No pressure on rear brake line

[Sarcvicious]

I’ve rebuilt the caliper, new brake line, new boot on the yoke. Doesn’t seem like fluid is coming through at all.

any tips on trouble shooting? Not sure where to start

Side note, last time I tried to bleed the brakes after the rebuild, I noticed the fluid was leaking through the boot on the yoke. Now fluid isn’t leaking anywhere after I changed the boot, but it’s also not draining in the MC as we pump the brakes.

[salty_monk]

You probably need to prime it. Either inject fluid using a syringe from the bleeder at the caliper or get yourself a Mityvac or Harbor Freight equiv. and use that to pull it through. Some people will bleed it through by cracking the nuts at the banjo's whilst they are wrapped in a rag too..

I'm assuming you know correct bleeding procedure? I'm assuming your master cylinder is not shot and is able to hold pressure?

[Sarcvicious]

You probably need to prime it. Either inject fluid using a syringe from the bleeder at the caliper or get yourself a Mityvac or Harbor Freight equiv. and use that to pull it through. Some people will bleed it through by cracking the nuts at the banjo's whilst they are wrapped in a rag too..

I'm assuming you know correct bleeding procedure? I'm assuming your master cylinder is not shot and is able to hold pressure?

I’m doing the old fashion brake bleeding procedure w tubing and a water bottle on the bleeder valve. Pump the brake, open the nut w pressure still on the brake lever, close the nut, repeat.

I haven’t heard of priming before

[salty_monk]

Yep you're doing it right but usually the GS's need a bit of help just until you start getting fluid through.... As I say the easiest way is a Mityvac. Bleeding through to each banjo bolt in turn can also work. I've also done it by sucking on the hose whilst rapidly pumping the pedal...

[Sarcvicious]

Thank you! I’ll try it tomorrow.

[phydeauxmutt]

You can bleed the master by removing the banjo from the top, placing a finger over the hole, releasing some of the pressure on your finger, then moving the brake pedal. With the pedal at the bottom, press hard on the top of the master cylinder to seal the hole, let the pedal come up. Release some of the pressure on your finger, press on the pedal. Repeat until you see fluid coming out past your finger. Put the banjo back on, then move to the rear caliper.

I have found it much easier (and quicker) to loosen the bleeder, push the pedal down. While it's down, close the bleeder, then let the pedal up. Loosen the bleeder, push the pedal down, etc.

If you do the older pump, pump, pump, crack the bleeder, all you are doing is compressing the air bubble, then letting it expand in the other direction when you crack the bleeder. You will only move the air bubble less than its own size every time. If you crack the bleeder then push the pedal, you can move that bubble several inches with every attempt.

[Maddevill]

You didn't mention you rebuilt the rear master. I'd look for gunk in there blocking a passage. Also, did you REMOVE the bleed
nipple on the caliper and verify that it was clear along with the PASSAGE it screws into. They can get plugged and are easily
overlooked.

Mad

[Sarcvicious]

I finally got the vacuum pump/brake bleeder tool and primed the line. A small amount of Fluid is coming out but it’s a much smaller amount than what should come out (drips into the tube). There’s no leaks along the line.

however we discovered that the piston is not engaging on the rear caliper so the brake pads are not clamping down on the disc when the rear brake is pumped.

any ideas? I’m hoping the two issues are related.

[phydeauxmutt]

Once you have the master primed and bled, the rest should go easily enough, which will push the pistons against the pads so you can finish the job.

[Sarcvicious]

The fluid is not coming out as expected. It’s little dribbles. It’s not filling up the tube. I’m not finding any leaks, but I also failed to clear the bleeder screw passage. do you think the pistons not engaging could be a related issue?

im completely stuck right now. The vacuum seal pulls little drips into the tube attached to the bleeder screw. Pistons not engaging. This is my first time doing a rebuild and I’m super stuck/discouraged