NP241 Drain plug thread size

Discussion in 'Transfer Cases' started by Schurkey, Sep 18, 2019.

  1. Schurkey

    Schurkey I'm Awesome

    Messages:
    1,010
    Likes Received:
    397
    Joined:
    Jan 14, 2018
    Location:
    The Seasonally Frozen Wastelands
    Decided to dump and refill all the fluids on my new-to-me '97 K2500. Got the transfer case drain plug out, there was only about half-a-quart of fluid in the thing, and it was brown-black when I expected red ATF to come out. Smelled like burnt ATF, thin like ATF.

    Anyway, I go to take the fill plug out...and the Allen socket just spins in the rounded-out fill plug.

    I had to weld a bolt in the Allen hole, then turn the plug out with a socket on the bolt head.

    I've got a bunch of pipe-thread plugs of various sizes, so I grab one that looks the right size, and stick it in the drain hole. The NPT plug threads more loosely that I'd expect, and it goes in way deeper than I'd expect. It also leaks even though I used a good pipe thread compound on the thing before it went into the case.

    I really don't want to have to re-use the reamed-out, bolt-welded plug to seal the case.

    WHAT THREAD SIZE IS USED ON THE DRAIN PLUGS? Metric? It sure doesn't seem to be standard pipe thread.
     
  2. studigggs

    studigggs OBS Enthusiast

    Messages:
    92
    Likes Received:
    24
    Joined:
    Feb 19, 2018
    Location:
    CA
  3. evilunclegrimace

    evilunclegrimace Does not always play well with others

    Messages:
    733
    Likes Received:
    244
    Joined:
    Sep 18, 2017
    Location:
    pennsylvaina
    Thread size should be M22x 1.50 Dorman makes a replacement Part number 090061. Rock auto has them in stock for $3.56 .
     
  4. Schurkey

    Schurkey I'm Awesome

    Messages:
    1,010
    Likes Received:
    397
    Joined:
    Jan 14, 2018
    Location:
    The Seasonally Frozen Wastelands
    The thread size might be right, but the shape of the plug is entirely different. The Dorman unit has a large head with a flange, and a gasket.

    The original plug was simply an external thread, with an Allen recess. No flange, no gasket. That's why I figured it was pipe-thread.

    The case looks like it might accept a flange and gasket, though. I'll have to see if the boss is rough-cast or machined flat. I didn't pay any attention to that while I was under there welding.
     
  5. Schurkey

    Schurkey I'm Awesome

    Messages:
    1,010
    Likes Received:
    397
    Joined:
    Jan 14, 2018
    Location:
    The Seasonally Frozen Wastelands
    Yes, the Dorman plug you recommended worked. The threads must be 22mm X 1.5.

    It may be a good thing that the Dorman plug has a flange and gasket, as the threads would be damaged after I crammed the pipe-thread plug into the case.

    Thanks, folks.
     
  6. evilunclegrimace

    evilunclegrimace Does not always play well with others

    Messages:
    733
    Likes Received:
    244
    Joined:
    Sep 18, 2017
    Location:
    pennsylvaina
    I am glad that you got it fixed. I have never seen a 241 with out the style plug with the flange on it. I believe that all of the aluminum t cases that GM uses take the flanged style plug. The older 205's took a pipe plug as did most of the cast iron t cases
     
  7. Schurkey

    Schurkey I'm Awesome

    Messages:
    1,010
    Likes Received:
    397
    Joined:
    Jan 14, 2018
    Location:
    The Seasonally Frozen Wastelands
    NOPE! Not fixed/not correct.

    Dorman plug still seeps. I pulled out the fill plug (original to the transfer case, at least it was there when I bought the truck) topped-off the fluid, and took a close look at the plug.
    1. My digital caliper shows 22.07 mm at the largest diameter, outside threads.
    2. When the parallel faces of the caliper are in contact with the plug, it's obvious that the plug is TAPERED PIPE THREAD. I didn't see the taper without the caliper as a reference. (Usually I can see the taper of NPT plugs.)
    3. My metric thread-pitch gauge shows that the original plug seems to have a pitch of 1.5.
    4. The NPT plug I tried to use is about one millimeter smaller. The transfer case plug hole has got to be Metric.

    So: YES, the plug appears to be M22 X 1.5, but it's not straight thread like the Dorman plug, and it's not intended to seal with a gasket. The plug is Metric tapered pipe-thread, apparently made to DIN 906 standards (but I'm not absolutely sure about that.)

    I don't see much on Amazon that seems to be correct, unless I want to buy a box of 5 for a hundred dollars.

    For now, I'm turning the Dorman plug tighter, and hoping the gasket stops the seepage. I probably screwed-up the original threads by cramming the SAE pipe plug into the hole. If that doesn't stop the seepage, I'll have to use the fill plug as the drain plug, hope the transfer case threads are OK, and then put the Dorman plug in the fill hole where seepage should be less of a problem.

    Or find another tapered, M22 X 1.5 plug somewhere.
     
    Last edited: Sep 25, 2019
  8. east302

    east302 I'm Awesome

    Messages:
    1,761
    Likes Received:
    555
    Joined:
    Oct 4, 2013
    Location:
    Jackson, MS
    Here’s a link to a parts catalog that has the exploded diagrams with GM part numbers. Maybe having the GM number will help in finding the correct replacement.

    At a glance, it looks like it’s # 14037987.


    https://nemigaparts.com/cat_spares/epc/chevrolet/

    [​IMG]

    [​IMG]


    Sent from my iPhone using Tapatalk
     
  9. Supercharged111

    Supercharged111 I'm Awesome

    Age:
    37
    Messages:
    3,559
    Likes Received:
    1,430
    Joined:
    Aug 20, 2015
    Can you just swipe one from a pull and pay?
     

Share This Page