Quick question re: brake pistons

"and 100 more" (nth256) 10/06/2015 at 13:20 • Filed to: None

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I put some new pads on the front brakes this weekend, and noticed that inside the caliper piston, the interior is dome-shaped. Is this normal? I’ve never noticed that before on other vehicles.

See attached cutaway MSPaint masterpiece.

HammerheadFistpunch > and 100 more 10/06/2015 at 13:24

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Yeah, that’s normal.

and 100 more > HammerheadFistpunch 10/06/2015 at 13:24

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Awesome, thank you.

EL_ULY > and 100 more 10/06/2015 at 13:36

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Si :]

dogisbadob > and 100 more 10/06/2015 at 13:38

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most brake fluid in cars on the road today is black :(

Verdog ~ manual Bro, Bro - HellHawk Equipped > and 100 more 10/06/2015 at 13:43

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HEMI Brakes, brah

McMike > and 100 more 10/06/2015 at 13:43

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Why did you remove the pistons to change pads?

RamblinRover Luxury-Yacht > McMike 10/06/2015 at 13:46

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I don’t know why he did, but I can imagine some real horror stories leading to that. Some of which would be if a parking brake adjuster failed, but that wouldn’t have originated this question.

and 100 more > McMike 10/06/2015 at 13:54

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I didn’t. I just looked inside the hollow portion of the piston.

and 100 more > Verdog ~ manual Bro, Bro - HellHawk Equipped 10/06/2015 at 13:55

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Yes! I can stop faster than I can accelerate!

and 100 more > dogisbadob 10/06/2015 at 13:55

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Artistic license.

and 100 more > EL_ULY 10/06/2015 at 13:56

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Muchimas gracias, muchacho.

McMike > and 100 more 10/06/2015 at 14:05

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I’m confused. Which side of the piston were you describing as “dome shaped?” A or B?

This piston was inside the caliper when you did your brake job. I can’t imagine how you would see anything else other than “A.”

—-edit—-

I just read your sentence again, and know what you meant. You looked inside the piston while the pad was out of the way, and saw a convex surface, which meant the back of the piston was concave.

Yes, that’s normal*

* the piston, and my habit of replying for fully understanding a simple sentence.

and 100 more > McMike 10/06/2015 at 14:10

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Yeah, you’ve got it now. Glad to know the convex surface is normal, thank you!

I was trying to find a way to describe it that wasn’t just a technical-jargon word salad, but it came out more vague than I intended.

I cannot into English today.

BigBlock440 > dogisbadob 10/06/2015 at 15:32

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Really? DOT5? I don’t have any DOT 5 cars so I don’t know what color it is.

Even still, I don’t think I’d say most cars, as there are still a lot that use DOT 3/4.

Also, I’m skeptical that people do brake fluid flushes at recommended intervals, so yellow is probably accurate.

dogisbadob > BigBlock440 10/06/2015 at 15:34

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DOT5 is purple.

I was referring to people that never change their (DOT3/4) brake fluid, which turns black after absorbing too much moisture from being in service way too long.

BigBlock440 > dogisbadob 10/06/2015 at 15:43

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Black? All the brake fluid I’ve seen turned yellow, like dehydrated pee or apple juice. And the worst was 15 years, 175k (I assume, it could have been 5/75 though), made a huge difference in brake feel, but was still not black. I can only imagine how old it would have to be to turn black, and how squishy the brakes would be.