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Discussion Starter #1
I have owned my ZX12R A1 for just over a year, what a fantastic bike....apart from the brakes. I have started to use the crappy UK weather and masses of downtime I have due to the pandemic destroying the industry I work in, to start making improvements to my bike. I thought having something to keep me occupied would keep me sane, but these brakes are driving me nuts.

Firstly, the brakes have been terrible since I bought it, but I thought I'd see what the bike was like for a season before deciding to spend out on it. Apart from the usual sponginess that the Tokico 6 pots are apparently renowned for (I've read up a lot in these forums), there is also what feels to be warped discs. Pulsating through the lever and an on/off feeling as the bike comes to a halt.

I stripped the brakes down, lots of pistons seized. In one caliper, only 2 pistons, both of which were on the same side were moving. I removed all the pistons, removed the old seals, cleaned up all the corrosion and fitted a new seal set from Wemoto, as well as new stainless banjo bolts and bleed nipples. I won't go into detail of the fun and games with a torque wrench shearing bolts and rounded bolt heads, or the new seals leaking. All of that is sorted now.

I fitted EBC HH pads, bled the system (a previous owner fitted a brembo radial MC, I'm assuming from a KTM/Aprilia/Ducati which made that process easier). Took the bike out for a spin and the pulsating/juddering is still there!! I don't think the discs are warped from posts I have read about discolouration etc, however they may well have been bent. I have removed the front wheel and disks and under the plastic disc gasket there are a few layers of paint, and the gasket is misshaped. I understand there should be no paint on this surface? The wheels have been painted at least 3 times by the looks of it, the disc hub is a mess so will be cleaning this off tomorrow.

Do I need to replace the disc plate gaskets? I've never heard of these while watching numerous online brake related vids. I have to order some new disc bolts from Kawasaki, just wondering if I should add these gaskets to the order, as they are £9 each for a really thin, flimsy piece of plastic that doesn't appear to do a lot. I may well be wrong though, hence hoping someone that knows what they are doing might chime in.

Also, is there anything I may have overlooked with regards to my braking problem? I know a common reply to anything brake related on here is to junk the calipers and get Nissin 4 pots, or to take it to a dealer. I am looking to firstly limit my total spend on this, so new calipers are out of the question before anyone mentions the above. Also I would like to exhaust all possibilities first before forking out for a mechanic to look at it. Also, this is giving me something to do while the world falls apart, so there is that as well.

Brembo MC
Braided hoses
Rebuilt Tokico 6 pots
EBC HH pads
Grimeca discs (can't find any info online about these discs DS291FTA and KBA 61219 are the only details on them)
Thanks in advance!
 

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Have you lifted the front wheel, set up a indicator that is set close to the leading edge of the rotor and spin the wheel? You will see the run out of the rotor to know if it’s bent.

I have always used the rotor “gasket” on the 12 rims. Seems to be a damper of sorts?

cmg
 

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I recently cleaned and freed up the rotor rivets which were seized absolutely solid . My brakes were pulsating hard and that smoothed them right out. Bought the 12 last year and have been fixing the years of neglect the previous owners inflicted so it might not be an issue you have but it did work for me.
 

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Do what CMG told You. What about this Brembo MC? Maybe its to small for 6 pot calipers. Do You have any numbers on it?
Did You bleed everything right? You can buy special bleed hose with valve to make it easier.
 

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Discussion Starter #5
Hi all, thanks for the speedy replies.

I have lifted the wheel, and although I don't have a dial gauge, I found a suggestion of rigging a ball point pen to the forks with the tip nearly touching the upper part of the rotor. I tried this and there is barely any lateral movement, if any at all in fact from what I can tell by eye. Obviously I'm aware this is not as accurate as putting the correct gauge on it and taking a measurement. Thought I'd try it out to see if there was an obvious problem. In doing this also, there was no obvious addition rotational pressure from the rotor contacting the pads at any part of the rotation.

Forgot to mention, freeing the bobbins was the first thing I tried before removing the calipers to rebuild them. They were definitely jammed up, but I don't think it made a great deal of difference to the feel of the brakes.

The MC appears to be an 18. I have trawled the Internet to identify it as ideally I would like to rebuild that too. The only info I can find is someone suggesting it may be from an Aprilia RSV, a KTM Duke or perhaps a Ducati. I used a vacuum bleeder as well as doing it the old fashioned way. Tried all the tips of tapping the calipers, tieing the lever to the bar overnight. The reason for mentioning the MC is it has a bleed nipple on it, saving having to bleed the banjo bolt. Which is a double as it is a two line race setup.
 

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Discussion Starter #8
Thanks for all the suggestions. I sanded the layers of paint off the hub, fitted the new gaskets, and also went to town on the disc bobbins again. Bolted it all back together and took her for a spin today and hurrah! The brakes feel amazing! It's a shame the weather is turning now and I didn't get the opportunity to do this 6 months ago. The summer would have been far more fun!

Here is a pic of the state of the wheel hub if anyone is interested. Definitely something worth checking out before forking out for new brake discs
16945
 
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