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Need help removing trapped air in master cylinder.

KEITH KRAUSE

KEITH KRAUSE

Forum Guru
Past Site Supporter
TGSR Superstar
Charter Member
Hope you guys can help me. This is actually the clutch master cylinder on a ZX14 (hydraulic clutch). But it's the same basic principles as a braking system master cylinder.
I was changing fluid and screwed up and allowed the reservoir to get too low and sucked some air into the M/C. Now I've got a little play in the lever that shouldn't be there. I've tried the basic bleeding method (pump/squeeze/crack open/close/release until I'm blue in the face. All I get is fluid and no bubbles. I bought a Mityvac and hooked it up but it can't pull out the trapped air either. I DO know how to bleed but I'm getting nowhere.
Apparently this M/C would be very messy and difficult to try removing the banjo fitting and doing a compromised bench bleed while mounted on the bike. That method worked well on my GS once but the 14's M/C has a bleed valve mounted on it so I think removing the banjo is pointless.
I've tried everything I know.
Maybe someone here knows a method that works well for TRAPPED air? I know there's air in there but I can't move it. If I have to I'll even buy a bleed tool/equipment if I know it will work in this case. Maybe one of those bleeders that uses a compressor or?
Any tips appreciated.
 
Well I've never had a hydraulic clutch but the following worked for me on my brakes. Opened the reservoir - pumped and bled into the vac till it came out solid at the bleeder then compressed and then manually pushed the pistons back in as far as I could - then bled again - repeat if necessary. Then put a zip tie on the handle and leave it overnight compressing- should make all the bubbles float up and out.

Good luck - not sure about the clutch though. Can you get to the pistons?
 
Thanks for the replies.
DCrippa, I've heard of tie-strapping the lever to the grip but never tried it.
Do you think compressing the piston assembly could cause any trouble with sagging the small spring inside? I'm not sure the spring can handle being compressed that long, though I haven't heard of any complaints and I know many owners have tied down their levers.
I appreciate the help.
 
Keith, sometimes it's best to work backwards by forcing fluid from the slave cylinder back up to the m/c. The air isn't fighting gravity then.

This works really well when bleeding dual front brakes. Just make sure you don't spill fluid on your paint.
 
49er said:
Keith, sometimes it's best to work backwards by forcing fluid from the slave cylinder back up to the m/c. The air isn't fighting gravity then.

This works really well when bleeding dual front brakes. Just make sure you don't spill fluid on your paint.
Click to expand...

Ian, can I have an explanation on how you force fluid from slave cylinder/caliper back up into the master cylinder. I've just fitted a ZX10 m/c to my 550 and I too have bled the crap out of it, but still feel there is a bit too much movement in the lever before the brakes 'come on'. I have loosened the banjo bolt where it holds the two lines to the m/c and with a piece of rag soaking up the fluid as it comes out bled the m/c that way. Still think there could be some air in there though.

Thanks Mate.
 
Keith I'm sure you're aware and have broken the manual out but if it's anything like my ZRX it has a bleeder valve on the slave cylinder as well. This is all new territory for me as well, as the slave is attached to the CS sprocket cover and requires removal for changing the CS sprocket. Pita. But fortunately they've put that bleeder valve there to ease bleeding. I think another poster mentioned forcing air up thru the slave cylinder will help push air out as well. I'm guessing that can be done by feeding fluid via the bleeder valve? Or maybe pulling the slave and priming it first? I'll be watching this as I will have to disassemble mine fairly soon for R&R... I'm learning with ya!
 
Yeah the tieing the lever back works great in desperate times. Just make sure everything is set so air will flow up and out. Might mean leaning the bike againt a wall with the handle bars turned to the right overnite.
 
Suzuki_Don said:
Ian, can I have an explanation on how you force fluid from slave cylinder/caliper back up into the master cylinder. I've just fitted a ZX10 m/c to my 550 and I too have bled the crap out of it, but still feel there is a bit too much movement in the lever before the brakes 'come on'. I have loosened the banjo bolt where it holds the two lines to the m/c and with a piece of rag soaking up the fluid as it comes out bled the m/c that way. Still think there could be some air in there though.

Thanks Mate.
Click to expand...

Don, all you do is loosen off the banjo nut on the master cylinder, then fit a clear hose over the bleed nipple on the caliper, open it and force brake fluid into it. Keep forcing the fluid upward until it reaches the master cylinder with no air coming through. Now close the nipple and change to the other caliper and repeat the process. You will need plenty of rags to prevent brake fluid from reaching your paint work though.

Once the air has stopped flowing through the banjo, tighten it up and try your
brake lever. With light pressure on the lever, crack the banjo to expel any small air pocket on the m/c side of the banjo. Now re-tighten the banjo.You should now have no air in the system and have a good firm feel to the lever.

This system should work on Keith's clutch too.
 
Ian what do you use to force the fluid into the caliper nipple with?
 
