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Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 12:48 pm
by katana
So, I disturbed a bleed nipple. Well used it to reverse bleed a caliper with new lines.
Now it seems that nipple leaks. The nipple didn't leak before, I think. The nipple hasn't been turned more than a half turn, so can't be cross threaded.
Yes, it is tight but not overtight. Any ideas?
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 12:52 pm
by mangocrazy
I've had bleed nipples that were poorly machined and leaked from new. Perhaps your bleed nipple was marginal on clearances and disturbing it has pushed it over the edge? Or perhaps there is some grit or other contaminant on the mating face between bleed nipple and caliper? Is the bleed nipple the one that the caliper came with as OE?
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 3:03 pm
by Le_Fromage_Grande
Because the thread is fecked and fluid is coming up the thread.
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 3:26 pm
by katana
mangocrazy wrote: Sun Mar 03, 2024 12:52 pm
I've had bleed nipples that were poorly machined and leaked from new. Perhaps your bleed nipple was marginal on clearances and disturbing it has pushed it over the edge? Or perhaps there is some grit or other contaminant on the mating face between bleed nipple and caliper? Is the bleed nipple the one that the caliper came with as OE?
Don't believe that they leaked in the past, Was hoping for the grit to be honest but don't know how it got there.
Le_Fromage_Grande wrote: Sun Mar 03, 2024 3:03 pm
Because the thread is fecked and fluid is coming up the thread.
Probably right, but don't know what fucked the thread in the first place.
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 4:42 pm
by v8-powered
Bit of PTFE tape around the threads should sort it.
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 6:28 pm
by Le_Fromage_Grande
katana wrote: Sun Mar 03, 2024 3:26 pm
mangocrazy wrote: Sun Mar 03, 2024 12:52 pm
I've had bleed nipples that were poorly machined and leaked from new. Perhaps your bleed nipple was marginal on clearances and disturbing it has pushed it over the edge? Or perhaps there is some grit or other contaminant on the mating face between bleed nipple and caliper? Is the bleed nipple the one that the caliper came with as OE?
Don't believe that they leaked in the past, Was hoping for the grit to be honest but don't know how it got there.
Le_Fromage_Grande wrote: Sun Mar 03, 2024 3:03 pm
Because the thread is fecked and fluid is coming up the thread.
Probably right, but don't know what fucked the thread in the first place.
If it's an old bike it was probably done by a previous owner who has then bodged a fix
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 7:46 pm
by katana
v8-powered wrote: Sun Mar 03, 2024 4:42 pm
Bit of PTFE tape around the threads should sort it.
Great bodgers think a like
Slacked the nipple off and tightened it up again, then cable tied the brake on so lets see what it looks like tomorrow evening.
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 7:48 pm
by KungFooBob
Because it hates you.
Re: Why would a bleed nipple leak, when tightened.
Posted: Sun Mar 03, 2024 8:32 pm
by kendo57
If the Taper on the bottom of the bleed nipple seats properly then fluid won't reach the treads i would think
Re: Why would a bleed nipple leak, when tightened.
Posted: Mon Mar 04, 2024 10:19 am
by dern
kendo57 wrote: Sun Mar 03, 2024 8:32 pm
If the Taper on the bottom of the bleed nipple seats properly then fluid won't reach the treads i would think
This is the right answer, check the condition of the taper on the screw and the caliper. If you can't get a fluid tight seal on these you will need to get the faces machined or a new caliper/screw.
The threads do not hold the fluid in, they just allow the faces to meet and hold. If you 'solve' the problem with ptfe tape you will be trying to hold the full pressure of the brake fluid with tape. That won't work and you will probably die. Good luck
Re: Why would a bleed nipple leak, when tightened.
Posted: Mon Mar 04, 2024 10:55 am
by David
I would bet that there is shit in the seat.
Re: Why would a bleed nipple leak, when tightened.
Posted: Mon Mar 04, 2024 6:54 pm
by katana
KungFooBob wrote: Sun Mar 03, 2024 7:48 pm
Because it hates you.
Ah it is forin, keeps looking at me funny. Is it pissing on me?
kendo57 wrote: Sun Mar 03, 2024 8:32 pm
If the Taper on the bottom of the bleed nipple seats properly then fluid won't reach the treads i would think
Yeah that is what i thought (well know), hence not needing much force to keep the fluid in place evenunder preasure.
dern wrote: Mon Mar 04, 2024 10:19 am
This is the right answer, check the condition of the taper on the screw and the caliper. If you can't get a fluid tight seal on these you will need to get the faces machined or a new caliper/screw.
The threads do not hold the fluid in, they just allow the faces to meet and hold. If you 'solve' the problem with ptfe tape you will be trying to hold the full pressure of the brake fluid with tape. That won't work and you will probably die. Good luck
The problem solved itself, so no idea what caused it. That was the odd thing only coming up the thread not the actual central bore.
Re: Why would a bleed nipple leak, when tightened.
Posted: Mon Mar 04, 2024 8:07 pm
by David
As I foretold...shit on the seat (how often should I do this?)
Re: Why would a bleed nipple leak, when tightened.
Posted: Mon Mar 04, 2024 10:23 pm
by katana
Go for at least another three times.
Re: Why would a bleed nipple leak, when tightened.
Posted: Tue Mar 05, 2024 10:04 am
by Mr. Dazzle
katana wrote: Mon Mar 04, 2024 6:54 pm
The problem solved itself, so no idea what caused it. That was the odd thing only coming up the thread not the actual central bore.
Dirt and/or scratches on either the nipple or the caliper, for sure.
As dern says, they seal at the bottom. If it's coming up the thread it ain't sealing and PTFE is just a bodge.
.
Re: Why would a bleed nipple leak, when tightened.
Posted: Tue Mar 05, 2024 10:36 am
by dern
katana wrote: Mon Mar 04, 2024 6:54 pm
The problem solved itself, so no idea what caused it. That was the odd thing only coming up the thread not the actual central bore.
You should really pull that bleed screw out and make sure the seat, taper, thread and bore are clean and intact. I'd want to know or at least to be sure that it's ok, things don't fix themselves.
Re: Why would a bleed nipple leak, when tightened.
Posted: Tue Mar 05, 2024 12:28 pm
by wull
After bleeding brakes you sometimes have fluid left within the thread area that works its way out, the thread area is tapered so some fluid gets trapped in there and seeps out, I’ve had this quite a few times, all you do monitor it for a few days and almost 100% of the time it stops.
Re: Why would a bleed nipple leak, when tightened.
Posted: Tue Mar 05, 2024 12:45 pm
by Mr. Dazzle
wull wrote: Tue Mar 05, 2024 12:28 pm
almost 100% of the time it stops.
Just what you want from your brakes of course
Re: Why would a bleed nipple leak, when tightened.
Posted: Tue Mar 05, 2024 12:53 pm
by wull
Re: Why would a bleed nipple leak, when tightened.
Posted: Tue Mar 05, 2024 5:04 pm
by katana
Mr. Dazzle wrote: Tue Mar 05, 2024 10:04 am
katana wrote: Mon Mar 04, 2024 6:54 pm
The problem solved itself, so no idea what caused it. That was the odd thing only coming up the thread not the actual central bore.
Dirt and/or scratches on either the nipple or the caliper, for sure.
As dern says, they seal at the bottom. If it's coming up the thread it ain't sealing and PTFE is just a bodge.
.
Yeah I get how a bleed nipple works, just wondering as I suspect that the reverse bleed forced fluid up the thread. Not sure where the dirt would have come from. No signs in the reservoir, syringe or the bottle of fluid.
