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iThinkergoiMac

Rear Brake Locking After Pressing Pedal

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Hello VFRoz, I can only presume that if the Pushrod length was set too long that it might block a return port.

I have now rebuilt both Front Calipers, secondary Master cyl, replaced PCv,Re built Front master cylinder, rebuilt rear caliper.

Cleaned the "Filter / one way valve" as mentioned earlier.

I was going to replace rear master cylinder as mine has a slight amount of wear, but have been told this item is now discontinued.

This is the second attempt at fixing properly, and we still have the centre rear piston locking onto the brake rotor.

We have blown all lines out and flushed nearly 2 Litres of brake fluid through.

 

It feels as if the only thing we have not done is check the installed length of the Secondary Master Cyl pushrod.

 

There are two mentions of the secondary master cylinder pushrod in the manual.

But no dimensions.

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Is the secondary master cylinder pivot (bottom mount) free to move?

Or is the front left caliper dragging?

Is the secondary master spring ok?

Does the pushrod go in straight to the master?

I'm running out of ideas.

No sure which manual you are using, I could not find any reference to push rod length.

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Sorry, I did find it.

I can measure my old one I pulled out when I delinked.

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IMG_3935.jpg

 

It is flush with the bracket

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Thanks VFROZ,

As a matter of interest / Frustration what did you do to delink the brakes?

I am getting so frustrated with what on every motorcycle is a simple hydraulic circuit.

I tend to agree with your earlier comments that most problems are caused by essentially years of neglect.

This doesn't however make it any easier to correct, esp now as more and more parts are being obsoleted.

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On 3/20/2018 at 4:18 PM, pd1335 said:

 

Has any one just tossed the screen out or does the one way valve / check valve have a real function ?

 

 

As per my post in the article I read - "When the foot lever is actuated, the secondary master located on the front left caliper is back-pressurized so that the braking of the front wheel does not cause additional braking at the rear. In short, using the linked foot lever for braking delinks the other system."

 

My SMC pushrod length was the same as VFROZ's during my trouble shoot.

TBH I never knew it was adjustable and I doubt would be the cause of concern, unless some ungodly modification has been made.

 

Follow iThinkergoiMac's steps

 

With the way the system works, you can pretty quickly narrow down the problem.

  • If loosening the bleeder on the caliper allows you to return the piston with thumb pressure, the caliper should be fine. If not, the piston is sticking in the caliper.
  • If loosening the PCV allows you to return the piston, the line itself doesn't have a problem. The bleeder is after the PCV mechanism.
  • If the outside pistons retract, the return to the RMC is clear.
  • This leaves the SMC; if all the other steps clear, the SMC must be the problem.
  • Either the SMC needs rebuilding or the screen is an issue like on mine.

I was able to bleed and retract the center piston at the PCV

Remove the green screen cover, remove and clean, then retract the center piston. You'll get a squirt of brake fluid from that hole (just to warn you)

 

Probably the two most important steps I took in my process was

1. Ensure that center piston is NOT sticking in the caliper, especially if there are no pads and disc and it's hanging all the way out there.

2. Bleed the system exactly how it tells you... ensure you remove and tilt the front left caliper (approx 15 degrees) and remove the rear caliper and have all bleeders facing upright.

 

I bled everything (bar the fronts) with the foot pedal. 

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Delinking can be complicated or simple.

 

The path I followed was to replace the forks with VTR1000F parts, brakes from a CBR954 (front calipers) CBR600RR (master cylinder) and CBR600F4 (rear master). All of the above are bolt-ons that use the stock wheels and brake discs, and the rear brake hoses. You can just use VTR1000F fork lowers with VFR uppers and innards, the VTR parts have the correct mounts for Honda 4-piston brakes. VTR1000F brakes are not particulalrly good in my opinion. The only thing that needs fabrication is mounting the 5G mudguard, again not a big deal.Can't use a VTR mudguard as the fork leg spacing is narrower on those.

 

You could opt to keep the VFR front calipers and fork, but would need to source a suitably-sized master, and then connect all 6 pistons to that.The stock MC is a small diameter and I think would make for a grabby front brake, but you could try it and see; a 14mm master should be about right I think. 

 

The inner pistons in the front 3 piston calipers can be activated by drilling between the chambers within the caliper, or by using a bridging hose. At the back you can connect both standard brake hoses to the master using a double banjo, which will be freed up when you dismantle the LBS.

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