Spongy lever on disc brakes after travelling

Discuss light weight issues concerning road bikes & parts.
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PaulH
Posts: 71
Joined: Mon Jul 10, 2017 9:50 pm

by PaulH

When I travel abroad I have a spongy brake lever and have to do a mini bleed to get lever feel back . I am sure I’m doing bleed correctly and there is no air left in system. Does the reservoir in the lever have a small amount of air in (to allow for pad wear) do others have this problem after travelling / inverting the bike , if not is there a bleed trick to alleviate this or should I Cable tie the levers down before travelling , many thanks in advance for any advice.


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spud
Posts: 804
Joined: Sat Feb 07, 2009 5:52 am

by spud

to me, anytime you invert the bike you invite air bubbles to migrate from the reservoir into the master cyclinder. I always store disc bike level, or by hanging from the front wheel. I once hung a disc bike by the back wheel, and got a bubble in the rear line which required bleeding.

by Weenie


1415chris
Posts: 1285
Joined: Sat Apr 18, 2009 8:59 am
Location: Surrey UK

by 1415chris

No experience with road hydraulics but I can't imagine they can be different to mtb. In the case I get spongy lever knowing that the system is bled correctly, I pump the levers for a while till I get desire response.

PaulH
Posts: 71
Joined: Mon Jul 10, 2017 9:50 pm

by PaulH

So I guess it isn’t possible to get absolutely all the air out of the system


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Alexbn921
Posts: 231
Joined: Wed Apr 10, 2019 6:39 pm

by Alexbn921

There is a rubber bladder to compensate for fluid expansion and pad wear. A good bleed will get all of the air out of a sealed system. Air does disolve in fluid though and you need to put a vacuum to get this disolved air out. Changes in pressure and temperature can release this air giving you a spungy lever. Also a bad bleed can leave air in the system. Air loves to hide in the nocks and crannies. Degassing is essential for a nice solid lever feel.

Hexsense
Posts: 936
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

hmm, interesting.
So is there any difference in air dissolvability between fluid used (Mineral oil vs DOT)?
Can we add heat to get rid of air when we bleed the system?

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Alexbn921
Posts: 231
Joined: Wed Apr 10, 2019 6:39 pm

by Alexbn921

The two fluids are different and have individual properties related to water and gas absorbing.
Big no to heat. You need to pull a vacuum. Use a bleed kit and it's easy to degas.

TheRich
Posts: 422
Joined: Tue Jan 01, 2019 1:36 am

by TheRich

PaulH wrote:
Fri Aug 02, 2019 4:58 pm
When I travel abroad I have a spongy brake lever and have to do a mini bleed to get lever feel back . I am sure I’m doing bleed correctly and there is no air left in system. Does the reservoir in the lever have a small amount of air in (to allow for pad wear) do others have this problem after travelling / inverting the bike , if not is there a bleed trick to alleviate this or should I Cable tie the levers down before travelling , many thanks in advance for any advice.


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Tie down the lever after arriving.

PaulH
Posts: 71
Joined: Mon Jul 10, 2017 9:50 pm

by PaulH

Thanks


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spdntrxi
Posts: 3131
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

1415chris wrote:
Fri Aug 02, 2019 5:35 pm
No experience with road hydraulics but I can't imagine they can be different to mtb. In the case I get spongy lever knowing that the system is bled correctly, I pump the levers for a while till I get desire response.
This is what I do and 9/10 times it's all I need.. that 10th time I bleed

TobinHatesYou
Posts: 4192
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

spdntrxi wrote:
Sat Aug 03, 2019 1:20 am
1415chris wrote:
Fri Aug 02, 2019 5:35 pm
No experience with road hydraulics but I can't imagine they can be different to mtb. In the case I get spongy lever knowing that the system is bled correctly, I pump the levers for a while till I get desire response.
This is what I do and 9/10 times it's all I need.. that 10th time I bleed

Even then, I just do the mini bleed procedure where I zip tie the lever for a couple hours, come back, use the bleed syringe or cup on the lever size with a small amount of fluid and just flick the lever a few times to shake the bubbles out. With a SRAM system and syringe you can do one better and push/pull on the syringe plunger to further pull the gas bubbles out.

spdntrxi
Posts: 3131
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

TobinHatesYou wrote:
Sat Aug 03, 2019 3:14 am
spdntrxi wrote:
Sat Aug 03, 2019 1:20 am
1415chris wrote:
Fri Aug 02, 2019 5:35 pm
No experience with road hydraulics but I can't imagine they can be different to mtb. In the case I get spongy lever knowing that the system is bled correctly, I pump the levers for a while till I get desire response.
This is what I do and 9/10 times it's all I need.. that 10th time I bleed

Even then, I just do the mini bleed procedure where I zip tie the lever for a couple hours, come back, use the bleed syringe or cup on the lever size with a small amount of fluid and just flick the lever a few times to shake the bubbles out. With a SRAM system and syringe you can do one better and push/pull on the syringe plunger to further pull the gas bubbles out.
yeah sorry.. I dont do a full bleed either.. just get a few bubbles out of the lever with the cup deal and I'm done.. < sub 5min job and it only takes that long because the lever screw gets stripped super easy so I take my time.

by Weenie


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