Master cylinder replacement: Single/Dual Disk issues

[Alphamazing]

I'm looking at replacing my front master cylinder so that I don't have the clearance issues with the tach housing due to SM2 bars.

I found one that's made for an old (1980) GS750, which is a dual disk bike. Are there any issues with brake over sensetivity with that type of master cylinder? It was designed to push fluid for two calipers, so I'm not sure how well I would fare with my single disk.

Ideas, anyone?

[JamesG]

Its the bore size that determines lever effort and feel of the brakes. I can't recall the two different standard sizes on Japanese hyd. brakes off the top of my head, but here are some of the general basics from my experiances with cobbling together bike brake systems:

A dual rotor brake system has to displace twice the amount of brake fluid for the amount of caliper piston travel (naturally), than a single rotor system. If you were to try to hook up the OEM GS's master cylinder to a dual rotor system, you would find that the brakes seemed to feel weak and require alot of lever travel. On the other hand if you used say, a GSXR master on the GS's single rotor, or even a smaller set of dual rotors (like GSF/SV calipers), the lever would feel very stiff and unresponsive. I would say try to retain the original complete system of what ever is donating the parts if you can. Those Nissin or whoever enigineers knew what they were doing and besides better pads and lines, its hard to improve on.
As for using a old 80s master on your GS. I wouldn't.  For one its going to be clunky, with a big assed brake lever. Also unless its NOS, the piston seals and other parts are going to be suspect.

[Alphamazing]

It's off a bike with 200 miles on it, so I'd assume it's in fairly good condition.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=4628315680&sspagename=STRK%3AMEWA%3AIT

That's the eBay auction for it.

I've searched on here, but no one confirmed much about the GSX1100 master cylinder. That's the "reccomended" replacement one by people on here, but I think it'd have the same issues: it's designed for a dual-rotored bike.

I'd like to retain the original master cylinder, but I'm worried about the clearance between the tach housing and the banjo bolts. I'm also REALLY concerned about the bars and the silver tach trim ring. My bars are touching that ring right now and produced a dent in my last tach ring (my tach was recently replaced). I want to rotate the ends of the bars down to eliminate that clearance issue.

My other option is to get some bar end mirrors and use the master cylinder off an R6 or something similar.

[ninja_steve]

i have an R6 master cylinder on mine.  i installed it because i had it left over from my old fzr race bike and i stripped the dang screws off of my gs one.  works great.  i got it for free froma  friend and the banjo bolt was only ~$4.  coolest mod yet imo...i still have the stock banjo in case i do some radical front end conversion and need to run both calipers.

[ninja_steve]

oh yeah, and i was able to use the stock back end of my gs master cylinder and it bolted right up to the R6 one, that way i can stilluse the stock mirror mount.  also, the gs lever bolted up to the R6 mount...i went ahead and replace it anyhow since the r6 lever is adjustable.

[Alphamazing]

I like that, but the R6 resevoir and zip tie isn't as clean as I'd like. You don't notice any lever issues or over/under sensativity though?

[ninja_steve]

nah.  i just run it.  when i redid the brakes they had a completly different feel.  new caliper + hh pads + ss line + new master cylinder + motul fluid = was just about right.  i woudlnt say it is over sensative...but then again being able to adjust the lever makes it a lot better. 

and yeah the zip tie is ghetto, but it wont be long until i can afford my new bikes so i dont really care. 

[Alphamazing]

How do you have it adjusted now? I have mine set on click 5, the furthest from the bar it should be. What setting "should" it be at? Whatever feels good?

[ninja_steve]

i think its set to three.  any closer and it feels too soft. further away and its too uncomfortable and far of a pull.  i dont think there is any universal setting...set it to where it feels best. 

[Alphamazing]

Hmm. The banjo bolt on the R6 one sticks out towards the guages like mine does. If there was a cleaner way to mount the resevoir then I'd probably go for it.

I'll look around. Maybe get some bar end mirrors and use something from an FZ1 or FZ6.