Dual Disc Master Cylinder Options

EvenmoreXS

1981 XS650
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Hi everyone. Im getting ready to replace my clutch lever assembly and master cylinder. I have clip-on's so I'm considering the sloped 14mm bore.

https://www.mikesxs.net/yamaha-xs650-master-cylinder-with-sloped-reservoir-oem-3g1-25850-00-00.html

Or the standard non sloped 13mm bore.. Because that's what I currently have.

https://www.mikesxs.net/yamaha-xs650-1mh-master-cyl-assembly-13mm-bore.html

I'm not sure what my MC bore size is currently... Installed by PO... But feels good and stops well. Lever travel is good.

Both of these options from mikes xs say they are for single disc... But I found this quote in a thread

"MMM 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"


Anybody have any experience with either of these specific options from mikes used in a dual disc setup. Recommendations? Are they decent products? Never sure with mikes...

I have an 81 special. SS lines. Single piston calipers.

Also. Any advice on measuring my current MC bore to verify its diameter? Never had to do anything with my brakes before besides new pads so I've never disassembled my MC.

Got any pics 5twins? I know you do!


Thanks everyone.
 
I like the feel of the 14mm MC with dual stock calipers braided steel line set up. It works well.
Have a close look at your current MC most I have seen have the bore size cast into the underside of the housing.
 
image.jpeg
Great advice Signal. I assume I have a 16 mm bore...

Please confirm.
 
Yeah and that's old school huge, running a dual disc with a stock slanted special MC it's good, real good.
madness front detail.jpg
 
Thanks gggGary. I'm prepared to order the sloped mc but the lever doesn't have the finger scallops and the clutch lever does. I don't want mismatch levers. Should the sloped brake lever be interchangeable with mikes replacement lever that has finger scallops? I assume so but thought I'd check before hitting the order button. Im concerned because it looks like the sloped setup lever doesn't have a adjustment screw....

Thanks again guys.
 
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I've decided to go with the standard non sloped 13mm bore based on MMM's comments... plus the vanity associated with having mismatched levers... I haven't been able to find a replacement lever that matches the sloped MC lever... no finger indents. I've also ordered a couple of motion pro levers, clutch and brake, as they are aluminum and appear to be better quality than mikes. I'll keep mikes levers on hand as replacement parts should I need them. I'll let you know how the 13mm MC feels once installed. I expect a significant difference from the current 16mm I'm running now...
 
I thought that would be the case. If others are running 13mm based on MMM's recommendation then I should be ok. I like the sloped 14mm but having mismatched levers would be weird. I also looked around for some 14mm's on amazon and some other places but the ones I found there were either chrome or newfangled that belong on a crotch rocket. Just wouldn't fit on my vintage ride. I haven't installed anything yet so if you have any suggestions Im open to them.
 
I fitted dual disc on both the 75 and 81. I used 14 mm stock M/C's. They work well together. A friend gave me a Honda M/C that was 12.8 mm.
Scary good brakes. Avery gentle touch of one or two fingers can make the front tire complain.
I went back to the 14 mm. I can be a bit hammer handed at times and the too good of brake may have caused issues.
I run 5 mm slotted discs on the 75 and 7 mm slotted disc on the 81. The 5 mm are quite a bit lighter. I guess about 28 percent, the 2mm difference divided by the 7 mm thickness gives you about 28 percent lighter, Never thought to weigh them.
Leo
 
I did. You save about 1.5 pounds. Can't say I've noticed any handling difference or improvement though. What I did notice is the thinner disc heats up more/faster.
 
I installed my dual disc front brakes using the 14mm single disc master cylinder.
Rebuilt both brake calipers and installed new rubber brake hoses. OE brake rotors
Very nice feel,gentle ,smooth pull, but hard end,not spongy...and she will stop on a dime and give you change
 
I can't say I'm very impressed with the weight savings from drilling mine full of holes either. It was only a few ounces. I was hoping it would be more.
 
I agree 5Twins very poor return for the amount of time invested ( however it does look the part). Much better weight savings to be had with a single Brembo 320mm disc and R1 caliper. I am very happy with that set up.
 
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