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Technical TH350 transmision Cooler line 1/4" NPS question.

Discussion in 'Traditional Hot Rods' started by roju1985, Apr 22, 2019.

  1. roju1985
    Joined: Apr 22, 2019
    Posts: 5

    roju1985

    Hello all,

    So I'm working on swapping a TH350 into my car, I've never really messed with a lot of this stuff before so I'm figuring it out as I go along. From what I've gathered the cooler lines are tapped 1/4" NPS (straight thread) into the transmission case. I've ordered the standard 1/4" NPS to 5/16" inverted flare adapter that you're used to seeing for the cooler lines (https://www.amazon.com/gp/product/B0013FFKE2/ref=ppx_yo_b_asin_title_title_o00_s00?ie=UTF8&psc=1). My question is how do I proceed to seal the NPS threads? Do they need a crush washer or something or is thread sealant enough? it's a tight fit in my car so a leak would be a pain to say the least haha. Thank you.
     
    Last edited: Apr 22, 2019
  2. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    The fittings I've seen have a crush washer. I'd use the ARP thread sealant as well, not teflon tape.
     
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    they usually have aluminum washers. I think that's what they are....
     
    olscrounger likes this.
  4. roju1985
    Joined: Apr 22, 2019
    Posts: 5

    roju1985

    Interesting, I wonder why the fitting didn't come with a crush washer... Thank you.
     

  5. Oilguy
    Joined: Jun 28, 2011
    Posts: 663

    Oilguy
    Member

    If it is straight thread with a sealing washer the threads do not seal anything; it's all done by the washer. I would not put anything on the threads.
     
    olscrounger likes this.
  6. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,216

    ekimneirbo

    Not sure what you need but I would make sure that you have the right thing before you screw it in tight. Learning about different thread types can be confusing and EXPENSIVE. Something I would reccommend to everyone is to go to "Discount Hydraulics" and order a set of their hydraulic fittings charts to hang on your shop wall.
    You need to understand that there are "tapered pipe threads" which tighten and seal as they go in. There are also "straight " pipe threads. Additionally, there are AN fittings which have straight threads usually with a tapered seat
    or somthing to provide sealing. An industrial fitting called JIC is also available that is essentially the same as AN fittings but without the same Military Spec rating as the AN fittings. The JIC are for industrial use and are quality fittings....plus they have sizes which are not available in AN specs. Make no mistake that they are quality components, just not for use on space shuttles etc. Go to this site for their "Thread Identification Guide" and the fitting charts I mentioned.
    https://www.discounthydraulichose.com/free-thread-id-guide.html
    One thing you will find when fooling around with threaded things is that you can do a much better job if you buy the proper tools to work with. Most people buy the cheapo tube benders that bend 3 sizes of tubing. They will get you thru a lot of places, but if you want to make tight bends, you need to watch for ones made like this Rigid bender.
    They have to be bought in individual sizes. YOU CAN RESELL THEM LATER if you want your money back, but they are much better for tight bends in tight places. https://www.ebay.com/itm/Ridgid-Num...056538?hash=item3b2f810ada:g:61cAAOSwXUNcs6QY
    Also you need to familiarize yourself with the angle used by flaring tools. Most automotive and AN flares are going to be 37degrees rather than the 45 degrees used on NPT (National Pipe Threads). If you mismatch, THEY WILL LEAK. A good 37degree flaring tool will cost you more than the cheapo 45 degree tools. I recently purchased a really good 37 degree flare and am really happy with it. You can find some cheaper ones, but this one kind of rolls the 37 degree flare rather than just pushing straight in. What that means is that you won't split the tube while flaring.
    There are also a whole lot more expensive ones out there, but this is a well made tool and I think its fairly priced considering how well its made and how it works. https://www.ebay.com/itm/37-Degree-...920080?hash=item2a74f63990:g:bTMAAOSwfqFaoY8q

    Actually anyone who fools with old vehicles a lot will find that getting the right tools to straighten, bend and flare tubing is a major tool investment. There are tool kits out there that have hydraulic squeezers for making different flares. The difference in price is often reflected by how complete they are. Be sure to get one that has the dies to form the push on fuel lines in addition to the angles. You always have to plumb fuel lines and if you use fuel injection you will need them.https://www.ebay.com/itm/Mastercool...726127&hash=item1a33a046ec:g:stwAAOSw3GFZmzfG
     
    Last edited: Apr 23, 2019
    mgtstumpy and deathrowdave like this.
  7. roju1985
    Joined: Apr 22, 2019
    Posts: 5

    roju1985

    I have ridgid branded benders, and a full master cool flare tool set. I have the correct fittings (NPS NOT NPT), my question was how do those threads seal? I had read conflicting reports that the NPS to inverted flare fitting could seal without a crush washer, presumably on a machined seat of some kind. I'm simply looking for clarification of that.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    I just took a fitting off a virgin transmission case, it's an aluminum washer, indeed.

    washer.jpg
     
  9. roju1985
    Joined: Apr 22, 2019
    Posts: 5

    roju1985

    Thank you for looking, it seems so strange to me the crush washer is the same material as the case itself...
     
