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My bike has Shimano BR M775 brake calipers and BL M775 brake levers. The right lever for the rear brake has a broken screw in the reservoir, so it needs replacement. As BL M775 is no longer available here, my second thought is to get the latest XT levers - M8000.

However after I asked this question about Shimano brake hose compatibility I realize that the newer models use a different type of brake hose (BH 90), with a narrow bore, as opposed to the older BH59 with wide bore.

What does this mean for compatibility - will "narrow bore" levers work properly with older "wide bore" calipers?

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  • My guess would be "highly unlikely" The smaller bore in the lever would push less fluid down the line, so less pad movement. You're best off to replace both caliper and lever and line. Downside, your front and rear calipers might end up using different pads. – Criggie♦ Jan 4 '18 at 1:40
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    @Criggie the volume of displaced fluid depends on master cylinder and not hose volume (which bore affects), your guess is wrong. It's like saying brakes work only with a certain hose length. – Klaster_1 Feb 7 '18 at 13:09
  • @Klaster_1 Thinking about it - you're right. The only two bores that matter are the master and slave cylinders, which means their ratio. The hose bore doesn't really matter. – Criggie♦ Feb 7 '18 at 20:56
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Ok, I upgraded and I might as well provide an answer for my question, in case anyone else is interested.

The bike is now sporting a BR M775 rear caliper, a BL T8000 brake lever (XT three finger model) and a BH90 narrow bore hose and everything works perfectly. Putting the bits together was completely straight forward.

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