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Bleeding Jamar finger brakes

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rob(at)Neils.US
Guest

Posted: Sat Dec 29, 2007 12:49 pm Post subject: Bleeding Jamar finger brakes

I’m having a devil of a time with my Jamar finger brakes in my 

tri-gear motorglider.



I can only bleed the brakes when the master cylinders are oriented 

vertically with the back of the Jamar master cylinders higher than 

the front.  As soon as I mount the brakes horizontally, they no 

longer bleed – after one effective stroke the lever no longer pumps 

brake fluid.



Here’s some data which may help you help me get this problem solved:



I’m using DOT 5 brake fluid.



I mount a reservoir filled with brake fluid about 9 inches above the 

master cylinders.



The Jamar squirts fluid from both sides when the levers are pulled 

back while he Jamar master cylinders are horizontal on my bench and 

when mounted horizontally in the plane.



When the Jamar is mounted in the plane and the brake lines are 

disconnected from the ends of the master cylinders then the cylinders 

squirt brake fluid when the levers are pulled back.  However as soon 

as I connect the brake lines from the cylinders to the brakes, the 

brakes don’t work.  (This makes me suspect the problem is in the 

brake lines – probably air bubbles.)



When one side is working and the other side isn’t, if I disconnect 

the brake lines and switch the line which isn’t working to the side 

which does work, then that the side which didn't work now does and 

the other doesn't.  (I therefore again suspect the problem is in the 

line rather than in the Jama but I could very well be wrong.)



I bleed the brakes in two different ways.  The first way I connect a 

clear tube filled with brake fluid with no bubbles to the brake 

nipple.  I open the nipple and, using about 20# of air pressure, blow 

brake fluid up the brake line to the Jamar.  I have loosened the 

brake line connection at the master cylinder and watch the brake 

fluid leak out.  At first I get bubbles, then, when only brake fluid 

is leaking, I tighten the connection at the master cylinder and close 

the nipple.  The Jamar system then works.  The brake lever is not at 

all spongy.  However, over a long period of time with many 

applications of the brakes, the lever must be pulled further and 

further back and the brakes get spongy, needing bleeding.



The second way I bleed the brakes is by pulling back on the brake 

lever while both connections (the brake line to the master and the 

brake line to the brakes) are tight.  When pressure builds on the 

lever, I loosen the nipple and brake fluid gushes out the nipple into 

the clear tube I’ve connected to the nipple.  I then close the nipple 

and release the lever which returns to its forward position on its 

own.  I can see brake fluid leaving the nipple on the first stroke 

and I can see the fluid level in reservoir go down..  However, on the 

second pump there’s no pressure against the movement of the lever, no 

brake fluid leaving the nipple and no descent of the fluid level in 

the reservoir.  This is when the Jamar is horizontal.  However, when 

I have the Jamar master cylinders vertical the brakes bleed well 

using this technique.  (I really don't understand this at all but I 

guess that air in the master cylinder is pumped out the "top" end of 

the cylinder and therefore the brakes work.)



When both sides are working and mounted in the fuselage horizontally, 

I try the bleed the brakes.  I pull back on the lever the first time 

while the nipple is open and I see fluid leave the nipple and the 

fluid level in the reservoir drop.  On the second pump the lever has 

little resistance, no fluid comes out of the nipple and the fluid 

level in the reservoir doesn’t drop.



Why is it that I can successfully bleed the Jamar only when it’s 

aligned vertically?



I’d like to be able to bleed the brakes without having to orient them 

vertically or having to disconnect the brake line from the master 

cylinder and blow fluid up from the nipple, letting the master 

cylinder to brake line connection leak.

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craigb(at)onthenet.com.au
Guest

Posted: Sat Dec 29, 2007 2:28 pm Post subject: Bleeding Jamar finger brakes

the only way i have ever bled brakes is by pumping up and holding pressure,

and then releasing the pressure

at the brake piston bleed point. Generally this requires two people, as the

pedal/lever should be allowed to follow

the pressure and sink right out to full travel, but NOT allowed to return

until the bleed point at the brake is locked up tight

again. this is normally done as many times as needed to ensure all air is

purged from the line. Its not a bad idea to switch

brake fluid to one of a different colour if you can get it part way through,

that way you know you have pushed out the entire

contents of the line and master cylinder when you see the colour change.

