Bad master cylinder? - Wrist Twisters
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post #1 of 39 Old 05-02-2016, 07:59 AM Thread Starter
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Bad master cylinder?

What are the signs of a bad master cylinder? Can the master be bad and not leak? Is it worth rebuilding, or just say f* it and buy one off fleaBay (but with my luck, that will need rebuilding as well)?

So here is my problem. I bled my braided lines 2x and definitely made sure there were no air bubbles coming out on the 2nd bleed. I did however notice if I cracked the bleader open enough, I would get almost a dark cloud in my clear tubing (both sides)... So maybe I've got gunk in my lines?

Before and after bleeding, the brake lever takes a LONG pull to get the brakes to bite. On the farthest adjustment I can pull the lever all the way to the bars with one hand (and I'm just a little guy).

Now for the odd part. If I let the bike sit for 20 minutes or so, I can pull the lever all the way to the bar on the first pull fairly easily. If I pump the lever, it feels like the brakes 'pressurize' and it takes more effort to pull lever all the way to the bars (or brakes bite more). I'm not seeing any leaks, and the brakes work fine... I just mash my fingers when I try to brake with only 2 fingers.

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post #2 of 39 Old 05-02-2016, 10:31 AM
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Zip tie the lever tight to the grip overnight... come out tomorrow, problem (hopefully) solved

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post #3 of 39 Old 05-02-2016, 12:05 PM Thread Starter
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I'll give that a whirl. What does that do exactly? I'll probably have to google how a master cylinder works (mechanically), but I assume its something akin to using a plunger on a toilet.



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post #4 of 39 Old 05-02-2016, 01:11 PM
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did you push the pistons back into calipers all the way before bleeding?

also i think there's a trick regarding the banjo bolt, i think you squeeze the lever, crack the banjo at the M/C loose, so it lets out any air, tighten it up and pump your brakes till firm. wait for a "+1" on that method though, not sure if i recall correctly.

i'm also curious what a failing M/C feels like though.

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post #5 of 39 Old 05-02-2016, 01:19 PM Thread Starter
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What do you mean by pushing the pistons back into the calipers before bleeding? The calipers and rotors are on the bike so I would assume that the pistons are in the correct place...

I'm finding LOTS of good information about M/C swaps, but I've got an unpopular GSXR non-radial/axial brake setup... so not much information about piston sizes and such. I'm sort of tempted to see if I could get a Hayabusa M/C to work since it's got a coffin style reservoir instead of the cup design.



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post #6 of 39 Old 05-02-2016, 02:02 PM
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Quote:
Originally Posted by crakerjac View Post
I'll give that a whirl. What does that do exactly? I'll probably have to google how a master cylinder works (mechanically), but I assume its something akin to using a plunger on a toilet.
Best answer I can give is a guess: when you put the fluid under pressure originally, the bubbles either get pushed down the line, which doesn't allow them out into the reservoir, or the extra pressure forces them into solution so they also cannot be let out. when leaving it overnight the bubbles precipitate out and rise to the top, and when you release the pressure they are sucked back into the reservoir where they can rise to the top and stay out of the line where they cause mushiness. A similar idea is behind the reverse bleed.

Either that or FM

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post #7 of 39 Old 05-02-2016, 02:17 PM
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Reading into it a little more seems like some people are of the idea that all this does is force the air bubbles into solution until you heat the fluid up (like during repetitive hard braking, the last place you want mushy brakes) and then the bubbles come out of solution and make everything mushy again. Hopefully Rob or someone will chime in that knows more than I do.

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post #8 of 39 Old 05-02-2016, 04:23 PM
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One sign is brake fade: if you pull the lever to engage the brakes it should stop at a certain point. If however you're sitting at a light with the lever pulled and you feel it moving toward the handle bar, then you either have a leak somewhere or your master cylinder is going bad.

If you do the rubber band method and wake up to the lever touching the handle bar, and are certain there are no leaks, then I would look into getting a new one.

Question: did you decide to bleed the brakes for maintenance or did you do that to try and fix an issue ??

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post #9 of 39 Old 05-02-2016, 04:26 PM
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Use it as an excuse to replace it with a proper aftermarket M/C

Once you install a Brembo aftermarket master cylinder like an RCS19 or even the older forged units you will never be satisfied with an OEM unit again.

