front disk brake on 1980 gsx250

[ukjules]

A just mechanically restored bike and been riding it a while when
yest my disk brake stuck on . Single Front type .
I sorted it now buy using a clamp , releasing bleed nipple , and forcing
piston back and using brake lever to force it out again to free up system.

Note: I have put in a new kit , seals and piston a while ago.

One thing .
When doing the same on my gs 550 I could force fluid
Back up to the reservoir pushing the piston in.
On the gsx 250 , the bike which had stuck pads, no force
Was strong enough to push fluid back up to the reservoir ?
Of course undoing the bleed nipple the piston went back easily.

Is this right ? I can't see what can be stopping the fluid being pushed
Back into the reservoir ? It should be easy ? Indeed I sometimes
Reverse bleed brakes.
They are free now and work but I can't see how this is right ?

Any ideas ? Or is it a strip down if fails again ?

 

[Guest]

Sounds like a booger in the brake fluid/line plugged the pressure relief/return orifice. When you pumped the lever to refill the caliper you pumped it downstream away from the orifice. Or I may be totally mistaken but it's happened to me but on a Honda.

 

[ukjules]

Yes i pumped lever - so went downstream .... and forced open the piston and would come out freely of the
bleed nipple if it was open.
If however i pushed on the piston it would not push fluid up into the reservoir !
if i pushed piston it would come out of the bleed nipple if i undid it !

where is the pressure relief thing orifice ??
just wanna know what to strip down and blow out ? is it the brake master cylinder reservoir area
or the calipers ?

How did you fix it ? you didnt say ?
As i say the brake seems to work but the fact above is still present !"

 

[Johnny]

That return port is just a little hole on the base of the MC reservoir. It's covered by that half-round plastic(?) thingy that you see when you look down to the reservoir with the cover off. The reservoir itself can be popped off from the MC, once you have removed the cover with the four bolts and drained the fluid (and maybe detached the brake hose?? can't remember from the top of my head...). Pry a flat screwdriver (or something alike) under the reservoir and it will pop off, then just make sure that hole isn't clogged!

 

[Guest]

I bought a rebuild kit for the m/c. I had to pull the whole thing apart because the hole/orifice was under the plastic reservoir. The next time I had a problem I just bought a new generic m/c off the interweb and started with new along with S.S. braided lines. That combination (along with new pads) made the whole system almost good! All my bikes are over 30 years old so high performance braking isn't part of the program but they can be modified to work as well as possible.

 

[Gorminrider]

That return port is just a little hole on the base of the MC reservoir. It's covered by that half-round plastic(?) thingy that you see when you look down to the reservoir with the cover off. The reservoir itself can be popped off from the MC, once you have removed the cover with the four bolts and drained the fluid (and maybe detached the brake hose?? can't remember from the top of my head...). Pry a flat screwdriver (or something alike) under the reservoir and it will pop off, then just make sure that hole isn't clogged!

This return port is so important I tore the little plastic covering tab off, where it exists. So, now, I can check operation. Yes -the little fountain spurt that can be suprisingly strong but it's worth the small nuisance of remembering not to get brake fluid on my eyeball just to be able to check it and clean it if necessary. The fluid should always be clean so I don't see that the covering tab offers much "protection" to the return hole...obviously, it didn't help in this case (or my own)
Other reservoir-types -the alloy ones-have a tiny removeable cover which is easier. Either type on old neglected bikes often shed filth from various places that can encrust that port unless they are totally "gone over" and even then, that process loosens stuff up that can cause problems if not flushed regularly...
Goes without saying? that always cover tank with drop-cloth when refilling or fiddling with reservoir ,uncovered spurt hole or not...

 

[ukjules]

A total dismantle has been done.
MC housing off boiled in lemon juice and water !
(I am now converted to this cleaning method when I had great success on carbs
on my 750 kwak)
Blown out.
It must work now !
New MC KIT ordered.

But the original fault was that it was impossible to reverse bleed.
The bike when I got it this year was a wreck mind .