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Cbr600f4i rear master


StormShadow3

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On 3/19/2023 at 10:26 AM, ducnut said:

Yep. Use the complete CBR master cylinder and just shorten the threaded rod. Did the same on mine and works perfect. For a reservoir, I just went to the bike breaker and found something smaller. I used Sebspeed’s adapters and Chinesium rearsets, for the rest.

Hi ducnut,

 

If you look at the first image, you will see that the vertical tab(?) to the right of the Banjo Bolt and Brake Line Connectors is on the opposite side compared to the Master Cylinder of the CBR600F4i as you can see in the 2nd image. The vertical tab on the CBR version is in the pathway for the de-linking brake line configuration of my bike.

 

20230319-1-VFR800Fi1De-linkedRearBrakeMasterCylinder.jpg

 

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With a 1/2" rear master, you would really have to un-plumb/remove the centre piston and just use the outer two (2x 22.65mm for a 5th gen).  All three pistons would give you a 10.89 ratio, which would result in a very powerful rear brake, which could go from nothing to locked up fairly quickly.  That's the opposite of what you want in a rear brake--most people would prefer to weaken it and get more feel as a result.  (Danno reminded me of another issue: the smaller piston also gives you more lever travel.  However, too much lever travel and the lever can hit the end of travel before the brakes are fully engaged.)

 

This is more critical for front brakes, but the rule of thumb is the same:

 

Increase slave piston area = decrease master piston area to maintain the same ratio.

 

Ciao,

 

JZH

 

 

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Re: tabs

 

You do have access to a hacksaw, I take it?  :happy:

 

Ciao,

 

JZH

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18 minutes ago, JZH said:

With a 1/2" rear master, you would really have to un-plumb/remove the centre piston and just use the outer two (2x 22.65mm for a 5th gen).  All three pistons would give you a 10.89 ratio, which would result in a very powerful rear brake, which could go from nothing to locked up fairly quickly.  That's the opposite of what you want in a rear brake--most people would prefer to weaken it and get more feel as a result.  (Danno reminded me of another issue: the smaller piston also gives you more lever travel.  However, too much lever travel and the lever can hit the end of travel before the brakes are fully engaged.)

 

This is more critical for front brakes, but the rule of thumb is the same:

 

Increase slave piston area = decrease master piston area to maintain the same ratio.

Yep, I have a hacksaw. 🙂

 

Looking for better feel. There was practically no feel after I de-linked the brakes.

 

However, how does the smaller diameter piston give you more lever travel if you cut the rod down to match that of the VFR?

 

Is the range of movement within the cylinder the same or more than the VFR unit?

 

Thanks!!

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On 11/4/2022 at 2:19 PM, Terry said:

I agree with the Captain. There are some critical dimensions between the brake pushrod (which locates the piston) and the master housing and its ports, and assuming the ports are clean then your lock up may be due to fluid being unable to escape after applying the brake.

 

I used an unopened CBR600F4i rear master when I delinked my last VFR and did as Mike suggests and cut some length off the threaded rod to get the VFR pedal in the right location for my big feet.

Hi Terry,

 

Do you have photos please?

 

Did you cut to the same length as the VFR?

 

Thanks!

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It's not that the lever is moving any more because of the piston diameter, it's that it may need to move more before the brakes stop the bike.  And once it gets there, it is likely to be more like an off-on switch.  But this is only if you get the ratio significantly wrong.  There are probably a range of ratios that will work fine on the street.

 

You have a 5th gen with 11/16" master cylinder and all three rear pistons?  That would be a 5.76 ratio, which you said was too wooden?  In that case, a 1/2" using two pistons might not be that different (6.37).  The better rear cylinder for you might be the 5/8" one, using all three pistons (6.97).  That ratio is somewhere between the 8th gen and the F4.

 

Ciao,

 

JZH

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35 minutes ago, JZH said:

It's not that the lever is moving any more because of the piston diameter, it's that it may need to move more before the brakes stop the bike.  And once it gets there, it is likely to be more like an off-on switch.  But this is only if you get the ratio significantly wrong.  There are probably a range of ratios that will work fine on the street.

 

You have a 5th gen with 11/16" master cylinder and all three rear pistons?  That would be a 5.76 ratio, which you said was too wooden?  In that case, a 1/2" using two pistons might not be that different (6.37).  The better rear cylinder for you might be the 5/8" one, using all three pistons (6.97).  That ratio is somewhere between the 8th gen and the F4.

 

Ciao,

 

JZH

 

I looked at the specs for the VFR750 RC24 (I had one of those) and it uses a 12.7 mm (1/2") Master Cylinder Piston with 2 x 27.0 mm Caliper Pistons which produces a ratio of 9.04 according to the information you previously posted. Never had any issues with that configuration.

 

A 14 mm M.C. Piston with the 3 Caliper Pistons of the VFR produces a ratio of 8.97.

 

How much does the diameter of the disc come into play?

 

Thanks!!

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I think disc diameter is mainly related to disc temperature, but there could be some other benefits.  Larger discs can be worked harder before overheating.  But this is more of a race-track issue...

 

Ciao,

 

JZH

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