Rear brake resivoir.

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Pete - 05 Aug 2007 20:19 GMT

What is the black plastic thing in the reservoir with the hole in it
on a yzf600?

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Albrecht - 05 Aug 2007 21:00 GMT

>What is the black plastic thing in the reservoir with the hole in it
>on a yzf600?

Item #24, reservoir diaphragm, expands as the fluid level drops due to rear
brake pad wear. The expansion keeps the brake fluid over the intake hole and
prevents the fluid from mixing with air.

Item #25, bush, diaphragm, pushes the diaphragm down as the filler cap is
turned. It keeps the rubber diaphragm from being damaged.

http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=2419247

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Pete - 05 Aug 2007 23:14 GMT

>>What is the black plastic thing in the reservoir with the hole in it
>>on a yzf600?
[quoted text clipped - 9 lines]
>
> http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=2419247

First off I'd like to say thanks for all the help, its really appreciated.

Now the reason I asked about the diaphragm is that my rear caliper is
sticking and
and the rotor is getting smoking hot. I attempted to clean it to no avail.
Next I decided
to try vacuum bleeding it to see if I could get it work. Now when I took the
cover of
the reservoir the black plastic bush was against the top of the reservoir
and the
diaphragm was about halfway in the middle of the resiveroir. The fluid was
brown
and I pulled chunks of sh.t out of tha caliper and lines while bleeding but
it still
does not want to back off when you release the pedal.

I think I'll have to replace the caliper since idont think that diaphragm
was on there
right. Am I right in thinking that the flat lip on the diaphragm goes on the
top of the
reservoir to seal out air and water?

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Albrecht - 06 Aug 2007 00:22 GMT

>I think I'll have to replace the caliper since idont think that diaphragm
>was on there
>right. Am I right in thinking that the flat lip on the diaphragm goes on the
>top of the
>reservoir to seal out air and water?

Yes, the top of the diaphragm acts as a seal to keep air and water out of the
reservoir and the diaphragm expands as the brake pads wear.

The lower end of the brake system is, of course, the caliper.

The square o-ring is all there is to keep water out of the caliper, and water
will get past it and the piston will rust or the o-ring will wear and little
bits of rubber will build up inside the caliper and it will jam up, causing
the rotor to get very hot.

Also, the clearance between the piston and the aluminum caliper is very small,
maybe 1/1000th of an inch, so it's difficult to line the piston up when re-
installing it. When I did a brake job on an old Datsun, the previous owner
had forced the piston back into place with a screwdriver and the piston would
stick because it was very slightly bent. I had to replace that piston.

I replaced the fluid on one old motorcycle that hadn't had a fluid change in
16 years. The rear
brake would make a horrible groaning noise when applied.

So, I removed the caliper and pumped the brake pedal until one of the two
pistons popped out.

Then I was faced with the problem of how to get the other piston out.
Fortunately, the banjo bolt
that connected the brake line was centered on the piston and I was able to
remove the banjp bolt and stick a drift through the hole and gently tap on it
and drive the stuck piston out that way.

Most calipers are not constructed with banjo bolts on the side though and
sometimes a mechanic has to use a c-clamp to hold a piston that moves easily
while he pumps the other piston out.

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Motorcycle Forum / General / Yamaha / August 2007

Rear brake resivoir.