TECH: Make a tiny brake fluid reservoir

A few have asked so here ya go.
You want a front brake but you also like the minimalist look up front. Follow me down the rabbit hole.
I say rabbit hole because if you’re going to change up your master cylinder during this process, you’ve gotta make sure your get the correct size master cylinder. I kinda cheated and used the Internet to determine what other master cylinders worked with my Buell’s six piston caliper. The stock master cylinder was massive and the replacement (Nissin) was relatively small and inexpensive.



For simplicity’s sake we’ll assume you only need to replace the reservoir. If you don’t know how to bleed brakes, stop here and learn before going forward.



1. Remove reservoir
2. Remove the stem (part #13159 in the diagram)
3. Most stems, at least on the Nissin master cylinder, are L shaped
4. Cut the stem at the elbow
5. Ensure the cut is clean and there are no plastic filings waiting to get jammed into your master cylinder
6. Install the stem
7. Don’t replace the dust cover (part# 49016a in the diagram). You can install the dust cover but it will leave you little room to install the clear reservoir tubing. I tried it this way (see first picture) only to have it fall to the ground after a hand smack.
8. Connect 6” of clear tubing to the stem. You’ll be cutting the tubing down but the extra few inches will prove valuable during the brake bleeding process
9. Secure tubing with safety wire or a small zip tie
10. Fill tubing with brake fluid and bleed brakes
11. Find a stainless allen head bolt that is a bit bigger than the diameter of the clear tubing. I made a nice aluminum a cap for version one (see first picture) of my mini reservoir set up but it would pop off now and then. The threaded bolt will allow any fluid or air to escape under pressure while keeping water out of your master cylinder. I put the bolt in a lathe and turned down the top. Since most allen head bolts are etched on the side, it makes it easier to twist into the clear tubing.
12. Cut the clear tubing and install the cap.



I've got several thousand miles and rain storms on this set up. Works great.

Credit: I got the idea from a Bling Cycles bike and Tha Nutz’s Mr. Roboto as seen below.

At least when the brake fluid starts breaking down that hose, it's cheap and simple to replace.

Originally Posted by framus

At least when the brake fluid starts breaking down that hose, it's cheap and simple to replace.

It's DOT 5. No worries yet.

Good, simple tech Ed, thanks for posting this. We did the same thing on BFJosh's Triumph and it's been working fine ever since.

Cool set up, i've been running the same set up for awhile. I got the idea from road race bikes. Some of us run the same set up on the rear to save a little weight. I would never run it on my front brake on my race bike but my choppers good to go.

This is something I have been wondering about. Thanks for the info. I want to do this on my Sporty.

you guys just saved me like 200 bucks thanks, great tech

Can confirm that a 5/8" Nissin master cylinder fitted as standard to Kawasaki ZX6 up to about
'07 can be used. I'm matching mine to a GMA Model B caliper. I'll post some pics when I'm done.

OK. I'm almost ready to give this a try. But what are yooz guys doing for brake lines and clutch cables??? I doubt the japper controls are gonna hook up with Harley components.

Originally Posted by ARBY

OK. I'm almost ready to give this a try. But what are yooz guys doing for brake lines and clutch cables??? I doubt the japper controls are gonna hook up with Harley components.

i like the goodridge ebony stainless lines. look like old hoses but you get modern performance.


they use AN-3 fittings. great for when you need address crazy angles. the have the straights too:

I have been following this post now and got to thinking about mc sizing for my rear brake set up. How does the resivor effect the operation of the brakes? Would a minimal set up work on my dual caliper rig I have been working on? Any input would be appreciated

does this badass mod work on stock harley master cylinder or only on the nissin set up?

i dig the sweet set up and the tech...always looking for new designs and american ingenuity. thats what this country was founded on...

I just did mine the other day thank for the great idea I love it

I just put on a hydro clutch on my ironhead chop, the specs state 11/16" bore.
I've looked everywhere and cant seem to find any nissin or the like, just the big chrome gross looking ones.
I would realy like to do this as it looks clean as hell, thanks guys.

Originally Posted by kylezero

does this badass mod work on stock harley master cylinder or only on the nissin set up?

I would think you could modify any set up that has a remote reservoir. I don't know of any Harley units that do.

Originally Posted by 5akers

I have been following this post now and got to thinking about mc sizing for my rear brake set up. How does the resivor effect the operation of the brakes? Would a minimal set up work on my dual caliper rig I have been working on? Any input would be appreciated

Fuck man . . that is some SERIOUS looking stopping power!

Originally Posted by zoid

Fuck man . . that is some SERIOUS looking stopping power!

It's not as effective as it looks, the tire and traction is the limiting factor. A recent Horse issue did a story on a dual caliper build and it's use, an interesting read.

Do you know what issue i can find that in? I don't usually buy the horse.