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Author Topic: caliper bleed screw leaks air  (Read 4730 times)

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Offline jdub

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caliper bleed screw leaks air
« on: March 13, 2018, 10:18:18 PM »
My front caliper bleed screw seems to not tighten enough to completely seal. it visually looks ok. when bleeding and squeeezing it shiws a slight leak, although really tight. is changing that screw the best place to start? anyone know the size?  i cant find anything online. thanks in advance.
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Offline TwoTired

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Re: caliper bleed screw leaks air
« Reply #1 on: March 13, 2018, 11:07:30 PM »
The caliper is filled with fluid.  If it leaks, it would be a fluid leak.

If you are using a vacuum siphon for bleeding brakes the air is coming past the threads of the screw.  Not of concern.  The actual seal portion is in the base of screw hole with a tapered cone point pushing into a similar shaped seat.  If the cone seat is damaged, best to look for a machine shop or another caliper body.

Cheers,
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Offline Yamahawk

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Re: caliper bleed screw leaks air
« Reply #2 on: March 14, 2018, 05:43:11 AM »
If it is air leaking when you are bleeding the brakes, I have had some success using teflon tape on the threads of the bleeder screw, just be careful to wrap it the same way you screw it in so the end doesn't unwind as you thread it into the hole. Also, don't let it overlap the taper at the end of your bleeder, blocking the hole.
If it is sucking air after you have the bleeder tight, then you have another problem, and replacing the bleeder probably won't work. If that is the case, as Lloyd said, you might need a new caliper.
Charlie
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Offline DaveBarbier

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Re: caliper bleed screw leaks air
« Reply #3 on: March 14, 2018, 06:00:42 AM »
+1 with what TT says. Vacuum bleeders are good, but they can give you a false notion of air in the system as, under a vacuum, it will pull outside air in through the threads into the bleeder and up your clear tube. You should finish by doing a normal bleed procedure to make sure you’re good to go.

One thing to note, if you’re finished bleeding and fluid seems to be seeping out the threads when the bleeder is tightened down, it could very well be the fact that the bleeder is filled with fluid and it’s leaking backwards down the hole and up the threads (I guess due to capillary action?). Spray brake clean into the bleeder when you’re done and dry it out with a light shot of compressed air and see if it still happens.
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Offline jdub

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Re: caliper bleed screw leaks air
« Reply #4 on: March 14, 2018, 11:34:47 AM »
yes i was using a vacuum- thats good to know. with regular  bleeding no there is no air in the system.  still diesnt brake as string as i’d like , but its better.

good info guys, thanks 
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Offline TwoTired

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Re: caliper bleed screw leaks air
« Reply #5 on: March 14, 2018, 11:47:40 AM »
Quote from: jdub on March 14, 2018, 11:34:47 AM
yes i was using a vacuum- thats good to know. with regular  bleeding no there is no air in the system.  still diesnt brake as string as i’d like , but its better.

good info guys, thanks

Does the lever feel hard, or spongy?  Are the pads dry and uncontaminated?  What are you comparing to in your assessment?
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: caliper bleed screw leaks air
« Reply #6 on: March 14, 2018, 12:21:37 PM »
Speed Bleeders
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Offline jdub

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Re: caliper bleed screw leaks air
« Reply #7 on: March 14, 2018, 01:40:59 PM »
the lever feels fairly hard,  not very spongy. . i couldntcompletely stop the bike with it.
(ive had a 1000 Goldwing and a 70s sportster. ) pads look good.
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Offline TwoTired

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Re: caliper bleed screw leaks air
« Reply #8 on: March 14, 2018, 01:45:48 PM »
Quote from: jdub on March 14, 2018, 01:40:59 PM
the lever feels fairly hard,  not very spongy. . i couldntcompletely stop the bike with it.

You using more than one finger?  Does the lever hit the grip when squeezed?

It should stop the bike without using the rear brake, for sure.
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline jdub

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Re: caliper bleed screw leaks air
« Reply #9 on: March 14, 2018, 02:08:29 PM »
doesn't hit grip when squeezed. no air in system either.  maybe just the cylinder is weak . 
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Offline Bodi

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Re: caliper bleed screw leaks air
« Reply #10 on: March 14, 2018, 02:16:16 PM »
There's no weak cylinder, it either works or doesn't. The bore diameter ratio sets how "strong" the caliper squeezes with a given lever force. If all is stock, the caliper piston and brake pad are free... then it's working OK that far. Using a pad that's had oil or brake fluid on it dramatically reduces brake power...?
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