Replacement for dual disc M/C

[Austblue]

G'day everyone,

I'm setting out on my first bike rebuild and I'd like to find a nicer front brake master cylinder for my XS650 SH ('81 model special). It functions fine but I want to clean up the bars and that great big yellowed plastic m/c just ain't cutting it.

From what I have read I am after a 14mm bore m/c and I've found a nice looking unit on ebay but it looks like a no-name and also has the mirror mount which I don't want since I'll be running bar ends.

http://www.ebay.com.au/itm/BRAND-NE...cessories&hash=item20c4f34f7b#ht_20096wt_1397

I like this idea from chop cult running the small tube in place of the reservoir but the stock m/c reservoir is part of the lever unit and I guess you need a front brake with a remote reservoir to do that mod.

http://www.chopcult.com/forum/showthread.php?t=1285

Appreciate any help.

 

[XSLeo]

Get the Ebay one, grind the mirror mount off, fill as needed to smooth it out, a fresh coat of paint and your golden.
Leo

 

[OakBehringer]

I wanted to do that CC mod, too, but I couldn't find an 11mm MC for my single disc front end with a remote reservoir. I could have run a bigger bore, but for me a good brake feel trumps aesthetics. Since you're running dual discs, and consequently a larger bore MC, you should have better luck. Figure out the bore size for common sport bikes and get a use MC off eBay. A lot of them have remote reservoirs. Maybe a GSXR?

 

[Austblue]

Thanks guys I was hoping you'd both chime in as I've read your posts and it seemed you knew a bit on the topic. I'll take a look around to see if there is a remote reservoir set up but I'm not too fussed I just want something that looks slim and functions at least as good as the stock unit.

Cheers for the help

 

[OakBehringer]

I'm not familiar with What bore size you need, but compare it via mr google in metric and English to other bikes to find a match. Keep in mind, bigger is not better. Try calling 650 central, dude will set you up. He is the king of brake knowledge.

 

[Austblue]

I've dug around quite a bit and found a pretty decent source for the Brembo m/c range but there's no 14mm listed. I don't know the stock caliper specs but I took a look at the stock m/c and it says 11/16 which is 17.4mm Unless anyone can guide which direction to head 13 or 15 I'll just take a look around tomorrow to find the stock caliper size so that I can use this chart.
http://www.vintagebrake.com/mastercylinder.htm

Brembo source is
http://www.yoyodyneti.com/category.aspx?categoryID=3006

13mm with remote reservoir looks good. I'm a noob with buying brakes so I'd appreciate if anyone could confirm that this unit is complete minus the switch+banjo? That little clear cap on the black stub is the reservoir right?
http://www.yoyodyneti.com/ProductInfo.aspx?productid=10.5053.51

16mm with remote reservoir looks good also.
http://www.yoyodyneti.com/ProductInfo.aspx?productid=10.5053.10

standard integrated reservoir 15mm
http://www.yoyodyneti.com/ProductInfo.aspx?productid=10.4620.67

15mm with remote reservoir in gold
http://www.yoyodyneti.com/ProductInfo.aspx?productid=10.6870.18
this looks like it'd sit a long way off the bars though??

If I get a chance tomorrow I want to see if the 1 to 2 splitter can be relocated somewhere cleaner too or if there's a smaller set up available.

 

[KeithB]

This subject has conflicting info from the sources I have checked.
Mikes XS has a part listed...

Master Cylinder Assembly - 13mm. bore (for single Front disc brake)
Yamaha OEM type. Recommended for 1977-84 650's

Also listed...

Master Cylinder Assembly - 16mm bore. - Recommended for late dual disc Front
brakes on 1977-84 XS650's or single front disc brake (1972-76 650's). Yamaha
OEM type.

Then I see this...

Replacement Front Master Cylinder assembly with sloped reservoir for
bikes with bars that situate the master cylinder on a slope - "Specials".
14.0mm. piston bore. .

I am using the stock MC on an '80 Special and added the second disc.
Works great! But is it a 17mm? Will try to find out and post results.
ALso, smaller bore = more lever travel for same braking force.

 

[gggGary]

This guide is helpful when deciding on an MC bore size
http://www.vintagebrake.com/mastercylinder.htm

From Mike Morse an acknowledged XS650 guru and all around nice guy.

 

[Austblue]

Thanks Gary, I posted that above but I'm not sure on the caliper specs for the dual disc setup. Much closer to solving this little puzzle (after hours of searching!)

 

[larksnostril]

XSLeo..always appreciate your ciomments.
I've got a question about '81 special..replaced both front brake calipers/pads and MC...new parts from Mikesxs.already head braided brake lines on. /there are no leaks anywhere..using correct DOT3 fluid
Problem:
I'm almost done with bleeding the system and the front caliper does not consistently release so wheel will run free.
What can cause this and what area my next moves to figure out and fix?
Tnx
Charlie

 

[XSLeo]

