Master cylinder front twin disc

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jacksdad

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Hi, I've converted my 650D to twin discs, but the lever has no feel at all, the brakes work well but I need to replace the master cylinder to get it right.
I've been given an early Yam round master cylinder, its 11/16" diameter: do you think this will improve things?
Next, I want to recondition it so I can use/sell...is a repair kit available?
Has anyone any ideas what this cylinder might have been fitted to?:D
 
I'm using the stock 14mm master cylinder(we didn't the dual discs for some reason) and works OK for me. My XS650 is an '80
 
Jacks Dad, hi. Btsidigttsgtm

Sunny Manchester, huh? I'm from the Black Country... says it all

The m/c for twin disc is the 11/16, same as xs750, 850, 1100, and various RDs and FJs

The m/c rebuild kits are easily available on fleabuy, I got one from a bloke in the US for 20doll$, my m/c was leaking finest purple silicone fluif from the piston hole...

When I stripped it I found it was full of rusty "sand" from the corrosion of the top lid seal insert as a result of dot3 water absorption. Having refilled and with the benefit of braided steel hoses the lever feel is rather like squeezing a wooden block. I had become accustomed to the give of rubber hoses.

So, do an eBay search for xs brake master cyl rebuild kit and set aside a few quiet hours to strip clean and rebuild it

Jbin
 
I've done some experimenting on brakes. Using the single piston 77 up calipers the stock 77 up 14 mm masters work very well with a dual disc set up. On a single disc use a 10 or 11 mm bore.
I recently bought a 14 mm master of Ebay, late last summer. It was sold as a factory duplicate for the XS400. It looks very much like the 77 up 14mm master of the XS650's. The finish is a bit rougher but it so close to the same the factory lever fits.
It comes with a spare rebuild kit. For about $29 shipped it is a very good deal.
It works very well.
Leo
 
Thanks for the replies everyone: I have fitted braided steel hoses as well, so that does firm up things: The 11/16 cylinder has freed up nicely, so I'll just try it and see how it feels!
I've read that a smaller cylinder is fitted to twin discs than with a single, its all physics and a bit much for me....
Here's my bike prior to the conversion :D

041-4.jpg
 
I have twin disks on both my 77XS and SR 500. I can say from experience that the 14mm MC is the proper way to go. Get all the air out and use good pads.

Tom
 
I think a 16 mm master cylinder should be optimum for twin calipers and stainless lines. There's a good chart on 3M's Vintage Brake site.
11/16 is what's on my twin caliper XS11. It works, but the feel is rather wooden.
 
The wooden feel is from to large a bore size M/C for the calipers used.
I did a write up on how brakes work. I explained how the M/C builds pressure and showed how a smaller bore size creates more pressure. I don't know how to link to it or I would.
With too large a M/C you won't build enough pressure to get good feel. On the stock front brakes of the XS650, early or late feel this way. Wooden feel is when you pull on the lever and not much seems to happen till just before the brakes lock. swapping the stock M/C for one smaller increases the feel. The brakes work better with less pull on the lever.
I just did a search for my brake thread. Search "Brake Upgrades"
Leo
 
Yes. Thanks for the clarification. Just as a reminder, go too small and the handle reaches the grip before you stop. It's not something to be taken lightly.

The wooden feel in my Yamahas is factory stock, made worse with the addition of stainless lines. With mine, it isn't so much nothing happening, but more like squeezing without much lever travel. More pressure=more stop There isn't that nice pull with brake coming on as the lever moves.
 
Jbinnington said:
Hmm, I have a 11/16" xs1100 front mcyl on my as yet untried twin disc cafe racer, I also have the 14mm single disc mcyl that it came with.

Room for some development further down the line then
Click to expand...

The 11/16" master is going to work. It's just a very short pull and a strong squeeze. That's how the mothership designed it.
 
XSLeo said:
The wooden feel is from to large a bore size M/C for the calipers used.
I did a write up on how brakes work. I explained how the M/C builds pressure and showed how a smaller bore size creates more pressure. I don't know how to link to it or I would.
With too large a M/C you won't build enough pressure to get good feel. On the stock front brakes of the XS650, early or late feel this way. Wooden feel is when you pull on the lever and not much seems to happen till just before the brakes lock. swapping the stock M/C for one smaller increases the feel. The brakes work better with less pull on the lever.
I just did a search for my brake thread. Search "Brake Upgrades"
Leo
Click to expand...

Here is the link for that write up.
http://www.xs650.com/forum/showthread.php?t=26232
 
Further update, twin front discs, braided hydraulic hoses, yahmahama callipers and discs. 11/16 mcyl from xs1100 gave a very unforgiving, wooden lever feel. Swapped for a 14mm single disc calliper with the result of a lighter pull and some "squeeze" in the lever.
The mcyl I've used is one of the "on the scunt" 80-81 custom master cyls that fits nicely level on clip-ons.

It might be that using rubber hoses there would be too much "give" using 14mm mcyl, hence the 11/16.

Using silicone brake fluif as well.
 
Well crap.

I've pieced together every part I need to do a twin disc on my,,,,wait for it,,,, 73 TX750. :D

I read that guys were using an early Goldwing master for a dual disc conversion. So I found one that was 11/16" just like the original TX750 dual master that I have. Looks like the identical part. Tall reservoir and all.

I guess I have to proceed with the parts I all ready have. I assume at this point I will not like the feel of the lever. But I will let you guys know. :wink2: What sucks is I originally robbed the master off of my XS2 to put on the TX. Now the XS2 build has come to where I need a master for it. Turns out that the XS2 is propritary,,,if you want the original brake switch. So I had to put it back on. So I'm kinda forced into the dual master on the TX for now. Gonna just have to try it. :shrug:

What pads do you guys recommend.
 
Hi again, bit of an update!
I've today found the original master cylinder that was fitted to my bike, when I imported it (from Ihio) :thumbsup:
Its a 14mm, with a 'offsquare' lid retained by 4 screws. I had totally forgotten about this, the brake didn't work so I replaced the cylinder with a Custom model, as these are readily available over here.
I also remember trying a repair kit, which didn't help, so I'm assuming the cylinder is worn out or pitted.
SO.....
Has anyone got a decent 14mm cylinder to sell?
I'd rather get the correct standard part, and it sounds as if its the correct one for the twin disc option as well!
How I forgot about swapping the cylinder is beyond me....but I did totally rebuild the bike in under 6 weeks.....:yikes:
 
I don't have one to sell but once you get a good working 16 mm and 14 mm master's, try both. You decide which feels better.
Leo
 
I think the discussion of how Yamaha did this would be helped by realizing that disk brakes were "new" in the 70's if they had installed a small bore "2 finger" MC that era's old farts would have gone straight over the bars when they grabbed a hand full of lever like they were used to doing on drum front brakes. To this day the cruisers and old man's bikes have a much higher lever feel than the crotch rockets that can easily stoppie with 2 fingers on the lever. I may be old but prefer my stopping without having to "vice grip" the lever. I use a 10mm dirt bike MC and teflon lines on my stock single piston single disk set ups with MM's aggressive pads and am quite satisfied with how the brakes work. They seem to be well matched to the XS chassis and engine power. My more modern bikes have higher HP, better chassis, and stronger brakes, those also work well together.....
 

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