Master cylinder fails to pump

Rebuilt the master cylinder about 20 months ago. Recently the front pads started this horrible squeaking. It seemed that the caliber was not relieving pressure after releasing the brake handle. Ok, remove the caliber, inspect the seal, clean everything, new seal, and heck, since everything else is new, went ahead and ordered a new glass for the master cylinder. Now the system sat for about 3 weeks with no brake fluid as the holidays got in the way of shed time. So I get everything done and reassembled start putting in fluid, but it won't pump it into the lines. Tried with the bleeder open and closed, with the line attached at the handle removed, even removed the pump and spring to verify all the little holes were clear. Still nothing. Let it sit overnight thinking maybe the seals need to be resaturated, but still nothing. Any ideas before I order another rebuild kit?

 

been quite a few threads on this recently, seems a favourite method is to "reverse bleed" the system by pumping fluid in through the caliper bleed screw using a suitable syringe.
here's the thread on it
http://www.xjbikes.com/forums/index.php?threads/bleeding-brakes.48160/
stu

 

I HATE reverse bleeding!

One tough thing with the 650 Max is the up angle on the banjo bolt due to the buckhorn bars. That can trap an air bubble that makes life miserable. You can improve the angle by turning the bars all the way to the left.

The other thing you can do is loosen the banjo bolt, squeeze the lever, tighten the bolt then release the lever. Do this several time until the fluid coming out at the bolt doesn't have bubbles. This job is much easier with an assistant.

 

Gravity over two nights has filled the caliber and the lines. The master cylinder has never been allowed to become empty. Cracked the bleeder nut and some fluid came out. The problem is that no matter how many times I pump the handle, no fluid moves, either with the bleeder open or closed. I know that the little holes are clear as I visually verified that I could see a needle probe from the inside when I had it apart, but when I pump I don't get that little spurt from the small brass port. All i get is a very fine air foaming on the lower port. Any suggestions

 

Make sure that you installed the rubber seals (on the corkscrew piston) in the correct orientation:


FRONT MASTER CYLINDER REBUILD PARTS:

mc41) OEM and aftermarket brake MASTER CYLINDER REBUILD KITS contain all the operational parts you need to correctly rebuild your master cylinder: piston, piston seal, piston spring, piston rubber sealing boot, and retaining circlip. NOTE: the piston seal does not come pre-installed onto the piston, and at first glance, you may wonder "how the heck do you get that small seal opening over that large piston?". Well, lots of lube (brake fluid) and patience and a small, dull pry tool works wonders. Make sure that you install the seal with the flared seal "lip" facing towards the fluid outlet!

Yamaha actually specifies that your master cylinder should be rebuilt every 2 years.

Master cylinder rebuild kits contain the piston, the piston seal, the spring, the plunger end seal, the plunger dust boot and its retaining circlip.


A pictorial overview of the master cylinder rebuild process can be observed at:

http://xjbikes.com/forums/index.php?threads/18377



You can check the condition of your master cylinder by disconnecting the brake hose at the master cylinder and performing a bench test by plugging off the fluid exit port and operating the hand lever to see if it will build pressure. If it does, then the master cylinder seals are in good condition. If, however, the master cylinder spurts fluid back up through the pressure-relief port, then a rebuild is definitely in order! NOTE: it is proper and correct for brake fluid to squirt up through this pressure relief hole only when the piston is retracting (hand lever released), as this is how the master cylinder relieves excess pressure from the brake calipers so the pads back off the rotors. But if the relief passage is plugged, your brakes will drag.

Of course, once you rebuild the master cylinder, you should perform the bench-test procedure once again, to make sure you have rebuilt it correctly. In either situation, you should bleed your brakes (and perhaps flush all of the old fluid) whenever the brake system has been opened, as well as replacing the crush washers at the master cylinder union bolt.

NOTE: if your master cylinder fails to build pressure after a rebuild, you may have installed the rubber piston seals or the plunger spring incorrectly (backwards).



Frequently, the question comes up as to how the various component bits and pieces of the replacement master cylinder kits should be installed.....as the fluid plunger (piston) can be installed in two different orientations within the bore, and the rubber fluid seals can also be oriented in two different directions. In order for your master cylinder to operate properly, it is vital that you get all of these orientations correct!

Also, please be aware that the factory diagrams and illustrations in both the factory service manuals and in the aftermarket service manuals illustrate the original factory piston and components, and thus tend to appear to be "wrong" in comparison to the contents of the currently available rebuild components.....actually, the illustrations are correct, but aftermarket master cylinder rebuild kits do away with the separate rubber spring "cup seal" that is illustrated in the original factory diagrams. Instead, the aftermarket kits place the forward fluid pressure seal onto the piston itself (rather than resting at the end of piston), and this combined "forward pressure seal and spring cup" is thus eliminated in the replacement rebuild kits-----the spring fits over the end "snout" of the piston unit, rather than into the original rubber "cup" seal.

