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Originally Posted by Richardrky
"Driver, it looks to me that what probably happened here is that when the "pins were lubed" the caliper pistons were probably pushed back in their bores. whadda ya think?"
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Richardrky, Not observing how your caliper pins were serviced, it is possible that if the pistons were pushed back they could have presented the problem that you are experiencing.
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What is the correct procedure to lube the caliper pins? Jeez, are you saying if I did not have the pins lubed the problem may not have occurred?
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The correct procedure to lube the pins is to remove the tire, remove the pins and dismount the caliper. Inspect all surfaces for anomalies. Inspect and clean the surfaces that meet one another as necessary. Restore the caliper & shoes. Insert and torque pins, leading and trailing pins are different. I believe this procedure is detailed in the Bosch brake manual we have here in the stickies you may want to go and check that.
When the caliper is restored to its operating position it's likely that the pads will be pushed back so the fit over the rotor will be easier. This will push back the piston in the bore and that might present a problem.
I believe that you can lube the pins monthly and it would possibly not have been effective in preventing a seizure. The root cause of the problem is the fluid in the piston bores that accumulated moisture and imparts that to the piston.
The field expedient of removing and lubing the pins and reinserting the pins will only assure that the pins have lubrication on them however that will not rule out any other issues that may impact the brake unless the unit is disassembled.
From what we have been seeing here and reading in the reports as the logical point of failure, the most effective maintenance procedure would have been to flush the brake fluid on a periodic basis from when the vehicle was placed in service. The indicator for this is because RVs sit around a lot and don't enjoy constant repetitive brake cycles.
The same brakes on Workhorse commercial chassis which are driven daily with hundreds of cycles per day do not exhibit this type of problem. Those guys just simply wear out their brakes.
Over the past couple of years since we've begun speaking about brakes, I made recommendations along the lines of bleeding the calipers on an annual basis even if it were only 1 good pump per wheel - that would have dumped a lot of the water overboard and possibly have extended our brake service life. I have worn a lot of band-aids for suggesting this in the past.
There are excellent reasons why phenolic was chosen as the piston material however (>total wild guess on my part<) what was unavailable to Bosch engineers at the time is how infrequently these vehicles would be driven.
I can see the think tank session at Bosch now ..... lets build a Class 6 vehicle, let it sit around unused for months at a time and then run the heck out of it for a few days and then put it away wet until the next time.
I guess that this vehicle use requirement is going to be considered quite heavily going forward since close to 180,000 calipers are going to need to be replaced.