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Old 09-04-2013, 03:11 PM   #1 (permalink)
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Shitake Mushrooms - Caliper Piston Stuck

The front brakes on my ML430 are apart at the moment. I was looking into a noise that the brakes make when pedal is pushed and found that on both driver and passenger sides one of the lower caliper pistons was not coming out with the other pistons.
After blocking the other three pistons from moving i stepped on the pedal and was able to free up the lower stuck one on each side.

Of coarse now i can not get either one to depress and go back in.
The pump action clamp i usually use for depressing them surprisingly does not have the force to push it back in, nor does any type of pry system i can come up with.

I will go and buy a proper metal c-clamp if needed, but would like to check on what may be happening and what i may destroy if i push to hard with the clamp.
I'll add a pic later if anyone can't understand whats happening.

Thanks Folks
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Old 09-04-2013, 03:27 PM   #2 (permalink)
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From what I gather you pressed the break pedal while caliper was removed and probably locked them up. Try to turn these pistons with some sort of pliers (make sure you do not damage them or the boots) and then press them back using a C clamp.
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Old 09-04-2013, 03:33 PM   #3 (permalink)
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They were not actually removed. All of the other pistons were blocked by the pad except the one which was stuck. Then I depressed the brake pedal so fluid could only move that one piston.
The picture is of my drivers side with the pads removed. As you can see, the lower inside piston is stuck out.
Would opening the bleeder valve help?

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Old 09-04-2013, 03:47 PM   #4 (permalink)
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In my opinion it is too far out and locked up, be careful as if you extend it out any further it may pop out and that will be a pain. Try what I suggested first.
BTW is that piston missing its protection boot?

Last edited by bula; 09-04-2013 at 03:49 PM.
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Old 09-04-2013, 03:53 PM   #5 (permalink)
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Will do. I'll see what I have that I may be able to turn it with.
I have the boot on the ground beside me. Was mostly popped out of the holding spot and I wanted to see if there was fluid under it.

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Old 09-04-2013, 03:56 PM   #6 (permalink)
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Quote:
Originally Posted by Oeschj View Post
Will do. I'll see what I have that I may be able to turn it with.
I have the boot on the ground beside me. Was mostly popped out of the holding spot and I wanted to see if there was fluid under it.

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that tells you is out too far, as you turn it left and right get some one to press on it (pry it with a piece of wood against the rotor)
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Old 09-04-2013, 04:10 PM   #7 (permalink)
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Nearly did that with mine Oeschj a couple of weeks ago. Was cleaning and adjusting rear e brake shoes and got in vehicle for something and pressed the foot brake to the floor. Then thought shit the caliper is on a bungee.
Phew piston had not popped out like yours but was well out.
Sound to me like you got fluid lock out. Undo the bango bolt on the rear and re install dust cover and push piston back in. You will need to bleed the system after though.
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Old 09-04-2013, 05:15 PM   #8 (permalink)
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Got them back in. A little tap tap taparoo with a hammer and putting the c clamp on each side of the piston a little at a time did the trick.
Thanks fellers. :thumbup:

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Old 09-04-2013, 05:43 PM   #9 (permalink)
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I'm loving the little phrases like "tap tap taparoo" ...made my day

Quote:
Originally Posted by Oeschj View Post
Got them back in. A little tap tap taparoo with a hammer and putting the c clamp on each side of the piston a little at a time did the trick.
Thanks fellers. :thumbup:

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