Once again, this stuff comes from a bunch of different sources. I stole it myself, saved it to a file, then cobbed it all together so even a knucklehaid like me could make some sense of it.

I

Master Cylinder to Wheel Cylinder Ratio

The overall ratio determines brake "feel". There is a "sweet spot" in the range of ratios. A ratios in the 27:1 range gives 2 finger power brakes, and feeling some line and/or caliper flex. A 23:1 ratio is at the other end of the spectrum; firm. Ratios lower than 20:1 can result in a feel extremely stiff and give a toggle switch effect; nothing seems to happen until the wheel locks. (By the way, this ain't good!)

Disc and wheel diameters must be taken into consideration, also. A 10 inch disc working against a 19 inch wheel doesn't have the leverage that a 13 inch disc working a 17 inch wheel. And the hand or foot lever ratio counts, too.

Of course for most of us dummies a quick and dirty “formula” is needed. After all, how many of us can figure out these ratios? Heck, I don’t even know what the basic formula is, let alone what figures to plug in! So, on to Part II.

II

Bore Sizes

2 pot single caliper: 9/16 bore.
2 pot dual calipers: 9/16 or 5/8 bore.
4 pot single caliper: 9/16 or 5/8 bore.
4 pot dual caliper: 11/16 or 3/4 bore.
6 pot single caliper: 9/16 or 5/8 bore
6 pot dual caliper: 11/16 or 3/4 bore.

A smaller bore master cylinder will increase line pressure and therefore braking power, but it also may not move enough fluid to completely activate the piston(s) in your caliper(s). The feel of the brake system is greatly affected by bore size. A too small master cylinder will give a stiff feel; too large a bore, a mushy feel.

 

Skip,

Good post, I think I understand 90% of it, and with a 'basic' understanding of hydraulics, I got 9% more. The only thing I'm not clear on is what a "pot" is...is this slang or a term.

Mac

 

You got all that? I'm at about 65% I think...maybe more. Any pics, Skip? Then it'd really be for dummies like me.

 

"Pot" is a slang term for "piston". Most HDs, especially the older ones, come with a single piston caliper. I don't have a clue about the new models, though. There are 2, 4, and 6 piston aftermarket calipers available, usually with what are called "differential" bores, meaning the bore sizes are not all the same. The better brake calipers will have more pistons for better stopping ability, and better "feel", all other things being equal.

I don't have any pictures, but you can check out calipers in the J&P catalog (http://www.jpcycles.com), or go to a metric bike shop and look at the front brake calipers. J&P carries Performance Machine, Billet Concepts, Milwaukee Twins, Hawg Halter, GMA, and stock-type replacement set-ups. In the metric shops you'll usually see the name "Tokico", or another Japanese name that I forget, or maybe Brembo, a European design. The Tokico calipers are great and easily adapted to HD front ends. You can get a caliper, brackets, and hardware to fit any 41 mm HD front end for $150 from this guy: http://www.fabkevin.com/ You'll see alot of his stuff on bikes in The Horse Backstreet Choppers magazine.

I'm not plugging him specifically, but I'm familiar with his work thru the magazine, and from talking to some folks he's made stuff for.

I'm not a "purist" who believes in only buying HD parts. I want whatever works best, and whatever I can afford. If I was building a bike, or customizing one, and going to redo the brakes, I'd go with FabKevin's kit. His whole setup is 1/2 or less the cost of the "custom" ones, and you can get parts any place for 'em. And besides, every Tom, Dick, & Harry has bolt-on custom parts, and if you can have a truly custom set-up for way cheaper, why not go for it?

 

Skip,

Got it, thanks!

Mac

 

Does anyone have any ideas about how changing master cylinder diameter would effect the travel distance on the brake lever.



[QUOTE=

The overall ratio determines brake "feel". There is a "sweet spot" in the range of ratios. A ratios in the 27:1 range gives 2 finger power brakes, and feeling some line and/or caliper flex. A 23:1 ratio is at the other end of the spectrum; firm. Ratios lower than 20:1 can result in a feel extremely stiff and give a toggle switch effect; nothing seems to happen until the wheel locks. (By the way, this ain't good!)



Of course for most of us dummies a quick and dirty “formula” is needed. After all, how many of us can figure out these ratios? Heck, I don’t even know what the basic formula is, let alone what figures to plug in! So, on to Part II.

II

Bore Sizes

2 pot single caliper: 9/16 bore.
2 pot dual calipers: 9/16 or 5/8 bore.
4 pot single caliper: 9/16 or 5/8 bore.
4 pot dual caliper: 11/16 or 3/4 bore.
6 pot single caliper: 9/16 or 5/8 bore
6 pot dual caliper: 11/16 or 3/4 bore.

A smaller bore master cylinder will increase line pressure and therefore braking power, but it also may not move enough fluid to completely activate the piston(s) in your caliper(s). The feel of the brake system is greatly affected by bore size. A too small master cylinder will give a stiff feel; too large a bore, a mushy feel.[/QUOTE]

 

Old thread yep , Ive read this thread before .

could a man use a 1/2" mc very similar to Brembo rear mc on a 2 x 41mm AP caliper and get away with it ?


http://www.oppracing.com/category/22...ster-cylinder/

^^^^ careful when looking a the prices ..... some is $1900 !!


the mounting holes are generally 40mm centres