When the shoe doesn’t fit
When the initial lining wears off your truck’s brake shoes, to maximize their life you’ll want to have them relined or remanufactured. Just don’t think those two terms are interchangeable.
Many fleets choose to have their brake shoes relined, which may do little to ensure the shoe is still suitable to redeploy back into service. Brake manufacturers say this is a concern.
“Probably half, if not more, of the brake shoes out there are relined, not remanufactured,” Frank Gilboy, product line manager, remanufactured wheel-end products with Bendix, told Truck News in an interview. “Relining is literally just as it sounds: stripping off the lining and putting on another piece of lining and not really addressing any of the problems with the shoe itself.”
Slapping a new lining on a damaged shoe does not ensure the brake will perform as intended. However, remanufacturing the shoe restores it to original quality while still providing about a 30% cost savings over purchasing brand new brake shoes.
The remanufacturing processes employed by companies such as Bendix and Meritor are highly sophisticated and can’t be matched by a reliner. It begins with a thorough inspection of the shoe.
“The first thing we do when the core or the used brake shoe gets returned back to us, is wash it so we can give it a good inspection. That’s really to make sure this shoe is worth moving forward with,” Gilboy explained. “There’s probably anywhere between 4-6% of the shoes that get returned to us that aren’t suitable to go back out into the field. The first thing you need to do is wash and inspect it and make sure you have a core that’s worth remanufacturing.”
Even the removal of the old lining is done a certain way during the remanufacturing process.
“There are a lot of different ways to do this in the industry,” Gilboy explained. “There are some ways that could seriously damage the core, such as sheering the lining off. What we do at Bendix is, we use automated delining machines which are computer-controlled.”
This ensures the holes in the table are perfectly rounded and sized for a proper fit with the new rivets so that there’s no movement of the rivet within the holes.
“The precision delining makes sure we move forward with getting the lining off without doing any additional damage to the shoe at that point,” Gilboy added.
Next, the delined shoe is put through a blaster, which further cleans the shoe and prepares the surface for its future coating.
“Out of the blaster, you now have a clean shoe ready for coating,” Gilboy explained. “Now, probably the most important step is the coining of the shoe. What happens to these shoes over their life out in the undercarriage of the vehicle is, a tremendous amount of force goes through them. Some of these could see hundreds of thousands of brake applications over their life out there and every one of those applications is putting force and temperature through the shoe. That builds up over time to the point where the shoe starts to get distorted. So they can get stretched, they can get twisted. All sorts of things could happen that really knock that shoe out of geometry.”
Every shoe is recoined by being placed back into a press, which conforms it back to its originally designed shape. The next step is putting a new coating back on the shoe. And then finally, the new lining is riveted to the shoe.
“Here, there is an opportunity to really mess it up if you don’t have the proper controls in place,” Gilboy warned. “We’re looking at the torque of the rivet, we’re looking at the geometry of the rivet and making sure that we’ve properly formed that rivet so that we get a secure attachment of that friction to the brake shoe. Now, it’s ready to go back out for another full life on the truck.”
If the shoe is properly remanufactured and maintained in the field, it could live to see three or four remanufactured lives, Gilboy said, and even more in climates where it’s not subjected to road chemicals.
Brake shoes that have been relined without going through the process described above can be an invitation for brake-related problems.
A poor seating of the lining upon the shoe surface can lead to all kinds of issues.
“Cracking is probably one of the bigger things that could occur if you don’t have a shoe that’s really mated with the lining material very well,” said Joe Kay, director of engineering, North American brakes, Meritor, noting even shoes that appear to have a smooth surface could have underlying issues. “There’s a tremendous amount of torque that goes through the brake. Every time you apply the brakes, it’s heating up – that’s its job – it converts energy. This brake pad is heating up, cooling down, heating up, cooling down and depending on the duty cycle, you could see temperatures of 600, 700 degrees Fahrenheit.”
Starting out with a low-quality brake shoe heightens the risk of problems and will limit remanufacturing opportunities. Many low-cost aftermarket brake shoes have poor welds and weak anchor points and the core will not qualify for remanufacturing.
“A lot of times we’ll see an aftermarket shoe come in as a core and the welds are already all cracked and the anchor points are already mushroomed out,” Gilboy said. “Really, it’s just a low-quality piece of steel that doesn’t live up to the requirements of the job.”
Cracked welds and mushroomed anchor points will lead to brake noise and poor performance.
“As the weld starts to break, the entire assembly now is going to have a lot more movement in it, so it might be more likely to squeal or groan upon engagement,” warned Gilboy. “And when you talk about the anchor points, if they’re not hardened and they start to mushroom out, now you’re going to get kind of a sluggish brake shoe because it’s not going to be pivoting correctly. It might get wedged out, you might have some brake drag, which could hit you as far as brake temperature, fuel mileage and things like that go.”
Meritor’s Kay said technicians should inspect the lining for uneven wear, which could indicate the lining is not seated properly on the shoe. Drivers should report vehicles that are pulling to one side or the other while braking.
A properly remanufactured brake shoe, on the other hand, lined with OE-quality friction material, should deliver performance and a service life that’s the equal to that of a brand new brake shoe and at a fraction of the cost.
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