Dodgy brakes

Now I've got the Z650 going again, I'm back to a problem I had before the
rebuild. The brakes occasionally come on of their own accord! It's happened
front and rear at different times. All the calipers have new seals and
pistons, as does the front master cyl (back m cyl repair kit seems to be
unavailable). What happens is that pressure seems to build in the system,
causing the brakes to be applied; the only way to release it is by slacking
a bleed nipple off after which it's ok for a while. It can even happen while
the bike's been standing, you go to push it and you can't until you've
released the pressure. Any ideas, I must admit to being a tad foxed...
TIA,
Ian

 

I know someone who had the same symptoms when they inadvertantly used
some DOT5 brake fluid. The resulting reaction with the DOT4/5.1 in the
system caused the seals to swell, building up pressure & forcing the
pistons out.

 

My money is on the master cylinder not returning all the way back
to its normal rest position, which blocks the return bleed port,
or the bleed port is clogged.

A less likely problem, but one that seems to get mentioned a lot,
is aging rubber hoses that have deteriorated inside, forming a sort
of one-way valve which lets brake fluid flow into, but not out of,
the caliper.

Whether the hoses are causing the problem or not, on an old bike of
that age, it's time to replace the hoses with braided stainless anyway.
You'll be amazed at how much better the feel will be, it's like having
servo assisted brakes compared to the old 'inflatable' hoses.

 

Ian Morgan vaguely muttered something like ...

Think I'd at least bleed the system fully, with new fluid, and try that. If
that didn't work then it's be a change of all hoses. After that .. er ..
eBay ...

--
Paul ...

(8(|) ... Homer Rocks

"A tosser is a tosser, no matter what mode of transport they're using."

 

What he said.

 

I'd agree with this too. Have you adjusted the free play out too far,
which will cause this, especially as the brakes heat up?

^^^^^^^^^^^^^^^^^^^^^ got to agree also^^^^^^^^^^^^^^^^^^^^^^^^^^^^^