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Discussion Starter · #1 ·
Morning everyone.

I'm having a right nightmare what I hope some gsxr guru's will be able to guide me in the right direction.

So my set up is gsxr 600/750 standard 4 pot calipers (the 6 pots were very bad condition and I heard the oem 600/750 calipers are a good upgrade)
The calipers have been cleaned, new seals, bleed nipples etc.
Braided brake lines with a nissin 14mm master cylinder.

The problem I'm having is no matter how many times I bleed the system there is a mushy feel at the leaver and with enough force it will touch the handle bar. I have bled the system over and over, tried all the different techniques, reverse bleeding, leaver held to handle bar over night, calipers removed and bled etc.

I'm confident now that it's not air in the system but something in the set up causing problems.

I have tried another master cylinder, a brand new L1 gsxr master what gave me the exact same amount pressure at the leaver as the nissin one currently on there.

I believe the nissin is 14mm as its got 14 stamped on it and nothing else?, the l1 gsxr one is 17.4mm (11/16) and I belive the original gsxr k1 1000 master would of been 16mm (5/8) with the 6pot calipers.

Is the size of the master cylinder causing me problems? Does anyone know the size of the 600/750 master cylinder what originally ran with the 4pot tokico calipers?

Would really appreciate help with this as I have rebuilt the whole bike and this is holding me back.

Thanks in advance chaps.
 

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2017 Gsxr 1000R
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I’ve found on gixxers, that air gets by the bleeder screws on the brake calipers and master cylinder.
A little Teflon tape on the threads of the bleeder screws may solve your problems.
I’ve had this same issue on a 01, 07 and 2017 gixxer 1000’s and air bleeding by those screws was the problem.
 

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Discussion Starter · #4 ·
A freshly opened bottle has been used, gone through 2 500ml bottles so far.

That's the last thing I tried, new bleed nipples with a small amount of Teflon tape, unfortunately still the same issue.
 

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Lots of reading here. Post #76 and #79 may be helpful.
 

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The service manuals are generally very informative regarding the MC and caliper diameters. Look in the Service Data section of the Servicing Information chapter.
 

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Discussion Starter · #7 ·
Thanks for the heads up that the info is in the service manual. Just found it.

k1 1000 MC with 6pot calipers is 15.8mm
K1 600 MC with 4pot calipers is 19.0mm


So I'm running the k1 600 4 pot calipers on my k1 1000. I have tried a 14mm and 17.4mm MC with no luck, so this is due to me needing a 19mm 3/4 mastercylinder?

The only reason I'm confused is when I was reading up about the k1 600 calipers on the k1 1000, no one mentioned the MC would need changing to work with the calipers.
 

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pressure or gravity bleed as well, tap on everything caliper upward to chase air bubbles up into the reservoir, some guys will clamp the lever overnight to chase bubbles out as well..

your real test is the actual braking test, getting them heat cycled see how they behave, are you using stainless steel braided lines? it's not line squish is it? lines expanding?
 

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Calculate the caliper-to-MC area ratio for whatever combination you're considering. It should ideally be about 27, though Suzuki OEM is commonly around 22. The usual rule of thumb is 20 is wooden, 23 is firm, 27 is the sweet spot, and 30 or more is soft. It won't make much of a difference but the service manual normally lists both the OD of the piston and the ID of the housing. Which one to use depends on where the seal is. The calipers normally have the seal in the housing so it doesn't move. In that case the piston OD is used. The MC normally has the seal on the piston so the seal moves with the piston. In that case the housing ID is used. A 14 mm MC sounds small but it depends on the caliper diameters.

There are posts here about prepping the discs with something like ScotchBrite to remove any glaze.
 
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