Some master cylinders will self bleed to a small degree, which i bet is what

you are seeing when you stand yours on its end. Unless you have a small leak

somewhere, possibly on the seals in the master cylinder

itself, once the lines are free of air, you shouldnt have any further

problems. You also mentioned the remote reservoir, If that is tightly

sealed then once you suck a vaccum in it with the first bleed, then the

system could find a weak point and suck air around a seal or fitting.

You may laugh at this, but remember, a hydraulic brake system can have

several hundred PSI of pressure in it or more, so you could potentially be

creating a few hundred psi of suction. This would account for the level not

dropping after the first bleed.



good luck



craig



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rob(at)Neils.US
Guest

Posted: Sat Dec 29, 2007 4:54 pm Post subject: Bleeding Jamar finger brakes

My reservoir is not pressurized.

  

 I bleed the brakes as Craig describes but I can't get any pressure on the second stroke unless the Jamar brakes are verticle instead or horizontal.

  

 I can get all the air out of the system by working the cylinders only when verticle then pumping fluid up from the brake nipple to where the brake line loosely connects to the clylinders until I get no bubbles the I tighten the cylinder/line connection.  Doing this makes the brakes work well...for quite a while but when I have to bleed the system again I have to dismount the cylinders and loosen the cylinder/line connection allowing bubbles and brake fluid to seep out until I tighten the connection.  It's a real pain to go through all this to simply bleed the brakes...and it makes a mess.  

  

 There's gotta be something wrong with the system that I haven't yet been able to figure out.  Maybe a leak?  Maybe a piston part in backwards?  Maybe poor machining on the cylinders allowing leak-by on the return stroke?  

  

   



   [quote][b]

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jeff(at)rmmm.net
Guest

Posted: Sat Dec 29, 2007 8:52 pm Post subject: Bleeding Jamar finger brakes

Rob,

I had a similar problem along with bleeding. The DOT 5 fluid kept going 

down after a few flights and long taxies. After a lot of re-bleeding 

and re-filling the fluid, plus cleaning off the undercarriage I finally 

found the leek.  Air was getting in, and the fluid was leaking out from 

the bleeder set screws on the side of the master cylinders. I put some 

Permatex gasket dressing on the bleeder screws and haven't had the 

problem since. Hope this helps.

Jeff R.

A258 - N128LJ / Gold Rush 100 hours and climbing slowly.

On Dec 29, 2007, at 6:53 PM, rob(at)Neils.US wrote:



 	  Quote: 	
		   My reservoir is not pressurized.

  

 I bleed the brakes as Craig describes but I can't get any pressure on 

 the second stroke unless the Jamar brakes are verticle instead or 

 horizontal.

  

 I can get all the air out of the system by working the cylinders only 

 when verticle then pumping fluid up from the brake nipple to where the 

 brake line loosely connects to the clylinders until I get no bubbles 

 the I tighten the cylinder/line connection.  Doing this makes the 

 brakes work well...for quite a while but when I have to bleed the 

 system again I have to dismount the cylinders and loosen the 

 cylinder/line connection allowing bubbles and brake fluid to seep out 

 until I tighten the connection.  It's a real pain to go through all 

 this to simply bleed the brakes...and it makes a mess. 

  

 There's gotta be something wrong with the system that I haven't yet 

 been able to figure out.  Maybe a leak?  Maybe a piston part in 

 backwards?  Maybe poor machining on the cylinders allowing leak-by on 

 the return stroke?

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Ivor Phillips

Joined: 16 Jan 2006
Posts: 253
Location: London UK

Posted: Sun Dec 30, 2007 2:30 am Post subject: Bleeding Jamar finger brakes

Some Jamar cylinder’s had poor machining on the bores, Definitely worth checking,      When checking the bore’s also check the seals, On my first cylinder I had mis-match seals of different materials, this prompted me to replace all my seals with good quality ones,     When both piston’s are at rest they should be clear of a cross drilled connection in the body of the master cylinder, check it isn’t obstructed, On the front of the piston seals are  plastic washer’s these can stick in the bores so reduce there size slightly, I have done away with the DOT5 Silicone fluid entirely , replacing it with the DOT 5.1 glycol based fluids,  But if you do this all your seals will need replacing including the seals in the handbrake valve and calipers,  

Bleeding was as simple as putting a small funnel on top of the reservoir filled with fluid so the master cylinder had a good head of fluid, Undoing a caliper bleed nipple one at a time and watch the air being expelled, The reason DOT 5 Silicone fluid is recommended is because it is combatable with both types of rubber seals used in the Master cylinder and Calipers/handbrake valve, If you check the archives there is a lot of information  

Regards  

Ivor  

   

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