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Old 10-24-2005, 05:06 PM   #1
clintnz OP
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Location: Rotoiti, New Zealand
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Air in 640 Front Brake, Again!!

Went to pull the 640 ('03 Enduro) out of the shed this morning, (she's been there for 3 weeks all lonely while I've been holidaying in Europe with a newer model ) & discovered a very mushy front brake, When I had this a while back & I checked all the brake fittings & bled the system which fixed it, now it's happened again. Does anybody have any clues on where the air might be getting in? Do I need new seals somewhere?

Cheers
Clint
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 10-24-2005, 05:34 PM   #2
creeper
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Quote:
Originally Posted by clintnz
Went to pull the 640 ('03 Enduro) out of the shed this morning, (she's been there for 3 weeks all lonely while I've been holidaying in Europe with a newer model ) & discovered a very mushy front brake, When I had this a while back & I checked all the brake fittings & bled the system which fixed it, now it's happened again. Does anybody have any clues on where the air might be getting in? Do I need new seals somewhere?

Cheers
Clint
You might want to completely flush the system with fresh dot 4 or 5.1 Clint... prolly has water in it.
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Old 10-24-2005, 06:02 PM   #3
clintnz OP
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Did a full flush last time, the fluid was clean, but there was definitely air in there.

Cheers
Clint
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 10-24-2005, 06:49 PM   #4
creeper
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Quote:
Originally Posted by clintnz
Did a full flush last time, the fluid was clean, but there was definitely air in there.

Cheers
Clint
Strange... fluid is hydroscopic... but very little rubber in the system exposed to atmosphere, no rubber in the hose at all. Front side of the caliper piston O-rings... backside of the master cylinder O-ring… that's about it.

Oh well... it only takes a little bit.
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Old 10-24-2005, 07:14 PM   #5
yater
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back bleed your system. I haven't seen anything on backbleeding on this site but it's BY FAR the easiest way to ensure there is no air in the line. Simply fill from the bottom nipple...takes 5 minutes and works everytime. If you don't find any info on parts needed when you search, pm me and I'll start a "how to" thread
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Old 10-24-2005, 07:56 PM   #6
clintnz OP
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Cheers for that, but it's not the bleeding that is the problem, when I bled it last time the lever came up nice & hard, & it was good for the couple of months & several thousand km's until now. I'm really looking for any ideas on how the bike is getting air in the brake system while sitting in the shed??

Cheers
Clint
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 10-24-2005, 08:22 PM   #7
creeper
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Quote:
Originally Posted by clintnz
Cheers for that, but it's not the bleeding that is the problem, when I bled it last time the lever came up nice & hard, & it was good for the couple of months & several thousand km's until now. I'm really looking for any ideas on how the bike is getting air in the brake system while sitting in the shed??

Cheers
Clint

It's obviously Air Elves.
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Old 10-24-2005, 08:34 PM   #8
clintnz OP
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Of course... how could I be so silly...

I'll remember to spray the bike liberally with Elvicide before the next time I go away.

Cheers
Clint
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The wilderness, the desert - why are they not crowded
.................................................. .....with pilgrims?
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Old 10-24-2005, 08:41 PM   #9
creeper
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Quote:
Originally Posted by clintnz
Of course... how could I be so silly...

I'll remember to spray the bike liberally with Elvicide before the next time I go away.

Cheers
Clint
There ya' go...

You get South Park in NZ? There was a Underwear Elves bit a few years ago that was funny as hell.

Ya' had to be there I guess.
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Old 10-24-2005, 08:45 PM   #10
Donkey Hotey
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Here's my two guesses:

1) Are you running glycol or silicone based fluid? I don't know if they use 'DOT' ratings for fluid down there but there seems to be confusion in the types of fluid and some people still insist on using silicone based fluids. There are many problems with silicone fluid which I'll spare you but the biggest problem is that it absorbs air bubbles that won't come out until the fluid is heat-cycled. I used to run the stuff many years ago but completely gave up. I was constantly bleeding the brakes after a change. It took 3-4 bleeds to get it all. Make sure you stay with a glycol based fluid and you shouldn't have this problem.

2) It may not be 'air' but rather some other kind of gas being generated by active corrosion inside your caliper or master cylinder. As it corrodes, gas is given off and collects inside. Clean fluid won't allow that to happen but once it starts, it might be your source. In such a small caliper, a little gas goes a long way.
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Old 10-24-2005, 09:36 PM   #11
Esteban
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master cylinder seal leakage
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Old 10-24-2005, 09:49 PM   #12
Scoot Jockey
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My 2003 Adventure does the same thing if I let it sit for more than two or three weeks. As far as a permanent fix, I haven't found one. Air must be creeping into the caliper somehow. Two tricks that have helped me are:

1. First, I purge the caliper by carefully and firmly squeezing the piston side of the caliper towards the disc, thus creating a gap between the opposite "fixed" brake pad and the disc.

2. Next turn your handlebars to the left, raising your fluid reservoir to the highest point. Hold the upper curve of the brake line down to create a downwards run from the reservoir to the caliper, then begin squeezing the brake lever slowly, and firmly to bring the air bubbles up. You could even have the cap off of the reservoir at this point to check the air release, and monitor the fluid level.

A lot of times I will just do the second step, and it will make things rock solid again.

Regards,
Scoot
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Old 10-25-2005, 01:49 AM   #13
Buckster
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I get this with my rear brake and plan on stripping the entire set up down for a look see, I suspect it is the seals in the piston chamber or something to do with the banjo's, if it is the banjo's I will replace the pipe with a custom Venhill unit, now winter is here I could really start needing the rear brake, otherwise I rarely use it.
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Old 10-25-2005, 03:22 AM   #14
Taki
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I just had this problem with my hydrolic clutch this past weekend. I am very careful to purge all the air from the system periodically and completely flush the fluid twice a year. I noticed the clutch starting to loose its release power while on some technical trails, gradually the clutch started to fail over the next few hours. Each time I stopped and turned the bike off the clutch pressure returned only to dissappear again when the vibration started. Back at home I checked the fluid level and it was sufficiently high, but the entire line was full of "frothed" fluid. My only guess is that air entered the system when the bike fell on its side and I grabbed the clutch, another possible reason for the brake line problems in this post.
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Old 10-25-2005, 05:22 AM   #15
Trevor S
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Quote:
Originally Posted by creeper
You get South Park in NZ? There was a Underwear Elves bit a few years ago that was funny as hell.
Undepants Gnomes :) Ranks in the top 5 episodes ...

Business Plan
1. Collect Underpants
2. ...
3. Profit.

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