The factory drawings can lead one to believe that the plunger/piston is originally of a 2-piece design; this is not correct, they are always a 1-piece design and the original separate forward pressure seal/spring "cup" makes the drawings appear as if the not fully or correctly illustrated piston is actually two pieces!


Here's how it really works: by the way, it is very helpful if you carefully note or mark the original piston as it is extracted out of the master cylinder bore, in order to eliminate confusion later.

The replacement piston has three seal location "lands" where a seal fits ("lands") onto the piston. Two of these lands are for the fluid pressure seals....one on each end of the three spiraling "corkscrew" fluid reliefs....while the one land near the "fat" end of the piston is where the large rubber weather-tight boot is placed.

Please note carefully that the two fluid pressure seals have different size internal diameter openings, and thus fit onto their corresponding smaller and larger diameter seal lands at each end of the "corkscrew". These seals fit with their open face or "lips" facing towards the fluid output port of the master cylinder.

The tapered return spring has different sized ends; the smaller end fits over the small "stud" or "snout" of the piston. The larger end of the spring will thus be the first object that "enters" the master cylinder bore as you re-assemble the piston into the master cylinder bore.

Please note right here that the drawings in the factory service manual do not illustrate this small "snout" on the piston end (where the small end of the return springs fits over), and thus the entire diagram can lead you to believe that this small "snout" actually fits toward the hand lever, which is incorrect!

If you ever get confused as to which end of the piston is which, look at your original piston, and note which end face has scars and (probably) metal displacement from it very end face..........the one that shows the metal displacement is the one that the hand lever was operating upon!

The large rubber "boot" fits into the ring land that is near the lever-end of the piston, and it fits "down" towards the length of the piston, not "outwards". You will note that the large open end of this boot actually has a stiff metal ring embedded within it.

This rubber boot will be the last thing that is installed, after the piston unit has been installed into the master cylinder bore, the piston depressed, and the retaining circlip installed. Only then can the rubber boot be installed onto the end of the piston.



Assembly Notes:

- make sure that the internal master cylinder bore is completely clean, smooth, and free of nicks, junk, gunk, and old fluid or rubber remnants.

- lubricate the master cylinder bore and the entire piston assembly with clean brake fluid before trying to install the piston into the master cylinder bore.

- make sure that the seal lips do not "turn inside out" or "roll back" on themselves as the plunger is inserted into the m/c............a "rotating" motion of the plunger as it is being inserted can be useful in preventing such as occurrence.

- the wide end of the spring goes toward the fluid outlet port.

- the piston rubber pressure rings that goes around the plunger have an open face with a lip on it....and that lip should be oriented "in" towards the fluid outlet port.

- the metal circlip that retains the plunger in the cylinder bore goes on before the outer plunger dust boot is installed.

If you are re-using the original master cylinder components, then:

- the open end of the hat-shaped rubber cup goes over the narrow end of the spring.........and that lip should be oriented "in" towards the fluid outlet port.

 

this was my first thought too.

CN

 

After I rebuilt my front brake system, I had to prefill the hose. Air was compressing and not escaping the bleeder initially. After I filled the hose and installed, I could bleed the system.

I highly recommend one thing first....

Before opening the bleeder, slowly compress the lever... hold for 15 to 30 seconds... then quickly release the lever.

This allows any air trapped in your upper hose near the banjo bolt to be released into the master cylinder reservoir.

 

I think Chacal is probably correct, either the seal is reversed, torn, or crimped.

With respect to reverse bleeding, I rebuilt my calipers, replaced the brake lines, and rebuilt the master cylinder. Using this syringe and some plastic tubing, I reverse bled my brakes and was finished and riding in less than 30 minutes. Once I had forced fluid up into the master cylinder it took a few minutes of lightly compressing the brake lever until all the bubbles in the master cylinder disappeared and get a firm brake. I then re-bled the calipers through the bleeder valves and was finished.
http://www.tractorsupply.com/en/sto...0005&cm_mmc=Affiliates-_-Linkshare-_-Link-_-1

 

Took me a few days to get my brake working. Tried bleeding it the old fashioned way, no dice. Finally gave up and bought a vacuum pump to bleed the lines. 2 mins later, I have braking action.

 

I'm having the same issue as OP (BruceB). I have left new brake fluid sit in the master cylinder with the lid (cover) off for several days and no change - it won't pump down through my new brake lines. I am beginning to think I installed the seals reverse and should orient the lips the other way.

