining to glaze and not do its share of the braking. Never do a one-wheel brake job.

7.  Inspect drum surface for even wear, glazing and/or heat checking. Heat checks, cracks and blue spots are indicators of excessive heat (hairline heat checks not over 1-inch are normal). Never reuse a drum if: wear is over .080 or several heat checks are aligned across the braking surface or hard spots exist.

8.  Check S-cam for wear at the inner and outer bushing surfaces, S-cam head and spline areas. Worn S-cam or S-cam bushings will contribute to longer than normal pushrod stroke.

9.  Check brake adjusters for proper settings and operation. Check clevis pins and anchor brackets for wear. Never mix automatic brake adjusters with manual brake adjusters, or use different makes of automatic brake adjusters on the same axle. Never operate automatic brake adjusters with worn components.

10. Check the wear difference between the front and rear axle shoes (if relining a truck or trailer). If the wear is not equal, this can indicate an air timing imbalance or different rated friction materials. Check for inconsistent use of elbows in air lines (90° elbow is equal to 7 feet of extra hose).

11. Inspect spiders. Pay special attention to the anchor pin-hole area and for squareness and s-cam bushing bore, and to anchor surfaces that are not replaceable.

Reassembly steps

During reassembly it is important to note:

a.  Select the proper friction material based on your type of loads, application, duty cycle and operating terrain. Consult your supplier if you have any questions.

b.  Many shoes look alike, especially the new extended service design. Therefore, be sure to install the same shoe that is removed.

Always replace all shoe attaching parts, anchor pin bushings, cam bushings and oil seals. All parts being reused should be cleaned with solvent, rinsed and dried. Replace S-cams, bearings and cups, as necessary.

Lubricate anchor pins, brake rollers and bushing area of camshafts. Never lubricate the face of the roller (contact point with the s-cam). Only lubricate the bearing area of the roller that contacts the shoe web.

Install new drums, if necessary. Do not mix light- and heavy-duty drums as this will result in uneven brake shoe wear.

Spindle lubrication

Lubricate axle spindle to insure bearings slide on easily. Slide hubs onto the axle far enough to be able to install the inner and outer bearing and inside axle nut. Never slam the hub onto the axle. Adjust bearings to manufacturer’s specifications. Install spacer/lock ring and outer nut (if applicable) and new hub cap gasket. Ensure proper hub oil or bearing grease, depending on the type, is applied.

Always adjust all brake adjusters on all wheels of the vehicle. Adjust all manual brake adjusters for .015 drum clearance. Automatic brake adjuster drum clearance is .018-.025 (check manufacturer’s specifications for proper setup). Follow the same procedure for each brake adjuster on the vehicle.

Inspect all brake hoses leading to chambers, replacing if cracks are found. Inspect all spring brakes for center seal leakage, replacing if needed.

Check brake release. If slow on the trailer, install a quick release gladhand on the service side of the trailer to speed air exhaust.

Inspect spring brakes for proper installation of rubber dust plug in release tool hole. If you replaced any brake chambers, ensure you did not mix sizes. Never mix long stroke with standard stroke chambers on the same vehicle. If relining trailer brakes, replace both gladhand seals.

Always road test after reassembly to check for satisfactory brake performance. Automatic brake adjusters are typically backed off half turn from lining contact. Final stroke will not occur until brakes are cycled and lining is “burnished in.”

Re-examine wheels for excessive end play. Re-check brake adjusters and chambers for proper and equal stroke.  ♦