Why would a bleed nipple leak, when tightened.

[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?

[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?

[Le_Fromage_Grande]

Because the thread is fecked and fluid is coming up the thread.

[katana]

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.

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.

[v8-powered]

Bit of PTFE tape around the threads should sort it.

[Le_Fromage_Grande]

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.

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

[katana]

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.

[KungFooBob]

Because it hates you.

[kendo57]

If the Taper on the bottom of the bleed nipple seats properly then fluid won't reach the treads i would think

[dern]

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

[David]

I would bet that there is shit in the seat.

[katana]

Because it hates you.

Ah it is forin, keeps looking at me funny. Is it pissing on me?

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.

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.

[David]

As I foretold...shit on the seat (how often should I do this?)

[katana]

Go for at least another three times.

[Mr. Dazzle]

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.

.

[dern]

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.

[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.

[Mr. Dazzle]

almost 100% of the time it stops.

Just what you want from your brakes of course

[wull]

[katana]

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.