Thread sealer that resists brake fluid

[Fman]

I am getting ready to bleed my brake system, I have the triple CNC brake reservoirs. I need to find a sealer to use on the threaded barb fittings that attach to the bottom of each reservoir. I was told not to use PTFE because brake fluid will dissolve it. I found some Permatex 54540 which is $28/bottle. Are there any other options out there?

Thanks

[TMartinLVNV]

This is what I used:

https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-thread-sealant-with-ptfe/?locale=en_us

Economical general-purpose fitting sealant. Outperforms tapes and pipe dopes. Seals and resists pressure in air, oil, diesel fuel and hydraulic systems. Remains pliable at higher and lower temperatures. Temperature range -65°F to 300°F (-54°C to 149°C); resists common shop fluids.

Our brake system is essentially a "hydraulic system". Brake fluid is pretty nasty stuff, but I've never heard of it breaking down PTFE thread sealant. I had to redo one fitting on my brake system at a caliper because of a slight leak. Everything has been holding up fine since. I've used it on the brakes on my Maxima and Jeep with many thousands of miles and no issues.

[edwardb]

I have used whatever Permatex or Loctite sealant was at my local parts store. Also had some Loctite 567 from Mark at Breeze that I've used. Typically have PTFE and no issue for the 1/8 NPT fittings on the CNC reservoirs. Not sure who told you that. Hope it wasn't me. :rolleyes: Many suggest not using tape (me included) but your typical automotive sealant should be fine. BTW, pretty good chance the NPT threads will seal without sealant. That's just gravity pressure. But the sealant also provides some lubrication to make sure seated firmly plus provide some anti-seize protection.

[frankeeski]

.......... the sealant also provides some lubrication to make sure seated firmly plus provide some anti-seize protection.

There's your answer right there. The thing when working with any threaded automotive application is lubrication. Make sure to use a drop or two of brake fluid when assembling your double inverted flare joints as well.

[NAZ]

I'm a fan of Henkel products so I use the LocTite thread sealer on NPT brake fittings. I like the stick form as it's more convenient but the paste works well too.

DO NOT USE TEFLON TAPE ON ANYTHING AUTOMOTIVE OR HYDRAULIC. Leave Teflon tape to the plumbers.

[Briansshop]

I'm a fan of Henkel products so I use the LocTite thread sealer on NPT brake fittings. I like the stick form as it's more convenient but the paste works well too.

DO NOT USE TEFLON TAPE ON ANYTHING AUTOMOTIVE OR HYDRAULIC. Leave Teflon tape to the plumbers.

That's funny! I've been using tape only for over 40yrs and never had any issues. I've never tried any paste, but only because tape has always been fine. Maybe technique is involved?

[JohnK]

If I could piggyback on this thread for a moment... what should be used on the threads of the flared fittings? Clearly no teflon tape (not a fan of that anywhere) and I don't think they even need a PTFE thread sealer since it's the flare that seals, not the threads. But if I'm using stainless steel fittings and am worried about galling them, do I use a touch of anti-sieze or loc-tite or just a few drops of brake fluid to lubricate them when assembling?

Thanks!

[NAZ]

If I could piggyback on this thread for a moment... what should be used on the threads of the flared fittings? Clearly no teflon tape (not a fan of that anywhere) and I don't think they even need a PTFE thread sealer since it's the flare that seals, not the threads. But if I'm using stainless steel fittings and am worried about galling them, do I use a touch of anti-sieze or loc-tite or just a few drops of brake fluid to lubricate them when assembling?

Thanks!

I mostly work with JIC/AN style taper fittings and usually run them dry as they seldom need to be that tight to seal. However, I also know that lubricating the threads (especially on SS & alum) is a safer way to assemble them but be cognizant of the fact that lubrication will also make it easier to over tighten them.

[NAZ]

That's funny! I've been using tape only for over 40yrs and never had any issues. I've never tried any paste, but only because tape has always been fine. Maybe technique is involved?

If that works for you I happy for you. However, you should be aware that yes there is a technique to wrapping that nasty stuff as it is directional. Teflon tape is not a "sealant" and really only lubricates the threads. Works great for PVC water lines if there are no small orifices in the system. The problem with the tape is most don't know how to properly apply it and even when it is properly applied it can still shear and introduce small stringy pieces into the system that can clog small passages.

I've used Teflon tape a lot in my early career and have seen the failures and problems it creates. Enough so that I have learned it has no pace in automotive or hydraulic systems -- there are many superior products that actually are "thread sealants".

If you're happy with the tape, good for you. For those that want to learn more about thread sealants, start your education here and keep searching the internet for more on the subject: https://www.plantengineering.com/articles/guidelines-for-choosing-a-pipe-thread-sealant/

[Briansshop]

...you should be aware that yes there is a technique... I'm aware,my comment was a jab at sarcasm.

[edwardb]

If I could piggyback on this thread for a moment... what should be used on the threads of the flared fittings? Clearly no teflon tape (not a fan of that anywhere) and I don't think they even need a PTFE thread sealer since it's the flare that seals, not the threads. But if I'm using stainless steel fittings and am worried about galling them, do I use a touch of anti-sieze or loc-tite or just a few drops of brake fluid to lubricate them when assembling?

Thanks!

Sounds like you're talking about brake lines? I use brake fluid. Sparingly. Hate that stuff... A little on the threads and a little on the flare itself. Then tighten firmly but not crazy. With the right kind of line wrench (also sometimes called flare nut wrench) that wraps around the nut.

[JohnK]

Thank you. Yes, apologies if I didn't make it clear in my question but I was asking specifically about brake lines. I'm using SS brake lines and SS fittings. I've learned (the hard way) on other SS fasteners (not related to brake lines) that dry assembly sometimes results in galling, and am hoping to avoid that with the brake fittings. I now use anti-seize on all SS fasteners but wasn't sure if that was a good idea on the brake fittings, as I don't want to risk contamination. Definitely planning to use flare nut wrenches also. I appreciate the help.

-John

[Railroad]

I use a drop of brake fluid on the flare and tighten, loosen and retighten new lines.

[toadster]

FYI - more details on types of fluid to use - DO NOT use DOT5

but DOT 5.1 looks good! :)

https://blog.amsoil.com/dot-3-and-dot-4-brake-fluid-whats-the-difference/