We have had a problem with our brake shoes rust jacking. Anyone know if there is a way to prevent this? It gets costly to replace when they are far from worn out.
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We have had a problem with our brake shoes rust jacking. Anyone know if there is a way to prevent this? It gets costly to replace when they are far from worn out.
This has been a truck industry-wide problem as long as riveted brake shoes have existed. There really is no hard solid answer. It's not a problem for trucking companies, as their brakes dont sit around long enough to develop the problem. The fire service, on the other hand can and will see the issue, more so for slower rural companies.
I cannot recall our apparatus ever having the problem, we are not busy, we are not slow either. We also regularly drive the rigs, whether it be drills, driver training, etc. We wont experience the problem any more as our 1989 Duplex/Quality and the 2007 Spartan Toyne both have discs all the way around.
I understand Meritor now has a shoe specifically designed to prevent this problem, but dont know much more then that.
Rust jacking is a major problem within the trucking industry. It is caused by some of the newer chemicals being used on the roads to fight snow and ice. Most highway officials have been in denial ever since the problem first surfaced, and refuse to admit that it is the cause. But the evidence is pretty convincing.
As Buff mentions, brake manufacturers have done a lot of research and are developing new materials to combat it. The problem is not limited to brakes, but to any part of a truck that gets exposed to the chemicals.
Most trucking industry publications have done extensive reporting on it. "Heavy Duty Trucking" is one such magazine. If you can find a way to search back issues, you can get alot of good info. As a member of the American Trucking Associations' Technology and Maintenance Council, I know that they are aware of it and are working on standards to combat it. When I get to the firehouse later this morning I will look through my copy of their "Recommended Practices" and see what has been developed.
I didn't realize that it was this bad nowadays, back when I worked at Ironside Court, those chemicals were not in widespread use.....Quote:
Originally Posted by chiefengineer11
It was just starting to be recognized as a problem around that time.
I know just enough about brake shoe mix formulations to be dangerous. First, the binder for most, if not all is a phenolic resin. The manufacturer "cures" the binder enough to make the mix into a solid form at the time the "blocks" are pressed into the rough shape, before being machined and installed on the "shoe". Phenolic resin is selected because as the cure advances, the ability to bind the friction particles is destroyed by excessive heat generated at the drum/rotor and friction material interface. Think of it as burning away the resin (Thermo-set, but softends slightly before curing hard at elevated temperatures) exposing fresh friction particles. This softening of the resin allows some of it to adhere to the drums or the rotors. To scrub this material from the rotors or drums, steel wool (rovings) is added to the mix. The pieces of rovings scour the sticking resin off of the rotors or drums and prevents excessive grabbing of the shoes to the rotating members of the system. The rovings also serve a second function, by helping to carry the heat of friction through the friction material and out to the steel shoes for heat dissapation. For many years, when copper and brass was not nearly as expensive as today, brass rovings and chips were used for the same function. The use of brass rovings, combined with a slightly more agressive friction material could be a solution for the rust jacking problem. At the same time you should be looking for a mix with some graphite, since more agressive friction material will begin to GRAB in wet conditions. The graphite tends to lubricate the surfaces to even out the friction when wet. Incidently the phenolic continues to cure through out the use. Each time the brakes are applied, the thermal cure progresses. The cure system causes ammonia and water vapor to evolve from the mix. Hard & long brake applications actually generate internal steam / gas pressures inside the friction material. The escape of these gasses can be the cause of "Brake Fade" by creating a gas cushion in the interface between the friction material and the rotating member.
While you are experiencing the "rust jacking" have your driver place the rig in reverse and move slightly back before starting out of the station. The S-cam or wedge brake systems are designed in such a way as to increase pressure on the shoe when going forward. Backing a few inches will aid in pulling the shoe away from the drum prior to moving forward. Try to avoid spraying the wheel / brake system with rinse water if rigs are routinely washed after returning. Sprag the brake for the last several hundred feet before backing into the station to dry the drums after running in wet conditions. This will raise the drum temperature and aid in drying the drum under the shoe when the parking brake is applied.
With all due respect to KuShinse and the well written description of braking issues...it is my understanding that "brake jacking" is simply rust "growing" between the friction material (Block or lining) and the what it is called the "table". Most quality brake manufacturers using electrostatic epoxy paint processes to coat the table, have addressed this problem as the epoxy paint is very effective in resisting the chemical reactions caused by road de-icing materials both granular and liquid.
Here's a link to a diagram of the brake shoe that shows the different parts of the brake shoe
http://en.wikipedia.org/wiki/File:BRAKE_SHOE.jpg
Ooops, thanks firemech1 that should have said "rust jacking" not "brake jacking" ...I should have re-read my post before...
With all due respect don120, what you are referring to is called "Rust Jacking". That is when the rust gets between the brake material and table. Brake jacking is "unofficially" the term for when wet/contaminated brakes sit against a hot brake drum, and fail to release properly. Best way to overcome this, as has been said, is to back up a couple inches to break the shoes away from the drum. This will release the natural tendency built into the brake system to help braking while moving forward.
FM1
EDIT: Linky: http://www.meritorplatinumshield.com/RustJacking.aspx
If anyone has access to ATA's "Transport Topics," the issue dated Jan. 23 has a pretty good article on the subject.
Thanks for all the great information. We are indeed experiencing a problem with the brake shoes themselves seperating from rust/corrosion. We are looking at a $2300 to $2700 brake job for just the rear axle (drums and shoes). The roads here are heavily salted and I think the salt/brine mix they use makes it even worse.
I will have to look further into the Meritor shoe if it will fit our application. Thanks again.
Found this article regarding rust jacking
http://www.todaystrucking.com/news.cfm?intDocID=27891