New 12mm master cylinder wont build pressure

[Joshtjeerdsma]

I purchased a new 12mm master cylinder for my 850t from MGcycle and I cannot get it to build pressure. This is the last thing I need to do before I can drive it. Even when I pull the line off the master cylinder, it wont pump any fluid when pumped. When I put my thumb over the outlet and pump the lever it builds a little pressure, but wont move any fluid. Any ideas? Im at my wits end and just want to ride the bike. Thanks

[Huzo]

I purchased a new 12mm master cylinder for my 850t from MGcycle and I cannot get it to build pressure. This is the last thing I need to do before I can drive it. Even when I pull the line off the master cylinder, it wont pump any fluid when pumped. When I put my thumb over the outlet and pump the lever it builds a little pressure, but wont move any fluid. Any ideas? Im at my wits end and just want to ride the bike. Thanks

Sounds like it might be your piston is not retracting far enough to expose the primer hole. I would put a small amount of fluid in the reservoir and see if it appears out of the end where the brake line goes on without actually pumping the lever, I expect it should. I'm happy to be corrected though.

[normzone]

Somebody who knows what they're talking about will be here any moment, but in the meantime...

Out Of Box (OOB) failures are not uncommon in my field (computer equipment) but they should be damn rare in a hydraulic widget.

Is there a protective plug somewhere inside the reservoir that was not obvious and is preventing fluid intake or output ?

[Triple Jim]

I have a vague memory of having this happen once.  I put my hand over the reservoir where the cap goes, and pushed down, pressurizing the fluid a little, and it got things going.

[Red Dog]

From automotive experience:
I always bench bleed a master cylinder before installing it. 
Many years ago the rubber compounds & the assembly lubes changed & when they did that the cups had a habit of inverting or sticking in the bore.  I'm not sure I explained that clearly.

Bench bleeding was done a number of ways:
Poor mans: Fill up the resevouir (can't spell) & allow it to sit over night or until the fluid was running out of the line connection then gently work the piston.

Poor mans hurry up: Fill it, count to 20 then use very short strokes (go ahead say it) on the plunger to get the cups lubed, then increase stroke while holding ragged finger over line connection.

"Professional" shops used a vacuum bleeder after installing & connecting the lines.

The main thing was to NOT push the piston all the way in on the first couple of strokes because that is what caused the damage.
You can try vacuum bleeding the system & it may work.

[Joshtjeerdsma]

I tried the vacuum bleeder and the hand over the resevior. Still no go. I did do full squeezes on the handle right away. Maybe i screwed the cups up doing that.

[Huzo]

Somebody who knows what they're talking about will be here any moment, but in the meantime...

Out Of Box (OOB) failures are not uncommon in my field (computer equipment) but they should be damn rare in a hydraulic widget.

Is there a protective plug somewhere inside the reservoir that was not obvious and is preventing fluid intake or output ?

The suggestion was so that he could ascertain that there was communication between the reservoir and the outlet to the line. Years ago I had the same problem and found that the adjuster on the lever had been screwed in a bit too far ( not by me) and was not allowing full retraction of the piston and when the adjuster was wound off, the piston exposed the primer hole and normal service was resumed. Just a quiet one also, when you said someone would be along who "knew what he was talking about", I'm given to wonder how you presumed the post before yours was necessarily garbage ??? But time will answer all questions, as it inevitably does.

[Triple Jim]

The suggestion was so that he could ascertain that there was communication between the reservoir and the outlet to the line. Years ago I had the same problem and found that the adjuster on the lever had been screwed in a bit too far ( not by me) and was not allowing full retraction of the piston and when the adjuster was wound off, the piston exposed the primer hole and normal service was resumed. Just a quiet one also, when you said someone would be along who "knew what he was talking about", I'm given to wonder how you presumed the post before yours was necessarily garbage ??? But time will answer all questions, as it inevitably does.

Looking that the times that reply #1 and reply #2 were made, I would think that normzone was probably typing at the same time you were, and your post just happened to get in the thread first.

[Huzo]

Looking that the times that reply #1 and reply #2 were made, I would think that normzone was probably typing at the same time you were, and your post just happened to get in the thread first.

Ok mate that's maybe true so I'll leave it for this thread, sorry if I mis read you normzone

[normzone]

The suggestion was so that he could ascertain that there was communication between the reservoir and the outlet to the line. Years ago I had the same problem and found that the adjuster on the lever had been screwed in a bit too far ( not by me) and was not allowing full retraction of the piston and when the adjuster was wound off, the piston exposed the primer hole and normal service was resumed. Just a quiet one also, when you said someone would be along who "knew what he was talking about", I'm given to wonder how you presumed the post before yours was necessarily garbage ??? But time will answer all questions, as it inevitably does.

HAH! Let's talk about presumption - When I typed mine, there were no other responses posted yet. His went in with mine hot on it's heels.

Ah, the power of conclusion jumping    Apology is unnecessary. You can buy me a  some day.