One particular tidbit I could add to describe my situation that may or may not confirm what the problem is: after I open the bleeder screw in my brake caliper all the way and let the fluid simply rest in the opened master cylinder without any pumping action, eventually the entire brake lines & master cylinder will drain itself within a minute or so. Therefore I know fluid is going through the system, but perhaps my bore seals on the master cylinder piston are installed incorrectly??

 

BruceB, did you get anywhere on this similar issue?

I really miss having Fitz around. If anyone were to respond, he would've at least responded by now. I always felt Fitz kept the forum alive.

 

As a matter of fact, I did. Without the fancy bleeders.
I put a small closed end wrench on the bleeder, attached a length of tubing to the bleeder and fed that into a old coffee can.
Poured brake fluid in master cylinder and then squeezed the brake handle while having the bleeder open.
Don't release the handle until the bleeder has been closed.
So you end up standing on the brake handle side of the front tire, left hand on brake handle, right hand on wrench on bleeder.
Repeat the procedure for as long as it takes to remove all air bubbles, about 3 or 4 times filling the master cylinder reservoir.
Make sure you do not let the reservoir get too low that it sucks air.
After you see no more bubbles coming from the bleeder then keep the bleeder closed and continue to pump the brake handle, you should feel it stiffen up.
I had my bike on the center stand with a floor jack under the frame to keep the front tire off the ground. Easier to tell when the brakes are grabbing.
Hope this helps

 

Air naturally floats to the top of any liquid. Using that fact, I reverse bled the brakes which pushes the air out of the lines and master cylinder as the fluid level rises to fill the caliper, lines and master cylinder. This way there is not way of getting an air block. I was finished in about 20 minutes and could do it much quicker the second time.

 

So how do you reverse bleed? Where do you put in the brake fluid and how to you move it to the top of the handlebars into the master cylinder. Moellar and I do not have a vacuum pump or speed bleeder or any other type of bleeder pump.

 

Get one of these from Tractor Supply, or any feed and seed store that sells horse stuff, and about 1 foot of 1/4" tubing that will slip over the end of the syringe tip and also the bleeder valve.

http://www.tractorsupply.com/en/sto...-_-1&cm_mmc=Affiliates-_-Linkshare-_-Link-_-1

Take the top off of the master cylinder. Fill the syringe with brake fluid and attach the tubing to the tip and the bleeder valve. Hold the syringe up to allow any air in the tubing to evacuate into the syringe. Open the bleeder valve and push down on the syringe plunger to force fluid into the cylinder. Do it slowly so that air is forced up the lines ahead of the fluid. When the fluid begins to enter the master cylinder close the bleeder valve and repeat the process on the other caliper. When all the air is pushed out of the lines you can bleed the brakes as normal just in case some air remains.

Since I had rebuilt everything and started with a dry system, I still had some air trapped in the master cylinder which I easily removed by simply turning the wheel to the left to raise the master cylinder and lightly compressing the brake handle several times to clear the residual air. Took about 20 minutes total.

 

tabaka45: thanks for a good explanation, makes sense I might give it a try this weekend.

Took apart the master cylinder for a 3rd time just to double check orientation of my seals. The seals taper, down, towards the brake lever side of the plunger so by virtue of chacal's lengthy explanation (see above) I want to believe my seals are correctly oriented, correct? The long spring is the outport side of the master cylinder where fluid is pushed through the brake lines.

 

Yes, that is the correct orientation.

 

Would one be able to "suck" the fluid through the brake lines and caliper using a syringe? I've got a syringe connected with tubing on the bleeder nipple and pulled the syringe back, put a set a locking pliers on the syringe, and walked away from it last night. I'm frustrated

I tried the syringe method of trying to reverse bleed like tabaka45 explains above, and to my disbelief the syringe was not able to push any fluid - as if something was blocking (yes I opened the bleeder valve when trying to pump the fluid with the syringe). I've tried normal bleeding (yes I know how to do it - done it previously when I got the bike in '08 as well as on my 550) and the brake lever never gets pressure built up as if the caliper never gets tight. I could use any other advice folks! Thanks

 

try cracking the banjo bolt loose on the master cylinder then pushing brake fluid up from the caliper. be sure to put a rag under the fitting to catch dribbles.

FU

 

Is the bleeder screw plugged up?
When I took mine apart it was so packed full of crap, there was no way anything was getting through it.

 

If you can't pump fluid in with the syringe then there is some sort of blockage. The entire system is just a straight shot from the calipers to the MC. If you are certain the the bleeder valve is open and will allow fluid to pass through it, then I would start with loosening the banjo fitting at the caliper and using the syringe see if you can pump fluid to that point, and work your way up the line until you find the blockage.

