SOME companies say they will accept any brake-shoe core for relining, while others might not check the cores carefully enough before accepting them.
But Scott Walpole, friction product manager for Haldex, says the inspection process is a critical step in quality control. He says an estimated 10% of the shoes returned to Haldex do not meet the criteria to be relined.
“Shoes are built with specifications, just like anything else,” he says. “Once a shoe has exceeded the tolerance, the shoe is no longer any good. There are some issues when it comes to stretch and collapse. Some people think they can be bent back into shape by a coining process, while others like to rebuild certain portions. With Haldex, if a shoe doesn't pass our inspection, it's time to get a new one. To try to rebuild them or bend them back into shape is not necessarily the answer.”
What steps should a technician take to determine if a customer's brake shoes should be relined or replaced with new brake shoes?
Walpole says a technician should examine the brake shoe being taken off in order to make that determination, first looking for visual signs of damage, broken welds between the web and the shoe table, and any deformities to the structure like bent webs or shoe tables.
Then all the wear spots should be examined, searching for excessive wear in cam and anchor areas; if it looks oblong, then it probably has too much wear.
Next, examine the lining edge for cracks. Horizontal cracks can be signs of shoe table distortion or major rust buildup on the shoe table.
“If you find any of these problems, you're probably holding a shoe that isn't worth relining and should consider buying a new shoe replacement,” he says. “Many of the biggest issues have to do with fatigue — stretch and collapse of the shoe — which changes the whole geometry. The lining then doesn't fit correctly and you have gaps between the lining and the shoe table. Once you rivet that shoe down, you've got pressures and it can crack the lining.”
He says Haldex will reject a shoe if any of the following conditions are present: more than .025" of wear on the anchor pin hole; stretched or collapsed shoes; bent web near the anchor pin hole or unparallel channels; cracks in the weld between the table top and web; excessive roller end wear; bent table top; excessive rust on the table top of .018" or more; three or more elongated bolt or rivet holes.
Another issue: Rust jacking, which can reduce lining life by 50% of what might normally be expected. Rust jacking is caused by corrosion, and Walpole says the main culprit is road-treating chemicals.
“Once the chemicals get under the lining and start attacking the steel, the process has begun,” Walpole says. “Rust creates a corrosive layer and it continues to expand and forces the friction material off the shoe table. But the rivets are trying to hold it down, and so you have these two forces, and the lining cracks.
“The layer of rust could be up to 1/8" thick in some cases. We've had shoes that are just a glob of rusted steel affixed to the friction material itself. At that point, the shoe table is pitted, and no longer usable.”
Walpole says that once the shoe has started the rusting process, there is nothing that can be done to stop that rusting or reverse it other than to galvanize the shoe or some other expensive means.
“Most of the manufacturers of new steel have started switching over to powder coatings,” he says. “We switched to powder-coated shoes to prevent rust buildup.
“Haldex has incorporated a new paint system to our relined shoes. We're rolling the new coating out region by region across the country as we equip our Service Centers with the proper drying equipment.”
Walpole says the brake relining process consists of multiple stages, as does the inspection process.
“When we're picking up the cores from our distributors, the shoes are checked there, given a good visual inspection,” he says. “The ones that need gauging are inspected at that point. During every step of the reline process, the shoes are inspected for damage. After the lining is taken off, the shoe table is inspected. It costs us money to let a shoe go through the process and then reject it in the end, so we inspect every shoe upfront to find the bad ones early in the process.
“During every step, the shoes are visually inspected. We look for cracks, deformities, and anything that looks suspicious. Once the shoe has been delined, it's cleaned and blasted.”
The first step of the relining process is delining the shoe. Each shoe is run through a laser-controlled automatic deliner, which removes rivets and old linings.
The laser technology used by the Haldex Service Centers improves the speed and accuracy of the relining process. Once a shoe is delined, it is shot-blasted to prepare it for painting and eventual relining with a specified friction material. Each cleaned, delined and shot-blasted shoe is coated with a protective paint, designed to provide longer life.
After painting, a specified friction material is securely attached and riveted to each shoe. The shoe is then inspected once more to ensure proper painting and correctly attached friction material.
The automated relining process improves efficiency and performance for Haldex Service Centers, enabling more than 10,000 relined shoes to be processed each day. This means there are no back orders or downtime for relined brake shoes.
Walpole says fleets should always buy a percentage of new shoes to replace worn or out-of-spec shoes that come off their vehicles.
Haldex has seen some fleets that have decided to forgo any relined shoes and replace all worn-out brakes with new shoes. Walpole says the cost is higher, but the advantage is a new shoe that should always be within specification.
“A new shoe will typically cost $5 or more than a relined shoe with the same friction material attached,” he says. “Plus, using relined shoes relieves a fleet of disposal issues that in some states can be very strict. A fleet that is buying new shoes should request help from Haldex to help them dispose of the friction material properly. We may even buy the used shoe from those fleets.”
He says that in today's litigious atmosphere, there is no reason a fleet should take on the liability of remanufacturing a brake shoe. Also, the equipment needed to properly reline a shoe would not be cost effective for a fleet to make the investment just for its needs.
“In the end, it would be very difficult to match the quality, cost, and expertise that Haldex provides versus an in-house reline shop at a fleet.”