Continuous frozen rear caliper and even brake wear

dhman2006 · Jan 14, 2018

ChapmanF said: ↑

Oh, good. I just had to ask, because with some mechanics, you just never know. And if you heard a mechanic say the rear pistons were really hard to force back, and he wasn't using a rotating tool, well, they would be really hard that way, and even if he succeeded (especially if he succeeded!), I'd have my concerns about the caliper.

But from your report it sounds like he knew to rotate it.

Remember that was in the context of my asking how he forced the piston back in.

But it does sound as if the pistons did not go back easily. You want them to move easily, because that's the only way the brakes let go. Applying the brakes isn't the problem, you've got 2000-psi-and-up brake fluid going back there so those pistons will extend out. But when you let go of the pedal, there's nothing but the rubber piston seals and those dinky V springs on top of the pads to make those brakes let go.

I gave some info in post #8 on how you can test the calipers you have and make sure they let go appropriately. I'm not an advocate of replacing things unnecessarily, so if you can test yours and get them to pass, that's great in my book. If they don't pass because the pistons don't move easily, yes, you can take them apart to find out why, if you're comfortable with that. You can get the rubber kit from Toyota in advance, it's cheap and has all the rubber parts (plus miscellaneous metal clips, etc.) to do both rear calipers. It doesn't include new pistons; if you find those to be non-salvageable, new pistons they sell a la carte.

Probably, at the very least, you would do well to replace the rubber piston seals (these are the square-cut ones inside the bore, only visible with the pistons out, not the visible rubber boot). Even if they were not the problem originally, if the brakes have been dragging for long, they've been very hot, and those seals are now probably cooked. And it's the exact way those seals twist and spring back that's needed to make your brakes let go.

I'm not certain that all the internal parts of the rear calipers are available over the counter. I seem to recall that the rubber kit did not include the seal where the parking brake shaft goes in from behind (or, at least, didn't seem to, in the diagram I was looking at). So be sure you know what replacements you have and what you don't, before going too wild with disassembly.

There's kind of a long-running controversy over whether to open the bleed screw when forcing the piston back. My inclination is to do so, which can make it easier to push the piston back, and avoids pushing a bunch of fluid from your brake line backwards through the brake actuator valves. In the end you have to add some fluid to make up for what came out, which means you've removed some old, dead-ended fluid from the lines, and put some nice fresh fluid in up front.

Some people never bother doing that, and just happily force the fluid backwards, and never have a problem. On the other hand, if a problem were going to result, it might well manifest as dragging brakes (if, say, a piece of grot were forced back into an actuator valve, preventing it from completely closing). I wouldn't worry about that, unless you end up with a new, or newly overhauled and tested, caliper, and it still drags anyway.

-Chap
Click to expand...

Thank you so much for your help. Looks like I have a lot of work cut out for me. I'm hoping the weather heats up again so I can do all those tests. I'll update this thread once I do all those. Thank you all for your help and suggestion.

Continuous frozen rear caliper and even brake wear

dhman2006 Member

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Continuous frozen rear caliper and even brake wear

dhman2006 Member