Author Topic: Front Brakes keep getting air in the system  (Read 583 times)

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Offline Russ

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Front Brakes keep getting air in the system
« on: March 25, 2020, 08:49:23 pm »
The bike is a 2008 non abs with about 44K miles on it.

A few years ago I changed the brake fluid all the way around and now if the bike sits for more than a few weeks, it gets air in the front brakes.  There are no fluid leaks and I havent changed the pads yet. 

The last two times I've re-bled it, I found most of the air at the master cylinder bleeder.  Since I'm not the best at bleeding brakes (Although I'm getting much better..) I bought a Motion Pro Easy Bleed Brake Bleeder and just got done bleeding them again.  I noticed as I bled them that I had a little bit of air in the left caliper, no air in the right, and a $41t ton of air in the master cylinder.  I also noticed that when the lever got tight, it started to kinda bind - It isnt smooth operating and clicks when pulling it back.

I was going to change the brake lines with some trick Galfers but after reading an old thread here, I may need a new master cylinder.  With the age of the bike, I'm tempted to change the lines anyway. 

I can take some video of lever depression.  The Motion Pro Easy Bleeder is a great tool to have - I recommend it. 

Should I replace the master cylinder? Brake Lines?  Both??  Thanks in advance.

Russ

08 C14
SOLD - 05 Victory Ness Vegas, 06 KLR650, 04 VT1100 Spirit, 01 VT750 ACE, 1986 VFR750F, 1991 CBR1000F
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Offline Syxxphive

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Re: Front Brakes keep getting air in the system
« Reply #1 on: March 25, 2020, 09:04:19 pm »
Rebuild/replace the master cylinder. It’s toast.

Offline Russ

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Re: Front Brakes keep getting air in the system
« Reply #2 on: March 25, 2020, 09:24:34 pm »
Rebuild/replace the master cylinder. It’s toast.

Looks like Murphs Kit's carries the rebuild kit - cheap too - I'll try it.

Thank You

08 C14
SOLD - 05 Victory Ness Vegas, 06 KLR650, 04 VT1100 Spirit, 01 VT750 ACE, 1986 VFR750F, 1991 CBR1000F
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Offline SteveJ.

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Re: Front Brakes keep getting air in the system
« Reply #3 on: March 26, 2020, 02:12:23 am »
Rebuild/replace the master cylinder. It’s toast.

Looks like Murphs Kit's carries the rebuild kit - cheap too - I'll try it.

Thank You

A few years way too long to go without flushing the fluid, especially iffin' you are on the wet side. As long as you now have that fancy bleeding kit use it to purge new fluid in the clutch system while you are alredy playing with brake fluid.
Yeah, if you want true ram air tuning, you better be willing to ram some air! (SiSF)
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Offline Russ

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Re: Front Brakes keep getting air in the system
« Reply #4 on: March 27, 2020, 04:35:13 pm »
Rebuild/replace the master cylinder. It’s toast.

Looks like Murphs Kit's carries the rebuild kit - cheap too - I'll try it.

Thank You

A few years way too long to go without flushing the fluid, especially iffin' you are on the wet side. As long as you now have that fancy bleeding kit use it to purge new fluid in the clutch system while you are alredy playing with brake fluid.

We live and learn....  I changed the clutch fluid out last year - I think the rear brake was done two years ago.

I've been using Prestone DOT 4 Synthetic but is there a better fluid?

I've been under the impression that the DOT 4 fluids all meet the same standard. 

08 C14
SOLD - 05 Victory Ness Vegas, 06 KLR650, 04 VT1100 Spirit, 01 VT750 ACE, 1986 VFR750F, 1991 CBR1000F
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Offline Russ

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Re: Front Brakes keep getting air in the system
« Reply #5 on: March 30, 2020, 11:13:54 pm »
I just learned the hard way...

Look closer when ordering parts...  I have a rebuilt kit for a Concours, not a Concours 14   :))

Amazon Prime to the rescue - K&L 232-0855 (Murph doesn't carry this as far as I can tell)

