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Online Scotty001

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Re: Spongy brake issue
« Reply #10 on: October 23, 2018, 12:13:06 PM »
*Originally Posted by Ninjamaster [+]
So there's a vent hole on the master cylinder or reservoir somewhere?
*Originally Posted by mdr1970 [+]
I've had this problem after riding with my friends who have adventure bikes. They typically choose more...off road/bumpy routes. Looking at my reservoir I can clearly see lots of tiny bubbles, that can't help but get pushed down the lines under braking  :oh_no:

So, No, they are not vented; the time simply allows the micro air bubbles to rise & accumulate in the only space available, rather than in the line...



Although if you wanted to you could undo the lid on the master cylinder reservoir and remove the rubber stopper and leave over night / over as many days as you like, to make it a fully vented system ( I would recommend just putting the cap  / lid on by 1/4 turn to keep any dust / debris from getting into the brake fluid.

Offline mdr1970

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Re: Spongy brake issue
« Reply #11 on: October 23, 2018, 12:37:16 PM »
*Originally Posted by Scotty001 [+]
Although if you wanted to you could undo the lid on the master cylinder reservoir and remove the rubber stopper and leave over night / over as many days as you like, to make it a fully vented system ( I would recommend just putting the cap  / lid on by 1/4 turn to keep any dust / debris from getting into the brake fluid.

Opening the lid allows air in, which can in turn allow moisture, which equals water, which lowers your viscosity and boiling point = more baking problems and earlier fluid changes  :006:
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Offline Rocky the Dog

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Re: Spongy brake issue
« Reply #12 on: October 23, 2018, 01:32:49 PM »
*Originally Posted by mdr1970 [+]
Opening the lid allows air in, which can in turn allow moisture, which equals water, which lowers your viscosity and boiling point = more baking problems and earlier fluid changes  :006:

 :461:  Yep - spot on MDR - Brake fluid is hygroscopic and will absorb water from the atmosphere at a fairly rapid rate - leave the cap off for a day on a humid day and you really need to replace all the brake fluid.  The absorbed water content will cause the brake fluid to boil if you really heat the brakes up and can, in extreme cases, lead to total loss of brakes though you should initially get spongy brakes first. Sorry but you need to ignore Scottys advice completely.  Brake systems have a system of seals for a reason - to keep the air, and hence the moisture away.  Have never in 40 odd years of tinkering with bikes and other vehicles seen a brake system with any form of vent or opening to the Air - other than a brake nipple when you are bleeding them - and even then that should be attached to a pipe that has the end covered by a jar into which to are bleeding the brakes.

Rgds Steve
« Last Edit: October 23, 2018, 01:42:17 PM by Rocky the Dog »
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Online Scotty001

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Re: Spongy brake issue
« Reply #13 on: October 23, 2018, 02:10:08 PM »
*Originally Posted by Rocky the Dog [+]
:461:  Yep - spot on MDR - Brake fluid is hygroscopic and will absorb water from the atmosphere at a fairly rapid rate - leave the cap off for a day on a humid day and you really need to replace all the brake fluid.  The absorbed water content will cause the brake fluid to boil if you really heat the brakes up and can, in extreme cases, lead to total loss of brakes though you should initially get spongy brakes first. Sorry but you need to ignore Scottys advice completely.  Brake systems have a system of seals for a reason - to keep the air, and hence the moisture away.  Have never in 40 odd years of tinkering with bikes and other vehicles seen a brake system with any form of vent or opening to the Air - other than a brake nipple when you are bleeding them - and even then that should be attached to a pipe that has the end covered by a jar into which to are bleeding the brakes.

Rgds Steve

You learn something new every day, ive done that at least once on a few bikes ive owned to rectify a spongy break and never had an issue once the break was solid again.

Offline Rocky the Dog

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Re: Spongy brake issue
« Reply #14 on: October 23, 2018, 04:24:18 PM »
*Originally Posted by Scotty001 [+]
You learn something new every day, ive done that at least once on a few bikes ive owned to rectify a spongy break and never had an issue once the break was solid again.

Scotty - just for your info, I looked this up  http://307lubricants.com/need-know-brake-fluid/  which pretty much echoes what I said but if you google brake fluid and moisture there are loads of hits which will say the same.  Sorry if I was a bit blunt but used to have a mechanic who was paranoid about brakes and drummed into me the effects of water and overheating brakes.  Still, on the TZ,  I was personally more worried about the damm thing seizing - which it did twice putting me through hedges on both occasions - amazing how effective a locked back wheel is.  Anyway ride safely and enjoy.

Rgds Steve
« Last Edit: October 23, 2018, 04:26:44 PM by Rocky the Dog »
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Offline Ninjamaster

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Re: Spongy brake issue
« Reply #15 on: October 23, 2018, 05:02:33 PM »
*Originally Posted by mdr1970 [+]
I've had this problem after riding with my friends who have adventure bikes. They typically choose more...off road/bumpy routes. Looking at my reservoir I can clearly see lots of tiny bubbles, that can't help but get pushed down the lines under braking  :oh_no:

So, No, they are not vented; the time simply allows the micro air bubbles to rise & accumulate in the only space available, rather than in the line...

 :028:

Offline Baldyone12

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Re: Spongy brake issue
« Reply #16 on: October 23, 2018, 09:27:57 PM »
Hi guys just a quick update, lever was tied up for 24hr released it drove around the block all seemed good, got all my gear on and headed off to work less than 100 yards tried the brakes back to square one.
Tied the lever back again and shall leave it for couple of days and try again.

Offline mdr1970

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Re: Spongy brake issue
« Reply #17 on: October 23, 2018, 09:55:24 PM »
If it ain't sorted after the first 24hrs you have a more serious problem I'm afraid!  :006:

Something is leaking/not sealing properly allowing air into the system.
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Offline maccmike

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Re: Spongy brake issue
« Reply #18 on: October 23, 2018, 10:06:16 PM »
The most common damage after forgetting a disc lock is a bent disc. As the disc turns it pushes the pistons back further than normal then when you pull the lever the pistons have too far to travel and the lever needs to be pumped. I would be checking the disc if I were you.

Offline mdr1970

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Re: Spongy brake issue
« Reply #19 on: October 23, 2018, 10:27:45 PM »
I don't think that's likely Mike. You'd feel a bent disc through the lever and at walking pace,or with the bike on paddock stand. Easy enough to check!
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