Author Topic: Front Brake: The $21.99 Solution  (Read 246 times)

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Offline berniebee

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Front Brake: The $21.99 Solution
« on: August 16, 2019, 06:37:46 PM »
The XS500 single disk front brake is, well, an indifferent beast. At least my '76 front brake is. I've completely rebuilt the master cylinder and caliper,  installed new SS brake lines and new pads. Adjusting the lever closer to the bar so that I could squeeze with my whole hand instead of just my finger tips helped somewhat. But the feel is wooden and there is simply not much stopping power.

So what's the problem? The  caliper to master cylinder piston ratio is plain wrong!
If you want a detailed explanation go to http://www.vintagebrake.com/mastercylinder.htm for chart of ratios.
In the second to last sentence on that page, Michael "Mercury" Morse explains that "Single piston calipers are much happier in the 14:1 to 12:1 (ratio) range. "

The caliper/MC ratio is calculated as the square of the caliper piston diameter divided by the square of the master cylinder piston diameter.
For the XS500C with a 38mm caliper piston and a 14 mm master cylinder piston, the ratio is: (38 x 38)/(14 x 14) = 7.37 .  That's well outside the ideal 12-14 range.

The solution to wooden feel? A MC with a smaller diameter piston. An 11 mm piston gives a ratio of 11.93, which bumps up right next to the range of ideal ratios. Yamaha uses an 11mm piston MC for many models.

Available for $21.99 ($Canadian) on Amazon.ca, the Dolity master cylinder assembly  is promoted as a fit for  the Yamaha XT600 XT550 XT350 TT250 XT225 . It has the left handed 10mm thread for a mirror and includes the brake switch and a black dog-leg style brake lever.  With this MC, the brake line attaches at a right angle from the original master cylinder, so you may have to order a new line. (I didn't) The other downside is that the brake switch wire connector is the wrong type for the XS500. You can solder on the bullet style connectors to replace the connector. But I used the original brake lever and brake switch.

The result? As my son would say: Sweet!  A much more controllable and powerful front brake. You still won't be doing stoppies and or make the front tire howl, but it's a great improvement over the original master cylinder.

https://www.amazon.ca/DOLITY-Hydraulic-Cylinder-Motorcycle-Handlebars/dp/B078WT4XXF/ref=sr_1_1?keywords=D+DOLITY+Right+Handle+Hydraulic+Brake+Master+Cylinder+Fits+for+Yamaha+XT600+XT550+XT350+Motorcycle+7%2F8inch+22mm+Handlebars%2C+Black&qid=1565981259&s=gateway&sr=8-1
« Last Edit: August 16, 2019, 10:55:13 PM by berniebee »

Offline Joffa1

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Re: Front Brake: The $21.99 Solution
« Reply #1 on: December 03, 2019, 08:14:19 AM »
So will this work ok with the dual front disc setups too?

Offline guylr

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Re: Front Brake: The $21.99 Solution
« Reply #2 on: December 03, 2019, 12:38:39 PM »
No because the second caliper would double the piston area which would make you pull the lever twice as far to move the caliper pistons the same distance. In that case the stock master cylinder might be just right.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline Joffa1

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Re: Front Brake: The $21.99 Solution
« Reply #3 on: December 03, 2019, 09:26:36 PM »
Ok makes sense.