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It's usually not that hard to get that hole opened up, just hard to see it if you are over 50. You have to take the reservoir off to get to it. Twist and pry on it and it will come off.
 

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The hole being mentioned is very small. There are two holes between the reservoir and the master cylinder bore. The one closest to the banjo bolt end of the cylinder looks like the same size as the rear one but it's only drilled partway through, looks like a dead ended hole but there's a much smaller hole drilled through the bottom of that larger hole. I use a piece of wire brush bristle held in a vise grip to poke that small hole out. It's that small. Check it with a very thin stiff piece of wire, if the hole's not open it will be impossible to bleed the cylinder because that little return hole is the only place the master cylinder can vent off any air in it's bore. Any air is pushed up into the reservoir as the piston starts to move forward insuring there is none ahead of the piston during the main part of it's stroke. That's the first place to check when having difficulty getting a master cylinder primed.
 

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exavid wrote:
The hole being mentioned is very small. There are two holes between the reservoir and the master cylinder bore. The one closest to the banjo bolt end of the cylinder looks like the same size as the rear one but it's only drilled partway through, looks like a dead ended hole but there's a much smaller hole drilled through the bottom of that larger hole. I use a piece of wire brush bristle held in a vise grip to poke that small hole out. It's that small. Check it with a very thin stiff piece of wire, if the hole's not open it will be impossible to bleed the cylinder because that little return hole is the only place the master cylinder can vent off any air in it's bore. Any air is pushed up into the reservoir as the piston starts to move forward insuring there is none ahead of the piston during the main part of it's stroke. That's the first place to check when having difficulty getting a master cylinder primed.
I have a feeling that that is the culprit. I can't get a strand of wire thru there. And to front brakes did bind up last time I rode it.
 

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DaveO430 wrote:
It's usually not that hard to get that hole opened up, just hard to see it if you are over 50. You have to take the reservoir off to get to it. Twist and pry on it and it will come off.
I don't think that's ging to work. That whole unit clamps on the handlebar with two allen head bolts.
 

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Sometimes bleeding the brakes and clutch can be a challenge.
I have an 84 Gl1200 and getting the air out of the hyd clutch was a challenge. What finally worked, like you mentioned getting a syringe, I used a plastic bottle connected to the slave cyl and pushed fluid back up through the lines and into the clutch master. To my surprise, lots of air bubbles came out of the clutch master. After that, it is perfect.
The bottle has a tube that runs down into the fluid and ends
about 1/2 inch from the bottom. Filled it with brake fluid, connected it with a hose to the clutch slave, opened the bleeder and squeezed the bottle. Had the top off the clutch master to see the results.
Perhaps this procedure could work with your front brakes.
C ya
Ron
 

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Bike...and Dennis wrote:
DaveO430 wrote:
It's usually not that hard to get that hole opened up, just hard to see it if you are over 50. You have to take the reservoir off to get to it. Twist and pry on it and it will come off.
I don't think that's ging to work. That whole unit clamps on the handlebar with two allen head bolts.
What are you talking about Dennis? On an 1100 it has a plastic reservoir that comes off the master cylinder. 1200s have the reservoir cast as part of the MC.
 

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Medic Mike,



FYI.... It's pretty tiny!



Tim.
 

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DaveO430 wrote:
Bike...and Dennis wrote:
DaveO430 wrote:
It's usually not that hard to get that hole opened up, just hard to see it if you are over 50. You have to take the reservoir off to get to it. Twist and pry on it and it will come off.
I don't think that's ging to work. That whole unit clamps on the handlebar with two allen head bolts.
What are you talking about Dennis? On an 1100 it has a plastic reservoir that comes off the master cylinder. 1200s have the reservoir cast as part of the MC.
Well now, that's a brain fart. I thought, (assumed)when they went to the dual-piston, linked system...

...oh well,one should know that when one assumes...

Sorry
 

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Mr Magic Fingers wrote:
Medic Mike,



FYI.... It's pretty tiny!



Tim.
It is definitely blocked. I removed the master cylinder once again and tried to run a few different size wires thru it with no luck. I can even see the bottom of the hole in the cylinder wall and no part of the wire strand is passing thru.
 

