MC18 R4K. Suspected master cylinder leak because the calipers are rebuilt and brand new braided brake lines. Lever comes back to the handlebar. It can be pumped up but then comes back again. Would appreciate referral to the applicable master cylinder rebuild kit.

Thanks!

https://www.fowlersparts.co.uk/parts/view/45530-KV3-305
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Why do things simply when you can complicate them

Thanks Rob. I can always count on you!

My OEM MC21 Nissin is (was) an absolute b*tch to bleed, yet I've seen others that bleed up in a couple of pumps. I replaced it with a CBR1000RR radial master, and never looked back. Not sure how authentic/original you want to keep things, but at least it's an OEM Honda part.

As a bonus, the difference in feel and performance is even noticable by a complete Muppet such as myself! 😀
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Andy.
NSR-WORLD.COM

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My technique is to bleed both calipers, then stop for a beer and come back again the next day
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Why do things simply when you can complicate them

Andy wrote:My OEM MC21 Nissin is (was) an absolute b*tch to bleed, yet I've seen others that bleed up in a couple of pumps. I replaced it with a CBR1000RR radial master, and never looked back. Not sure how authentic/original you want to keep things, but at least it's an OEM Honda part.

As a bonus, the difference in feel and performance is even noticable by a complete Muppet such as myself! 😀

I also have the cbr1000rr radial master cylinder on mine and it’s definitely a worthwhile upgrade.

Thanks Andy and Rob. Unfortunately my vintage club rules won't allow a radial master.
Rob any particular beer you find most effective?

So the problem is that I can "bleed" the system by pumping the brake lever and/or tying it back to the handlebar and get reasonable braking pressure but then after a few days the lever will come back to the bar again with no braking pressure. I presume air is getting in somewhere. Any diagnostic suggestions or just rebuild the master?

Have you tried a suction bleeder on the calipers. I've got a mityvac.
On my RD400, I had my master cylinder fitted with a stainless liner. I can't remember if I did the same on my NSR. All my calipers and master cylinders have had cerakote refinishing as well. It's brake fluid resistant and looks much better.
If the caliper seals weren't damaged when they were fitted and the hoses are securely fitted, then the only thing left is the master cylinder. It's a fairly easy job.
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Why do things simply when you can complicate them

Thanks Rob. Just waiting for the MC rebuild kit to arrive from Fowlers, will rebuild and then bleed everything.