2009 Kia Sedona - unusual wear on rear disc brakes

Joined
Jul 7, 2014
Messages
2,400
Location
Winnipeg MB CA
This is regarding my son's vehicle, a 2009 Kia Sedona van. We replaced the rear brake pads and rotors about 18 months/25K km ago. He and his family are on a road trip. One rear brake started making a bad grinding noise. We've been troubleshooting together by text and phone to try to get this sorted out.

He's visiting relatives, excellent people, and has good weather and the use of tools and a good level spot to work outside. He's found, on the driver's side, that the outer brake pad has worn down to metal, and has chewed up the rotor badly. The inner brake pad still has lots of meat on it.

This seems weird to me; in my experience here in the rust belt, the usual cause of uneven pad wear is due to the caliper not sliding well on its pins. When that's the case, the inner pad wears way faster than the outer one. (This assumes that the caliper's piston(s) are on the inner side of the caliper; I've never seen otherwise.)

He's found that the caliper still moves freely on its pins, but that the brake pads are not sliding freely within the caliper housing. I believe that the inner pad (i. e. the one that the piston contacts) must move freely, but that it's not essential for the outer pad to move.

Due to this unusual wear, we're wondering whether the caliper is sticking on hydraulically - that is, is the piston not retracting properly when the brakes are not applied. I can't think of any other reason the outer pad would wear more than the inner. But wouldn't that wear both pads prematurely? What if the inner pad is binding, and the caliper is stuck? The piston would meet resistance from the stuck inner pad before the inner pad contacts the rotor, and the caliper would then move inward, pulling the outer pad into contact with the rotor.

Does this make sense? Any other theories? Many thanks in advance.

At this point, he's done a cheap pad slap to get them home safely, accepting that the pads will be sacrificial. Once they're back, and we have our driveway back again (which is presently not accessible due to our street being rebuilt), we plan to change out the calipers, rotors, and pads on both sides on the back.
 
Joined
Mar 21, 2004
Messages
26,743
Location
Upstate NY
You have the caliper pins, the piston and the pad ears within the clips.

One needs to remove the clips and file that rust off where the clips fit into the caliper bracket. Wire brushing tends to polish it and not remove it. Then some paste lube or never-seize, then new clips and lubricate the pad ears with a lubricant (I use the purple). Cheap pads might not slide properly in the clips. Some file the ears. But then you loose the powder coating or paint that prevents rust. Quality pads should not need to be filed.
 
Joined
Feb 27, 2009
Messages
6,713
Location
down in the park
This is regarding my son's vehicle, a 2009 Kia Sedona van. We replaced the rear brake pads and rotors about 18 months/25K km ago. He and his family are on a road trip. One rear brake started making a bad grinding noise. We've been troubleshooting together by text and phone to try to get this sorted out.

He's visiting relatives, excellent people, and has good weather and the use of tools and a good level spot to work outside. He's found, on the driver's side, that the outer brake pad has worn down to metal, and has chewed up the rotor badly. The inner brake pad still has lots of meat on it.

This seems weird to me; in my experience here in the rust belt, the usual cause of uneven pad wear is due to the caliper not sliding well on its pins. When that's the case, the inner pad wears way faster than the outer one. (This assumes that the caliper's piston(s) are on the inner side of the caliper; I've never seen otherwise.)

He's found that the caliper still moves freely on its pins, but that the brake pads are not sliding freely within the caliper housing. I believe that the inner pad (i. e. the one that the piston contacts) must move freely, but that it's not essential for the outer pad to move.

Due to this unusual wear, we're wondering whether the caliper is sticking on hydraulically - that is, is the piston not retracting properly when the brakes are not applied. I can't think of any other reason the outer pad would wear more than the inner. But wouldn't that wear both pads prematurely? What if the inner pad is binding, and the caliper is stuck? The piston would meet resistance from the stuck inner pad before the inner pad contacts the rotor, and the caliper would then move inward, pulling the outer pad into contact with the rotor.

Does this make sense? Any other theories? Many thanks in advance.

At this point, he's done a cheap pad slap to get them home safely, accepting that the pads will be sacrificial. Once they're back, and we have our driveway back again (which is presently not accessible due to our street being rebuilt), we plan to change out the calipers, rotors, and pads on both sides on the back.

