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Discussion Starter · #1 ·
Morning all.

Pulling my hair out with a problem on my gsxr I'm currently rebuilding.
I rebuilt the bike from the ground up and had no real problems. Whilst rebuilding I got rid of the oem 6 pots and fitted a good set of 4 pot calipers off the 01 750 gsxr.
Along with the calipers I fitted new braided lines, new condition 2017 gsxr mc and rebuilt the calipers with new seals, bleed nipples etc.
I have tried to bleed the calipers over 10 times now and only get the slight pressure and the leaver is easily able to touch the bar.
I have tried a different mc and still have the same problem.
Took the calipers apart and double checked everything and seems fine.
Anyone else have this problem with putting the 4 pot 750 calipers on there 1000s?
It's usally something I never struggle with, when I do my yearly service on my other bikes re bleeding the front brakes is a 5 minute job.

The seal kit I bought for the calipers came with 4 smaller seals for the inside where the caliper splits, but from what I see only one seal goes in between the calipers and thats what I have done. Picture attached with the seal in question.
 

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If they worked fine before and there aren't any obvious leaks, I'd revisit the master cylinder and make sure it is bled well. It's not building up pressure for a reason.
 

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Discussion Starter · #3 ·
First time fitting the 2 pots so can't say they worked fine before hand. No obvious leaks and the master cylinder is pretty much brand new as its off a 2017 gsxr what the previous owner replaced with a Brembo mc when he bought the bike from new. I have also tried the original mc what gives the exact same amount of pressure so with this I believe the mc to be fine.

I have bled at the mc end many times with nothing but clear fluid coming out with no avail.

So to break it down, new master cylinder, new braided lines, banjo bolts and copper washers, breaks rebuilt with new seals, bolts, bleed nipples etc.

That's why I question the above with the amount of small rubber seals that are ment to go inbetween the calipers. I have fitted one in each caliper, yet four came with the kit 🤔
 

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First time fitting the 2 pots so can't say they worked fine before hand. No obvious leaks and the master cylinder is pretty much brand new as its off a 2017 gsxr what the previous owner replaced with a Brembo mc when he bought the bike from new. I have also tried the original mc what gives the exact same amount of pressure so with this I believe the mc to be fine.

I have bled at the mc end many times with nothing but clear fluid coming out with no avail.

So to break it down, new master cylinder, new braided lines, banjo bolts and copper washers, breaks rebuilt with new seals, bolts, bleed nipples etc.

That's why I question the above with the amount of small rubber seals that are ment to go inbetween the calipers. I have fitted one in each caliper, yet four came with the kit 🤔
I don't know what kit that is, but that's not what I see on their website for an 01, 750. From what I've seen, six pistons require two of those rings per caliper. Regardless, that's not your issue. If you're asserting that the parts are fine, then you did something wrong :) If there are no leaks and you're not building up pressure AT ALL, you have air in the system.
 

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Put a brembo RCS19 on it. Bleeder is on the top. Not only will it bleed fast, it will feel a 1000 times better braking.
 

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try a different bleeding method, maybe a pressure type where it feeds fluid under pressure you just crack bleeders and close, done deal

are the SS lines the proper diameter?
 

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The outermost seal is a dust seal and the innermost is the hydraulic seal. Race calipers don't have a dust seal in the expectation that they will be regularly cleaned. It sounds like you have a slug of air in the MC. If so, you'll just have to keep fiddling with it until you flush it out. Perhaps you can orient the MC so the slug will flow out. Something like a MityVac can help. There are posts here about bleeding methods. Piston sizes have gotten smaller over the years. The area ratio may not be correct if you mix a late model MC with older calipers. So you need to measure things and calculate the ratio; 27 is considered optimal.
 

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Discussion Starter · #9 ·
The knowledge on here beats any other forum, thanks chaps.

I have tried reverse bleeding the fluid, bleeding with my vac, leaving the leaver zip tied all night etc and have no luck so do believe it to be something more then a bleeding issue.

The weird thing is I have tried a few different mc and get the exact same amount of pressure.

I'm going to look into the "area ratio" as this is something I havent done so anymore info on this would be helpful. Also the ss lines being the right diameter, how would I go about this?

Thanks in advance, really appreciate the advice.
 
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