? about changing the master cylinder

[mrhammer2u]

I want to try and change my master cylinder because of a clearance issue. The handle bars I’m using now are longer than I would like but it’s the length I need so all the controls fit. (I'm using a straight drag bar, 31.5"). I want to use a 27 or 28".

I think the factory bore for the output (where the brake fluid leaves the reservoir) is 16mm on the specials with the dul front disc,...right? There is a MC I can buy that is narrower which would allow me a shorter bar BUT the bore seems to be only 10mm. You know anything about this and how it would effect braking?

Here is the MC I'm looking at http://www.ebay.com/itm/Motorcycle-F...18c49f&vxp=mtr

[mrhammer2u]

I'm a dumb noob so forgive me,....I have no idea what the 16mm represents. The more I research the more confused I get. Any help would be appreciated. Dime City seems to have a good selection of aftermarket MC's that may work for me. Just want to make sure I buy the appropriate one. Thanks!

[CatatonicBug]

The "bore" is the diameter of the piston that moves inside the MC when you squeeze the lever. That is what determines the volume of fluid that is compressed into the brakes. Assuming the lever travel remains the same, the larger the bore, the more pressure will be applied to the brakes. You can even go bigger, but be careful, as this might lead to locking up the wheels in a panic stop.

[crazy steve]

The critical measurement is the master cylinder bore; how big (or small) this is determines how much fluid is displaced when the lever is stroked. Too large, and the lever won't move far and you won't develop enough line pressure to operate the calipers (very 'hard' lever) because of poor mechanical leverage. Too small, and the lever may not move far enough to operate the calipers. A smaller bore will also give higher pressure for the same mechanical input.

The stock bore is 11/16" (roughly 17.5mm). A 14mm bore is marginal, 15-16 is workable. This will cause you to have more lever travel before the brakes are fully applied. The listing shown doesn't give the bore diameter, you need to find that out....

[mrhammer2u]

Thanks all. I get it now. The ebay cheapo is only 10MM. I found one at Dime City Cycles that will do the trick. Way more $$$ but a much better product.

Check it out here...any input is welcome
http://www.dimecitycycles.com/vintag...-717-651s.html

[TADracer]

Thanks all. I get it now. The ebay cheapo is only 10MM. I found one at Dime City Cycles that will do the trick. Way more $$$ but a much better product.[/URL]

ITS YOUR BRAKES !!!! Don't put yourself in danger to save a few bucks !!

I am missing something here but I had 28" drag bars on my special several years ago and the only problem fitting everything was the length of the brake hose. A shorter one did the trick. Biggest problem was the bars came too close to the tank at a full turn.

[jetmechmarty]

Mr. Hammer,

I can point you to a brake expert who will remove all doubt and guesswork. Michael Morse at 650Central.com or VintageBrake.com will hook you up with exactly what you need. I believe the latter site has a master cylinder chart on it. Michael is on the left coast and he's usually reached PM PST.

That being said, the stock MC with stainless lines is rather wooden feeling. Go smaller to get away from that. As Steve said, too small and the lever comes all the way back and you won't stop.

Looking at your Dime City link, you're spendy enough to give Michael a call and get exactly what you need to get stopped.

[bikerphil]

The large single piston calipers of the Special won't work with anything less than a 16MM (5/8") MC piston. Like mentioned, a 10MM won't work in your case. I run a 16MM on mine which has better linear feel than a the stock 11/16" (17MM) unit. This only applies if SS braided lines are being used, remember rubber lines will flex which is the reason for larger MC bore from the factory, GL

[mrhammer2u]

ITS YOUR BRAKES !!!! Don't put yourself in danger to save a few bucks !!

I am missing something here but I had 28" drag bars on my special several years ago and the only problem fitting everything was the length of the brake hose. A shorter one did the trick. Biggest problem was the bars came too close to the tank at a full turn.

I had the 28" bar mounted and there was not enough room for all the controls. Did you have the straight drag bar? Regardless,...I have a 31.5" on it now and everything JUST fits. But now they look too wide.

[TADracer]

Yeah, it was mostly straight. No back sweep but had about a 1" rise.

[mrhammer2u]

Yeah, it was mostly straight. No back sweep but had about a 1" rise.

It's that 1" rise that gave your MC the clearance. I have the bar with no rise, just a little sweep back.

Hopefully the Nissin MC I just ordered will shave off enough space to get the shorter bar back on.

[CatatonicBug]

It's that 1" rise that gave your MC the clearance. I have the bar with no rise, just a little sweep back.

It's probably the same bar, just rotated differently!