Oh well...  It'll be here Friday

08 C14
SOLD - 05 Victory Ness Vegas, 06 KLR650, 04 VT1100 Spirit, 01 VT750 ACE, 1986 VFR750F, 1991 CBR1000F
AMA# 2794531

Offline MAN OF BLUES

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Re: Front Brakes keep getting air in the system
« Reply #6 on: March 31, 2020, 02:10:09 am »
before you spend mega $$ on new lines, or a master cylinder... spend a couple bucks... replace all the bleeder fittings on that circuit, with new ones.. think logically.... the Only way AIR can actually enter the system... ain't the master cylinder "guts",.. but likely thru a bad seal on a line / banjo bolt, or the actual bleeder valve fitting..
yes, you find air at the master bleeder.. well, air RISES up to that point, and is stopped..
I am amazed at times, the way people toss out the simplest check points, and say to buy a new major component, but I do understand, as the comprehension level of many that don't really work on, or see these issues will suggest.... some times the most simple little $1 part, is the cause. Start with the simple, and progress from there.. ( a funkey piston in a filled reservoir, like a master cylinder, does not let air in.. because the master is filled with fluid..) it may not effectively push fluid, but it's not the point of air ingress. If air is in the bleeder there, it didn't come from the fluid filled reservoir...  :-[ :-[  again, bleeder valve, or compromised line seals..
Now, back to the AIR issue; the only other way air can be drawn into the system, is thru a malfunction of a stuck/dirty/crusty caliper piston, that refuses to "slide back as the lever pressure has been released", thus the piston and is stuck by a ring of crud, extended, and can't retract, the piston's seal is now under vacuum, and will allow a slow ingress of air (piston seals work great on fluids, not so great on air.. when in a vacuum situation)

so basically It's a scrub the pistons when extended, using brake cleaner and a toothbrush, then pushing them in a bit to expel fluid back up to the master, replacing the bleeders, all of them, and flush and fill, and re-bleed... manually.
I am not a fan of the vacuum bleeding systems, I know they work, but when dealing with variables of seals, and contamination, I see them as being able to create a false positive, and have actually seen master cylinder cup seals, deformed from incorrect usage. I've dis assembled many, and found that on some, even questionable seals may have worked fine for years to com, but when subjected to the vacuum at high levels, would cause compromise, and failure, to necessitate replacement after being subjected.

best of luck, start simple, be careful, and let us know the outcome.
« Last Edit: March 31, 2020, 02:41:50 am by MAN OF BLUES »

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and if you are gonna call me names... it's MR. Analdweeb if you please...

Offline Russ

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Re: Front Brakes keep getting air in the system
« Reply #7 on: March 31, 2020, 05:35:50 pm »
before you spend mega $$ on new lines, or a master cylinder... spend a couple bucks... replace all the bleeder fittings on that circuit, with new ones.. think logically.... the Only way AIR can actually enter the system... ain't the master cylinder "guts",.. but likely thru a bad seal on a line / banjo bolt, or the actual bleeder valve fitting..
yes, you find air at the master bleeder.. well, air RISES up to that point, and is stopped..
I am amazed at times, the way people toss out the simplest check points, and say to buy a new major component, but I do understand, as the comprehension level of many that don't really work on, or see these issues will suggest.... some times the most simple little $1 part, is the cause. Start with the simple, and progress from there.. ( a funkey piston in a filled reservoir, like a master cylinder, does not let air in.. because the master is filled with fluid..) it may not effectively push fluid, but it's not the point of air ingress. If air is in the bleeder there, it didn't come from the fluid filled reservoir...  :-[ :-[  again, bleeder valve, or compromised line seals..
Now, back to the AIR issue; the only other way air can be drawn into the system, is thru a malfunction of a stuck/dirty/crusty caliper piston, that refuses to "slide back as the lever pressure has been released", thus the piston and is stuck by a ring of crud, extended, and can't retract, the piston's seal is now under vacuum, and will allow a slow ingress of air (piston seals work great on fluids, not so great on air.. when in a vacuum situation)

so basically It's a scrub the pistons when extended, using brake cleaner and a toothbrush, then pushing them in a bit to expel fluid back up to the master, replacing the bleeders, all of them, and flush and fill, and re-bleed... manually.
I am not a fan of the vacuum bleeding systems, I know they work, but when dealing with variables of seals, and contamination, I see them as being able to create a false positive, and have actually seen master cylinder cup seals, deformed from incorrect usage. I've dis assembled many, and found that on some, even questionable seals may have worked fine for years to com, but when subjected to the vacuum at high levels, would cause compromise, and failure, to necessitate replacement after being subjected.

best of luck, start simple, be careful, and let us know the outcome.

While not replacing the master cylinder makes sense - this problem doesn't make sense....  There are no fluid leaks - It's air getting in while it sitting.  I'd think that if a bleeder is letting air in, I'd assume that it would probably let fluid out.  None of the banjo's have ever been loosened, only the bleeders - I ordered a speed bleeder kit from Murphs.  The Master Cylinder seems a bit crunchy, I'll change the piston out in that. 

I dont agree with you on the calipers - I've never changed the pads, and they've never been reset.  It's supposed to be a closed system - no fluid out and no air in.  There are seals in the Master Cylinder that can leak - not sure how they'd get air in them, but I've been wrong before.  I've never seen a caliper (On a car) that leaked air in but wasnt leaking fluid out.  Had plenty of them that leaked fluid that were not leaking air in.  This issue started when I changed the fluid for the first time - through the bleeders.  Of course, I've had the calipers off of the rotors to change tires many times but I've never had to reset them to get them back on - and never pushed all the crud across the dust seals of the calipers. 

