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Question on bleeding SRAM hydraulic disc brakes . . .

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Question on bleeding SRAM hydraulic disc brakes . . .

Old 08-19-21, 07:54 PM
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RNAV
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Question on bleeding SRAM hydraulic disc brakes . . .

I picked up my first hydraulic disc brake bike the other day and have been researching brake bleeding procedures. I'm a former automotive mechanic, and the SRAM bleed procedures seem way overly complicated compared to the relatively simple bleeding method on vehicles. So, why can't you bleed SRAM hydraulic brakes like you do with a car?
  • Undo bleed port at lever, insert hose/syringe
  • Undo bleed port at caliper, insert hose & drain into a bucket
  • Pressurize system via syringe at lever
  • Reinsert bleed port at caliper
  • Squeeze brake lever; release bleed port while under pressure, close before lever goes full home
  • Repeat until bubbles are gone
I guess I don't understand the point of having two connected syringes, pulling a vacuum at both the lever and the caliper to try to remove bubbles, squeezing the lever 10 times, and pulling a vacuum again. Looking for a little education on why the procedure is so different from an auto system. Thanks!
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Old 08-19-21, 09:47 PM
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I'm gonna go with 'because that's what works'. Also because of the proprietary fittings at both ends you pretty much have to do it their way. You probably could use the same procedure as a car but you have to use the syringes. Vacuum seems to do a pretty great job of getting air out.
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Old 08-20-21, 03:24 AM
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Originally Posted by RNAV
I picked up my first hydraulic disc brake bike the other day and have been researching brake bleeding procedures. I'm a former automotive mechanic, and the SRAM bleed procedures seem way overly complicated compared to the relatively simple bleeding method on vehicles. So, why can't you bleed SRAM hydraulic brakes like you do with a car?
  • Undo bleed port at lever, insert hose/syringe
  • Undo bleed port at caliper, insert hose & drain into a bucket
  • Pressurize system via syringe at lever
  • Reinsert bleed port at caliper
  • Squeeze brake lever; release bleed port while under pressure, close before lever goes full home
  • Repeat until bubbles are gone
I guess I don't understand the point of having two connected syringes, pulling a vacuum at both the lever and the caliper to try to remove bubbles, squeezing the lever 10 times, and pulling a vacuum again. Looking for a little education on why the procedure is so different from an auto system. Thanks!
No idea why they made it that complex...shoudla got Shimano, but here you are. It's not hard, just a lot of steps.
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Old 08-20-21, 05:08 PM
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I did my first SRAM brake bleed earlier this year. I found this video extremely helpful:

I don't think I got it quite perfect, but it definitely helped a lot. I agree that it seems unnecessarily complicated, and I do not like the DOT fluid. Nonetheless, that's what this bike came with.
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Old 08-21-21, 05:59 PM
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Originally Posted by RNAV
I picked up my first hydraulic disc brake bike the other day and have been researching brake bleeding procedures. I'm a former automotive mechanic, and the SRAM bleed procedures seem way overly complicated compared to the relatively simple bleeding method on vehicles. So, why can't you bleed SRAM hydraulic brakes like you do with a car?
  • Undo bleed port at lever, insert hose/syringe
  • Undo bleed port at caliper, insert hose & drain into a bucket
  • Pressurize system via syringe at lever
  • Reinsert bleed port at caliper
  • Squeeze brake lever; release bleed port while under pressure, close before lever goes full home
  • Repeat until bubbles are gone
I guess I don't understand the point of having two connected syringes, pulling a vacuum at both the lever and the caliper to try to remove bubbles, squeezing the lever 10 times, and pulling a vacuum again. Looking for a little education on why the procedure is so different from an auto system. Thanks!
The problem has to do with the frictional drag of the fluid in those tiny hydraulic lines vs the relatively huge auto lines. There is so little hydraulic fluid in the bike lines that the slightest air will cause complete non-function of the bike disks. Once bled, there is almost NO motion of the fluid in the brake lines unlike a car or truck in which brake action may move half a pint of liquid.