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Many hobby shops have micro sized drill bits, if you can find one that's as small as the original hole it's easy to clean the hole out using the bit by hand. Other than that a fine needle ground off with a chisel point clamped in a small vise grip or such can be worked through the hole. The crud is softer than the aluminum so a piece of wire, drill or whatever will stay in the hole and not enlarge it as long as the whatever is no larger in diameter than the hole. Open that hole and I'd guarantee you'll have no problem with bleeding the master. This kind of plugging up isn't uncommon at all, when I had my old shop I found several 1100s with that probem in their master cylinders. It took me a while to figure out what was going on with the first occasion but after that it didn't take me long to cure this kind of problem. Leaving the old brake fluid in the reservoir for years is the cause. Once the fluid accumulates enough moisture over time it will cause corrosion in the aluminum alloy of the casting. Change the fluid once in a while and you'll never have a problem with crud.
 

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MedicMike wrote:
I can even see the bottom of the hole in the cylinder wall and no part of the wire strand is passing thru.
...make certain the wire you are using is not larger than thecompensating orificehole. Sounds simple enough, but easily misjudged.

If that is good, and you do get through the hole, then make sure the cup seal isn't worn anywhere or in backwards. That too sounds simple enough, but...

If the hole is plugged, or if the cup is not right, you'll never get the air out of that portion of the system in the master cylinder. You'll just be pushing fluid back and forth.

To me, because you were able to build some pressure, sounds like the rebuild parts are somehow not right, and not the cleaning portion of the rebuild. As long as the wire/pin/needle you're using is smaller than the orifice hole you should be able to push through any sediment build-up. Sounds like something is up with either the parts or the assembly procedure of the parts... Ablock port is a blocked port, and with that port blocked you're not going to build any pressure, but you had pressure (at least some), ...right?

Quadruple-check your rebuild...
 

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I had problems with my front MC and finally took it to a dealer. They drilled the hole out and told me that they had enlarged the hole slightly to increase the return flow. I haven't had a problem since !



Ron

aka Big Brown
 

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Thank all you guys for your collective effort and knowledge. It's fixed and I rode it today with no problems. I realized had a tiny drill bit that was about the same size. Drilled it out, cleaned it really well and voila... nice and easily bleed brakes. All better. Now to replace my speedo cable that arrived this morning and back on the road. Thanks again and ride safe.
 

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i had to do the same exact thing, drill mine bigger for it to work rite. that was 4yrs ago an it still works great
 

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MedicMike wrote:
Thank all you guys for your collective effort and knowledge. It's fixed and I rode it today with no problems.



:claps::claps::claps:
 

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Be careful with drilling that port out larger. It's a compromise on the size of the hole. Too small and it won't help clear air or let fluid return easily to the reservoir as it heats up. Too large and you won't get the same volume of fluid pushed out toward the calipers. A much larger hole will allow more fluid to go back into the reservoir as the piston moves forward resulting in less for the caliper(s).

One other thing that hasn't been mentioned is installing the spring into the cylinder backwards. If you do the master won't work.
 

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Tiny hole !!!!!!!!!!!!!!!!!!!!!!!!!! Awwwwwhhh !

I spent so much time rebuilding my master cylinder and even knew about that tiny hole. I had to take a small drill bit and turn it by hand to remove the powder corrosion to where i could see tiny hole that was till plugged. I used carb cleaner and air hose and then my wires were still too big to push thru that hole but i finally got it and could see the carb clean spraying in the bore! After al that i assembled the new kit and installed everything and after working the frozen brake pedal free, i had the rear steel line leaking. Half the treads for that fitting are gone! Crap !!!!!! So now trying to find another one kind animal master for my 83 aspencade is not easy to find! Anyone got an extra master for baby ????? Thanks jack in michigan
 

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I use guitar strings to clean out the small holes. Try that before drilling. Try the B string.
 

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I use guitar strings to clean out the small holes. Try that before drilling. Try the B string.
I'd hate to cut up my neighbours guitar but I'll do what I have to.:ROFL:
By the way which one is the B string and will he miss it?:?
 

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Or you could just use a single strand of copper wire.

Just cut a couple of inches out of you bike's ignition circuit, strip the insulation off and you have several tiny probes.
 
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