[Red Dog], that's very interesting. I work in QA (manufacturing), and I can readily imagine that being an unintended consequence of the design change

[Penderic]

Caution! Brake/Clutch fluid is bad for your paint and this technique can sometimes cause some to squirt out of a open master cylinder reservoir. I hold a rag over the open unit and point the unit away from the tank.

The two or three times I had the same problem with my clutch or front brake master cylinders, I found that slowly squeezing the lever fully and then quickly releasing the lever, very quickly, yes, very quickly, release the lever and a tiny bubble of air would be expelled out of the cylinder into the reservoir.

Do that several times in a row and several more tiny, little bubbles should come out, one by one, and the feel during squeezing the lever should firm up.   

[Huzo]

HAH! Let's talk about presumption - When I typed mine, there were no other responses posted yet. His went in with mine hot on it's heels.

Ah, the power of conclusion jumping    Apology is unnecessary. You can buy me a 

Ok normzone, another guy said the same thing. Apology is required, so sorry.... Come to Nordkapp next year and I'll buy you dinner at the tip.. Huzo

[normzone]

Ok normzone, another guy said the same thing. Apology is required, so sorry.... Come to Nordkapp next year and I'll buy you dinner at the tip.. Huzo

Thanks [Huzo] - that caused some Google searches, for sure.

Alright, I endeavor to win the lottery between now and Nordkapp. Then my wife and I can meet you at Nordkapp, you can buy us dinner, and I'll buy you a Guzzi 

[Huzo]

I'm ok for Guzzis, I ship mine over each year, but the offer for you and your lady stands. Huzo.

[Perazzimx14]

I tried the vacuum bleeder and the hand over the resevior. Still no go. I did do full squeezes on the handle right away. Maybe i screwed the cups up doing that.

Reverse bleed the brakes. You drive fluid in from the caliper with a syringe and tubing. This method pushes all the air up and out of the master cylinder and fills the system with fluid. Vacuum bleeding the brakes can suck air into the system and your trying to pull the air down and out the caliper in a unnatural direction. Air in a fluid wants to rise.

[Joshtjeerdsma]

I think Huzo may have been tight. Went to the garage before work and screwed the lever adjuster out. Now there are bubbles with every pump of the lever and there appears to be fluid getting in the system. I will give it a proper bleed this evening and see how it goes. Does this mean that I have to leave the adjuster all the way out after the brakes are bled also?  Thanks so much everyone.

[Triple Jim]

You certainly need to be sure the piston uncovers the hole.  If pressure can't get out, it can be disastrous.

[Huzo]

I think Huzo may have been tight. Went to the garage before work and screwed the lever adjuster out. Now there are bubbles with every pump of the lever and there appears to be fluid getting in the system. I will give it a proper bleed this evening and see how it goes. Does this mean that I have to leave the adjuster all the way out after the brakes are bled also?  Thanks so much everyone.

All you need mate is a small amount of play  between the lever and the piston so the brakes are not being "held on" as it were. It's not terribly critical, 1 mm or so would be good.

[redrider90]

I have 2 thoughts
1. attach the unit and get one or two screwdrivers wedged in between the brake pads and push the caliper back until it bottoms out which hopefully push enough fluid back up through the master cylinder so it primes it.
Make sure you have the cap off or loose with a rag over it.
2. I have managed to break off both 6 mm  bleeding nipples off a F09 caliper. In order to bleed I very gently, and I mean gently and slowly work the brake lever as I tap the caliper with a rubber mallet. I do it slowly and can see the bubbles rise through the master cylinder reservoir.  I cover my tank with a large towel.

[normzone]

[Huzo] and [redrider90], good counsel, both of you, thanks - I will take these to heart on my bike as well.

But I'm worried about [redrider90] - what will you do for thoughts now that you selflessly shared these with us ?

(forgive me, I think I'm funny today...I suspect I may be mistaken)

 

[twhitaker]

Speedbleeder.com sells bleeders with built in check valves that make subsequent fluid changes a breeze. Get the bleed bag too.

[Huzo]

[Huzo] and [redrider90], good counsel, both of you, thanks - I will take these to heart on my bike as well.

But I'm worried about [redrider90] - what will you do for thoughts now that you selflessly shared these with us ?

(forgive me, I think I'm funny today...I suspect I may be mistaken)

 

It's just the relief of knowing you've solved a vexing issue !!! Hope you have more success. Don't know about redrider90, but I've got a reservoir full of unsolicited and sometimes worthless advice, if you want more just bring along your wheelbarrow....Huzo .

[redrider90]

[Huzo] and [redrider90], good counsel, both of you, thanks - I will take these to heart on my bike as well.

But I'm worried about [redrider90] - what will you do for thoughts now that you selflessly shared these with us ?

(forgive me, I think I'm funny today...I suspect I may be mistaken)

 

Well I said i had 2 thoughts but I did not say they were my only thoughts. So maybe I am holding back on you.

[Joshtjeerdsma]

The lever adjustment was it. I bled the brakes with my vacuum bleeder and they are good to go. Thanks all for your help.

[Huzo]

Good news, enjoy !!!