SRAM flat bar disks (formerly Avid) are a royal pain in the ass to bleed and you end up pumping the brake lever while feeding fluid in from the bottom port with the LARGE syringe. The road levers are more straight forward but remember the problem is even a small bubble that will stop the damn things from working.

The Shimano system is far more well engineered.

It took me 10 minutes to bleed both ends with my Shimano setup. It took me THREE days with the Avid and I think that bubbles were slowly working their way up to the top which is why it suddenly began working (or rather bleeding) with some effect. I believe that once your get it bled properly the first time that the wetting of the inside of the hydraulic lines makes it easier from then on.
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Old 08-21-21, 06:03 PM
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Originally Posted by mattcalifornia
I did my first SRAM brake bleed earlier this year. I found this video extremely helpful: https://www.youtube.com/watch?v=-_tGOPniwgo

I don't think I got it quite perfect, but it definitely helped a lot. I agree that it seems unnecessarily complicated, and I do not like the DOT fluid. Nonetheless, that's what this bike came with.
SRAM and Avid brakes specify DOT fluid. I MUCH prefer the Mineral oil of Shimano. Shimano claims that theirs is permanent while DOT should be replaced once a year. But I would replace the Shimano a for a year or two before not worrying about it unless you pushed a piston out and drained the fluid out onto your disks.
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Old 08-21-21, 08:42 PM
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Shimano mineral oil gets very very dirty from pistons, bores, and o-rings. If you ride a bunch you should do a full bleed at least once a year. It obviously doesn't absorb water like DOT but it needs to be replaced once a year if not more.
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Old 08-22-21, 12:22 AM
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Originally Posted by cxwrench
Shimano mineral oil gets very very dirty from pistons, bores, and o-rings. If you ride a bunch you should do a full bleed at least once a year. It obviously doesn't absorb water like DOT but it needs to be replaced once a year if not more.
Short hijack, on.

How do you do it in a shop environment for Shimano? At home I just push new fluid in from the “bottom” (calipers) and collect the old in the cup on the levers, discard that, and continue on my way. It has never failed me. Though recently a guy I know suggested I should drain the system, then reinstall the fluid.
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Old 08-22-21, 06:33 AM
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Originally Posted by RiceAWay
It took me 10 minutes to bleed both ends with my Shimano setup. It took me THREE days with the Avid and I think that bubbles were slowly working their way up to the top which is why it suddenly began working (or rather bleeding) with some effect. I believe that once your get it bled properly the first time that the wetting of the inside of the hydraulic lines makes it easier from then on.
Yeah, I took the bike to my LBS and my buddy (mechanic there) showed me how to bleed them. I picked up a used 1x bike and converted it to 2x, and I had to cut the line on the front brake to feed it through the fork, so that's how the whole thing started. He mentioned Shimano was much easier to bleed. I much prefer Sram shifting/ergonomics, so I'm not going to choose a group based on ease of bleeding. That said . . . I was struck but what appeared to be a lot of unnecessary steps. I can do it, but it feels like bleeding AND doing the hokey pokey dance at the same time.
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Old 08-23-21, 05:02 PM
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Originally Posted by Badger6
Short hijack, on.

How do you do it in a shop environment for Shimano? At home I just push new fluid in from the “bottom” (calipers) and collect the old in the cup on the levers, discard that, and continue on my way. It has never failed me. Though recently a guy I know suggested I should drain the system, then reinstall the fluid.
You're doing it correctly.
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Old 08-23-21, 11:07 PM
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Originally Posted by Psimet2001
You're doing it correctly.
That's what I figured. I've never had any issues. I just couldn't;t wrap my head around taking all the fluid out and then trying to purge all the air, I'm happy to know that I still don't. /hijack, now back to SRAM brakes...
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