Rear brake bleed

Paul H

Paul H

Fearless OOS Poser
Frt brake comes out awesome... but rear brake always comes out mediocre.
I even tried uninstalling the rear caliper so it will hang down so gravity can assist but it's the same. Is there a secret for the rear?
Maybe it's because my rear pads are more worn out than the frt?
 
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My experience with Shimano (2 and 4 piston) XT's - occasional lever bleed will firm up the lever. For fluid flush, I've had good results with unbolting rear caliper and letting it hang, and doing a gravity bleed. For any new installations where brake hose has been opened, I usually find I need to use a syringe to push/pull fluid from the caliper to the bleed funnel to get all the air bubbles out.
 
Since we're discussing failed bleeds here, have a M8000 brake which doesn't seem to hold pressure. Did a full bleed but no pressure on the levers after. Right after the bleed levers are firm but the next day, they go limp. Don't see any leaks so if this repairable?
 
qclabrat said:
Since we're discussing failed bleeds here, have a M8000 brake which doesn't seem to hold pressure. Did a full bleed but no pressure on the levers after. Right after the bleed levers are firm but the next day, they go limp. Don't see any leaks so if this repairable?
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I had one m8000 leak from the reservoir/overflow
The leak was so small... couldn't detect it but noticed the shifter had a gunk of oil. Assuming a seal got fucked.
 
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Paul H said:
I had one m8000 leak from the reservoir/overflow
The leak was so small... couldn't detect it but noticed the shifter had a gunk of oil. Assuming a seal got fucked.
Click to expand...
What was the solution? I'm not able to figure out if it's the lever or caliper. It doesn't seem to be a slow leak as it goes from good to zero in just a few hours. Leak makes the most sense, but I'd expect to see pooling some where
 
qclabrat said:
What was the solution? I'm not able to figure out if it's the lever or caliper. It doesn't seem to be a slow leak as it goes from good to zero in just a few hours. Leak makes the most sense, but I'd expect to see pooling some where
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New lever.
The brake lever is one of the few things I have not taken apart.
 
Get a manual vacuum bleed kit from the auto-parts store, and vacuum-degas the fluid you are using--mineral or DOT, doesn't matter. Once you are confident you aren't leaving any huge bubbles in the systems using your bleed methodology, the degassed fluid will happily gobble up any tiny stragglers. Feels firmer/works better in the long run, too.

Don't try to hook the vacuum equipment up to the brakes, since they aren't designed for it, and will probably ingest air/break seals.
 
Karate Monkey said:
Get a manual vacuum bleed kit from the auto-parts store, and vacuum-degas the fluid you are using--mineral or DOT, doesn't matter. Once you are confident you aren't leaving any huge bubbles in the systems using your bleed methodology, the degassed fluid will happily gobble up any tiny stragglers. Feels firmer/works better in the long run, too.

Don't try to hook the vacuum equipment up to the brakes, since they aren't designed for it, and will probably ingest air/break seals.
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Damn. That is smart! Can I hook HVAC vac pump to the can?
 
Can't speak for SRAM bleeding because it's weird. I like Shimano's method and mineral oil a lot more. In either case, the bleed block is great when you want to swap fluid and then throw on new pads. If you put old ones back in, I usually do the lever side top off/bleed afterwards to take up the slack from the worn pads. If that's possible on SRAM, maybe that's it?
 
Karate Monkey said:
Uh, I guess...do you have a vacuum gauge? Ball jars can hold ~10-15HG vacuum.
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Can I give you a hug?

I actually found I had way too much air in my DOT fluid and was getting annoyed using the syringe to pull it out. I grabbed a jar, put a bulkhead fitting with a 1/4" push-to-connect tube connector and put it together with an automotive brake bleeder kit.

But then... got really concerned how much of a vacuum I could/should pull on a glass jar in my apartment.
 
Santapez said:
Can I give you a hug?

I actually found I had way too much air in my DOT fluid and was getting annoyed using the syringe to pull it out. I grabbed a jar, put a bulkhead fitting with a 1/4" push-to-connect tube connector and put it together with an automotive brake bleeder kit.

But then... got really concerned how much of a vacuum I could/should pull on a glass jar in my apartment.
Click to expand...

I switched to a polycarbonate vacuum jar, personally. I have no desire to clean up glass/hydraulic oil, even if it won't explode all over.

Plus, it's got two outlets, so I can use it to vacuum bleed shocks.
 
Karate Monkey said:
Get a manual vacuum bleed kit from the auto-parts store, and vacuum-degas the fluid you are using--mineral or DOT, doesn't matter. Once you are confident you aren't leaving any huge bubbles in the systems using your bleed methodology, the degassed fluid will happily gobble up any tiny stragglers. Feels firmer/works better in the long run, too.

Don't try to hook the vacuum equipment up to the brakes, since they aren't designed for it, and will probably ingest air/break seals.
Click to expand...
Is it just me not understand what this is all about? I do have a vacuum bleed kit but where do I attach it? Not the brakes, so is it the BB or rear hub? What?

Jokes aside, I'm interested in the technique but I haven't got a clue how you would do that...
 
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