 

You stated earlier that the lines were clear in your first post. Try removing the brake line from the master cylinder and press your thumb over the opening in the master cylinder and pump the handle, if you get no pressure build up it is your master cylinder failing. If your master cylinder passes, replace the brake line and fill the master cylinder. Remove the brake line from the caliber and then clamp the brake handle in the open position like if you were braking. If brake fluid passes after an hour or two, then your caliber/bleeder screw needs to be serviced. If not, you have developed a clog in the lines and or banjo bolts.

 

This happens a lot more often than people realize...........

 

okay say I have a bleeder screw plugged up, how large of a hole needs to be in the bleeder screw to allow fluid to go through? i try to blow my breath through the bleeder screw (yes I put the bleeder screw in my mouth!) and its very difficult to pass anything. master cylinder does push air, I put my lips onto the opening (yes you read that right, my lips! its too cold for my fingers to feel anything) and felt a slight push of air onto my lips.

 

waltz on down to your napa store and get some new ones for about a buck each.
wrap the threads with teflon tape but keep the hole clear

 

^^^^^ do that ^^^^ it works. Actully you can probably get any air out just by cracking the banjo fitting at the MC and bleeding the MC normally. The angle of the MC on the Maxim bars lends itself to trapping air at the banjo fitting.

 

okay I have pumping action with the master cylinder and the bleeder valve has been fixed. got the air out of the hoses and I can pump my master cylinder, replenish it before completely going empty several times, and yet I never get pressure to pump the brakes! what is going on?? As soon as I fix one thing, another thing always comes up...If all the air is out of the lines wouldn't the pumping cause the cylinder piston in the brake caliper to start moving? I have zero brake action movement

Edit: already done the idea of cracking the banjo bolt near the MC with slight pressure on the lever to push any last air out near the MC. also I already done the reverse bleeding by opening the bleeder valve and pushing fluid up the system into the MC - doing this produces no air bubbles so one would think I have all the air out of the system! I don't know what else would cause no pressure buildup to pump the brakes... help please

 

you still have air trapped in the system. think like a bubble, it always goes up until it gets stuck somewhere, wheel cyl/fitting/splitter/loop in the hose. move things around so if there were a bubble there it has a way to go up the line. then pump it a few times and quit, by morning the air should be at the master.

 

Did you try tying the brake lever when you tried to push the fluid in with the syringe?

 

the brake system is essentially a one way valve with a relief, with the caliper bleeder open and no lever pulled fluid can just free flow. There's two holes inside the piston chamber, when you pull the lever one internal hole gets blocked by one of the piston seals forcing fluid out the second hole down to the caliper, when you release it the built up pressure is what returns the fluid back in the other, if one of the holes inside the piston chamber is blocked, fluid will fight to get back inside the master cylinder. If this happens you will have a slow return on caliper piton or sometimes almost not at all. Also, if you only move a small amount of fluid, and the caliper piston will not return. Then you most likely have air in the system. the master cylinder will pump anything (fluid/Air)... when you pull the lever does it bottom out, and/or have slight pressure and spongy? bottoming out says your master has air in it still, spongy says your pushing some fluid but not enough indicating the same issue.

Air bubbles rise, but not in all cases as noted above by a member noting the banjo bolt mounting position, and or the way the master mounts to the bars... you need to adjust the position of all component's so any air inside has no "Pockets" it can hide in while fluid passes right by it. once you have good brake fluid flow and pressure you can reposition them back to riding position. and he was correct by saying to turn the bars all the way to the left, this puts the reservoir in a more level position and at its highest point. Even reverse, or vacuum bleeding will not guarantee all air is out of the system, you may need to giggle lines or take a rubber hammer tapping on side of master cylinder, or dismount any etc.... no one has said the bike make that I have seen, does it have dual calipers with a center joint (proportioning valves)? I have had two tiny air bubbles make an entire lever pull feel so spongy the piston barely moved.

do this, fill reservoir up, put a clear hose onto bleeder long enough to have an arch curve and hang it above the caliper, open bleeder. and let it set for 1 minute, while you watch it. see any bubbles? It should gravity bleed by its self, and fluid should start to flow, because the master cylinder piston has not been pulled past the relief hole. the reason for the arching hose is to allow fluid into hose, letting air rise past it but still keeping fluid in hose right at the bleeder preventing bubble from being pulled back into it. Now pump (pull) lever, several times, you should see fluid move in and out. if a bubble/s come out hold lever position till bubble rises in hose and only fluid can be pulled back in. Now pull the lever and hold it, now close the bleeder and release the lever. you should see reservoir fluid level drop. repeat this several times till no more bubbles are seen coming into tube.

 

In reverse bleeding process, do you start out with a full or empty MC?.

 

I started with an empty MC. Keep an eye on it so it doesn't overflow.

 

Going to do the reverse bleeding with another MC . Can someone post how to do this step by step.

 

It's in the tech section