front brake

[john69]

I am having a heck of a time trying to get the front brake to work on my recently acquired 1981 650. There is no pressure when the break lever is retracted. I tied to bleed the brakes as described in several threads on this forum but to no avail. No air bubbles or movement of any sort in the resovior. I remove the banjo bolt at the lever and was able to pump fluid through the line. I also pumped fluid up to the upper banjo bolt through the bleeder valve on the brake caliper.
With the upper banjo bolt removed I can develop some pressure if I fill the area where the banjo bolt goes with fluid. If I don't manually fill the space I cannot get but a small amount of fluid to discharge when I pump the lever. Any thought on this subject? Is there any way to verify if the master cylinder is actually working as intented? Is there any such thing as gravity bleeding? Do I need to bleed the master cylinder?

 

[gggGary]

You need to strip, clean and reassemble the master cylinder.
This thread in tech covers the procedure. http://www.xs650.com/threads/master-cylinder-rebuilding.7862/
Do the same to the caliper. http://www.xs650.com/threads/help-with-caliper-rebuild.41676/ Both parts have a mix of old brake fluid and water that turns into a crusty rusty mess.

 

[gggGary]

A brake system in proper working order will empty the reservoir in less than 5 minutes if you open the bleeder on the caliper. Attach some tubing and a catch can. Old brake lines shed rubber internally and can even swell shut, exterior condition is no guide to the inside, replace them. Factory recommended replacement interval is every 4 years, stock lines are going on 40 years old. But hey it's just brakes.

 

[fredintoon]

Hi John,
do like they said to get that front brake working.
If you want to get it working properly:-
1) Replace the fabric reinforced brake line with a stainless steel reinforced line.
The stock m/c piston area is twice what it needs to be to work the one caliper that North American
XS650s have because it's the same m/c that works the rest of the world's dual caliper XS650s so:-
2) Replace the stock master cylinder with one that has an 11mm or 12mm diameter piston.

 

[john69]

Hi John,
do like they said to get that front brake working.
If you want to get it working properly:-
1) Replace the fabric reinforced brake line with a stainless steel reinforced line.
The stock m/c piston area is twice what it needs to be to work the one caliper that North American
XS650s have because it's the same m/c that works the rest of the world's dual caliper XS650s so:-
2) Replace the stock master cylinder with one that has an 11mm or 12mm diameter piston.

Thanks for the advise. Can you recommend a good economical replacement master cylinder?

 

[fredintoon]

Thanks for the advise. Can you recommend a good economical replacement master cylinder?

Hi john,
the search button and the tech section will find you several strings about replacing m/cs.
Several Yamaha m/cs have smaller diameter pistons and there's always MikesXS catalog.