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post #10 of 39 Old 05-02-2016, 07:26 PM
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I "reverse bleed" my front brakes for best results.
I made a cap that I can bolt to the reservoir that provides a vacuum port.
Pulling a vacuum on the master cylinder pulls the bubbles up working with gravity rather than trying to get them to exit the bottom via the bleeders.
I follow this up with a conventional bleed and do this pretty much every year in order to keep the junk out of the system.

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post #11 of 39 Old 05-02-2016, 07:28 PM
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Quote:
Originally Posted by LDH View Post
Use it as an excuse to replace it with a proper aftermarket M/C

Once you install a Brembo aftermarket master cylinder like an RCS19 or even the older forged units you will never be satisfied with an OEM unit again.
Interesting!
Any part numbers compatible with the 919 at hand?

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post #12 of 39 Old 05-02-2016, 08:33 PM Thread Starter
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So a little history on this basket case of a bike. From what I understand, it used to be an old CRA race bike. At some point, someone put USD forks on it from an 03 GSXR 750. The guy I bought it from was a track instructor and also raced SVs. He said he was selling his race bikes (2 SVs) because he lost his job and needed to get by... The first one he sold was his spares bike (that was actually wrecked this last weekend), then I came along and bought this one. I think he realized this bike was a mess and decided to cut bate. He claims he put an R1 master on it and said he couldn't get things working properly (whatever that means) so he switched back to the stock GSX-R master. When I bought the bike the guy said all it needed was a good bleed and everything would be fine.
It just dawned on me that I may have the wrong master... The bike has the wrong front wheel, so why not the wrong master as well...
@LDH, if you have a master that would work and the price is right, I'd be interested... But this is a old race whore that has been ridden hard and put away wet. Then I came along (story of my life)... So needless to say, I can't dump piles of cash into this mess of a bike.
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post #13 of 39 Old 05-03-2016, 09:39 AM
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Some R1's had 6 piston calipers so a master cylinder from one of those models might not work or feel as good on a 4 piston caliper set-up. That is also why I tell people to stop swapping one crap OEM part for another crap OEM part
http://www.rogueracing.org/zx10r/bremboanswers.htm

You can get a standard Forged Brembo 19X18 Master for like $250 shipped

I use them on every bike I own and prefer them over the latest and greatest Brembo RCS units




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post #14 of 39 Old 05-03-2016, 10:30 AM
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Regardless of the brand or style of master cylinder it should be possible to get the system bled out. It may not give the feel you want, but at least it will be possible to get a firm lever. If not, and there are no external leaks, the possibility of a defective primary seal. From your description of the symptoms (goes back to the grip initially, then gives a better feel when pumped up temporararily) there is air trapped somewhere that a conventional bleed cannot get rid of. Since there is no picture of it I have a question: where is the fitting on the master cylinder that connects to the reservoir? If it is at the front it will be difficult to bleed because the compensating port is not at a high point -- air will get trapped in the master and stay there. In this case loosen the master cylinder on the bar and rotate it upward until the fitting is at the top, tighten the clamp bolts down, then simply squeeze the lever. You should see air bubbles appear in the reservoir. This indicates where the problem is, and at this point simply retract the caliper pistons, forcing fluid and air back into the reservoir. Using this procedure usually results in a good firm lever.

I just remembered there is a recall of some GSXR master cylinders to address a symptom similar to what you describe. You may want to look into it.

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post #15 of 39 Old 05-03-2016, 10:33 AM
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Quote:
Originally Posted by robtharalson View Post
I just remembered there is a recall of some GSXR master cylinders to address a symptom similar to what you describe. You may want to look into it.

Rob

I had forgotten completely about that, mainly because I don't use OEM master cylinders, but you are 100% correct again!

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post #16 of 39 Old 05-03-2016, 12:07 PM
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Quote:
Originally Posted by LDH View Post
Some R1's had 6 piston calipers so a master cylinder from one of those models might not work or feel as good on a 4 piston caliper set-up. That is also why I tell people to stop swapping one crap OEM part for another crap OEM part
ROGUE RACING Brake Product Opinion

You can get a standard Forged Brembo 19X18 Master for like $250 shipped

I use them on every bike I own and prefer them over the latest and greatest Brembo RCS units



So would this be a drop in upgrade for most bikes? No (immediate) need for new calipers/pads/etc?