It's essential both pads move freely in the carrier. After brake activation the pad that doesn't move freely will keep rubbing the disc and overheating. The brake pressure can exceed 500 psi easily and will move the "stuck" pad towards the dic again after it wears down. Sadly As a hyundai mech I see this daily. Actually not as much anymore as I make sure everything is A-ok from the first service now. Didn't know what the inside of a caliper looked like before I worked on hyundais...

The pistons also have a habit of not retracting properly, but it's less severe and less common. This will wear the pads that are moving freely though.

So, pins should be free, the piston has to wind in or be pressed in with minimal effort. If pushed, you should be able to do so with your thumbs. And the pads must be able to move in the carrier.

When I assemble a brake caliper I use silicone grease with 100% succes so far under the piston booth and for the slide pins. Pads that are tight to go in the carrier need to have burrs and excess paint removed, and I put a thin coat of copper grease (Molykote or any brand that doesn't dry out, I use a bentonite clay based product) on the exposed metal. If the pad can move up and down a tiny bit when the brakes are applied, any rust that forms will break as it's brittle and the contact are becomes self cleaning.
 
Joined
Apr 30, 2004
Messages
1,532
Location
Indiana
I know this sounds nearly impossible but I actually experienced it on an 85 Chevy S10 pickup. The inside ply of the flexible brake hose debonded and was acting as a check valve holding slight pressure on the piston. I was trying to figure out why my front brake was not releasing and a smart old guy told me about this phenomenon. I told him he was crazy, but he had the last laugh. I cut the hose apart to verify what had actually happened.
 
Joined
Mar 21, 2004
Messages
26,743
Location
Upstate NY
I know this sounds nearly impossible but I actually experienced it on an 85 Chevy S10 pickup. The inside ply of the flexible brake hose debonded and was acting as a check valve holding slight pressure on the piston. I was trying to figure out why my front brake was not releasing and a smart old guy told me about this phenomenon. I told him he was crazy, but he had the last laugh. I cut the hose apart to verify what had actually happened.

But what was the wear for inner and outer pad?
 
Joined
Apr 30, 2004
Messages
1,532
Location
Indiana
But what was the wear for inner and outer pad?
The brake was getting hot and smoking after driving down the road for a couple miles at 50 mph or so. Not sure about comparison of inner vs outer but the pads had to be replaced and the disc was blued.
 
Joined
Sep 7, 2020
Messages
379
Location
Ontario,Canada
You have the caliper pins, the piston and the pad ears within the clips.

One needs to remove the clips and file that rust off where the clips fit into the caliper bracket. Wire brushing tends to polish it and not remove it. Then some paste lube or never-seize, then new clips and lubricate the pad ears with a lubricant (I use the purple). Cheap pads might not slide properly in the clips. Some file the ears. But then you loose the powder coating or paint that prevents rust. Quality pads should not need to be filed.

100% true!! People forget the clean rust from under clips, ....pads have to be free and move easy.(Dealer auto tech for 35+ years)
 
Joined
Feb 27, 2009
Messages
6,713
Location
down in the park
I know this sounds nearly impossible but I actually experienced it on an 85 Chevy S10 pickup. The inside ply of the flexible brake hose debonded and was acting as a check valve holding slight pressure on the piston. I was trying to figure out why my front brake was not releasing and a smart old guy told me about this phenomenon. I told him he was crazy, but he had the last laugh. I cut the hose apart to verify what had actually happened.

I thoughtthat happened earlier this year to me. Did a caliper rebuild and pad change on a truck as the pistons were rusty and dragging. during test drive after work, after a few brake applications the brakes started dragging and nearly cought fire. First right side, 2nd try left side (happened end of day so took a second test drive the next day). First thought was collapsed brake lines but loosened the lines a bit higher up and brakes went free instantly as pressure bled off. It was the master cilinder that had swollen o=rings and blocked off the return for the brake fluid when there was a little heat in the system. Sure makes you second guess your work lol. The issue must have been there before but with the stuck calipers wasn't noticeable nor as dramatic.
 
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