Modern brake master cylinder w/ old calipers

Hi. I’m curious- How would the brake lever pull feel if one were to install a front master from something newer like a zx6r on a 81 GPz550 (dual disc) with the original calipers?

What is the diameter of the zx6 piston? If it's smaller than 5/8" the lever feel will be more spongy, and if larger more firm.

There's nothung special about a "modern" MC.. nothing has changed in the design for 40 years. It's all about sizing the MC to the calipers.

It should be fine with the pre radial masters from my understanding they all had 16mm bores until the radial type came out. ( thats kind of close to 5/8" for you imperial types ) I imagine some of the radial may be better but i cant confirm which ones if any.

1995-1997 ZX6R integrated reservoir
also used on the 1995-2002 ZX6 and others

1998-up ZX6R remote reservoir
used on other models as well
Somewhere around 2005 they stated using radial master cylinders

The integrated reservoir looks similar to the early stuff but is a lot more compact with adjustable levers. This type is designed for handle bars that angle downwards like clip-ons to keep the reservoir level, . this is what i am using on my bike at the moment

As long as you size the MC to the calipers it makes no difference as to what bike it comes from.
The only advantage of using "modern" stuff is that it will have less wear , maybe look nicer , more compact and probably be easier to obtain new seals for as most newer bikes have been using the same generic Nissin, Tokico or Brembo stuff for the past 30 years.
Most dual disc use 5/8ths and singles use 3/8ths or 1/2 in so as long as you use an MC from a dual disc bike for your dual disc set up you shouldn't go far wrong.

zed1015 wrote: ................Most dual disc use 5/8ths and singles use 3/8ths or 1/2 in so as long as you use an MC from a dual disc bike for your dual disc set up you shouldn't go far wrong.

Exactly. Here's an image showing the bottom of the stock KZ650-C1 (dual rotor) master cylinder. Ed

Ok cool. Thanks guys, this answers my questions. I figured all I needed to do was match the bore size (5/8 or 16mm) but then I went down a google search rabbit hole that left me a little confused.

Wozza pretty much nailed what I’m looking into. I tried putting lower bars on my gpz but the huge stock MC runs into the gauges. I would need to replace it with something a little more compact in order to do so.

Lever geometry can also greatly affect feel.
Also, in the more recent modern era, not all dual-caliper masters use a larger piston. I'm not sure why not.

I tried a master from a 2009 - 2016 Ex650C9F-Ex650EGFL(Non-ABS)/Ex650FGFL(ABS)
Ex650xxxx
Ninja 650 Twin (ABS and Non-ABS) Marked as "14". 14mm ?
43015-0118 Front Master Assy. Diamond reservoir.
43020-0015 piston

It's a dual-caliper master, but it is 14mm. I don't recommend it. It was very grabby and slightly spongy compared to the stock master (81 gpz550). It took more concentration to moderate the braking power.

I recommend trying this one if you think it will give you clearance, at least that is my plan. I haven't confirmed the bore size yet:
Dual-Disk
2006 - 2008
Ninja 650 Twin (ABS and Non-ABS)
43015-0011 Front Master Assy. Rectangle reservoir.
43020-1054 piston

I've got an EX650 master on my 750 and it's 5/8". Not sure of the year.

P1010741 by nessism , on Flickr

Nessism wrote: I've got an EX650 master on my 750 and it's 5/8". Not sure of the year.

P1010741 by nessism , on Flickr

That looks like the older one I mentioned. I'll probably get that one as well. The later one I tried has a more "cut diamond" shape to it. It looks cool, so I was hoping to be able to use it, but it's too grabby. I'm not sure how it works on the Ex650 since it also has dual caliper, but the master is only 14mm. Maybe the disks and calipers are really small.

Not sure what year you are thinking about but wouldn't use the 05-06 636 mc . They are known to be junk . My son had trouble with his loosing pressure . Constantly had to bleed it . Then bought a brand new one same problem . The one on my 05 636 is the same way never can get a good feel to it always low pressure . If you check the web its a known issue for those years .

I should mention, just for reference, the 1981 Gpz550 front master looks like the other early Kz550 masters, but has a different bore. The output port is axial with the bore and is extended way out. This often leads to interference with gauges when using lower bars or clip ons, that is, if you have gauges, ha.

You can see it clearly since the fairing is gone on this otherwise factory-fresh bone-stock example.

The 1982 and later Gpz550's had the output port facing forward.