Front Brake

[gggGary]

One thing that's quite annoying is that without the top on the MC it leaks fluid from the bottom of the white plastic part of the MC, even with screws in to hold it down. My garage floor is getting a brake fluid bath...

This is not right; you need to remove the extension. It can be gently twisted/pried out with the aid of a couple screw drivers. There's a large neoprene o-ring that seals the extension to the MC body, it usually just needs all the spooge cleaned off, lube with brake fluid to reinstall. It'll fight going back together but with some pressure it'll pop back in place.

 

[Mikey]

Yes that piston has a large diameter, plenty of fluid to start to fill the reservoir.

I learn something new every month or so
Thanks

 

[gggGary]

I learn something new every month or so
Thanks

This is for late model single piston calipers, the early caliper like your 75 have 2 opposed pistons so you can't retract them with a c-clamp.

 

[Kevin Werner]

You rang?
Might want to review my method and do it completely.
"I like the patented gggGary brake bleed technique; slave piston inserted just enough so the rubber seal is engaged. Fill slave cylinder with fluid through port, install line. NOW with port pointed up push in piston til fluid shows in master cylinder reservoir, top off reservoir, done. You can pump out piston, squeeze back in an extra time or two if needed. But usually once n done."


It is a thing for OLD brake lines to become so soft and or start shedding rubber bits internally, as to be completely useless/dangerous.

When all of the fine members here were guiding me one my new to me XS650 2 years ago, my brake line at the caliper was very moist, fragile and , I thought, suspect to failure. Gary's method may be the best when replacing brake lines.

 

[5twins]

I've had and used a MityVac vacuum pump for many years with great success. I've filled many feet of new lines on my cars and quite a few dry bike systems too .....

For a totally dry bike system, I pump until I get fluid coming out. Many times I'll need to pull 2 or 3 reservoirs full of fluid through before I can feel any pressure in the lever (or pedal), but once that happens, I'm good - and it always has eventually. Then I can finish the job with the standard pumping of the lever or pedal.

 

[bul_racer]

This is the one I have been using for years $32.99:

Remove that useless nipple fitting on the hose of the tool and just stretch the tools rubber hose over the bleed nipple on your caliper.

As far as testing the hoses...put your finger over the back side of the banjo and blow through it with your mouth...feel the other banjo end...there will be next to zero air coming through. Then compare with a known new/good hose...no comparison in air flow, trust me on this.

The junction can get clogged with gunk too, but a quick spritz of brake cleaner will rinse it fine.

https://www.harborfreight.com/brake-fluid-bleeder-92924.html

View attachment 250912

Thanks Vincent. When I hear the word pneumatic I tend to think it means connected to an air compressor but, clearly, that's not the literal meaning. Thanks for the clarification.

 

[bul_racer]

This is the one I have been using for years $32.99:

Remove that useless nipple fitting on the hose of the tool and just stretch the tools rubber hose over the bleed nipple on your caliper.

As far as testing the hoses...put your finger over the back side of the banjo and blow through it with your mouth...feel the other banjo end...there will be next to zero air coming through. Then compare with a known new/good hose...no comparison in air flow, trust me on this.

The junction can get clogged with gunk too, but a quick spritz of brake cleaner will rinse it fine.

https://www.harborfreight.com/brake-fluid-bleeder-92924.html

View attachment 250912Thanks Vincent. When I see the word 'pneumatic' I tend to think it means an air compressor is involved. I know that's not the literal meaning. Anyway, thanks for the clarification.

 

[bul_racer]

Yes that piston has a large diameter, plenty of fluid to start to fill the reservoir.

Good to know. Was wondering about that.

 

[bul_racer]

I've had and used a MityVac vacuum pump for many years with great success. I've filled many feet of new lines on my cars and quite a few dry bike systems too .....

