Strange Brake Caliper Issue
 

In support of construction efforts we run a fleet of International flat bed trucks. They are robust and stout as can be - they have 4 wheel disk brakes. The following photos are of the second caliper that has gone bad in the last six months. To our eyes it looks like the steel pistons have crystalized - the leading edges are dissolving into a powder. We have confirmed we are using the right brake fluid, and we have never had this problem with any other calipers in the fleet. Any ideas from the brain trust?

http://forums.pelicanparts.com/uploa...1341945059.jpg

http://forums.pelicanparts.com/uploa...1341945080.jpg

Are you sure they are stainless? . I have seen caliper pistons that look like that when the caliper stuck and overheated. Your dust boots do not look to have been overheated though. Is there any evidence of overheating, at either the rotor, pads, or caliper piston dust boots? How about the slides on the brake caliper bracket? Do they move free?

Looks like galvanic corrosion from dissimilar metals.
Are you running the o.e. pads?

The dust boots are fine. We are running a variety of pads, but I certainly assumed all pads and pistons were steel. I have no doubt that they get hot, but these trucks are heavily loaded most of the time. I certainly agree with the galvanic corrosion, but I can't explain why it has just started now.

They look aluminum and have a bad case of galvanic corrosion. Put a magnet on them and see if they have any iron in them.

Chinese pot metal. Everything goes in.

AS far as we know these are the stock calipers. I will check them out tomorrow and see if they contain iron.

Our local brake supplier says that he sees this often - that the pistons are of a material that does its best not to transfer heat to the brake fluid. What really bothers me is we have never seen this before. Will be checking all trucks in the fleet for the remainder of the week.

salt and aluminum..........they are Al.

Salt. If you mean from ice etc we don't use that in So Cal.

I believe those pistons are some sort of phenolic plastic. GM used that material for a number of years.

Plastic? Wow! Really?

Kind of what I was thinking.