Zero front Brake Pressure | Page 3 | GTAMotorcycle.com

Zero front Brake Pressure

bitzz

Well-known member
I am 98.754% convinced OP's problem is a VERY common bleeding problem on sport bikes.
The bike has clip on handlebars which puts the master on an angle, which traps air in the banjo bolt connection on the master.
The master is a pump and for a pump to make pressure it needs resistance, something pushing back. It needs something to pump "against" With air trapped in that connection the master cannot develop any more pressure than it takes to compress that air... not much.
A vacuum pump or a syringe should eventually pull out the air bubble, but it may take a while because you're working against the ability to compress air and the pressure bleed back valve in the master
The best solution I have found are bleeder banjo bolts
so you can bleed it right at the master

If you don't gots the fancy smancy banjo bolts; pump up the master and crack that banjo bolt (just like you're bleeding any where else DO NOT RELEASE THE LEVER till you've sealed the connection)
You may have to repeat that a couple of times, and it gets real messy real fast.
When you get pressure, bleed the rest of the system normally.

You can avoid this whole ordeal by "pre" bleeding the master.
 

Wyled

Well-known member

Wyled

Well-known member
Can you put your finger between the plates and even feel movement?
even just using a syringe and plastic tube just pushed onto the bleed screw? .... careful that can get messy.
Yes there is movement, taking the calipers off and squeezing the brake handles closes the pistons ever so slightly thatI need to push them back to get them back on the rotors. Also when bleeding, I can feel the tightening around the rotors albeit very lightly and only one side of the pistons for both calipers
 

Trials

Well-known member
Yes there is movement, taking the calipers off and squeezing the brake handles closes the pistons ever so slightly thatI need to push them back to get them back on the rotors. Also when bleeding, I can feel the tightening around the rotors albeit very lightly and only one side of the pistons for both calipers
(y) good do more of that.
It only has pistons on on side doesn't it? or is it a 4 pot brake

It's pretty important to get the pistons all the retracted and hopefully they are installed in the right direction. (as in not installed backwards :/ that would suck.)
 

Trials

Well-known member
ooo nice ones,
usually.

I have a mono block one here that is crap, pistons are only moving on the inside. I'm not the first to have that problem either.
 

Brian P

Well-known member
Moderator
Site Supporter
There's an easier way to bleed the master cylinder.

Take the master cylinder off the handlebar, and hold it at an angle such that the vent hole to the reservoir is at the absolute top. Then wiggle the brake lever. With the vent hole to the reservoir at the top, any movement of the piston will push an air bubble out and then it will go up to the top of the reservoir and out (you'll see it). No need to crack any fittings loose.
 

Wyled

Well-known member
Alright not sure what I did but I spent the last three hours at it. Ended up somehow getting pressure until i realized one of my calipers were off the rotor. So i had to pull the pads out and get the pistons back inside but when i did that, one went at an angle and I think some air got back in so I was back to no pressure.

Tried doing my same random process all over again with the vacuum pump but I couldnt get pressure again. Ill try again tomorrow but good thing is i Know i can get pressure!
 

Trials

Well-known member
"realized one of my calipers were off the rotor."

Take them both off the rotors, the rotors are not fat enough to hold the pistons in the fully retracted position, use a wedge shape piece of scrap wood to push the pads apart and keep them there. now do your pump and bleed procedure.
 

Trials

Well-known member
Once you push the pistons all the way back there is almost no room for air:

 
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Wyled

Well-known member
Once you push the pistons all the way back there is almost no room for air:

I tried it. All pistons in. Didnt work. Did i do it correctly? All pistons in. Something in between. I used vacuum pump again but I did not press the brake lever in, I solely just did vacuum pump with crack of bleed nipple without touching the lever whatsoever. Or was i supposed to use the brake lever to build pressure, (without collapsing the pistons and keeping them open) and then crack and use vacuum pump. This ***** got me so confused. Its never been this much of a process ever for me
 

Trials

Well-known member
You got me, I've never used a vacuum pump to bleed brakes, I push the fluid in through the lowest bleeder with a big medical syringe and a piece of clear plastic gas line tubing. The syringe puts out enough positive pressure to move the pistons on its own and that's why you need to keep the pistons retracted, you fill from the bottom and the air comes out the top, if the air does not come out the top your brake master cylinder is plugged up and needs service too. Once fluid is returning to the master cylinder reservoir you can remove the wood block's, put the brake on the disc and pump it up. Watch you don't pump the reservoir completely dry or you will put air back in the system again.
If the brake is squishy at this point, I hold the brake on and crack the top banjo fitting just a tiny bit to see if air or fluid comes out, if you hear a little tiny pisst when you do that you found the air and it should come up solid, clean up everything reassemble and ride.
 
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Trials

Well-known member
... if you are using vacuum you are trying to suck fluid and hopefully the air out of the lowest point in the hydraulic system :/ where I live air rises in a liquid so I chose to push the air to the top.
 

Trials

Well-known member
Y'all realize, :cautious: all you can possibly do with a vacuum pump on the lowest point is to speed up something that gravity and atmospheric pressure already does. If you just open the bleed screw at the brake, all of your brake fluid will dump out of there anyway. Suck on it as hard as you like and you are still attempting to pull air bubbles down through a liquid.
 

PrivatePilot

Ironus Butticus
Site Supporter
... if you are using vacuum you are trying to suck fluid and hopefully the air out of the lowest point in the hydraulic system :/ where I live air rises in a liquid so I chose to push the air to the top.
Vacuum bleeders are typically used for cars where there is long horizontal runs of line.

That doesn't mean they won't work for bikes or vertical line runs....the big mistake most people make is trying to use too little fluid during the bleed - you can't be cheap, you need to pull a lot of fluid quickly during a bleed to drag any air bubbles through the system at the same time. There will be waste. It is what it is.

The difficulty with a MC is the size of the master cylinder - you really need 2 people at that point, one to be running the bleeder, and one to be adding fluid to the master cylinder to keep it from running dry while the other person is working at the calipers.
 

GreyGhost

Well-known member
Site Supporter
Vacuum bleeders are typically used for cars where there is long horizontal runs of line.

That doesn't mean they won't work for bikes or vertical line runs....the big mistake most people make is trying to use too little fluid during the bleed - you can't be cheap, you need to pull a lot of fluid quickly during a bleed to drag any air bubbles through the system at the same time. There will be waste. It is what it is.

The difficulty with a MC is the size of the master cylinder - you really need 2 people at that point, one to be running the bleeder, and one to be adding fluid to the master cylinder to keep it from running dry while the other person is working at the calipers.
Or a pressure bleeder with a reservoir. They can give you an entire bottle of fluid through by opening the bleeder once. Hader to fit on some mc though.
 

Trials

Well-known member
The difficulty with a MC is the size of the master cylinder - you really need 2 people at that point, one to be running the bleeder, and one to be adding fluid to the master cylinder to keep it from running dry while the other person is working at the calipers.
:unsure: don't you have that backwards, I can't work on a car or truck brake and operate the brake pedal at the same time, but I sure can do that on a motorcycle brake, especially if the entire brake system is off the bike and in my hand.
and holy your brake master cylinder only squirts a tiny bit of fluid with each pump, how many times did you pump it for the reservoir to go dry.

... you guys are making it way too complicated for the poor guy, it's just plumbing.
 

Wyled

Well-known member
I guess I can do the reverse method again. But i may need another bottle of fluid to get going again.
 

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