Randakk's Upgraded Front Master Cylinder

GL1000s have terrific brakes...for a '70s vintage bike. Compared to modern sportbikes, they are not so impressive.

The problem with the GL1000 front brakes is that the stopping power is excellent, but the lever effort is high and "feel" is quite poor. In fact, GL1000 front brakes are often called "wooden" by riders not familiar with these beasts.

Since I've spent so much time on GL1000 saddles over the years I've adapted to all this. I have normal hand strength, but since the GL1000 lever effort required is so high, I have used all 4 fingers for braking. On modern bikes I ride, I tend to use only 2 fingers for braking.

In the past year, I've considered and implemented many brake improvements on RC-003. After adding stainless steel brake lines, heat treated stainless caliper pistons, better rotors and stickier pads, I began to notice the severe limitations of the stock master cylinder.

The main problem with the OEM GL1000 front master is that the relative size of the master cylinder piston to the caliper pistons is wrong. The master cylinder piston is too large and hence under-leveraged. The 11/16" GL1000 master cylinder piston operates 2-38mm single caliper pistons. Comparing the area of the master piston (239.50 mm2) to the total area of the 2 caliper pistons (2268.24 mm2) yields a master cylinder/caliper piston ratio of 9.47. This is far from ideal!

See: Brake Ratio Chart courtesy of Michael "Mercury" Morse for more background on brake ratios. Michael is an absolute genius with vintage brake matters. He operates Vintage Brake a terrific source for vintage brake information. He is also a Yamaha 650 guru. Highly recommended!

As Michael points out:

"High lever effort and poor front brake feel is very common on '70-80s disc brakes. At the time, the general motorcycling public was not accustomed to the braking potential of hydraulic brakes and the manufacturers really didn't want to hear about locking the front wheel at 100 MPH. Plus, with rubber lines and flexy calipers, the "good" ratios would be perceived as wrong. We had always heard that you needed a very "firm" pedal (lever) from the automotive crowd. With the overly large master cylinder pistons, you don't notice the flex, feel the hydraulic switches, and they are not as sensitive to incomplete bleeding.

The ideal ratio for single-sided caliper pistons is in the 14:1 to 12:1 range. Combine "low" leverage ratios with sticky pads and unpredictable lockup is the result. The high effort require at the lever also results in undesired input to the bars. Disc and wheel diameters, as well as hand lever ratios must be considered as well.

Keep in mind that to a very large extent, leverage ratios are a rider preference item. I have two very fast customers, Daytona winners, that prefer 20:1, instead of my 27:1 preference (for dual-sided caliper pistons). Top modern racers will have a battery of pre-bled MCs on hand, depending on the rotor size and compound they have chosen for THAT particular track. "

No wonder GL1000 brakes feel "wooden!" After some experimentation, I've found a killer improvement for the GL1000. A modern Nissin 5/8" master cylinder absolutely transforms GL1000 braking to near-crotch rocket levels. This unit dramatically reduces lever effort and provides significantly improved feel. The lever is still quite firm, but not "wooden." Max braking near the threshold of lockup is much more predictable and easier to modulate. Best of all, I can now use 2 finger braking on a GL1000!

(I also tried a 14mm unit, but it was a bit over-leveraged. It transmitted a bit more line and caliper flex and felt too "squishy" for my taste.)

After fresh brake fluid and hoses, this is probably the best brake improvement you can make on a GL1000. The cost is reasonable compared to the time, effort and expense required to rebuild the 30 year old original master cylinder!

Randakk's Upgraded Front Master Cylinder

As Tested on RC-003

Features:

High quality unit sourced to my specs from Nissin - a leading supplier of high-end brake components
5/8" master piston size
Reservoir tank is separated to make master cylinder area more compact
Reservoir has safety retainer clip
Separate reservoir permits the exact brake lever angle you desire while maintaining perfectly level reservoir
Ergonomic brake lever shape
Lever distance from handlebar is adjustable to six different positions
Designed for use on 7/8 in. handlebars
Silver body with silver lever
Uses standard Honda M10 x 1.25 pitch banjo bolt
Has a built-in brake light switch. This is not needed on early GL1000s, but necessary for later GL1000s and other bikes that have the brake switch at the master cylinder. This is also useful if you decide to eliminate the early GL1000 OEM "splitter" and convert to a 2-line system as opposed to a 3-line system. 2-line set-ups will require a duplex M10 x 1.25 pitch banjo bolt (not supplied). Even if you retain the "splitter," you can eliminate the hydraulic OEM front brake switch on early GL1000s and employ the Nissin electric switch instead. This will eliminate a tiny bit of perceptible flex necessary to activate the hydraulic brake light switch. This is the set-up I'm running on RC-003
Includes a standard M10 x 1.25 pitch mirror perch (same as GL1000 mirrors)

Notes:

For use on any Honda GL1000 (1975-1979) which came equipped with 11/16" master cylinder piston
The Nissin master cylinder is slightly shorter in overall length than the OEM master. Factor this detail in if you're having custom hoses fabricated. The stock top brake hose should fit, but it may need to be re-routed. Moving the top hose outboard of the tach bracket should free up the necessary hose length. If you've added "bar risers" or non-standard handlebars, the stock top brake hose might not have enough slack to reach.
Works well on any other motorcycle requiring a 5/8" master cylinder piston with 7/8" handlebars (like CBX)
If you run without a mirror on the right side, you will need to source a M10 x 1.25 pitch bolt to secure the remote reservoir bracket
Installation on Suzuki models will need to source an M10 x 1.25 pitch banjo bolt to replace the oddball Suzuki banjo bolt
DOT4 is the recommended brake fluid for this unit. It's OK to add DOT4 fluid to vintage DOT3 systems (but not vice versa)
Avoid silicon-based DOT5 brake fluid with these bikes. More on brake bleeding and brake fluid compatibility issues here.

Note: Installation is quick and simple, but must be done by a competent mechanic. Incorrect installation could result in property damage, physical injury or death. If you lack mechanical aptitude, you should engage a professional motorcycle mechanic to perform the installation for you.

Thorough bleeding is required. Keep in mind that brake fluid is an excellent paint remover!

Considerable skill is required to install this high quality master cylinder assembly. Since I can't control this important variable, there is no warranty on these. Rest assured that they are of the highest quality materials and workmanship.

Price: $158.50 each including US domestic shipping and handling.

International orders: Read this and please contact me before placing an order! I will send special ordering instructions. PayPal "Add Item to Cart" buttons are for domestic United States of America customers only.

This is a "limited stock" item. Allow up to 2 weeks for delivery.

Please read: Disclaimers

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