  10. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    I expect it's a different alloy, it might even be a different material, but it feels and looks like aluminum.
     
  11. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    I have those fittings converting to -AN, the crushwashers are aluminum, I would use copper if none came with the fitting. Copper washers are easy to find, you can get those assortment kits for under $10 I think.
     
  12. H380
    Joined: Sep 20, 2015
    Posts: 483

    H380
    Member
    from Louisiana

    NPS threads need a gasket or O ring. NPT needs thread sealant. NPTF and NPSF (National Pipe Thread/Straight Fuel) also called Dryseal is naturally leak proof and needs nothing added.
     
  13. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 9,214

    mgtstumpy
    Member

    [​IMG]
    or
    [​IMG]
    Yep, 1/4 NPS with parallel thread and washer for inverted flare and double flared hard line with tube nut (1/2 20 for 5/16" tube or 7/16 24 for 1/4" tube). NOT NPT tapered thread which will crack your case.
     
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  14. deathrowdave
    Joined: May 27, 2014
    Posts: 3,518

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    A drop of blue locktite along with seal washers will secure a leak free seal till you don’t need to worry about it anymore
     
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  15. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,216

    ekimneirbo

    I was trying to point out some things that I thought might help you and others on HAMB who struggle with identifying what they have and what is available as an alternative. I still have to look at charts and think my way through plumbing connections. Take fuel lines for instance. I just ran the plumbing for a fuel injected LY6 in a 56 Pickup. I used a relocated S10 Blazer tank because it has a nice square shape and factory provision for a factory fuel pump and lines plus the stock factory connections. A problem surfaced when I realized that the return line had to work with a 5/16 fuel line. Lots of ways to adapt things, but being hard headed I was bound to use 5/16 line. Although AN fittings are sized in 1/16 sizes...they apparently do not make an AN in a 5/16 size. Couldn't find one listed anywhere, so I guess they don't make them. But, JIC fittings do make them in 5/16...which is a nice thing to know. Still not easy to find though. So, I hoped that some people (you ??? and others) who were not familiar with JIC would learn something from my post.
    I also learned how to solder steel in the process which I found to be very helpful with the way I wanted to do things. There are easier ways to do things, but that was how I wanted to do it.
    So back to your question. Both NPT and NPS are standard pipe threads that you can buy easily. The difference is simply that one has tapered threads for a jam fit and the other has straight threads....which means it needs something else to make a seal.

    Understanding NPT, NPTF & NPS Thread Connections
    NPS, NPT & NPTF

    NPS = National Pipe Straight
    NPT = National Pipe Thread
    NPTF = Nation Pipe Thread Fuel

    Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys. Tapered Pipe Thread is commonly found on ends of pipe, nipples and fittings (ex: couplings, elbows, tees, etc.).
    Sharply angled threads are very critical to joint being tight with no leaks. Thread sealant or tape is typically required to complete the seal. Straight Pipe Threads need a gasket or O-ring to create a seal. While NPT and NPS threads will engage, they do not seal properly with each other.

    That last line is what I wanted to be sure you were aware of with my first post.
     
    mgtstumpy likes this.
  16. Mike Colemire
    Joined: May 18, 2013
    Posts: 1,428

    Mike Colemire
    Member

    I have a pair of 6 AN fittings I was going to use in mine, NPS threads with an O ring. I went to put them in and mine are NPT.
     
  17. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,216

    ekimneirbo

    I don't know how every manufacturer made their transmission lines connect, or whether they all did it the same way.
    Then there is always the possibility that someone along the way substituted something. Below are some attachments which should answer Rojul's question. The thing about tightening a tapered thread into an aluminum case is that it could cause a crack in the case. To me it would seem logical to use a straight thread and a seal, but I don't know that to be correct for all manufacturers. Anyway, the reference below should answer Roul's question.
     

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