Brake master cylinder swap

[Chuckwagon]

Just thought I'd post my experience with changes to the front brake on my '77 XS650D. I decided to try something that a lot of people have tried, with my own spin on it. This weekend I installed a used master cylinder from a 2003 Yamaha Zuma 50 scooter, which is an 11 mm bore master cylinder that I purchased on eBay for $21 shipped. I'm pretty sure this is a Nissin master cylinder from the looks of it, though it has "Yamaha" on the cap. It has "11" cast into the bore body, which is typical of Nissin master cylinders (they are one of the manufacturers that cast the bore size on the part).

Along with the new master cylinder, I have braided stainless lines, a stock caliper, and a stock but drilled rotor. Can't remember the brand of pads I'm using.

I'm pretty happy with the setup. The lever has an easy pull and I can easily haul the bike down quickly with a two finger pull... with the stock lever & MC I had to use all fingers and really pull the lever in hard.

There are lots of retailers that can sell you a new 11mm master, so this is nothing new. What is nice about using the Zuma MC is it fits perfectly (the lever looks different) and the brake light switch is interchangeable with the original switch, as it seems Yamaha uses the same type switch on a lot of models. I simply detached the old switch from the old MC and popped it into the new one... I didn't eve have to cut any zipties. Easy.

I don't use the stock mirrors, so I can't recall if the new MC has a hole for a mirror... I don't think it does, so that is one consideration when swapping out.

I found this list that someone put together that lists bikes that use 11mm master cylinders. NOTE IT IS NOT TOTALLY ACCURATE. It is close, so use it as a guide. (For example, it claims that the DRZ400SM uses an 11 mm, which is not true. I know this because I have one in the garage, and it has 1/2 stamped on the bore (meaning 1/2"), indicating it is a 12.6 mm bore. At least based on my reasearch, the only DRZ400 variant that uses an 11mm bore is the DRZ400E. That model was/is dirt only in the US, so it isn't going to have a brake light switch... you'd have to add on a pressure activated switch for $10).

See post #13
List of 11mm master cylinders

Bottom line, I know the Zuma 50cc scooter (and likely a Zuma 125cc scooter) is a good-fitting 11mm master cylinder for the XS650. For others, it is best to check for "11" stamped on the body and/or ask the seller.

As far as bleeding the MC, it was easy. My original brake was bled, had relatively fresh fluid and ready to go. I installed the new MC (after cleaning the reservoir/cap/rubber gasket with clean brake fluid and a clean rag) on the bar and left the line attached to the old MC. I then filled the new MC with fluid, then quickly swapped the line. I then very carefully squeezed the lever a little. Not enough to push fluid, but enough to let the air burp out of the pressure release in the MC. I did this while moving things around and tapping with a screwdriver handle to get the air to rise up to the pressure release. After several minutes, I had a solid lever and took it out for a ride.

I think it is a big improvement, and that is even with my crapped-out glazed rotor and pads (soon to be addressed). It certainly has a different feel, and if you aren't accustomed to it, you could easily lock the front wheel with too big/fast a pull on the lever.

Happy stopping -

Mark

[grizld1]

Great writeup, Mark--thanks!

[Chuckwagon]

Thanks. I just figured someone trying to save some scratch (like me) would find the info useful. It seems there are a lot of scooters and dirt bikes that use smaller front brakes and therefore have small diameter master cylinders. I think I'd be willing to try the more common 1/2" bore if I were doing it again, as the 11 is a little squishy , but I'll stick with it for now.
First ride in to work of 2016 on the bike tomorrow. Makes it that much easier to get myself ther in the morning.

[grizld1]

Mark, I can just about guarantee you that your 11 mm. MC won't feel "squishy" when you deglaze the rotor and install premium pads. I took MMM's advice and installed Vesrah sintered pads. If you're concerned about rotor wear (hasn't been a problem with my bike after quite a few seasons), Ferodo Platinum pads will also do a fine job; I used them for many years, and they're a big improvement over the OE stuff.

There are quite a few ways to deglaze, but whatever method you choose, use garnet sandpaper--the stuff with real "sand" on it. Metallic wet-or-dry or other synthetic paper can embed contaminants in the rotor.