14 mm front brake master cylinder on XS1100SG

[jetmechmarty]

I just removed a nice 14 mm XS650 master cylinder in favor of an 11 mm master cylinder. It has better feel and I like it. Do any of you have experience with a 14 mm master cylinder squeezing the two front 1100 calipers? I'm not sure I want to experiment. I'm sure the larger XS1100 bowl will fit the XS650 master cylinder. Have any of you done it?

[bikerphil]

The 14mm bore will probably be too small for the Special's huge piston calipers (42.5mm IIRC) I believe. The lever will most likely be mush. The 16mm is the proper size to be used with SS lines. The 14mm is great for the Standard calipers with the 38mm pistons.. If you feel like experimenting, go for it, you never know.

[jetmechmarty]

If you feel like experimenting, go for it, you never know.

Nope. I don't. Thanks for the response.

[bikerphil]

Yep. Our friend "Mercury" has taught me a lot on this subject over the years, I wonder if he's still around. I have a question for him regarding rebuilding the PS-16 Brembo I use on my Special. I think a 15MM would also be OK but 14 may be pushing it.

[DEEBS11]

I use a 16mm for dual calipers. Plenty of stopping power.

[DEEBS11]

I have also used this economical version with success on several bikes. I have run one on my snow sidecar bike for almost 20 years with only brake light switch issues due to road salt. Have to protect it with grease.

[LAB3]

An 11mm piston and cylinder will move almost exactly one half the amount of fluid that a 16mm will, the pressure might be high enough but the volume of fluid would be considerably lower. Seeing that I haven't actually tried it my thought would be that you'd stand a good chance of pulling the lever all the way in only to find that you still haven't fully engaged the caliper pistons.

[DEEBS11]

After testing the economic master cylinder in the severe conditions for 10 winters, I found you can't just put in the cheap brake light switch again as this picture shows as it will fail and lock your brake lights on:





This is a genuine Honda switch (from which the Chinese switch is copied. It has better quality and sealing. The switch is on many Hondas late 90's - early 2000 VTX, Valkyrie, ect.




But I found the ultimate set up is a Goodridge 10x1.25 pressure switch with a double banjo sealed against the elements.







Of course the Chinese switch would last for many trouble free years on any Coffee Table Bike so this info would not apply.

[DEEBS11]

LAB3, I think the 11mm piston unit will activate the puck but it will do it weakly in comparison to the 16MM. 11mm is used on scooter sized single calipers and they work fine on that type of equipment. The 14mm would also be reduced hydraulic pressure against the piston.

[DEEBS11]

This is a replacement rubber diaphragm for the economic (Chinese) front master cylinder.

[LAB3]

LAB3, I think the 11mm piston unit will activate the puck but it will do it weakly in comparison to the 16MM. 11mm is used on scooter sized single calipers and they work fine on that type of equipment. The 14mm would also be reduced hydraulic pressure against the piston.

My answer was based solely on Pascals Law. The pressure is the same whether a smaller or larger piston is used to drive it, however, if the volume required to move the larger piston isn't available then it won't push it far enough to fully engage.

https://www.sciencedirect.com/topics...ng/pascals-law

[DEEBS11]

Copy that. I was reading more today on the subject in other forums and some guys use 14mm with no issues. If you want, you can use this chart to figure out what you can use.

[DEEBS11]

[DEEBS11]

This is what I run with a fully loaded sidecar rig. Excellent stopping power.

[DEEBS11]

Lots of info out there...

https://www.xs650.com/threads/brake-lever-travel-–-stock-vs-smaller-master-cylinder.48406/