Not a fan of vacuum bleeders either - been there, tried that, never works.  I've got a pressure pot for the cars and boat trailer but I do the motorcycles the old fashioned with but using a check valve.

Thanks for your thoughts and opinions - It did spur me into changing all of the bleeders!! :) 

08 C14
SOLD - 05 Victory Ness Vegas, 06 KLR650, 04 VT1100 Spirit, 01 VT750 ACE, 1986 VFR750F, 1991 CBR1000F
AMA# 2794531

Offline MAN OF BLUES

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Re: Front Brakes keep getting air in the system
« Reply #8 on: March 31, 2020, 08:12:01 pm »
I understand your skepticism on the explanation I gave about fittings, but please trust me on that; air is much easier to flow thru a threaded or compressed sealing surface, than the fluid it was designed to seal. Simple physics, air molecules are smaller, and much more difficult to seal than a liquid.

To show this further, when you receive your new speed bleeders, note that the threaded portion has a coating of sealant, located further up on the threaded section; this was added as a revision to the design, about 10 or more years ago, prior to that, the fittings had no sealant. Fact is, they found, thru repeated reports, that when using speed bleeders with a vacuum bleeding system, air would be sucked in along the pathway of the physical threads, giving the appearance there was more "air" in the fluid than was actually there: and when the valve was tightened, it did not seal "as well". People began "adding" things like "Teflon tape", in attempts to provide a better "air prevention" blocker to reduce that effect, but doing so, can and did end up with people having issues with small fragments of that tape, getting into the system.. not ideal.
They then found an alternative type of semi-hard sealant, and thus it is used today.

I wish you the best, and think when you go over the possible fittings, and insure they are tight, and replace those bleeders, you will be on the right track.

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW
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Offline TireguyfromMA

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Re: Front Brakes keep getting air in the system
« Reply #9 on: March 31, 2020, 11:16:35 pm »
+1 on what MOB described.  I was trying to bleed some brakes with a mighty-vac unit.  I'd pump up the mighty vac, crack open the OEM bleed valve and would see a stream of tiny bubbles come up in the clear tube.  Kept thinking the brake lines had air in them but no matter how much I bled those brakes I would still see air in the tube.  Decided to remove the OEM bleed valve and switch over to Speed Bleeders.  When I removed the old bleeders the threads were almost bare. Put the speed bleeders in and boom the air was gone from the tube after the second time I opened the bleed screw.  I also purchased a bottle of the gray colored thread sealant they sell and have fixed the same problem on a couple of bikes by putting new thread sealant on the bleeders.  I also use the little check valve bleeder from Motion Pro tools, just like Fred Harmon does when he bleeds...works great.
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Offline Russ

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Re: Front Brakes keep getting air in the system
« Reply #10 on: April 01, 2020, 12:45:33 am »
I've never vacuum bled the brakes on the bike - I tried to vacuum bleed brakes on a boat trailer with surge brakes and could see the stream of bubbles coming from the bleeder screws - you could suck a gallon of fluid through them and see air the whole time - I know what you are saying. 

I can get all of the air out of the front brakes now - I'll replace the copper washer on the master while I'm rebuilding it.

Thanks again!

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Offline laker9142

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Re: Front Brakes keep getting air in the system
« Reply #11 on: April 02, 2020, 06:06:01 pm »
My 2 cents on vacuum bleeders is that they work wonderfully. I've been using one for the last 12 years. I've used it probably 30 times on my bike and others and never had a problem of any kind. Mine is made by might vac and ordered off amazon 12 years ago for $80. Its powered by compressed air, not the hand pumped unit.

The bubbles you see are coming from around the bleeder nipple threads and go straight into the vacuum bleeders waste container, not into the hydraulic system. I just used it on my clutch system that was completely empty due to rebuild of master and slave cylinders. I filled the master cyl reservoir twice and had perfect lever feel.

I've never used a push type bleeding system, but have always wondered how they keep the air from entering the system from around the threads of the nipples.

Offline Russ

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Re: Front Brakes keep getting air in the system
« Reply #12 on: April 03, 2020, 02:16:20 pm »
Got a new K&S Master Cylinder Kit from Amazon - and it was correct!

Rebuild was pretty easy - the master cylinder was definitely toast.  It was full of brake fluid behind the dust seal - where I think it probably ought to be dry.  I'm not sure why it wasnt leaking there, the actuator rod  goes right through it.  Speed Bleeders should be here today.  Weather is supposed to warm up next week - maybe I'll defy the gov and take it out for a test wheelie..
« Last Edit: April 03, 2020, 05:21:41 pm by Russ »

08 C14
SOLD - 05 Victory Ness Vegas, 06 KLR650, 04 VT1100 Spirit, 01 VT750 ACE, 1986 VFR750F, 1991 CBR1000F
AMA# 2794531