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Full Version: Rear Brake Intermittent Loss of Pressure
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Hi All,

I've got a puzzling issue with the rear brake.

I changed the pads a while back, and replaced the fluid.

All was good for a while, then I started to loose pressure.
It went completely so, I drained the system, stripped the master Cyl., checked it over, all looked good, cleaned and rebuilt.

Good pressure after re-buld but after a short while I totally lost all pressure. Nothing.... then it came back... then it went again!

I resolved to replace all the seals in the master Cyl.
But now it's working again, with good pressure, after doing nothing but letting the bike sit around.

Just wondered if anyone had any experience like this.

I'm guessing a replacement of the seals might do it, but wondered if it could be anything to do with the ABS?

Any ideas appreciated...

thanks
Kev
I am guessing that air bubbles hanging up some where in the system might have caused the problems.
Years ago when trying to bleed the lines on some of my CBX's it was sometimes a pain to get the brakes hard.
I resolved this by taking the bike for a ride on a " rough " road and that loosened all the air bubbles.
On my CB 1100 's I installed speed bleeders and using a vacuum bleeder with air compressor made the fluid change a piece of cake.
Most the time when things are not right after doing something we did something not right.
I hear you.
The brake was rock tho. Then it went to a full loss... for a while... then, solid again.
Brakes are a pain to bleed, in the trad. way. I don't have a vacuum bleeder. That said, I've had trouble before, getting them up to pressure, and not having enough bite, but these were good.... then total loss... then good again.

Doesn't that seem unusual to you?
does sound like air in the system.
That's interesting Kev as I pondered on how to change the brake fluid on this complicated linked ABS system, and promptly kicked the thought into the long grass!
With the rear master cylinder also connected to the front brake calipers; complicated does not accurately describe the task.

I would hazard to guess that you have introduced air into this circuit. You should put the bike on the main stand and get some one to sit on it, with their foot on the rear brake pedal and the front wheel in the air see if you can turn the wheel (ie see if the linked front calipers are still working or air locked).

Rgds Robin.




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According to the service manual, only the ‘13 CB1100A has the combined Brake System. Is this not true? For bleeding non ‘13 CB1100A brakes, there are no real special instructions. Just basically bleed the left front, then right, then rear. For ‘13 CB1100A its a little more involved, but nothing difficult.
(11-04-2017 06:26 AM)popgun Wrote: [ -> ]According to the service manual, only the ‘13 CB1100A has the combined Brake System. Is this not true? For bleeding non ‘13 CB1100A brakes, there are no real special instructions. Just basically bleed the left front, then right, then rear. For ‘13 CB1100A its a little more involved, but nothing difficult.

That's what I thought. Just bled as a separate system. I could be wrong tho. I have a 2014EX. ABS but not linked as far as I know...

I'm not sure air in the system would right itself, they'd just be constantly soggy brakes. The peddle fell to the floor, nada! Then, as if by magic, returned to being A1 an hour later.

I've been looking and there is opinion on the web that worn seals in the Master Cyl. will sometimes give an intermittent fault.

I'm phoning round for a new piston kit and I'll see if that does the job.
I don't like throwing new parts at the problem esp. at £67 but think I should do it.
Replacing the brake fluid on my 2013 ABS model was not difficult at all , it just takes a little more time.
Trust me , it is worth investing in speed bleeders; I used the st. st. ones .
Beardy, check you PM
Ok, well I have a 2013 AE (from new) with the combined ABS system. The Owner's Manual makes little reference to this, apart from 'Your motorcycle is equipped with a brake system that distributes the braking force between the front and rear brakes' and 'For full braking effectiveness operate the lever and pedal together'. It wasn't until I tried to turn the front wheel by hand with the back brake operated that I realised what they were on about!

Looking at the braking circuits on this model, I would suggest that introducing air into the rear system could well eventually end up in the front too. In other words you need to do front and rear in one go or you risk compromising the brakes.

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