Master cylinder bore

[daddyp]

Can any one tell me if a 16mm bore, front master cylinder will be adequate for the XS 1100 standard (79). What is the stock piston bore for the XS 1100 any way?
This setup will include dual full length SS-braided lines & EBC full floating rotors.
I just want to improve looks as well as stopping power.

[SG-Olli]

If you get one, try a 14mm MC.
You get a bit more travel on the lever but much better feel.
It is a real two finger stopper.

[daddyp]

I was looking at a rectangular painted metal from Mixes XS. It is sold for a xs 650-850 with a dual disk conversion; however, These bikes weigh significantly less than our 1100 Beasts!

[TopCatGr58]

Hey DaddyP,

Yes, the 16mm is the standard size for the front dual disc system like we have. But this size was also for the old OEM vinyl/expandable lines with the single piston calipers, and so plenty of fluid pumping volume was wanted.

The SS brake lines DON'T expand, and so less fluid is needed, and provide a better feel all by themselves. My front MC was toast 8 years ago when I was doing my rebuild, and so I found a smaller MC at a local wreckers, looks to be the one for the XJ11 which only drives 1 caliper. With my old vinyl lines, I had to squeeze the lever essentially to the grip before I got any good braking pressure and action. Once I put on the SS lines, the feel was much better, and I'm only needing to compress the lever about 1/2 way to the grip.

SO...the smaller 14mm unit will drive the fronts with SS lines quite adequately, and as was stated you can get a better feel and control since you are not pumping as much fluid with the same amount of lever travel, so you can apply smaller amounts of pressure more easily with more control.

However, the 16mm units are available both on MikesXS as well as Partsnmore, about the same price. So....it's your choice.
T.C.

[AlanB]

Hi Guys,

The original front master cylinders on all of my XS11s were 11/16" bore.

Every other twin-disc system I have worked on has been either 5/8" or 16mm.

Single disc masters are usually 9/16" or 14mm.

My personal experiences of master cylinder swaps started with a twin-disc conversion on a seriously hot RD350; I fell of it under braking about every second time I tried to stop until I did some research and changed to a 5/8" master......

Many years later, I put flat handlebars on my 11SG, and fitted a non-angled Yamaha master from the spare parts pile; the brakes were not good, and I discovered that I had changed from 11/16 to 5/8. The smaller bore has worked for many others, but I did not like it.

The 5/8 master was not faulty; I refitted it after I changed to more modern forks and brakes, and it worked great until recently. It was replaced in the latest round of improvements.

AlanB

[daddyp]

Ok, thanks for the help. Sounds like there are multiple options for me to choose from. Ultimately, I am trying to get away from the plastic reservoir. I like the more classic look of the painted metal. I am going for a sudo cafe' chopper mix. (I'll try & post some picks when she is back together)I don't remember what the other offering from Mikes xs was in terms of bore size; I'll just have to go back and check.
One more question. Would the 16mm be too big with the ss lines? I really don't want to lock up the front end.

[SG-Olli]

Originally posted by daddyp

One more question. Would the 16mm be too big with the ss lines? I really don't want to lock up the front end.

No, the bigger the MC bore the more force you need to apply at the lever. It is easier with the smaller MC to lock the front wheel.
My rectangular, black metal MC is from a Suzuki GS400E.

[TopCatGr58]

To expound further on this,

It's a matter of leverige. The brake lever travels a certain distance displacing a certain volume of fluid with a certain sized piston. The larger piston diplaces more fluid with a specific distance of lever travel, but it will take a bit more finger pressure to apply the same amount of fluid pressure for that volume.

With the smaller piston, you actually have more leverige, so the brake lever does have to travel a bit farther to pump the same amount of volume, but the finger pressure is actually less, and so that's how you can actually apply more FLUID pressure to the caliper pistons with the smaller MC, you're moving the lever farther, but you have MORE squeeze leverige, and so can generate MORE actual PRESSURE with the same or less finger squeeze pressure!

SO...yes, you are possibly more able to lock the front brakes with the smaller MC, but you have MORE FEEL, control, and so since you have to pull the lever a bit farther you should be able to "feel" and tell when you are squeezing too much reaching the locking point! With the larger MC you have to squeeze HARDER to generate the same amount of fluid pressure to reach the locking point.
T.C.

[daddyp]

That makes perfect since. I was thinking along a different line (a simpler one). Now that you have explained it; it seems so logical. It's the same with any fluid, hydrolic, or pneumatic system... Du. I don't know why I wasn't thinking of a brake system, as it is a manual hydrolic pump
Thanks all, I think I got it now!