Do I need a new caliper?

Premise & Background: I have bought too many unnecessary parts over the years and have been trying to be more certain about what the cars need before I spend. Also, my 2010 Prius with about 310k miles --150k of which I put on myself -- has new tires. They're about ten weeks old and at most only have a few thousand miles.

Everything was working, then my wife said she heard brake grinding a couple of times, after the car had been parked overnight. I pulled the tire and saw there was visible pad, so I ignored it for a few days and tried to blame road dust until the grinding became more frequent and then, there was a new rhythmic sound that you mostly heard when going slow.

This prompted me to pull the brakes and I found that the pad on the back side of the front passenger side was unevenly worn. There was still some -- not much, but some -- pad visible from the top, but the bottom of the pad on the leading edge was worn past the ceramic down into the metal back.

The rotor was also shot, so I replaced it and the pads on both sides. While the bracket was off, I pulled the slide pins and filled the holes with Brakleen a couple of times, took a wire brush to the pins and clips, washed them also with brake parts cleaner, then lubed them up with brake-grade silicon grease.

After putting the car back together, the rhythmic noise was louder, more constant and more pronounced.

(I'd describe the noise to be like you used to get from a bubble on a recap or when there's a big worn spot with the steel belts showing. It's more of a flap than a rattle.)

I confirmed the noise was coming from the front passenger side, so I took it back apart after driving less than ten miles and switched the slider pins from one side to the other to see if the problem moved.

It did not and though it's only visible if you're looking for it, I'd say the new pad is starting with the same wear pattern.

My instinct is that I probably need a new caliper, but as I said, I'm trying to avoid buying unnecessary parts.

Another factor is that though I don't know what the previous owner did, I haven't drained and replaced the brake fluid over the eight years and 150k I've owned the car. I've thought about trying it before I buy a caliper because it can't hurt anything, but I'm also tied of popping the tires on and off.

Also, when I pressed the calipers for the pad change, the brake fluid reservoir was above "max".

Suggestions would be appreciated. Anything else to test or try? Any thoughts?

Thanks

 

Though I've done lots of brakes on my own cars for decades, this is the first time it is something other than replacing the pads or the rotors, so I'm not sure what you mean by "caliper slide" or "side to side". Please bear with me, as I learn.

The slide pins go in and out, and I did switch sides, but the sound didn't move.

There might be a slight catch when you first pull a pin on the problematic side -- that's the tire I have off with the caliper hanging -- but I'd say the pins slide easily and if there is a "catch", it is only slight.

When I slide the pins, I see nothing else moving on the bracket (with the pads out) and other than the piston, I don't see any obviously movable parts on the caliper. When all this started, when I first took everything apart to replace the rotor, I did have to use an 18mm box end to hold the pin while I took off the lower bolt, but that's really the only indication I've had of binding.

Otherwise, I have pressed the piston in at least three times and I did leave it hanging after the pin switch, while I started the motor to see what happens. What I found was that piston kept incrementally going out every time the actuator activated without anyone touching the brake. I let it go maybe three or four times, so the piston was extended out probably two inches. The rubber looked fine and everything was dry as a bone, if that means anything, then I pressed it back in totally flat.

(After my test drive on the new rotor with new pads, the piston was out a millimeter or so, but it pressed back)

In answer to your other questions: I feel and have not felt anything in the pedal -- it's just a noise that you hear both in and out of the car -- and I did the 12 o'clock/6 o'clock thing and there was no movement, so I don't think it's a bearing.

Thanks

 

I don't know if you intended to post a link, but I'm not seeing it.

As far as I know, it is the original caliper and I have no reason to think it's not.

As for the "above max", when my wife first told me about the grinding, I saw that the fluid was below minimum, so I poured a bit in to get it between min and max. I didn't max it out because I thought maybe I should flush the lines because it hasn't been done and I didn't want to waste fluid.

After I pressed both sides back in, the fluid now registers above max, probably by the amount I put in. I've topped it a couple of times and have kept a pretty good check on it over the years.

 

The reply from @ChapmanF helped me understand what should be moving then after trying both sides with the pads in place -- the only movement like the thickness of a business card -- I reread your reply and saw that you said with the pads out.

With the pads on the passenger (or problematic) side out, I can rock the caliper end out the full length of the sliding pin and I can pull it toward me enough that I'd call it bottoming out.

With the pads uninstalled, I had someone push the brake and when that happened, the caliper moved as the piston extended, but it didn't go back. Also, though it didn't happen the first two or three times she pushed the brake, after those initial applications, brake fluid came pouring out of the piston. She also said that every time, it felt like the pedal was pushing back against her.

