Front Brake Caliper Thoughts

No question. Just an observation I thought I'd share from the weekend. I took my truck for it's first "long" drive this weekend and it ran great until one of my calipers locked up on me. I pulled it over for a little to let everything cool down and to assess the situation. I eventually "limped" it back home and to my surprise, it didn't lock up again the whole trip.

Taking the caliper apart, I removed the cylinder head and was amazed to see it was made out of some form of ceramic/composite. The back side of the head had seized to the walls of the cylinder and broken off into fragments. The only thing I can think of is that one of those fragments floated around behind the head causing it to seize shut. It would close, but not open.

Long story short, I ordered a new set of calipers to replace them. I had just never seen something like this happen before. Is there a reason Ford didn't use some form of metal for the caliper piston heads?

The ceramic ones are supposed to hold up to heat better. But apparently they can break.

i have seen many that had chunks or chips out of them. i can only assume it is from some tool being used to pry the pads loose a little to remove the caliper but yes that's only an assumption. most of my experience with binding calipers has been due to the pins and the slots they ride in not being clear and greased. its a real easy part to take for granted but its a serious maintenance point. trucks being revived should absolutely have the calipers rebuilt if not replaced due to rust. sitting is hard on and old truck. harder in the field and even harder in the woods where I got mine

Metal pistons conduct heat right to the brake fluid and if they rust behind the piston boot they will be impossible to retract when you need new pads.

Phenolic is strong enough in compression, unaffected by brake fluid and a good insulator (just like a phenolic carb spacer)

Great observation!  

Back when I used to work on these for a living (in the ford dealer) here was what we learned about why they used this Phenolic caliper piston.  They are far more heat resistant than steel and cheaper than stainless.  They very rarely "crumble" from the inside but routinely crumble on the outside.  Chrysler used these a lot back in the 80's as well.  A lot of heat got transferred from the pad to the caliper causing intermittent caliper seizing on earlier models with steel pistons due to rust on the caliper piston.  No one ever changes the brake fluid and DOT 3 is hygroscopic so it was either phenolic pistons, or stainless.  Plastic is cheaper, so plastic won!  

Also, my understanding was that people would beef about brake "feel" back than (meaning that some engineers in Dearborn got together and started clucking about nothing) in earlier model vehicles, so ford switched to the phenolic caliper piston to be able to build them with a tighter fit, thus giving them better feel and sharper response over the steel predecessor.  

At ground level, the prevalence of frozen calipers went up about 50% over steel piston units, but Ford kept producing and forcing the dealerships to put on the calipers with phenolic pistons.  

Yada yada yada......after all the smoke cleared, what we learned after changing about a million of these things was the cause of the problem was frequently moisture in the brake fluid causing the caliper housing to oxidize, distort, than start digging into the piston (which was, IMO, too tight in the first place) to drag and eventually seize.  

Of course, this was the FIRST most common problem with calipers dragging on Bullnose trucks.  The close second was collapsing brake hoses.  For some reason, it always seemed to be the drivers side that first became the problem.  We observed left side caliper sticking issues 3:1.  Near as we could figure, it had something to do with the shorter brake line and how quickly rust contamination and debris would accumulate in the caliper reservoir vs. the right side, but that is just a theory.  

Just a little historical perspective from the dealership floor.

The fact that most people do not flush the brake fluid is the cause of most brake problems on any vehicle, including these trucks.  We have a Mercedes and take it in religiously to have them do the A and B services.  One of those includes flushing the brake system and replacing the fluid.  I think that will enable the system to function properly for many, many years.

So I guess I'd better do that for my "new" truck, Blue.  

I see you already ordered calipers, but did you know that the T-bird calipers will fit and have a much larger piston?

Chad - Have you used them on your Bronco?  If so, how did they work?

Hi Gary. I might be wrong but someone will have to doublecheck me. I used them on my 79 D44HP solid axle and they are great. Much better than the original for obvious reasons. I think the OBS front calipers are the same except for the port, but someone will have to keep me honest.

Ok, thanks.  I really don't know so will have to see what others say about the OBS ones.  

I have only had one vehicle that the calipers seize on and that is my 1990 Town Car and it had the phenolic pistons in the calipers and they were replaced with new calipers with steel pistons and a complete brake job with new brake pads/shoes front and rear including new wheel cylinders for the rear brakes.