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Discussion Starter #1 (Edited)
It's me again... Another 900ss rear brake thread. Thank goodness I don't really use it and the fronts work fantastic!

So last time, about 2 years ago today, I gave up completely and replaced the master cylinder AND caliper. A fresh start. The brake worked, I think (I really don't use it), when I put the bike up for the winter. Now it does nothing. When held down I can still roll the bike freely. So, I did a reverse bleed with my handy vacuum pump. The only problem, no fluid is being pulled out... I took a break to think and went ahead and bled my clutch, and the pump worked flawlessly. So it's the brake. I know I was cracking the bleeder valve enough because just a bit leaked. I took a stab at a normal bleed, which didn't work either. I'm flabbergasted. If the master cylinder or caliper were bad I could still do a reverse bleed, I think... I can't pull OR push fluid through. It can't be blocked, because the pressure from the pedal or vacuum would build up.

What would keep fluid from flowing through the system? I feel like I'm missing something super obvious (work has been crazy AND I'm sick...), so be gentle :wink2:
 

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Odd,... pull the line off the brake caliper and pump the pedal - does it squirt? If not, the blockage is in the line. If it does, the caliper is blocked, umm,... somehow,...

*Edit - Oh! Did you put the copper washer on the banjo bolt so the hole lines up inside the caliper for the fluid?
 

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Based on your observations it sounds like the hose has collapsed internally. Steel braided lines use a hard teflon tube as the fluid core. If this tube is ever "over" bent -or- bent into a too tight radius it can completely fudge up the core and cause a mechanical blockage. Once that teflon core creases it is toast. And the crease cannot be noticed from the outer sheath. I would think against gunk due to mechanical pressure is pretty darn high when applying pedal power to an opened bleeder - -something would have move when, with judicious foot power on the pedal you can rise pressure to over a 1000 PSI.

With reservoir cap off and bleeder plug opened fluid should flow freely. I am assuming you have removed your bleeder plug and used shop air to clear it? Could be as simple as that...

After taking my clutch master apart for the second time I bit the bullet and winced strongly as I pulled the inlet pipe from its rubber mount. That is where I found my blockage. The pipe had accumulated gunk and would let fluid flow into the master but not back into the reservoir. Which was causing a pump-up condition with loss of clutch after about 20 pulls. Thankfully I did not destroy that plastic inlet pipe and I was able to get it all back together.
 

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You may have a blockage, watch what I found below.

https://www.instagram.com/p/BZ1YK0RltjA/

Make sure the bleed is at the highest point when you do it and if you have no luck I would inspect the line and banjos for something plugging it up. The caliper should not be the issue but the small ports in the master can also get plugged easily and will not pass fluid. I do not recommend using too much pressure on a master as you do not want to damage the seals inside, it is a lipped seal not a o-ring so if you over pressure it in the wrong direction you could force the seal backwards.
 

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Discussion Starter #5
You may have a blockage, watch what I found below.

https://www.instagram.com/p/BZ1YK0RltjA/

Make sure the bleed is at the highest point when you do it and if you have no luck I would inspect the line and banjos for something plugging it up. The caliper should not be the issue but the small ports in the master can also get plugged easily and will not pass fluid. I do not recommend using too much pressure on a master as you do not want to damage the seals inside, it is a lipped seal not a o-ring so if you over pressure it in the wrong direction you could force the seal backwards.
Whoa! Makes sense it is a line or fitting. The caliper and master cylinder are basically new, but I reused everything between them (with all fresh fluid). Would the pedal be completely soft with a blockage though? I notice I didn't mention that in my first post.
 

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On the bike that the line came from it was the clutch but the fluid did not move given the blockages. I had not seen that before and the rubber like debris was in both the line as well as both Banjo fittings.

Also make sure the bleed down settings are right in the master or the master will only open one of the two ports needed to function.
 

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Discussion Starter #7
Also make sure the bleed down settings are right in the master or the master will only open one of the two ports needed to function.
Can you point me to some instructions? I'm pretty good at removing old parts and bolting on new ones, but that's about it. All I did with the new master cylinder was adjust it to lower the brake pedal a fair bit.

EDIT: This master cylinder
 

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The pin that fits into the master has a locknut on it and then threads into a clevis. The pin always needs to have some travel before the pin pushes on the piston inside the master, the trick is making the pedal at the right height while still having proper free play at the pedal. Start by making sure there is play and then reduce the play to a small amount (1/4" ish) of pedal travel. For some this is easiest set without a return spring as you can clearly see where the piston starts and what is free play.

Adjust until bleed down is right and then bleed the clutch as you normally would, when done be sure to tighten the locknut down. Pedal position changes will cause you to change this position so be sure to set height first and make it low enough so you do not ride with a toe on the pedal. You should have to reach for the pedal but have a solid lever after a short bit of movement. Too little freeplay and you will not allow fluid to return and your brake will be locked on.
 

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Discussion Starter #10
Update: There was a blockage in the hose, or a fitting, plus a whole lot of air behind it, which I assume was the reason for the completely spongy pedal.

I was lazy, and I didn't have new crush washers, so I decided to pull a high vacuum AND pressurized with the pedal instead of removing the hose and using an air compressor. A nasty black loogey shot out and now I've got it bled adequately. I used completely fresh fluid when I put on the new MC and caliper, so I'm guessing it was gunk left in the re-used brake line or fittings... My fault for not being thorough and doing it right the first time.

Now, if only I had read the last posts from Ducvet and Bradblack and adjusted the pedal BEFORE bleeding. It's definitely a tad spongey already, but good and firm after 1-2 pumps. The freeplay is also good. All in all, I'm calling this "good enough" and will enjoy a celebratory beer. If it were the fronts this would be a different story.
 

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That nasty black loogie was probably the dissolved interior line of the hose.
 

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Update:

Now, if only I had read the last posts from Ducvet and Bradblack and adjusted the pedal BEFORE bleeding. It's definitely a tad spongey already, but good and firm after 1-2 pumps. The freeplay is also good. All in all, I'm calling this "good enough" and will enjoy a celebratory beer. If it were the fronts this would be a different story.
I actually prefer a weakened rear brake - It keeps me from a rear tire low-side from being full tilt gonzo leaned over while going up the mountain and rounding a blind curve only to see a herd of Elk sunning themselves in the middle of the road........which of course causes sphincter clench and full-panic-brake...........
 

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I am open to suggestions for replacement hoses (preferably direct fit).
Consider a hose kit from Venhill. They keep almost all lengths they offer in stock, you pick the ends, and the assembly means you don't have to worry about poorly aligned banjo fittings. Was an excellent choice when I rebuilt my front end as everything was different from any of the OEM setups.

Venhill Make Your Own Custom Brake Line (1 Line Kit) | Venhill USA

Edit: They also sell those awesome dry-breaks you can put in in-line that are stupid expensive but make winter maintenance blindingly easy.
 

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Spiegler ready made kits are great. The Spiegler banjos allow you to rotate them so you can get them angled perfectly.


Sent from my iPhone using Tapatalk Pro
 
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