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post #17 of 39 Old 05-03-2016, 12:12 PM
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Quote:
Originally Posted by badmoon692008 View Post
So would this be a drop in upgrade for most bikes? No (immediate) need for new calipers/pads/etc?
For 90% of the bikes on the road using dual 4 piston calipers the 19X18 is a drop in upgrade and standard practice for any seasoned racer or trackday junkie.

There are some exceptions where a different master cylinder ratio is required like a 19X20 and the new Brembo M50 calipers used as OEM fitment on the newer Duc's Aprilia's and Gen5 ZX-10 require a 17mm piston in the form of the RCS17 to get an improvement, but yes you can always install a better master cylinder without changing other components of the braking system as long you match the new master to the components you already have.

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post #18 of 39 Old 05-03-2016, 01:36 PM
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Quote:
Originally Posted by crakerjac View Post
What do you mean by pushing the pistons back into the calipers before bleeding? The calipers and rotors are on the bike so I would assume that the pistons are in the correct place...
squeezing the lever pushes the pistons out of the caliper, against the brake pads, which push against your rotor. over time, your brake pads wear down, but your pistons never retract. so when you are going to bleed your brakes, you should always prise the pads away from the rotor and push them into the caliper as far as they will go. the fluid that is at the pistons is probably the dirtiest because it's at the bottom and the area filled with fluid as the piston is pressed towards the rotor can keep bubbles held up.

so unbolt your calipers from the fork, prise the pads apart, use a clamp or something and squeeze the piston/pad back in to the housing. Then bleed your brakes. if you don't replace your pads you'll need squeeze the lever a bit to get the pads up against the rotor again, but then you should get a firm lever.

The above is always a good practice. however based on Rob and LDH it sounds like you better investigate that recall, maybe bleeding them again would be pointless anyways. good luck!

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post #19 of 39 Old 05-03-2016, 01:51 PM
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Since we are discussing such things it is also important to note that as the seals in calipers get old and dry out they will shrink. This can cause the pistons to retract further than normal and when you go to squeeze the lever you then have to push more fluid to get the pistons to push out further to compensate. What you end up with is a feeling that when you first squeeze the lever you have to make more effort to get the pads to contact the rotor. Sometimes even a double squeeze which get the pads closer to the rotor and then you usually have better feeling at the lever for awhile or until enough time has passed to allow the pistons to fully retract again.

Sometimes when this happens you can use a special grease to remedy it, but usually it requires new seals...

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post #20 of 39 Old 05-03-2016, 09:38 PM Thread Starter
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All of this is good info. I'm stuck in St Louis for a couple days on business, but when I get home it looks like I'll try bleeding the brakes again with the M/C rotated and calipers pulled off the bike. I'll see if I can get a look at what the outer seals looks like... If they look bad, I'll see if I can replace them.
I looked into the recall and it looks like my M/C isn't part of that. The recall notice I saw was 04-13 which would make them radial masters.

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post #21 of 39 Old 05-04-2016, 02:31 AM
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"The recall notice I saw was 04-13 which would make them radial masters."

Yes, I was going to point that out too, but couldn't see in your thread where you said if yours was axial or radial.

I fitted a radial one from the recall period to my 9'er so took a bit of interest in the nature of the recall. Apparently, it was about some kind of coating on the piston that didn't take kindly to old fluid and would react with it in some way over time, creating bubbles and a spongy lever as a result.

Mine's been good, but a future rebuild kit will stop me even thinking about it.

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post #22 of 39 Old 05-04-2016, 05:42 AM
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Very similar to warped rotors also. Rotors with too much run-out will push the pistons back. Initial squeeze on the lever has to get them back up against the rotor before the braking starts.



Quote:
Originally Posted by LDH View Post
Since we are discussing such things it is also important to note that as the seals in calipers get old and dry out they will shrink. This can cause the pistons to retract further than normal and when you go to squeeze the lever you then have to push more fluid to get the pistons to push out further to compensate. What you end up with is a feeling that when you first squeeze the lever you have to make more effort to get the pads to contact the rotor. Sometimes even a double squeeze which get the pads closer to the rotor and then you usually have better feeling at the lever for awhile or until enough time has passed to allow the pistons to fully retract again.

