Both pistons not moving in together

magnus

Joined
Dec 18, 2015
Messages
16
Location
Phoenix, AZ
Does this look normal? Is there anything I can do to free up the pistons?

I've already cleaned and bled the brakes although the rear wheel is still off.

The stuck piston also refuses to unstick when the pedal is released.

Thanks!

 
What I've done personally in the past is spray WD-40 on the stuck piston and let it sit on there overnight. Then try moving it in and out with the brake lever. Once you get it free, you're going to have to fully clean everything and re-grease the piston before reinstalling it.
 
My guess would be A: that you have crap behind the pistons. or B: you have a failing part in the brake system.
Have you done a function test on the SMC, to make sure its not causing problems?
As stated, detail strip the caliper, remove the pistions, replace all the seals and piston's if needed, then do a complete and correct bleed again.
NOTE: These pictures were taken after the owner did a complete brake flush and bleed.

20190422_113354_1556742929804_001.jpg20190422_113410_1556742930485_001.jpg20190422_120315_1555962836955.jpg
 
Thank you for the feedback.
I'm so sorry for the typos...... Maybe I shouldn't be wrenching after work.

By pistons... I meant the two outer pistons operated by the front grip lever..... Not the center one or pedal. Sorry about that.

JF Heath,
My question was indeed on whether I should expect both pistons to move out together or if having one closer to the inlet port moving out alone was to be expected. So it doesn't seem that that's that abnormal
Thank you

Igofar,
Wow..... Those pictures are crazy. I suppose a detail strip is needed. I was hoping to avoid that. Sigh
Thank you


I did not know about the Wd40. I thought Wd40 was a no no on these piston seals.....no? But I was wondering if applying silicone grease to the seals would help lubricate them a bit
 
Those outer pistons look fine to me based on how apparently easily you push in on either piston and the other pops out. It takes only the very slightest difference of resistance for this to happen. A negligible amount regarding the brake caliper in operation.
 
What you showed in the video is completely normal,. If you squeezed the piston that was moving the other one would come out. Twin post hydraulic car lifts have a rotating cross bar the keeps them even. . It looks as if they needed service to prevent future problems but try the same thing when your done and one piston will come out first.
 
On Disc Brake Systems the Seals are actually the return spring used for pad to rotor clearance. As the brakes are applied the Piston moves out toward the Disc and stops when the Pad reaches the Rotor. The Flex in the Rubber Caliper Seal when Hydraulic Pressure is Released is what draws the piston back in maybe only a few thousands of an inch creating the clearance to eliminate Rotor Drag. It's important that Everything is Clean and that the Seals are Flexible. Not just Not Leaking.
 
The behavior of those outer pistons looks completely normal to me. When the caliper is installed and the the pistons are pushing against the backs of the brake pad, they will quickly equalize. In fact you could hold that piston that tends to move first with your finger and see how little force is needed to hold in in place while the other one now moves. Nothing looks stuck to me, they seem to move pretty freely in that video. As previously stated the center one won't move until you apply the rear brake pedal.
 
ST1300 Alicia said:
On Disc Brake Systems the Seals are actually the return spring used for pad to rotor clearance. As the brakes are applied the Piston moves out toward the Disc and stops when the Pad reaches the Rotor. The Flex in the Rubber Caliper Seal when Hydraulic Pressure is Released is what draws the piston back in maybe only a few thousands of an inch creating the clearance to eliminate Rotor Drag. It's important that Everything is Clean and that the Seals are Flexible. Not just Not Leaking.
Click to expand...

Good post, it's not often I learn something like this since I thought I pretty much understood most mechanical fix and repair stuff. This does make perfect sense once I've read it.

Thanks for the informative post.
 
Thank you for all the information. I'm still trying to figure out what is normal and what is not.

Perhaps one other thing I should mention is the amount of resistance I feel when trying to push the piston in. My 'feeling' is that the 'stuck' piston requires more force than I suspect it should. That is obviously hard to identify in the video. When I do the same test on the other side, both pistons move out together albeit at slightly different rates.

ST1300 Alicia said:
On Disc Brake Systems the Seals are actually the return spring used for pad to rotor clearance. As the brakes are applied the Piston moves out toward the Disc and stops when the Pad reaches the Rotor. The Flex in the Rubber Caliper Seal when Hydraulic Pressure is Released is what draws the piston back in maybe only a few thousands of an inch creating the clearance to eliminate Rotor Drag. It's important that Everything is Clean and that the Seals are Flexible. Not just Not Leaking.
Click to expand...

Interesting.....I did not know that. If that's the case, then I will at least try easing it up with some Silicone grease and if that does not work, I may have to take part and clean. Thank you for all the insight.

Slightly different question then.
- I understand I need new washers on the brake lines if I am going to take those off for caliper cleaning. Do I need the Honda part for that or does anybody have an Amazon link to something else that will work?

Thanks!!!
 
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