View attachment 250930

For a totally dry bike system, I pump until I get fluid coming out. Many times I'll need to pull 2 or 3 reservoirs full of fluid through before I can feel any pressure in the lever (or pedal), but once that happens, I'm good - and it always has eventually. Then I can finish the job with the standard pumping of the lever or pedal.

Another option. Thanks Fiver!

 

[bul_racer]

This is not right; you need to remove the extension. It can be gently twisted/pried out with the aid of a couple screw drivers. There's a large neoprene o-ring that seals the extension to the MC body, it usually just needs all the spooge cleaned off, lube with brake fluid to reinstall. It'll fight going back together but with some pressure it'll pop back in place.

Oh, Thanks Gary. I'll take a look. It's certainly been distressing with fluid all over the place. Looking at the parts diagram it seems neither the extension or the o-ring are available for replacement.

 

[arcticXS]

Unless we are talking about a 100% original bike, I would not bother with the stock MC. Like I have mentioned before, on my -74 RD350A, I have a 13 mm Brembo MC, and the RD has the same 2x48 mm caliper as all disc brake XS models up to and including 1976. With a single braided hose, this gives a really good brake feel and power. As the Brembo MC has a microswitch for the brake light, you can remove that monstrous brake light switch and use a single hose. Lighter, neater and more functional IMHO. You may want to retain the short steel line at the caliper though, to avoid fender clearance issues.

 

[gggGary]

Agreed ln for a penny. A 10 or 11mm MC is a huge improvement in brake feel!

 

[Mikey]

Agreed ln for a penny. A 10 or 11mm MC is a huge improvement in brake feel!

Where can someone buy this
I like the idea of a 1 piece line and having the MC with brake light switch

 

[gggGary]

Where can someone buy this
I like the idea of a 1 piece line and having the MC with brake light switch

If you can find one the MC from some Yamaha dual purpose bikes are ideal replacements, even have the LH thread mirror mount. the XS brake switch plugs right in!
They work best if you use the lever from the XS, which bolts right on.
Here's an ebay search (xt225,tw200) master cylinder.

 

[Mikey]

and the search is on
Thanks !!

 

[Mikey]

10 - 11mm too
To narrow the search down

 

[arcticXS]

Agreed ln for a penny. A 10 or 11mm MC is a huge improvement in brake feel!

Gary, I assume your recommendation of 10 or 11 mm MC for the 77 and later single piston caliper? For the 76 and older, I believe they may be on the small side. A buddy with another RD had good results with a 1/2" (12.7 mm) Grimeca master cylinder on his bike. So maybe 12 mm, for sure 1/2" or 13 mm for a 72-76 XS is my recommendation.

 

[gggGary]

Gary, I assume your recommendation of 10 or 11 mm MC for the 77 and later single piston caliper? For the 76 and older, I believe they may be on the small side. A buddy with another RD had good results with a 1/2" (12.7 mm) Grimeca master cylinder on his bike. So maybe 12 mm, for sure 1/2" or 13 mm for a 72-76 XS is my recommendation.

Yes! this thread (was) about a 1980 special brake system.

 

[bul_racer]

If you can find one the MC from some Yamaha dual purpose bikes are ideal replacements, even have the LH thread mirror mount. the XS brake switch plugs right in!
They work best if you use the lever from the XS, which bolts right on.
Here's an ebay search (xt225,tw200) master cylinder.
View attachment 250947View attachment 250948View attachment 250949

I'm gonna check into this.

 

[5twins]

Yes, I run an 11mm from an XT/TT225 on one of my bikes and a 1/2" from a 550 Vision on the other. I got both off eBay for around $20. It may take a while to find a nice 11mm one because coming off a dirt bike, many are really trashed, lol. Here's the 11mm on my '78, a little "weathered" but so is the whole rest of the bike, so it fits in well, lol .....

..... and the 1/2" one on my '83 .....

The only parts that I needed to replace were the screws for the tops. Both give better brake "feel" and modulation, but the 11mm gives a bit more of it than the 1/2" one. However, this is at the expense of more lever travel, but I've grown used to it.