Austblue, for a dual disc front with the stock later single piston caliper use a 14 mm M/C. It has great feel and works very well.
On a single front brake an 11 mm M/C is what works best.
I have several M/C's and have tried both a sungle and dual disc on the front. I have a 12-13 mm no name Honda M/C that works better than the stock 14 mm M/C with the single brake but is a bit much with the dual. I agree with MMM on 650central about the 11 mm being the best with a single disc.
The 14 mm works great with a dual brake, on a single it's ok but the feel is a bit more wooden.
I had the stock 16 mm from a 75 on with the duals and the feel was about the same as the 14 mm on a single.
If you get the duals on try a few different sizes of calipers and you will get the idea of "wooden" I didn't really understand it untill I started swapping parts around.
Larksnostril, Disc brakes will always have just a slight drag.
The piston is held in by a square section o-ring. When you squeeze the brake lever the fluid pushes the piston out of the caliper. The seal flexes sideways a bit, when you release the lever the piston is pulled back a very small amount by the seal. This isn't enough to fully retract the piston, so the pads very lightly contact the disc rotor. If you have the front wheel of the ground and give the wheel a good spin this drag stops the wheel after just a few turns.
If the wheel stops with less turns or turns with very much resistance, then there maybe a couple things going on. With all new parts, the only thing I can think of is that even new the M/C or calipers may not have been perfectly clean.
Even a tiny bit of crud can plug the return hole is the M/C and not allow the pressure in the lines bleed back into the reservoir.
The return hole is a very small hole. It can be hard to see when looking into the M/C. As you look into the reservoir you will see a large hole, the small hole is toward the output line side a 1/8 inch or so.
Seems like I have read a few posts about the return hole not being drilled all the way through. I might try probing this return hole to see if it is plugged.
I might suggest taking the calipers and M/C apart and cleaning them.
Leo

 

[Austblue]

Thanks for the help guys, I emailed 650 central also and here's what he said:

I recommend 13mm. The stock 14 mm also works well. SS line mandatory for
these high ratio applications. Due to the flexy nature of these calipers,
there is no room for error in bleeding

I didn't find a 14mm unit from brembo and the sloped unit on Mikes is not ideal but I did find that 13mm above so I'll try that I think. I'm not in a mad rush though so in the interim I'll keep a look out for a 14mm magura or other brand.

 

[larksnostril]

Leo, again thanks..looks like all the info I need.
Bleeding the brakes isn't going well. There are no leaks at banjo jts, using DOT3 fluid..new can...using mighty-vac..correct procedure. Does this info suggest any other possibilities?
I think I will take it all apart, clean it all and check the return hole. Is probing it with piece of wire ok or something softer?

 

[gggGary]

The hole is extremely small, one strand of copper from an automotive or motorcycle harness wire is about the size. the smallest drill in a number drill set is a bit large but has been reported used successfully by members. Yes we have had several members find the hole not drilled through in aftermarket master cylinders and others have found the hole plugged in dirty brake systems. IIRC the symptom is a very hard lever, brake drag, no retraction. I think the manufacturing technique is very careful control of the drilling depth of the larger diameter hole, it just breaks through into the piston bore. In some dirt floor Chinese factory it doesn't always work....... If the hole does need to be deepened/ drilled the piston has to come out and a light hone applied to the bore so you don't leave a burr that will cut the the piston seal.

 

[Tomterrific]

Buy the caliper frpm MMM at 650central and vintagebrake. The guy knows his stuff and will get you the right part. He has already helped you so step up and keep him in business.

I have a stock 14mm MC on my '81 SR500 with dual brakes. Way too much brake, just as i like it! My XS with the same dual brakes has a 16mm MC and doesn't feel as nice. I run the stock rubber hoses with both.

Tom

 

[Tomterrific]

Oooops!!!

 

[retiredgentleman]

Leo, again thanks..looks like all the info I need.
Bleeding the brakes isn't going well. There are no leaks at banjo jts, using DOT3 fluid..new can...using mighty-vac..correct procedure. Does this info suggest any other possibilities?
I think I will take it all apart, clean it all and check the return hole. Is probing it with piece of wire ok or something softer?

Bleeding of brakes on these bikes should go very easily. No need for any special tools.
The key thing is to pre-fill the lines and the calipers before connecting the lines to the calipers. If you have everything connected and full of air before you start adding fluid, you will have a hard time to bleed the air out.

I hang my brake lines in a "U" shape, so that both banjo fittings are at the high point. Use a syringe to add brake fluid to one end of the brake line, until you see fluid come out the other end (banjo). Next, fill the caliper with brake fluid (takes very little). Now connect the brake line to the caliper (keep both banjos at the same level so as not to spill any fluid). Connect the other end of the brake line to the M/C. Lastly, add fluid to the master cylinder reservoir. Use the bleed valve at the caliper to bleed the small amount of air, and you will have a hard lever/pedal in 5 minutes or so.

I just installed new calipers to front and rear of my bike. Following my method above, the air was bled in about 5 minutes per caliper.

 

[XSLeo]

Tom, do you have a 14mm M/C that you can try on your XS650? I found that it works very well. with dual disc brakes.
I have 12.7 or 13 mm M/C a no name Honda replacement, and that works well with a single but to much for the duals. It takes a very light touch and lots of practice to get comfortable with it.
Leo

 

[Austblue]

Buy the caliper frpm MMM at 650central and vintagebrake. The guy knows his stuff and will get you the right part. He has already helped you so step up and keep him in business.

I have a stock 14mm MC on my '81 SR500 with dual brakes. Way too much brake, just as i like it! My XS with the same dual brakes has a 16mm MC and doesn't feel as nice. I run the stock rubber hoses with both.

Tom

I have a $800 list of parts through central and the same again through Mikes so I think I'm doing my bit to keep the boys in business