Suzuki_Don said:
Ian what do you use to force the fluid into the caliper nipple with?
Click to expand...

Don, I use a plastic squeeze bottle, with a tapered nozzle that I slide the hose over. The hose must seal well there and on the caliper nipple too.

Make sure its a tight fit before gently squeezing the fluid from the bottle. Lock the nipple prior to releasing the pressure on the bottle, or you will draw air back down the brake line.

You can buy pumps that will do the same job too.
 
Is the master cylinder at a slight angle, with the banjo a bit higher? :-k

I know you said it would be hard to do the "bench bleed", but sometimes there is a bubble trapped in that upper corner. Can you remove the brake lever and push the piston ALL the way in with a screwdriver or dowel rod? It is usually possible to push the piston farther that way, which will get rid of that pesky bubble.

.
 
Suzuki_Don said:
Ian what do you use to force the fluid into the caliper nipple with?
Click to expand...

You can also use a medical syringe. They have a tapered point where the injection needle fits onto, and if you use a tube with a small enough opening, it fits very snugly. The larger syringes have 50 - 100 ml capacity, which unfortunately is less than the squeeze bottle volume.
 
Turning the handlebar until the outlet from the cylinder is at the highest point, as well as tapping the cylinder lightly with a piece of wood or rubber may help to dislodge an air bubble "stuck" somewhere, and allow it to rise towards the highest point, and hopefully down the hose.
 
Thanks a lot for the help. I'm out the door so can't give detailed reply but I'll check in later. Again, thanks!:)
 
Steve said:
Is the master cylinder at a slight angle, with the banjo a bit higher? :-k

I know you said it would be hard to do the "bench bleed", but sometimes there is a bubble trapped in that upper corner. Can you remove the brake lever and push the piston ALL the way in with a screwdriver or dowel rod? It is usually possible to push the piston farther that way, which will get rid of that pesky bubble.

.
Click to expand...
If I have to try bleeding at the banjo, this one would be difficult. Three hands needed. My banjo is directly on the bottom of my M/C and the clip on type bars close to the tank/bodywork. Trying to use your finger/thumb on the banjo hole and pump the lever and watch/refill the tiny reservoir level wouldn't be easy. I'll try it as a last resort but will maybe try 49er's method or even buy a pump style tool. My Mityvac (model MV8020) is near useless in my opinion.
What I'd like to try first is tying the lever back over-night but I'm trying to ask others if that could damage any small/fine spring inside. Probably not as I've heard others tying back to remove trapped air and never heard them say they damaged the spring and how the M/C piston rebounds. I just want to be sure.
If that doesn't work then I'd like to take the lever off and try manually pushing the piston assembly further in than the lever does. This MIGHT squeeze the trapped air out. But again, I need to ask how safe that method is. I'm not going to cram the piston in real hard, just poke it in until I feel obvious resistance that tells me to stop. I just don't want to push it in and find out I screwed something up by doing that. I don't need to add problems.
 
Keith, with this being a clutch lever, does the lever come all the way into the handlebar the same as a cable type lever does. And if so then there is a difference here in cable tying the lever to the handlebar.

When you cable tie the brake lever to the handlebar, the lever only comes in about halfway to the handlebar until the pressure builds up in the system and the lever reaches that position. But if the clutch lever comes all the way to the handlebar then I am unsure if this will create enough pressure to remove the bubble in the system.

I don't know whether this will cause a problem or not.
 
Suzuki_Don said:
Keith, with this being a clutch lever, does the lever come all the way into the handlebar the same as a cable type lever does. And if so then there is a difference here in cable tying the lever to the handlebar.

When you cable tie the brake lever to the handlebar, the lever only comes in about halfway to the handlebar until the pressure builds up in the system and the lever reaches that position. But if the clutch lever comes all the way to the handlebar then I am unsure if this will create enough pressure to remove the bubble in the system.

I don't know whether this will cause a problem or not.
Click to expand...
Good thought Don. I'm so thinking the clutch and braking systems are alike but that IS one difference. The hydraulic clutch doesn't continue to build that pressure the more you squeeze the lever like the brake. It does pump up but you can easily pull it to the grip which is how it's used in operation. Can't do that with a properly operating brake.
I'll probably still try it since others say there's no danger of damaging something in the piston assembly. But now I have less faith it will work.
I appreciate the help.
 
sharpy said:
Yeah the tieing the lever back works great in desperate times. Just make sure everything is set so air will flow up and out. Might mean leaning the bike againt a wall with the handle bars turned to the right overnite.
Click to expand...
Someone at a ZX forum mentioned the same thing about leaning the bike to the right. I haven't tried it but this bike seems like it would be difficult to lean. The bars don't stick out much beyond the bodywork and the mirrors stick way out. The mirrors don't like to be tampered with I've heard. They lose their ability to stay tight but still be adjustable.
I appreciate the help. I'll see about leaning it. If I can do it safely I'll give it a try.
 
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