Brake bleed question

T

timtune

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I'll be bleeding my project soon and I want to try applying vacuum with a large syringe on the bleeder valve. Should the brake lever be held in or in the released position for this to work best?
 
I would think out as it should block the passage from the reservoir to the caliper when it is pulled. I have never tried what you are doing.
 
There is a check valve in the master, which holds (IIRC) 7psi pressure in the system.
You need to overcome that check valve to push UP from the caliper.
No such issue if you use vacuum to pull DOWN.
 
timtune said:
I'll be bleeding my project soon and I want to try applying vacuum with a large syringe on the bleeder valve. Should the brake lever be held in or in the released position for this to work best?
Click to expand...
If it's your project CB750 it should be simple to do using a hose and bleed jar. Use a small mason jar, punch a hole in the lid and fix a bleeder hose to the bleeder and into the jar, leave the jar on the ground.

A bunch of slow squeezes and voila! Bled.
 
Mad Mike said:
If it's your project CB750 it should be simple to do using a hose and bleed jar. Use a small mason jar, punch a hole in the lid and fix a bleeder hose to the bleeder and into the jar, leave the jar on the ground.

A bunch of slow squeezes and voila! Bled.
Click to expand...
I always picture this method trying to force air "down" to the bleed nipple when it wants to floats up, especially when I'm starting with lines completely empty. At least I pictured that as the problem when I did a very similar thing on my old KZ650. Wasn't until someone mentioned cracking the banjo bolt that I managed to get a firm lever.
I'll find out soon enough - was distracted with a fork seal on the killer.
 
Are you trying a different approach from using a syringe to push the fluid in from the bleeder at the caliper? I'm not sure you'll get enough suction with a syringe at the top end to pull the fluid all the way through. Maybe with a suction pump?
 
No I was going to use the syringe at the bleeder to pull fluid down through.
 
Fill the master cylinder, then pump as many of the air bubbles out as you can.
Then tie the lever back with an elastic, that will open the piston, let it sit overnight and the line will fill and remaining bubbles will rise.
Then bleed from the bottom as usual.
 
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timtune said:
No I was going to use the syringe at the bleeder to pull fluid down through.
Click to expand...
I have used syringes for bleeding. It's very difficult but my most successful way was pushing it in with a syringe. Sucking with a syringe I found that I often just ended up sucking air in from around the bleed screw. Get the biggest syringe that yo can find so that you don't have to keep tightening the bleed screw to refil the syringe.
 
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