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Discussion Starter · #1 ·
I tried bleeding my XT rear brake today and it did not go well. I followed a Park Tool "tech Tuesday" video and it seemed really straight forward. Well I ended up letting the oil in the reservoir get too low and some air got sucked in the line. I've tried cycling fluid through the line to get the air out and it seems never ending. It seems like I get most of it out but I can hear it toward the back of the line. How the hell do I fix this? It's driving me nuts.
 

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Here's something that has worked for me, fill the reservoir ,leave top cap off ,squeeze the lever real slow ,watch the bubbles come up ,do it a few times. You might get more reponces it the brake forum.
 

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Discussion Starter · #3 ·
Try elevating the caliper above the handlebars, make sure you have the piston wedge doomawiki thing installed.
I zip tied a 10mm Allen in there because I don't have the block. I'll try elevating the caliper
 

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Magically Delicious
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Ok, let's take this from the beginning. Assuming that you placed a 10 MM allen in the caliper, I must assume that the wheel is off and the caliper remains mounted to the fork? You shouldn't have to remove the master cylinder from the bars. Rangeriderdavie's trick is the first thing I would try.

You DON"T want to elevate the caliper! You want to keep the caliper as far as possible below the master cylinder to encourage air to flow up. You elevate the master cylinder. GEEEZ!

Refill the reservoir and try to gently and slowly pump the brake lever and allow the air play its part by its trying to rise to the surface. Don't allow the reservoir to empty again. My assumption is this should do the trick if you exercise a little patience. Thump the brake lines and gently tap the associated components to encourage the air to rise upwards. You might need to do this repeatedly in an attempt to remove all air.

Report back on how this works for you.
 

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The Fastest of Bananas
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depends on how you do it.

this is messy, but it works well. I use a syringe and hose to force fluid through the line from the caliper to the lever. It overflows the lever, and my drip pan catches it. No fuss, some mess, but it only takes a minutes vs ten or more.
 

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Discussion Starter · #6 ·
well Im pretty sure I got all the air out. I can't hear it in the line any more when I press the lever but now the calipers aren't moving at all. Im losing it over here hahah!
 

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Discussion Starter · #7 ·
cleard2land-- it is the rear brake, and yes the caliper is still mounted to the frame and wheel is removed.

I tried getting the reservoir up as high as I could above the caliper. that seemed to get a lot of air out. I finally was able to get some resistance at the lever after the last bleed so I threw everything back together. it feels really spongey compared to the front brake which didn't need bleeding, just pads.

this is really frustrated and I'm sure somewhat confusing to read
 

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Magically Delicious
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cleard2land-- it is the rear brake, and yes the caliper is still mounted to the frame and wheel is removed.

I tried getting the reservoir up as high as I could above the caliper. that seemed to get a lot of air out. I finally was able to get some resistance at the lever after the last bleed so I threw everything back together. it feels really spongey compared to the front brake which didn't need bleeding, just pads.

this is really frustrated and I'm sure somewhat confusing to read
Doing a bottom up (caliper to master cylinder) bleed on the rear brake can sometimes a little more difficult because the brake line can sometimes have high points where mounted to frame that can trap rising air bubbles. If this presents a problem, you can simply cut the tie wraps where the brake line is mounted and place caliper on floor to create a straight, upward slope to the master cylinder. This will minimize trapped air and facilitate the rise of air towards master cylinder.

If you are doing this with a bike stand, you can make it easier my rotating the bike pointing up to place rear caliper below master cylinder. Then you only need to loosen the master cylinder mount to rotate it so that its reservoir is level.

Any sponginess is an indication that you have remaining air in the line and need to work it out. Patience is truly a virtue sometimes when bleeding brakes. Especially for the beginner.
 

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Discussion Starter · #11 ·
I think I need to do another bleed.

But just clarify because I am a bit confused. I am doing a top down bleed from the reservoir to the caliper , I don't have a syringe. In that case....do I still want the caliper below the reservoir?
 

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Magically Delicious
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I think I need to do another bleed.

But just clarify because I am a bit confused. I am doing a top down bleed from the reservoir to the caliper , I don't have a syringe. In that case....do I still want the caliper below the reservoir?
Doing a top down bleed is fine, but the reason I suggested a bottom up bleed was because you had let the reservoir deplete and pull air into the master cylinder. Because of that, most of your induced air would be located in the master cylinder and perhaps a little in the upper portion of the brake line heading out and down to the caliper.

