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post #1 of 11 (permalink) Old 07-15-2008, 03:50 PM Thread Starter
 
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Brakes are soft

Hello, I recently changed my brake fluid and pads and then bled the system. In fact I have bled the system 3 times with the constant pressure method - all 3 times for atleast 12 hours and yet after 2 days they seem to go soft on me. I have had no brake fluid on the ground therefore I am not convinced I have a leak. Anybody have an experience like this in the past?
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post #2 of 11 (permalink) Old 07-15-2008, 04:18 PM
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Make sure you are using DOT5 brake fluid...I think the manual recommends DOT4 or DOT5. I believe it has a higher temperature spec.
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post #3 of 11 (permalink) Old 07-15-2008, 04:27 PM
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Are you losing any from the resevoir? If the level is going down that says there is a leak, I'd have to guess that the level is staying about the same which would indicate the master cylinder is bypassing. The other thought that just hit me, is there is trapped air in the master cylinder. Try leaving it overnight on the center stand with the cover off or at least loose, just be careful that you don't get water (aka rain) in there as it will ruin the fluid. Also check the gasket on the cover for rips/tears.
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post #4 of 11 (permalink) Old 07-15-2008, 05:08 PM
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You say all is well for a couple of days after you bleed the system? When they go soft, is there a change in the fluid level?

Chris
Wayne, NJ
1989 VN750-A5
VROC #27781
-Replaced/Fused Stator & Replaced/Relocated R/R (15K mi.)
-MF Battery
-De-Goated/Re-goated
-Coastered
-Splines Lubed
-Stebel Nautilus Horn
-AutoMeter 2" VOM
-Silverstar Headlight
-Refinished Gauge Rings and Mirrors(Flat Black)
-Refinished Swingarm/Lubed Pivots
-K&S Turn Signals Clear Cover/Amber Bulb
-Kenda Kruz 110/90-19 front 170/80-15 rear
-Clear Alternatives LED tail light
-Plexifairing III
-Willie & Max Saddlebags and SissyBar Bag
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post #5 of 11 (permalink) Old 07-15-2008, 05:30 PM Thread Starter
 
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The level has gone down slightly - it only seems to go down just after I bleed it. But again there is no fluid on the ground. I even wiped my hand around both calipers and it is dry. I have not tried leaving the master cylinder off - I will try that next but what does bypassing the master cylinder mean? I have used DOT 4 fluid.
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post #6 of 11 (permalink) Old 07-15-2008, 05:47 PM
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Bypassing means the internal seals that push the fluid are not holding and the fluid leaks around them back into the resevoir. But the fact that the system holds pressure for a few days might say this is not happening. I'd try leaving the cover off overnight as the level has gone down, it's going somewhere... probably replacing super small air bubbles somewhere. Just a guess.
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post #7 of 11 (permalink) Old 07-15-2008, 08:36 PM Thread Starter
 
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I was thinking along the same lines, I will let you know what happens. Any other ideas please let me know. Thanks for the help so far.
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post #8 of 11 (permalink) Old 07-15-2008, 11:39 PM
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Have you tried the "tap the lines with a screwdriver" trick?

Chris
Wayne, NJ
1989 VN750-A5
VROC #27781
-Replaced/Fused Stator & Replaced/Relocated R/R (15K mi.)
-MF Battery
-De-Goated/Re-goated
-Coastered
-Splines Lubed
-Stebel Nautilus Horn
-AutoMeter 2" VOM
-Silverstar Headlight
-Refinished Gauge Rings and Mirrors(Flat Black)
-Refinished Swingarm/Lubed Pivots
-K&S Turn Signals Clear Cover/Amber Bulb
-Kenda Kruz 110/90-19 front 170/80-15 rear
-Clear Alternatives LED tail light
-Plexifairing III
-Willie & Max Saddlebags and SissyBar Bag
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post #9 of 11 (permalink) Old 07-16-2008, 11:00 AM
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I had to tap the master cylinder with a screwdriver to dislodge the air in the pickup hole at the bottom. It took about 15 minutes of tapping and squeezing the brake handle to get it all out. You could see the bubbles coming out when you tapped it. Went through about 1/2 a can of brake fluid bleeding the stupid thing until I discovered the tap method.

Jim W
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
21480 Miles
VROC #8542
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post #10 of 11 (permalink) Old 07-16-2008, 09:19 PM Thread Starter
 
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Alright I bled it last night with the master cylinder cover off (although it was only for 8 hours) and this morning it was tight. After riding 100 miles today it seems to be going soft again. Still no leaks but I do hear a rubbing or rolling noise that sounds like it is coming from the left caliper when I use it - even after I apply and then let off. I don't know if this has anything to do with it but just something else I noticed. Is there something else I should be looking for possibly in the calipers themselves or in the master cylinder. The diaphragm appears to be in good shape.
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