Sometimes when this happens you can use a special grease to remedy it, but usually it requires new seals...
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post #23 of 39 Old 05-31-2016, 06:42 PM Thread Starter
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So, with good seals, I should be able to squeeze the brake lever and the pads will make contact with the rotors. When I let off the lever, the pistons retract a smidge (very technical term, I know). If my seals are bad, the pistons would retract more on their own? If so, how much? Enough to let the pads rattle around?

Now I'm not so sure it's the M/C that's bad. What LDH said about the 2 pumps to get a firm lever seems closest to what I have going on... That and I think I have air trapped at the top banjo fitting as Rob mentioned.

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post #24 of 39 Old 05-31-2016, 06:59 PM Thread Starter
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Pictures if it helps... Not sure what everyone/anyone is looking for...





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post #25 of 39 Old 06-02-2016, 07:04 PM Thread Starter
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So... $30 for a rashed 19x18 Brembo M/C is probably too good to be true... But for $30 it's worth a shot...



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post #26 of 39 Old 06-06-2016, 08:37 AM
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Holy crap... deal of the century if it's not majorly horked or a bad knock off

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post #27 of 39 Old 06-06-2016, 08:50 AM Thread Starter
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Yup. First step is to verify it's genuine (maybe by running the serial #) and check to see if it holds pressure. If I find it's boned or not genuine, I'll go from there...

However, I did get all the squishy out of my current master over the weekend... I now have a nice firm lever. Just in time to swap masters.

Does anybody know if banjo bolts are fairly universal? I'm wondering if I could use the GSXR banjo from my master in the the Brembo lever...



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post #28 of 39 Old 06-06-2016, 08:56 AM
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Most OEM non-Brembo M/C's use 1.25 thread pitch while Brembo uses a finer 1.0

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post #29 of 39 Old 06-06-2016, 09:11 AM Thread Starter
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Quote:
Originally Posted by LDH View Post
Most OEM non-Brembo M/C's use 1.25 thread pitch while Brembo uses a finer 1.0
Good to know. Thanks for the heads up!

New MC should be here today. Once I give it the old once over and make sure nothing is obliviously wrong, I'll fire off a PM for a quote on some parts (I assume you have/sell Brembo stuff). Looks like I'll need a new banjo, bleeder valve and possibly a reservoir nipple (assuming there is no reason why my GSXR reservoir wouldn't work).



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post #30 of 39 Old 06-06-2016, 01:32 PM
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what solved your squishy lever?

(idk why but makes me giggle)

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post #31 of 39 Old 06-06-2016, 02:44 PM Thread Starter
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I strung the clip-on from a ladder and made sure that there was an upward path for bubbles to reach the reservoir (I can take a picture if you want). I zip tied the lever for a day and every time I walked past the bike, I gave each brake line and the MC a couple of good flicks. The next day, I removed the zip tie and flicked the brake parts every time I walked past the bike. Went back and forth a few days and it feels like I have worked all the air out of my system.

I think my problem is that my clipons angle my MC and brake lever in a downward angle... I think this was creating a high spot at the banjo bolt and wouldn't let me get the air out of my system (as seen below)



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post #32 of 39 Old 06-15-2016, 03:55 PM
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Did you change brake levers by any chance? I had some problems time ago when i changed my levers, and in the end it turned out that it was the lever touching too much the master cylinder

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post #33 of 39 Old 06-15-2016, 10:38 PM Thread Starter
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I just said f* it and installed a Brembo. It's a bit of a cluster fuck because I don't have a good way to mount my reservoir and it took some 'imagination' to get my lines to mount up, but it's there... All it needs now is a good bleed (hopefully) after I run to the hardware store to replace a nut I dropped in the motor.
I have a feeling I have opened a whole bucket of worms with this M/C swap.
More to come.

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post #34 of 39 Old 06-17-2016, 08:24 AM
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Quote:
Originally Posted by Avispao View Post
Did you change brake levers by any chance? I had some problems time ago when i changed my levers, and in the end it turned out that it was the lever touching too much the master cylinder
you mean the lever was constantly pushing in to the brake master?

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post #35 of 39 Old 06-17-2016, 08:35 AM
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hope the brembo helps. i saw a post in trackday junkies the other day about a gsxr with a brake pressure issues. i was reading it to see if something came up that could help you.. but i can't find it now.. it seemed that recommendations were all over the place but a few people said they still had issues even with the brembo. i think that guy said he replaced the lines and then it worked. others talked about replacing calipers but i forget what they switched to.

