Brake Piston Popped Out

Hi all,

This is my first post since I'm new to this forum but of course not new to Tundras.

I made quite a mistake when changing my brakes and rotors yesterday. When I thought it was going smoothly, I was compressing down one of the pistons on my passenger side caliper, and a piston on the other side got pushed out and popped off the caliper. I quickly reassembled it after cleaning out the area. I had to reassemble it again after I tested the brakes and it popped out again and made sure to bleed the brakes.

After everything was put back together and installed, I took my truck on two test drives (30 minutes apart) and noticed what looked to be some kind of liquid being slung around the inside of the rims (note I did clean the rims with some all purpose cleaner before putting them back on). Did a smell test but couldn't tell if it was brake fluid. The brakes worked completely fine though.

I took it out on another test drive this morning, again brakes worked perfectly though I did notice a squeaking noise possibly from the moisture build up overnight. The rims didn't have any liquid slung on the inside like it did yesterday.

Any advice on what I should do or look at? Of course, I'm considering taking it to a mechanic but I'm a little worried about taking it too far in case the brake piston were to fail.

 

Did you pull the wheel off and see if the caliper is leaking from anywhere?

 

I’m trying to figure out how this happened - did you have the cap sealed on the master cylinder when you were resetting the piston?

 

One piston is happy to move, the others are not, so it falls out.

OP as long as the caliper isn't leaking I wouldn't worry about it.

 

Sure - but wouldn’t the path of least resistance be to bubble the reservoir and not move a piston? I’ve done lots of brake jobs and never experienced this. Trying to keep it that way as I have brakes and rotors being delivered today.

 

I was gonna ask, have you ever changed brakes there is a ton of resistance to compress one side of the caliper, and instead of pushing through all the losses in the brake line and raising the level of the fluid, that same energy can just go to the other side of the caliper and pop a piston out, especially if one piston (and you're pushing on the other two) is stuck, then that fourth piston is the path of least resistance.

 

I guess it pays off to do one side at a time.

I’ve done brakes on my FJ Cruiser, GX470, 200 and Tundra.

 

All of this is in context of one caliper. Just watch the other pistons as you compress one side, especially if you pull one pad and the compress the other pad.

If it does pop out it's not a big deal, the piston is just a slug with an O ring. That's why you can get caliper rebuild kits, it's just some O rings usually to refresh the caliper.

 

^ sure - I’ve just always compressed the first side while the other side is still assembled, then reassemble side one before compressing the other side.

As I just mentioned in another thread - sometimes better to be lucky than good.

 

Yeah... forgot to mention that the cap was left closed which I opened up after what happened. To be honest it never really made a difference for me when opening the cap but I'll probably open it up as a precaution from now on.

 

Thanks for the advice. From what I can tell the caliper doesn't seem to be leaking. At least not yet.

I'm considering doing a rebuild in the event the caliper does leak. I tried ordering a kit from my dealer through their website but apparently, it was the wrong part. Would you happen to know what the part number is?

 

I do not. I had this happen a few months ago and had a spare set of calipers laying around so just grabbed one of those since the piston was fighting me to go back in. I would wash the corner, drive it more, and just watch for leaking. I think it's fine. The fluid you saw initially I would guess was just pooled up somewhere and finally splashed out of its cavity.

 

I'll definitely keep an eye on it. Thanks for the help.

 

Crack the bleeder when compressing the pistons to allow the filthy brake fluid in the caliper to be expressed, rather than forced back into the brake system. Refill the master cylinder reservoir with fresh fluid if low when finished.

 

Had this happened to me as well. Some fluid gets trapped in piston's rubber boot.

 

Yes and No. Physics says the path of least resistance is another piston. The path back to the master goes through an 1/8” ID tube. Forcing the fluid into such a small space adds resistance and requires more force. The path to the other piston is wide open. That said, the rubber seals add a lot of resistance and this changes the physics equation. Now the resistance due to volume change is less than overcoming the seals grip on the bore. My guess in this case is that the piston that came out has a worn seal (i.e. light grip on the bore)and therefore minimal resistance.

to the op, you likely had a bunch of fluid collect under the outter seal which is not designed to keep fluid in, just dust out. That is the most likely reason you got fluid on the first drive. Are you sure you got the outter seal on correctly? These pistons are not the mos intuitive to install. You need to make sure that you didn’t contaminate your pads with brake fluid. It greatly decreases braking efficiency.

 

If you get the piston compression tool, it’ll make the next brake job a lot easier with less headaches. I can see if you’re doing it one side at a time with a c-clamp, this will most definitely happen.

 

If you crack the bleeder screw open you can almost compress the brake cylinders by hand. I use one of the old pads and a pair of large channel locks to push them back in on each side. The fluid that comes out is always dark and nasty looking from water and contaminants. I don't want that stuff in my calipers anymore let alone in my brake lines. But maybe I'm the crazy one who bleeds all the old fluid out every 60k miles or so, which is actually more often than I change pads.