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Brake question. Can someone try it for me please?


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Hi VFRD,

I have a question regarding the linked brakes (no, I will not de-link).

I have ridden the VFR after winter pause and I noticed something. If I apply the front brake first, than the rear brake and let go of the front... The rear brake lever falls down by a few centimeters as if there was not enough brake fluid.

 

Normally I would not ask but I don't remember this happening before winter and the bike just had a fluid change. It is either a bad fluid change or my bad memory. The latter being slightly more possible. 

 

So can you please go out and try this on your 5th gen?

 

PS: My thoughts are that this should happen because of how the secondary brake cylinder works but I need it confirmed.... You know... I sort of don't want to crash... 

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 Since the two systems are completely separate hydraulically I would suspect you have an air bubble in the rear system. Very common because the rear system is difficult to bleed. I bet if you bleed it again you'll get some air out, and the problem will improve or go away completely.

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I used to have an ST1300 that would do the exact same thing. I don't believe I ever "solved" it or that there was any trouble.

My 5th Gen is fork swapped, so bye bye linked brakes.

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  • 5 weeks later...

Just to follow up. I have bled all brakes as per manual.

There is something seriously wrong with one part of the system.

On one bleeder connected from middle rear piston to rear brake there is no pressure going from lever to brake piston.

I will dig into it and share the results. 

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The rear middle piston is not controlled by either brake lever.  There is a master cylinder in the mounting bracket of the left side brake caliper - bleeding instructions can be found for this circuit starting on page 15-11 in the manual.  You will have to squeeze the brake caliper mount toward the fork tubes to pressurize this circuit.

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And the manual instructs to dismount the left caliper and SMC bracket and tilt it up so you can displace any air out of the SMC. If you don't do that there is a good chance air will just sit in the bottom of the SMC. 

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Make sure also that the rear pads are floating properly in the caliper and the exposed part of the slave pistons are clean. Do the same on the front calipers as well. The linked brake circuit might be interacting with the foot brake pedal because of some gooey shit in the caliper(s)?

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On 4/22/2019 at 9:48 AM, SportTouringCZ said:

 

On one bleeder connected from middle rear piston to rear brake there is no pressure going from lever to brake piston.

 

 Exactly. The secondary MC on the LF caliper is what actuates the center piston in the rear caliper. After initial fill of the rear system you must manually work the secondary MC to remove the remainder of the air. It's a bit of pain, but the system will then work as intended.

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On 3/24/2019 at 3:25 AM, SportTouringCZ said:

 

I have ridden the VFR after winter pause and I noticed something. If I apply the front brake first, than the rear brake and let go of the front... The rear brake lever falls down by a few centimeters as if there was not enough brake fluid.

 

So can you please go out and try this on your 5th gen?

 

Today I rode my gen 5 a couple hundred k's just as per your request.

 

Using various sequences and durations of the front and rear brake operation I was unable to detect any interactions between the front and rear brakes through either the brake pedal or hand leaver. There was no pedal drop when I put front brake on followed by rear brake and then released the front brake.

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3 hours ago, Zarquon said:

Today I rode my gen 5 a couple hundred k's just as per your request.

 

Using various sequences and durations of the front and rear brake operation I was unable to detect any interactions between the front and rear brakes through either the brake pedal or hand leaver. There was no pedal drop when I put front brake on followed by rear brake and then released the front brake.

x2 - I messed around a bit yesterday while I was out and could not create/identify any pedal drop.

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