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post #36 of 39 Old 06-17-2016, 08:45 AM Thread Starter
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Yeah. I'm hoping the Brembo works... I've had the bike at the track and the after hanging the brakes upside down, they worked alright. I just didn't like that if I did the two finger brake grab, I'd smash my other two fingers even with the adjuster all the way out.

All I have to do is bleed my dry system. I might see if I can borrow a MityVac and see how that works. I just don't want to buy one and it not work for me.



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post #37 of 39 Old 06-19-2016, 04:19 AM
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Quote:
Originally Posted by CKutz_GO View Post
you mean the lever was constantly pushing in to the brake master?
That's it.

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post #38 of 39 Old 06-20-2016, 07:33 AM
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@crakerjac - I just installed stainless lines on my 919 and I'm really happy with the bleed job i did on them. I think the mity-vac sucks (not in a good way) but maybe i was a bit more inexperienced when i used it. Also worth noting, i'm pretty sure i put teflon tape on my bleed screws threads. When I first used it, it just pulled in air bubbles from the threads or around the bleed screw.. it seemed way more complicated than it should be.

Having all the tubing attachments from the mity-vac was actually the most useful thing to me.

Here's what I do.

-Find a big syringe. Tractor Supply, or similar animal care places might have them. Walmart might even, i forget. It should be about 40 mL but it's not critical. The tip of mine fits nicely on to aquarium airline tubing. I'll have to measure ID when I get home.
-An attachment to go from the size tubing that fits the syringe tip, to the size that fits a bleed screw. Clear Fuel line tubing fits 1/4" i think but it's a little loose - won't leak air but it will pop off the bleed screw easily. Alternatively you can use the small airline tubing and stretch the end with a needle nose pliers so it fits over the bleed screw but it can be aggravating. Use about 3 ft of line so you can move around without pulling it off the bleed screw.
-brake fluid

-Start by compressing the pistons into the calipers, you may need to remove fluid from the reservoir to do this.
-If there's brake fluid in the system, suck it out of the reservoir and if you want you can attach the syringe to the bleed screw and suck it out of the line. you can leave it, you'll just have more old fluid to suck out of the reservoir before the new fluid fills the line. I did this with dry lines and i'm happy with the results.
-Attach syringe and line to bleeder.
-Fill syringe with brake fluid. elevate so the fluid runs down to the bleed screw (easier with 1/4" tubing than the tiny tubing). you don't need to fill the whole line with fluid, in fact it's probably easier if you don't. So the syringe can be detached when you need to suck fluid out of the reservoir.
-You'll want to have the handlebars turned in a way that makes your reservoir higher than the banjo bolt.
-crack open the bleed screw and slowly inject brake fluid. it helps if you have another set of eyes to tell you when the fluid comes out the reservoir because you'll probably have your eye on the bleed screw to make sure you don't inject air and aren't leaking fluid everywhere.
-Once new fluid is filling up the reservoir switch to the other caliper.
-repeat the injection processs. Once fluid is filling the reservoir start working the fluid both ways. inject it from the syringe, and push it back down from the lever. you can leave the bleed screw open during all this. the idea is to just work the fluid back and forth in the system to try and move any air bubbles.
-Repeat the back and forth process on the other caliper.

I figure if you can move enough fluid back and forth (it really doesn't take much to fill the lines) and have no air bubbles coming out either end you should be good.

I did this with the rear brake also, however because it looks like the banjo is higher than the bleed screw i filled up the reservoir with new fluid. Attached the syringe to the bleed screw. Applied vacuum. and crack open the bleeder, keeping an eye on the fluid level in the Res. inject it back in if it gets dangerously low.

you'll always want to have the wrench for the bleed screw handy so you can close off the bleed screw if you ever need to abruptly stop fluid flow to avoid sucking in air.
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post #39 of 39 Old 06-20-2016, 09:19 AM Thread Starter
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Thanks @CKutz_GO, I've got a smaller syringe that will fit with my clear bleeder tubing, it only 15ml, but it was free... so yay. I was going to bleed the brakes last weekend, but things got away from me with fathers day and all. I'm hoping to tackle it this week so I can get back on the track next weekend.



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