Brake system refill, prime and bleed

Having a weird issue getting the front brake system working on the bike.

1986 VFR 750
CBR F2 forks and triple
CBR F2 rotors, calipers and master cylinder
HEL braided brake line kit, two full lines from the master

Before connecting the brake lines, I put fluid in the reservoir and used my finger over the exit until it was squirting fluid out there. Then I connected the lines. The problem is that the reservoir does not drain. It pushes fluid or air through the lines but suctions back up the lines again instead of pulling fluid in from the reservoir.

I have clear tube on the bleed screws dipped into a jar of brake fluid. This is what I'm doing:

1. open a caliper bleed screw
2. slowly squeeze the brake lever, brake fluid and air comes out into the tube
3. close the bleed screw
4. release brake lever Now, when I re-open the bleed screw, the fluid backs up into the caliper again.

I've filled the tube on one bleed screw so when I crack the other open to push out air, I can open the opposite to suck in fluid. However, this only works so far... The reservoir is not draining fluid into the system. It only pushes fluid through, then sucks it back out again.

I had the master cylinder apart, checked both seals and cleaned it. Any ideas?

Other info: the master cylinder is positioned so that it is all down hill to the brake lines and calipers. No point on the brake line is higher than the exit of the MC.

 

how about using a mitey vac? easier than old skool...

http://www.sears.com/shc/s/p_10153_...21x00003a&ci_src=14110944&ci_sku=00947058000P

 

I'm not sure you've got your steps in the right order.

Press the brake lever several times and hold, then slightly release the brake caliper bleed screw until the lever hits the grip. Fluid and air should flow out of the tube and in to the tube & jar. Tighten the bleed screw back up while still holding the lever and repeat process. Do one side at a time. With new lines & MC it takes some time but keep going until the air is out and you're getting only fluid and a firm lever.

 

I love Spaceman Spiff!

Ok, the only difference in what I'm doing and what you suggest is that I am cracking open the bleed screw before squeezing. I also tried squeezing a little first, but the MC is not building any pressure. I can squeeze to the handle a hundred times without opening any bleed screw. Therefore it did not seem to make any difference

I have not tried a mityvac. That might be the next step if I can't get it to start building some pressure today.

I wonder if the air pushing through the system is just leaking in from the bleed screws. I'm only opening them a 1/4 turn, but it seems like these big air bubbles just keep coming out and never any pressure building. And never draining the reservoir.

 

This can happen also with the clutch reservoir, the air just downstream of the reservoir is causing a small air lock and your master cylinder is not really large enough to defeat it, or you have a tiny bit of crud just inside the supply hole thats not visible. Stick a Mighty Vac on the the bleeder with the bleeder closed, pump up the vac to about 10-15 hg open the bleeder. Do this a time or two and you will see fluid start to move from the reservoir. Then you may go back to the old school methods described here in earlier posts to finish it off.

 

Awesome, thanks for that! Guess I'll have to pick one up. I've tried everything else I can think of. I've been cycling fluid in one caliper and out another with an endless supply of large air bubbles coming out, and still nothing ever coming in from the reservoir. It just pumps fluid or air around the system. I hope the mityvac fixes this.

Thanks to all who offered some advice!

Blake

 

More fighting and crying over the dutch and I think the brakes finally work. I think there was an air pocket right up in the banjo near the MC. I used a bike pump to pressure fluid into the system and finally, eventually, she is bleeding like normal. At least something accomplished this weekend.

 

a good "get the last bit of air" trick is to pump the brakes to maximum, and zip tie the handle and leave overnight (or longer). Any air will be forced up the line (under pressure) and burp out the top. results are amazing

 

clean & bleed

I have had success when cleaning entire system. I remove exterior boot at MC, then remove circlip. Then pull plunger back just far enough to open open hole in res. Then I open bleed screws on both calipers and keep fluid in res. until fluid starts leaking from bleed screws. Then shutoff bleed and replace circlip and boot. Now system can be bled with no air lock.

 

I have a 86 vfr700f. I changed the front brake pads and drained all the brake fluid out just to put all new fresh brake fluid in (DOT 4)..Well to make a long story short -- for two days I tried to get a peddle back with no luck, pump,bleed,pump,bleed, well you get the picture. Finally I ask a person in the know and he said bleed valve closed-pump the handle, hold and then open the bleed valve note have a clear tube attached to the bleed valve--then pump several times and close the valve, well on the third time a big glob of air shot out and I started having some brake peddle. Did the other side and made sure all the air was out and my brakes are as good as knew. Just wish I had knowledge of this trick some two days ago. FYI...