Hey Randy. Maybe my loosening the caliper bolts every oil change so I can move the pins back and forth 1/4" as a check helps distribute the lube better preventing the issue. Again my take is once you start having a rust issue in the pin bores removing the crust doesn't stop the process.

I think I've done this before here but I'll throw up some of the pictures I still have from a pictorial I did for the aftermarket guys in the company on servicing details. I don't have them all.


When the boots get damaged which is usually from the heat, they let moisture into the bracket pin bore and corrosion starts to develop.





You usually can see some oxidation forming in the bores, it's usually much worse than this.




The original surfaces are a honed finish, not unlike an engine cylinder bore, but there is wear from caliper movement.



The best mechanical way to clean them after washing out the silicone is with a ball hone, which will be different sizes for the front and rear calipers. But you want to preserve the diameter of the bore as much as possible, and when doing this the factory anti-corrosion finish is removed. This process is often done with purchased rebuilt calipers. A wire brush will be less abrasive, which can be a tube brush or a gun barrel brush.




Sometimes we will see burned caliper piston boots, which is likely if the brake pads were replaced with high metallic aftermarket pads or the heat shields were not reinstalled from the early model design.









Those Gen 1 shields were eliminated during Gen 2 developments, and the mounted noise insulator extended up the top of the pads to protect the boots from high temperatures. However, many of the aftermarket pads do not do this, and it's even evident on the Motorcraft replacement pads, which is ironic.




While looking at those pads, many people get into trouble by not retracting the caliper pistons far enough in so the noise insulator retaining nubs clear the pistons during removal. It's very evident when there is this type of damage to the pistons and the person removing the calipers blames the phenolic pistons from cracking. That's not the pistons fault.




Trucks that snow plow, see extensive chloride de-icer exposure, or even sitting for long periods of time suffer from rusting within the caliper bracket. This can reduce pad freedom in retraction from the rotors or just lock the pads to the rotors. This will result in uneven wear of the rotor rubbing surfaces (pulsation) or overheating of the brake which will then be the cause of burned slide boots or piston boots.

These surfaces are critical on the pads for freedom of movement. In the aftermarket industry, the tolerance in stamping is not controlled as well as the OE manufacturer does (used to be me). With new pads, this freedom needs to be checked during installation and sometimes corrected. Sometimes it's just excessive paint, sometimes the steelback tab is too wide or high.

The OE stamping spec was +0.000"/-0.010". The aftermarket stampings, used to be from Aimco or NRS were =0.010"/-0.010". That little 0.010" takes up a lot of space in there. Today there are many stampings out of China.








But in-service as mentioned about can just develop too much rust, on the steelback tabs or under the stainless steel slippers from the bracket. Again this prevents freedom of movement of the pads. The caliper body and pistons may have moved away from the rotor on brake release, but the pads do not. And the clearance here is designed tight to prevent noise.











Cleanup can be as easy as just a wire brush, or at the pad's ends may need to be done abrasively.







Using a small amount of silicone based grease on these surfaces is the best choice to prevent any rusting, but only a small amount as to not contaminate the friction material surfaces as it can migrate in use.








Anyway, my quick tips for the day.

 

I use ceramic brake grease, blue, on the slide pins and flush the fluid every 2 to 3 years. Brake fluid is hygroscopic. Have never had a problem. Knock on wood. Hope I didn't jinx myself.

 

 

The rears never changed design, it was only the front caliper pins.

 

 

Nice post Jack!
Because I go no more than 6000 between taking them apart, no rusting or pitting here, just dry pins. I usually catch them at the right time avoiding a real mess. The OE pads from Ford are still reasonable from the dealer, around $40-45 a set. I never let the pin boots get ripped or torn and always replace one that may appear to be worn, they are cheap insurance.

So how does one retract the pistons to avoid damaging them when taking the calipers off? I've always just removed the bracket and caliper at the same time.

 

 

Nope.

Passenger side piston resistance to moving is either from the seals getting hardened from aging, or some rust getting under the boots or o-rings and grabbing the pistons. And sometimes it's just adhesion of the rubber o-ring to the piston and pushing the piston in breaks that up, its like being a caliper piston chiropractor.

During new caliper design testing measuring seal rollback and piston movement (knock back) force is tested. There typically are values for new components and then after the caliper has been oven baked for a set period of time and temperature mimicking in-service. Testing is done on a machine such as this from Link.



Typically you start out with a total clearance pad to rotor of about 0.015", half that each side. Brakes used to have wider spacing but that results in a longer pedal travel. The problem with the long wear mileage we get out of friction material today with some SD's getting over 100k before a pad change, the seals loos resiliency so they don't cool as well, rotor off-braking wear is higher from pad contact, and of course fuel mileage is lower. So sometimes even when you're at 100k and changing pads, you also need to think about seal aging.

But it sounds like you caught that caliper before it became a real issue.

 

The need to push the pistons in is dependent on the height of the pad's nubs (vary by manufacturer) and how well the caliper pistons rollback on brake release. I've not had an issue myself, but there's a lot of those type of caliper damaged pistons out there. But it's a safer to get some clearance, especially if the calipers resist coming off.

We had, and I have large C-clamps.




But you can go Neanderthal if your careful, prying the caliper while catching the edge of the rotor with a flat blade screwdriver.




Once the caliper is off you can use the C-clamp to further push the pins in or use a tool like I have from Blue-Point.






Over the years I used two different greases for the pads and the slide pins, the standard silicone caliper grease and Dow's 77. The 77 is a high temp silicone grease with Moly, it's the same grease used by Honda (another manufacturer we sold pads to) on the back of the pads for noise abatement. But it's really high in viscosity and when used for the pin slides created too high of a hysteresis. Iv emoted to nickel based anti seize on the pins for this last changeout, just a thin coating, and it seems to do well. Sometime this spring I'll probably find out how it does with parking lot rot of almost 2 years.

 

 

Jack is fine.

Its all a lot of eccentric data that only makes sense if your in the industry and detail the crap out of all this. Some mechanics have all this figured out, and some go Huh?

A rear brake doesn't yank the steering wheel like the front brake can. Heat with semi-metallic pads alters the friction coefficient, and these trucks have a high scrub radius (another detail) which make inconsistency left to right a bigger pull issue. It's why there was a TSB to replace pads with the same lot numbers if a customer complained about brake pulls.

Ah, the fun times ...... just do anything to get the warranty down.

 

 

70% of the stopping power comes from the front, why it pulls you to the one side or the other and the rears are generally a straight line drag. Also why a front will smoke before a rear, more stopping material and contact, builds heat faster. Next time you have the pads off, put a rear pad to a front and see the difference, about 25-30% more pad up front. Even looking at a the calipers, the fronts are much larger.

It seems that I replace fronts 2-1 as well, say's how much more the fronts are used for stopping.... ever notice the fronts are caked with dust and the rears hardly have any on the wheels?

 

 

That's exactly what I had when the cheap pistons started swelling - once I drove 200 miles, checked all the wheels were cool, drove once round the village, about 1 mile, and one side was so hot it took a minute with a hose to cool it off, which is probably why the hub failed later...