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Problem Bleeding RS785 Brake

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Problem Bleeding RS785 Brake

Old 06-11-17, 11:39 AM
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bitt3n
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Problem Bleeding RS785 Brake

I'm trying to follow the following guide to guide to bleed my Shimano hydraulic road brake.

I'm having a problem getting any oil at all to flow from the pot connected to the lever down the line. In the video it looks simple. After failing to see any oil flow out of the caliper, I cut off the line at the caliper, and I am now pouring the oil down a line that is not connected to a caliper at the other end, just to see if I can get any oil to flow through.

No matter how I orient the handlebars, and despite the fact that the line goes straight down, I see no oil flowing out of the end of the line. I received this groupset used with the line installed in the lever, so I didn't install that end of the line, but I find it difficult to believe that that's the problem.

What could I be doing wrong? It seems like if I dump fluid down one end of the line it should come out the other..
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Old 06-11-17, 01:46 PM
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wschruba 
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Check the brake reach and freestroke (both set under the hood) are set to factory normal. They can be accessed under the brake hood, and both can cut off the reservoir from the line, which will cause the issues that you described above, outside of any damage to the line/fittings.
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Old 06-11-17, 03:48 PM
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Someone on the paceline forums suggested blowing through the tube to see if I could push air through it, and I could, though it was hard to blow hard enough.

For some reason I can't find the reference in the manual for the brake reach and freestroke for the BR-RS785, but the guy in the video shows what he says is the brake reach screw, and he says that the default is backed off half a turn. So I did that.

The hydro fluid started flowing. I then installed the line in the caliper and tried again. It started flowing again, but I wasn't sure how much I should let flow out the plastic tube I installed in the caliper before I knew all the bubbles were gone, so I put the plunger back in to stop the flow and added more fluid.

Now it won't flow again! I have no idea why. No matter how I adjust the reach screw.
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Old 06-11-17, 04:26 PM
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wschruba 
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How, exactly, are you attaching the catch bag/bottle to the caliper, and opening the flow for it?
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Old 06-11-17, 05:29 PM
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like this



I held this up about four feet off the ground to take the picture, then put it down again, and for whatever reason the fluid started flowing again.

I think there's still something wrong though. The next step in that video, after closing the bleed port, is to squeeze the lever and see if it's firm. My lever goes all the way down to the bar with no resistance. It's definitely not firm. I've let a lot of fluid bleed through the line (way more than in the video) so I would have thought all the bubbles came out. There's still plenty of fluid in the pot too, so it's not like air got in that way.
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Old 06-12-17, 05:42 PM
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If you have purged the line system, by accident/purpose/whatever, a gravity bleed will usually require some effort to get started. Shimano sells a 'pro' kit with a syringe, and in that case, I will usually push fluid from the caliper up to the funnel, first.

That said, there are a few little bits that are often left out, or skipped that may be causing you grief. Not having watched your particular video (and being honest, I have no desire to sit through 16 minutes to see if they did it 'right'), all I can recount are the steps that I follow:

1) Set reach/freestroke back to default.
2) Remove pads, clean the pistons, especially the sides, with isopropyl alcohol, and push them in.
3) Insert bleed block
4) Straighten the system as much as possible
5) Attach the catch bag/bottle to the caliper
6) Attach the funnel to the lever, half full
7) Open the bleed port on the caliper enough to start flow. Sometimes giving the lever a small pump helps.
8) Gently tap 'problem areas' (caliper, mostly) with a plastic tire lever. Sometimes this dislodges some air.
9) After you are satisfied you are not going to get anymore air out, close the bleed port. Burp it (open and close it rapidly) a few times. You may remove the catch container now, if you wish.
10) Pull the lever a few times, watching for bubbles to appear in the funnel. Incline the bar/lever up 30 degrees from vertical, and do the same, then repeat with it down 30 degrees from vertical. At this point you should feel a firm lever.
11) Disconnect the funnel, and make sure that the fluid is all the way up the neck of the reservoir. Add a drop or two, if necessary. Cap the reservoir.
12) Remove the bleed block, and clean everything off with isopropyl alcohol, 90% preferably.
13) Install the brake pads, and use the pad spacer to set the gap. You may need to pull the brake lever several times for the pads to contact fully.
14) Re-install everything, and re-adjust the caliper to center it over the rotor.

It is 'simple' once you've done it a few times, but the devil is in the details.
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Old 06-16-17, 04:34 PM
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Using a syringe I was able to bleed the brake from the caliper, although even after I used the syringe I still couldn't get the brake to bleed using gravity. However the lever is now firm.

For step 13, do I just stick that little red plastic thing between the pads and then pull the lever a few times?
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Old 12-20-17, 02:38 PM
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Same problem

I also have this same problem, I've tried letting fluid go down and forced it up with a syringe but I still have no pressure in the system meaning the lever comes all the way back. I have repeated the steps in both directions multiple times and no difference. It is a new lever bought to replace a leaking reservoir lid (what no parts available? Avid does have some advantages!)
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