After the experiment with the caliper in place, I removed the bolts and hung it, so I could see. I, then, had my daughter depress the brake and each time she pushed it, the piston extended further and when she released it, you could see it easing back a bit. It did not recede a lot, but it was enough to clearly see..

Anyone have any thoughts? My instinct is this is how they're supposed to work.

Though, I'm not sure about the fluid or why I didn't see any fall to the ground when she first braked.

Thanks

 

Edit: Never mind. I see. When I went to compress it, the piston fell out.

It looks like I probably didn't need a new caliper until I had my daughter push the brakes while the caliper was hanging from the strut. Now it looks like a rebuild or the $80 part I had not wanted to buy.

2nd Edit: I'll read them again, but I did not initially see rebuild instructions in your previous link. I did find a video which I scrolled through... because it's almost dark, I'm going to pull the caliper and haven't actually looked at things, but is there a reason I need new rubber and can't just use the old parts?

 

I'm not a Toyota parts kind of guy. Maybe if the local dealer were to put his prices online, I'd consider their product when shopping for parts, but he doesn't and his place is over a half-hour away. While there are ten parts stores within twenty minutes with their prices posted. I'd pass four heading out to the dealership. The parts stores also have more reasonable hours, are easy for returns and they offer rewards.

With the discount for an online purchase, a caliper from Advance is around a $100. The junkyard I mostly use have a few for $40, so that's an option, but I popped out to pick up a rubber kit from Advance before they close and sometime later, I'll search through this forum and watch a couple of videos before I do anything.

Thing I learned today: Don't touch the brake when the caliper is not in place, which makes sense considering all of the cautions about leaving the keys in the house "to avoid making things difficult".

Again, thanks.

 

Earlier, I searched this forum and watched Eric the Car Guy, plus a couple of random YouTubers show how to rebuild non-Prius caliper pistons, neither of which used the metal ring. One showed the metal ring as part of the unboxing, but didn't install it.

This made me think that it might not be necessary, but then a ring came out when I was pulling the dust boot and the instructions @Mendel Leisk posted to an old thread showed one, so I now I know it was purposefully included.

The other conflicting things for which I'm fishing for guidance...

Eric and the YouTubers put the dust boot an the piston from the top down to the bottom edge, then after seating the bottom in the assembly, they pressed the piston down until the top popped into the piston groove.

As I read them, a few YouTube commenters to these videos said they had learned to do it -- again, on other cars -- by putting the boot in place and (supposedly) setting the piston on top of it, then puffing the rubber cover up and over with a blast of air.

Because I assume the metal ring goes at the bottom to lock the boot into the assembly groove, this makes sense and could explain why the videos I watched did not install the set ring.

It isn't really clear from the scans @Mendel Leisk posted, exactly how they say to put it together.

It looks like (starting on pdf pg 12) they say to put piston into the assembly, then put the boot on from the top of the inserted, "submerged", contracted piston and working it into the grooves. My interpretation is that once it's all together, the force with push the piston out and the new boot will stay around the top.

If anyone would like to say which option they use, point to instructions or link a video, I'd appreciate it.

Otherwise, I guess I'm going to try my interpretation of Mendel's scans. (Piston in, boot over, poke, then ring)

Any info would be appreciated. Thanks.

(Also, before I broke it, my ill-advised experiment made it look like the piston was working correctly, so I probably didn't need a new caliper. Though maybe reassembling it "fixed" something -- hopefully -- but I might still have the noise when all is said and done.)

 

Edit: Now, after setting the piston over the hole, I see there really isn't much difference between the video instructions and those from the scans. In theory, I'm thinking the scan one is less likely to damage the rubber, but I don't know.

 

Too late to edit, but as an update for the archive...

The method from the repair manual @Mendel Leisk uploaded (previously linked) appears to have worked fine.

I replaced the square-edge, pressed the piston in using lots of brake fluid as lube, then put the rubber boot followed by the metal ring in place. I tested by tapping the piston out (through the hose hole) about halfway and it looks like the boot held. Of course, as I understand it, the boot is really just for dust and the square-edged ring is what does most of the work.

The other helpful hint I'll offer, the metal set ring in the kit from the parts store was a little longer than the OEM. I messed a bit with trying to squeeze in the overlap, then just decided to use the old one which worked easily and fine.

Of course, now I have to install it on the car and bleed the lines, and there's a good chance that the noise will still be there because unless my misguided experimentation knocked something loose, it looks like the caliper was working right. I'll soon know for sure.

Thanks for the help and letting me sound things out.