Phenolic vs metal

[Denisefwd93]

Caliper Pistons! Almost always that's what you get unless you specify metal piston calipers. Why do they continue to make this junk and is it actually junk?

 

[RonD]

Phenolic is heat resistant resin, it transfers less heat to brake fluid and dissipates heat faster than metal pistons.
Also lighter.

But not good for heavy brake use, i.e. hauling loads

So not junk, for cars and light duty trucks they would be the correct choice.

Metal would be for more heavy duty use, and you can rebuild metal calipers yourself

If you have a piston problem, phenolic or metal, it is not usually caused by the material, its a brake system issue.

I have had more metal caliper failures then phenolic, but in fairness metal has been around ALOT longer
Metal can cause rust rings in the cylinder if vehicle sits for long periods, so piston doesn't move as freely, causing dragging pads


Just an opinion

 

[Denisefwd93]

Ron I'm kind of locked in the mindset of thinking some plastics are not as dimensionally stable as metal. It appears the phenolic they are using for these Pistons is pretty well-established as okay for "normal" duty.

 

[Denisefwd93]

It would appear the Pistons in the calipers I got from AutoZone have metal

 

[adsm08]

Phenolic caliper pistons are not just plastic. They are a phenolic glass resin, something like a high grade ceramic.

In addition to the advantages Ron mentioned they are not prone to corrosion, so if you don't get your brake fluid changed out on schedule the piston does not corrode, and jam itself in the bore as quickly. It can still happen, just not as fast.

The biggest issue I have ever had with phenolic calipers, and this is almost exclusive to Super Duty trucks, is that if the caliper had fozen (so you need one anyway) and overheated you will almost always fracture the piston while trying to remove the caliper.