NGC - auto brake caliper frozen symptoms?

[brider]

This question is more of a sanity check, because I've replaced calipers many times, some of them frozen.

But my wife's 2014 Kia Optima with only 47k miles on it needed a front pad and rotor change (slight pulsing at hard braking, and rotors are cheap), and the pads were original, so the limit sensors were screeching.

It all came apart easy, but when I got to the part where I take a big C-clamp and compress the caliper to compensate for the thicker pad stackup, BOTH calipers WOULD NOT BUDGE when I tried to compress them, and I tried all around the circumference of each piston.

BOTH calipers? at only 47k miles? I thought maybe there was some special one-way valve in the system that wouldn't allow piston compression without the engine running or something (I know, far-fetched), but then I cracked a bleeder and tried to compress it THEN, still would not budge.

The calipers SHOULD compress, right? Nothing special in 2014 that wasn't there in mid-2000 technology?

I suppose if she drove for a long time with the pistons at the limit of their travel, they might be more susceptible to binding/freezing?

Only thing I can think of to do is go buy 2 new calipers tomorrow. 47k miles. Sheesh.

[Tom H]

To start with, I'm not an expert. Hopefully someone who is will provide the answer.

Before you break something...stop. Wait for an expert opinion.

Now...From what I understand about "some if not most" newer cars, you can not just compress the piston in the caliper like a '70 Chevy. Some MUST be either manually screwed in or electronically retracted. My wife's Subaru is supposed to be done electronically from what I understand.

You would need to RTFM to know what has to be done for sure. And maybe as well wait for an expert opinion. I know manuals can make the job harder than it needs to be, when you KNOW the shortcuts.

Tom

[pat80flh]

  First of all, I am not an expert on Hyundais. But I am a professional auto mechanic with over 40 years in the field. As far as I know, yes the pistons should push in. The only brakes that require a scan tool to retract the pistons are on cars with an electric motor built into the caliper as part of the parking brake mechanism.
   
   I was taught to never push on the outside circumference of the piston, only in the center. If using a C-clamp, a suitable large socket should be placed in the piston so the force is centered. It is possible you have cocked the pistons. If you opened the bleeder and the piston still doesn't move, it means the piston is stuck mechanically, not hydraulically.

    47k on original front brakes is a lot. It is possible that having the pistons that far extended for a long time has let some corrosion in under the dust boot, especially if you're in the Rust Belt. Try taking a small hammer and tap around the piston, then try your C-clamp again centering the force.  If you still can't get it to move, it's junk. But it would be very unusual for a piston to be completely frozen in its bore, let alone both.

   You could also try mounting the calipers up, put something between the piston and rotor to limit travel, and use the brake pedal to further extend the piston, possibly uncocking it.  Or let the caliper dangle and use the brake pedal to pump that piston right out of there, then you'll see what's going on. Just make sure that you have new calipers first.

[brider]

RTFM!!! Got me there!

The reason I haven't searched for a service manual is because the configuration of the brakes is typical of every front brake I've ever seen. One brake line, a single piston, and single bleeder, that's it. I will remove the calipers, drain the fluid, and try to compress the piston from the center, as was mentioned. Thanks!

[Mike Tashjian]

If the calipers are frozen I would block one up and use the cars hydraulics to push the piston out of the other.  By far the easiest way to see what is going on.  Just pump the pedal until the piston comes out.  Then repair or replace them as needed.  Once the caliper is off the car it is much harder to deal with and get good results.  Pushing a corroded piston back in and then trying to get it back out is hard to do.  They are usually cheap enough to just trade for rebuilts if the originals really do have issues.  Mike

[analog kid]

FWIW, the front brake caliper  pistons on my 2011 Kia Soul do not require a special tool or procedure to retract. I've done the brakes a couple times, most recently in early Oct.

Kias are, mechanically, pretty simple (at least mine is) - though they don't age well. Early onset corrosion and some cheap component parts.

[brider]

Well, I applied C-clamp pressure at the dead center of the piston rather than the rim, and lo, they both compressed.

Makes complete sense, but I have never had to do that before, there must have been VERY tight tolerances between piston and bore to cause binding.

I learned something, and like I first said, this was a sanity check.

Thanks for all the input!

[Mike Tashjian]

If you had to apply any more than slight pressure they may be on their way out. Let's remember how they are suppose to work. Pressure pushes the piston out and the square cut seal flexes. As pressure is released the seal is suppose to pull the piston back a tiny bit so the pads will not rub.  I usually pull them apart if I can't make them go back in with very light pressure from a clamp. You can usually push the piston out a good bit(half to three quarters of an inch, like worn out pads) before it will release from the caliper. Then you can pull back the dust boot from the piston and see if there is corrosion in there. They can be cleaned up and reused unless they are really bad.  Cleaning the sliding surfaces and pins is also a must on single piston calipers especially in climates where corrosion is a problem.  Mike