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Upgraded Front Master Cylinder - Version A - 5/8" Piston

$163.55 163.55
In stock
Only 3 left

A and B Versions now available to fit a wide range of motorcycles:

Front Master Cylinder VersionFitment Chart Summary of Models Covered

A - 5/8 inch Piston

Typical model coverage: Appropriate for most motorcycles with
two (2) front brake rotors:

Honda GL1000
Honda GL1100
Honda DOHC4 models
Honda CBX

B - 14 mm Piston

Typical model coverage: Appropriate for most motorcycles with
one (1) front rotor:

Honda FT500 Ascot Single
Small & medium Honda twin-cylinder models such as CB350
Small & medium Honda four-cylinder models such as CB400F, CB550, etc.
Honda CX500

This is the same front brake master cylinder as used on Dennis Parrish's DOHC-4 vintage racebikes.

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

In the past, Randakk's has considered and implemented many brake improvements on the RC-003. After adding stainless steel brake lines, heat treated stainless caliper pistons, better rotors and stickier pads, we 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, we can now use 2 finger braking on a GL1000!

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

A, and B Versions now available to fit a wide range of motorcycles.

Proven on RC-003


  • High quality unit sourced to my specs from Nissin - a leading supplier of high-end brake components
  • Version A: 5/8" piston size for twin front brake rotor bikes
  • Version B: 14mm piston size for single front brake rotor bikes
  • 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 (great for riders with smaller hands)
  • 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 with 2 (male) spade terminals. 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.
  • Includes a standard M10 x 1.25 pitch mirror perch (same as GL1000 mirrors)


  • The Nissin master cylinder is slightly shorter in overall length than most OEM masters. 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.
  • Designed for 7/8" handlebars.
  • 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.
  • Not recommended for use on motorcycles equipped with linked brakes (where a portion of the front brake capacity is connected in some fashion to some aspect of the rear brakes.)
  • 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. Read more on brake bleeding and brake fluid compatibility issues on our blog.

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 Randakk's cannot control this important variable, there is no warranty. Rest assured that they are of the highest quality materials and workmanship.

To read more reviews on this and other products visit our Review Site,

Is Universal Part: No

OEM Number(s): N/A

Motorcycle Fitment:

  • 1975 Honda GL1000 GL1000 Goldwing
  • 1976 Honda GL1000 GL1000
  • 1976 Honda GL1000 GL1000-LTD
  • 1977 Honda GL1000 GL1000 Goldwing
  • 1978 Honda GL1000 GL1000 Goldwing
  • 1979 Honda CBX CBX
  • 1979 Honda GL1000 GL1000 Goldwing
  • 1980 Honda CBX CBX
  • 1980 Honda GL1100 GL1100
  • 1980 Honda GL1100 GL1100I Goldwing Interstate
  • 1981 Honda CBX CBX
  • 1981 Honda GL1100 GL1100
  • 1981 Honda GL1100 GL1100I Goldwing Interstate
  • 1982 Honda CBX CBX
  • 1982 Honda GL1100 GL1100
  • 1982 Honda GL1100 GL1100A Goldwing Aspencade
  • 1982 Honda GL1100 GL1100I Goldwing Interstate
  • 1983 Honda GL1100 GL1100
  • 1983 Honda GL1100 GL1100A Goldwing Aspencade
  • 1983 Honda GL1100 GL1100I Goldwing Interstate