What hole do i drill out on this master cylinder?

I have posted about it before but didnt have a good understanding on how a brake master cylinder worked or how to drill and machine metal before. So here it is again i have a front brake master cylinder off of a 1976 KZ400D3 that pumped fluid into a single disk front brake setup.
The conclusion after posting on here was that the master cylinder (un-modified) wouldn't be able to supply the duel disks on my 1981 KZ1000 if i just mounted it and tried it. Stopping quickly was kind of a big deal with my bike these last few rides so i would hate to need good brakes and not have them. When removing the cap from the master cylinder (where you would add the fluid) i see 2 small holes. Im guessing there are more when you remove the banjo bolt from the side of the master cylinder. What holes would i have to make larger for this to work? Im loving the look of this master cylinder and i think it would look damn good with my renthal bars.

Thanks guys,
KT

Sorry, but I do not believe you can modify it to do what you want (or at least not without a machine shop). The single disk MC has a different bore than the dual disk MC. The bore is the "hole" or cylinder in which the MC piston pushes the brake fluid. If you were to somehow bore that cylinder to the correct diameter you would also need to replace the MC piston with one that matched. Ed

Well damn And theres no possible way that single disk could stop my beast like dual disk? I thought some of the older Z900s and KZ1000s and had single disk in the front. I would still be using one of the KZ1000 Calipers and rotor but the MC would be off of a KZ400.

ONLY ONE WAY TO FIND OUT.. GUYS GET ME A BEER AND MY HELMET

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Ill look into it. I think this thread just morphed into some horrible version of my last one Thanks for the info though guys, i really appreciate it.

KT

i understand that it is posible, to bore the master and use a larger piston, but it is likely easier and cheaper to get a master from any modern dual disk bike.

Kitten Tooth wrote: ...i have a front brake master cylinder off of a 1976 KZ400D3 that pumped fluid into a single disk front brake setup.
The conclusion after posting on here was that the master cylinder (un-modified) wouldn't be able to supply the duel disks on my 1981 KZ1000 if i just mounted it and tried it....

Stock KZ1000 with single disc front brake has a master cylinder with 14mm bore.
Stock KZ1000 with dual discs front brake has a master cylinder with 5/8" bore (slightly larger than 14mm).
Am guessing the stock KZ400 master cylinder also has 14mm bore with single disc front brake.

When converting the front brake from single disc to dual discs, retaining the 14mm master cylinder will likely result in a more sensitive front brake, which may take some getting used to.

The increased sensitivity may result in unexpected locking of the front wheel during emergency braking, especially under less than ideal traction conditions such as wet road surface, or sand, or damp leaves, or oil film, or when leaned into a curve.

If the 14mm master cylinder is fitted with dual discs front brake, would take the time and practice to carefully adapt to the more sensitive feel, before undertaking riding conditions that might entail instinctively grabbing a big handful of front brake.

Good Fortune!

When me and my dad first got into metal casting, he was going to try and sandcast my Front brake master cylinder cap. (the square one from my stock MC) Before i removed the cap, my brakes were actually very sensitive. To the point where i could lock them up if i wanted too. I think during the time the cap was off and i wasn't riding, one of the little ones running around our house probably hit the front brake lever and sucked some air into the lines. So the brakes have been pretty spungy since then. Before i bled them again, it was so bad you had to pump them to use them. Im OK with more sensitive brakes. In situations of emergency i tend to use a combination of back brakes, front brakes, and downshifting. Im nota master at riding... but i know how to stop REAL quick Maybe ill try swapping them out. I tend to ride carefully too. The only time i really tear it up is on old 2 laned highways with very little traffic and large fields on either side during the day. Deer are everywhere here in Sioux City so i take them into account as well as other dummies behind the wheel .

I wouldn't depend upon riding carefully as a substitute for a good front brake.

For a dual disk: 5/8" ~= 16mm. ... single disk: 1/2" ~= 12.7mm. ... single/dual? = 14mm?

usa-motorcycles-inc has 12.7mm, 14mm, & 16mm. 16MM 5/8" DOUBLE DISC DISK ....
They may have something cheaper or the price may go down in a month or two.
The 14mm are less.