Sealant for NPT on hydraulic brake line?

Just drilled and tapped 1/8-27 NPT for a replacement brake-bleeder assy on a old Honda brake cylinder. Housing is a sort-of gummy aluminium, insert is plated brass. Should I use anything, anything particular between the insert and the housing?

The insert is a really nice bit of kit, from Aircraft Spruce; 9 dollars, stainless bleeder.

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wrote:

The threads are expected to seal at brake-line pressures? Sounds contrary to the way every other brake-line component is designed.

Did it come with instructions?

Dave

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On Fri, 24 Apr 2009 10:40:48 -0700 (PDT), snipped-for-privacy@yahoo.com wrote:

Don't know - that's why I'm asking if anything else is needed to keep the seal.

Hmmm.

A quick google shows that typical brake line pressures are on the order of 2000 si, and that fitting with NPT threads are commonly available rated in excess of 10,000psi.

No, other than those in the catalogue:

www.aircraftspruce.com/pdf/2009Individual/Cat09244.pdf

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Rector seal #5 maybe???

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_ wrote:

Look at the tip of the bleeder. The tapered part seals against a mating taper at the base of the insert. The insert itself seals using the taper of the pipe threads. No sealer required.

--
Steve W.

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That's most unusual for a brake application. Not that the threads can't seal or anything like that, it's just not something you'd see OEM. Since it will hold up against plenty of pressure above and beyond what a brake system can put out, I have to imagine it's only cost (that and there are only a few places where that type of a connection would have any advantage in a brake system) that prevents its use.

Dave

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snipped-for-privacy@yahoo.com wrote:

This is NOT OEM. It is a repair part to replace rusted/damaged bleeder screws. The other option is to replace the caliper/wheel cylinder, which may not be possible with older or imported vehicles.

--
Steve W.

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wrote:

Brake systems normally see 2K PSI - but you have to figure in shock loads when you stab your foot on that pedal (or hand grip on a bike) to initiate a panic stop.

It's just an educated guess on my part, but it wouldn't surprise me at ALL to see momentary peak pressures exceeding 5K PSI during the "water hammer" as the pads and shoes slam home on the rotors and drums, and send the shock wave back to the master cylinder.

Which is why you change out rubber flexible wheel brake lines after 12 to 15 years just from service life - old hoses pop. Especialy when you send forces like that through.

My first thought would not be a thread sealer per se, but check to see if the High Strength (Red?) Loctite is compatible with brake fluid. Because when you turn the bleeder screw you want the bleeder to turn in the insert, and the insert to NOT turn in the caliper.

If the female NPT threads in the caliper body are cut properly, they should dryseal without any aids. But perfection is a pain, so the sealants are an insurance policy and disassembly aid.

--<< Bruce >>--

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Steve W. wrote:

Not quite. Pipe threads have a tiny space between the root of one side & the crest of the other. This leaves a helical path for leaks. That's why pipe thread sealer is used. IIRC, there are special pipe threads that do not have this space, but the OP said that he did the tapping, so I doubt that these threads are special. No offense to the OP.

Bob

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On Fri, 24 Apr 2009 17:48:21 GMT, _

This is an insert, right? The bleeder screw threads into it? It never needs to come out again?

Install with extra strength loc-tite.

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On Fri, 24 Apr 2009 19:10:47 -0400, snipped-for-privacy@snyder.on.ca wrote:

603 is your man

Mark Rand RTFM

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My Kodiak disk brakes on the boat trailer do not use any sealer on the brass insert. Cast iron caliper. I might add some teflon tape to the insert. Especially in aluminum. May keep corrosion at bay.

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Teflon tape, Loctite 592, Rector seal if you careful.

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_ wrote:

Didn't the cylinder already have a bleeder in a tapped hole? I.e., couldn't you have just replaced the old bleeder with the new one?

Bob

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