Some background: It is a 2012 G37X with non sport brake. I found the front passenger side caliper piston got rust badly when replacing the wheel bearing with 70k miles. The rotor surface looks black, but the guide pins slides well, the brake fluid level is between min and max. I was trying to figure out the reason of wheel bearing went out so early.

I recall both the front passenger and rear driver wheels got hot after driving a while, and it is still getting hot after I replace the wheel bearing(noise is gone). I know the front passenger and rear driver side are the last two when bleeding the brake fluid. But I'm not sure it matters in my case. I'm guessing the problem is the rust caliper or the brake hose or tube is clogged. But I think I need more opinions on this. Thank you.

 

Your caliper pistons look badly rusted. That amount of rust can result in them sticking after braking and causing excess heat. You most likely need to rebuild the calipers and replace seals/dust boots and replace brake fluid. .

 

it must be a sticking caliper.... does the wheel even spin freely with the car off the ground?

 

Actually no, I can hear some friction noise when I rotate the rotor off the ground. The guide pins will be sucted back if I pull the pins out. And is this easy to rebuild the caliper piston and rings? Or just buy a new caliper? Thanks.

 

Another possible problem is the pads sticking in caliper bracket. I pretty much always end up grinding a little on the ears of new pads because they don't move freely. How difficult was it to push the pistons back in? If easy then that is not your problem.
The friction noise you describe could be the backing plate rubbing on the rotor. Very common issue. Or rust build up anywhere on the rotor. You can scrape that off without damaging the contact surface.

 

Rebuilding is easy, get a kit and alot of brake cleaner. Your pistons are definitely rusted and sticking to the rotor.

 

What they all said. Also, you from Ontario?

 

The pads move free, it should not an issue. And I agree with the backing plate rubbing noise. Thank you.

 

I don't have an air gun, which should remove the piston very easy. So I believe getting a new caliper is the best for me. Thank you.

 

I'm from north Ohio.