With most of your air being introduced in the master cylinder or brake lever area, it would be a quick bleed to conduct a bottom up (caliper to brake master cylinder) bleed because the air is already at the master cylinder. If you choose to do a top down bleed, you now have to work the air from the master cylinder all the way down through the brake line to the caliper. This is certainly a doable technique, but it will use more brake fluid and usually take longer to complete. Additionally, I sometimes have difficulty in air getting trapped in the caliper and have to manipulate the caliper to get the air up towards the bleed nipple to purge it. It's not really a big deal; just some have difficulty with purging calipers completely. My general 'Rule of Thumb' is to bleed in the direction of where the air was first introduced or take the shortest route back out.

Everyone has their preferred technique and I advise in doing what works for you.

I copied this Top Down Bleed Technique from Park Tool because it's pretty complete and covers all of the bases for a beginner:


Brake Fluid Bleeding & Replacement

Bleeding a hydraulic system is removing trapped air from the lines and calipers. Shimano brake systems use mineral oil. Never use an automotive D.O.T. brake fluid in a system requiring mineral oil. Remove the brake pads before bleeding or replacing fluid so they do not become contaminated with brake fluid. When servicing hydraulic brakes, work in clean condition. Use care to keeps hydraulic pieces, such as the bladder, clean and away from dirt.

The procedure for bleeding Shimano® XTR, XT, Deore, Saint brake fluid is as follows:
1. Mount bike in repair stand. Remove wheels.

2. Remove brake pads to avoid contamination by brake fluid.

3. Install Shimano® brake block #Y8CL18000 in place of pads. If blocks are not available, substitute a block of about 10mm wide block to prevent piston from extending. Substitute a clean 10mm hex wrench if the brake block is not available.

4. Rotate bike as necessary until tubing has a continuous upward slope from the brake caliper to the reservoir. Rotate lever on handlebar until top surface of reservoir is parallel with the ground.

5. Attach bleed tubing to end of bleed nipple at caliper. Attach plastic bag to end of tubing to catch waste fluid.

6. Clean dirt from lever and wipe around reservoir tank cover. Unthread screws at reservoir tank cap.

7. Remove reservoir cap and bladder. Fill reservoir to top.

8. Loosen bleed nipple, at caliper body, 1 turn.

9. Operate lever repeatedly. Bubbles will appear in reservoir tank, and fluid level may drop. Keep reservoir filled with fluid. Use a non-metallic lever to tap along brake line to encourage any air trapped in the line to rise toward the reservoir.

10. Keep reservoir tank filled with fluid. When oil begins to come out of bleed tube, close bleed nipple at caliper body.

11. Test lever by pulling. Lever will eventually become stiff and firm when pulled. If there is no resistance to lever, open bleed screw and continue to operate handle and pump oil into the system.

12. When lever resistance stiffens, close bleed nipple. Hold lever closed and maintain pressure.

13. Using a 7mm wrench, or a small adjustable wrench, loosen bleed nipple to open system. Open and close system within one second, noticing if any of the expelled fluid contains air bubble.

14. Open system briefly to expel air bubbles

15. Release lever. Check reservoir tank and add fluid.

16. Operate lever repeatedly. If lever feels stiff with resistance at the end of its travel, line contains no air and is fully bled.

17. If lever feels soft, repeat steps 8 through 16 after re-filling reservoir tank.

18. Check that reservoir tank is filled to top. Install reservoir bladder and cap. Expect some excess fluid to spill from lever. This is normal and insures no air is below bladder. Tighten cap screws.

19. After bleeding, disconnect hose from bleed nipple. Wipe lever and caliper of any fluid.
 

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Discussion Starter · #13 ·
Thanks for all your help, Cleared2Land. I'm going to try doing the top down bleed again tonight and hopefully that works. If not I will have to get a syringe and try it from the bottom. I'll keep you posted.
 

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Magically Delicious
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If not I will have to get a syringe and try it from the bottom.
Ok, If you don't have a syringe, here's something that I have done successfully, but not sure that it going to work in all cases. This is a last ditch effort to get results by Ghetto Method. Go back to what I addressed earlier about cutting tie wraps off of rear brake line and getting caliper and brake line to have as straight of an upward flow as possible to master cylinder. Better if you have a bike stand that you can rotate bike and pointing upwards. The point is to create as straight of an uninterrupted upward brake line flow to master cylinder. You will have to loosen master cylinder mounts to keep if using a bike stand to keep reservoir level.

Starting at caliper, begin tapping or thumping caliper with brake line on the uppermost point of the caliper. You are attempting to physically work the air upwards through the brake line with the intent of eventually migrating the air all the way back to the master cylinder. Continue to tap, thump, or persuade the movement of air upwards. Gently articulate or pump the brake lever with the hope that you can work the air through the master cylinder piston. Just make sure to keep fluid in your reservoir. Personally, I would remove the reservoir cap so I could see if bubbles are eventually making they way through. As bubbles come out, you will need to add fluid.

No guarantees on this method, but I have made it work. Good luck!
 
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