Author Topic: Rear piston and middle front won't return / combine brake questions  (Read 1066 times)

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Offline RavenCAN92

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Hello all,

This spring I've been going over my 2012 CBF1000FA ABS and decided to clean the brake pistons. I noticed that on the front right side, the middle piston wouldn't move for The front hand brake, only with the rear brake and that it was a pain to push back.

So I checked the rear, it is the single large piston and it wouldn't retract after cleaning either... i needed to use a C-clamp on it!!!

I'm wondering if this means the rear master needs to be rebuilt?

Also is this how the combined braking works? One middle front piston is hooked up to the rear and doesn't work with the front hand brake? I thought they all moved but I see there are 2 bleeds on the front right caliper... so maybe that's the case?

Thanks in advance!
Last Edit: 27 March, 2021, 01:22:13 PM by RavenCAN92


Online Art

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That's right, the front right caliper centre piston is operated by the rear brake. If the piston is difficult to retract into the caliper it could be that the fluid has been topped up between brake pad replacements. For example, topping up the brake fluid when the pads are worn and then replacing the pads leaves the system over filled and difficulty will be experienced in retracting the caliper pistons into the caliper. Try removing the rear brake reservoir cap, plate and diaphragm and then retracting the piston, possible removing some fluid from the rear brake reservoir first or placing some rags below the reservoir to catch any over spill. Tip - only top the brake fluid reservoirs to the upper fill limit when new brake pads are fitted, as the brake pads wear down so the brake fluid level will drop towards the lower fill level.

While your there why not replace the brake fluid? Some home mechanics have struggled with brake fluid replacement on the Honda CBS ABS braking system but it is an easy enough job using the flush and bleed in one method. In brief don’t drain the braking system but use the new fresh brake fluid to flush the old stale brake fluid out of the braking system in the following sequence:

From the front brake reservoir flush/bleed 1) front right caliper upper nipple 2) front left caliper upper nipple;

From the rear brake reservoir flush/bleed 3) front right caliper centre nipple 4) rear caliper lower nipple, 5) rear caliper upper nipple;

Once fresh fluid appears at the nipple move on to the next nipple when all 5 nipples have been flushed you’re done, no need to bleed as this method replaces, flushes and bleeds all in one.

If you haven't already you can download the Honda Workshop and Owners Manuals here.


Offline RavenCAN92

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*Originally Posted by Art [+]
Try removing the rear brake reservoir cap, plate and diaphragm and then retracting the piston[/color][/url].

I did replace the pads with HH pads last year, but I was careful to keep the right amount of fluid, plus Ive flushed the brake lines the year before.

Never the less, I attempted what you said and it did NOT effect how hard the piston was to return.

So I loosened the brake line at the caliper and tried again, the piston moved easily. Of course also dumping fluid.

I would perform this test on the front but I know that piston was also hard to push in. Im thinking there is a common issue effecting them both... so Im looking at the master cylinder again.

Any other suggestions?


Offline RavenCAN92

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For anyone following along, I decided to flush the rear brakes. I put 3 reservoirs worth of new fluid through the rear and front brake pistons each.

They seem to be a LITTLE better, when i let off on the rear brake lever, the pistons pull back ever so slightly and can be pushed in by hand.... although it is still hard to do so. Like both thumbs and tougne in cheek with some swear words.

The front brakes are nothing like this, they can easily be pushed in with one finger.

Without taking off all the brake lines and checking everythung, im not sure whag else to do or to test the brake system for faults.

Still looking for ideas 💡


Offline spinspin

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If you've got an ultrasound bath it might be worth taking it off the mounting and popping it in for a few long cycles, I've never tried it with a brake caliper but I've freed up plenty of other parts in one.


Offline Steelworker

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I had a similar problem with a Kawasaki Zephyr 750, one of the front brake pistons was very tight and eventually couldn't be moved without a g-clamp.
The reason was corrosion build up in the grove where the piston sealing ring sits. It was forcing the sealing ring against the piston.
I had to strip the caliper body and clean out the grove. I re-assembled the caliper (even using the old sealing ring) and all was fine after that.
If you do strip the calipers it may be something to check on.


Offline RavenCAN92

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Just as a reminder...
This isn't a stuck piston. Each piston moves freely and easily when their bleeder is open or if the line is cracked open at some point.

The issue is when they are hooked up and bled, when the brake is pressed it is easy to apply braking force, But the pistons will not retract without force from a c-clamp. Or cracking the bleeder/line. This happens to both the front and the back at the sametime.


Offline ivor hugh jarse

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I don't like with the time stuck pistons cost me ... Ive sent them here instead...
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