Master cylinder bore

Questions regarding the DR800

Master cylinder bore

Postby liamol » Tue Apr 03, 2018 6:54 pm

Like buses I know, nothing then two straight after each other.

At some point someone put a 1991 caliper on my 1990 bike. Looks awful as it is attached via a big alloy bracket and also hangs upside down so difficult to bleed.

Anyway I want to rebuild the MC but so far rebuild kits for a 1990 or 1991 are totally different to what I have here.

What's on it is a 11mm Nissin MC, didn't ever feel great but feels worse now that it is in my head.

No idea what the current one is off but was wondering what should it be??

Thanks again

Liam
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Re: Master cylinder bore

Postby spendango » Tue Apr 03, 2018 8:13 pm

Stick a 1200 bandit one on , bigger bore
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Re: Master cylinder bore

Postby liamol » Tue Apr 03, 2018 9:33 pm

Thanks spendango.
I'm not doubting you or anything but my limited knowledge is that suitable MCs depend on bore and "throw" which I assume means amount of travel with the lever?

Please notice the commas and ? Indicating i really don't have a great grasp of this issue.. :P I'm happy though

Thanks again
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Re: Master cylinder bore

Postby BigBob » Wed Apr 04, 2018 9:18 am

Standard m/c is a 14mm. It`s the same unit on all Bigs and the DR 650 1990-95.
I found that there was too much play at the lever however much I bled the system. Also, the lever is non adjustable.
All my Bigs now have the Bandit 17mm m/c, which doesn`t give as much feel but is more powerful and I get a span adjustable lever.
Plenty of them on fleabay too.
I suggest you sort out your brakes asap. After all, how much is your life worth?
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Re: Master cylinder bore

Postby nug » Wed Apr 11, 2018 11:40 pm

Bigger bore in the master cylinder gives less pressure at the caliper. I think the lever is longer on the Bandit? it will likely give more feel as does my current mongrel setup.

One of the most common misconceptions is that a larger master cylinder will create more pressure. While a larger master cylinder creates a larger displacement, it takes more force to create the same pressure as a smaller bore. While a larger master cylinder will take up system slack with less stroke, it will take more force to create the same system pressure. The result after adding the larger master cylinder is a harder pedal/lever which needs much more pressure to create the same amount of braking force. For instance, moving from a 3/4" master cylinder to a 1" requires 77.7% more force on the push rod.
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