Rear bleeder valve issue


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BIGBopper1956
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Joined: Fri Apr 12, 2019 12:40 am
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Motorcycle: 1993 GL 1500 Aspencade
1999 GL 1500 Valkyrie Interstate
1999 GL 1500 Valkyrie Tour
1999 GL 1500 Valkyrie Standard
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Rear bleeder valve issue

Post by BIGBopper1956 »



Just finished rebuilding the rear caliper on my 99 Valkyrie (ride a 93 GL 1500 also) and when bleeding the system ran into an issue. Using the Mighty Vac (speed bleeders on order) had tight connections and able to pull good vacuum but, with the bleeder closed was getting small amounts of fluid and air into the tubing. Two questions, 1) how much vacuum should you apply, and 2) Is this normal? I did the front calipers and did not see this. Thanks


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bluthundr31
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Motorcycle: 1991 GL1500 Interstate (Cinnamon Beige)

Re: Rear bleeder valve issue

Post by bluthundr31 »

The mighty Vac might be putting enough suction pressure that air is sucked in at the "nipple" when you close the bleeder, which is not a problem IF you're "sucking" out the old brake fluid, , , but that doesn't seem as effective as just using the brake pedal and opening/closing the bleeder. Maybe I'm not understanding what exactly you're doing, but it sounds a bit backward.

SDBerndt
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Motorcycle: 1998 GL1500 SE

Re: Rear bleeder valve issue

Post by SDBerndt »

I just had the same problem as you. A little Teflon tape on threads of bleeder worked for me. Not sure why because bleeder wasn't leaking brake fluid before. I tried cleaning threads and flushing where bleeder screws into caliper, but that didn't help.

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MikeB
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Re: Rear bleeder valve issue

Post by MikeB »

Contrary to the belief that the threads are the sealing portion of the bleed screw, it is not correct. The beveled base of the bleed screw and the caliper seat do the sealing. Sealing the threads helps to keep air from passing the threads while performing the bleeding process but has no effect overall in the sealing of the bleed screw. A clean bleed screw base tightened into a beveled seat will not allow fluid to pass.

The easy way to seal the threads for bleeding is to put some grease around the threads where the bleed screw goes into the caliper.
The grease is viscous and some of it gets pulled into the threads but does not allow air to pass. Thus no air bubble goes into your bleed hose.

Though the thread sealing Teflon tape will work, the big plus of using grease around the bleed screw is you do not have to remove the bleed screw to apply Teflon thread sealing tape.


MikeB
1998 - GL1500 w/184,500 miles ~ 2017 - GL1800 w/13000 miles
USAF Avionics Communications Tech - 18 Years / Flight Engineer C-130E - C-141B - 6 Years. Retired.
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CrystalPistol
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Re: Rear bleeder valve issue

Post by CrystalPistol »

Just finished rebuilding the rear caliper on my 99 Valkyrie (ride a 93 GL 1500 also) and when bleeding the system ran into an issue. Using the Mighty Vac (speed bleeders on order) had tight connections and able to pull good vacuum but, with the bleeder closed was getting small amounts of fluid and air into the tubing. Two questions, 1) how much vacuum should you apply, and 2) Is this normal? I did the front calipers and did not see this. Thanks
Atmospheric air pressure limits maximum vacuum. You can't use too much. Atmospheric air pressure is what a 1 square inch column of air from the ground to the edge of the atmosphere weighs. It varies by air density, temperature, ground altitude. With a Mighty Vac, 25" mercury is about the most you'll get. If you have the hose on the bleed nipple, if the bleeder is closed, if you see bubbles … you have a leak at hose to nipple letting air get sucked in and a liquid in the hose allows you to see the bubbles … or the bleeder isn't "so well closed"?


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