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  •  » AOD Swap Flexplate and TC drain plug

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    12/12/2025 11:22 AM  #1

    Jieve
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    Registered: 5/29/2014
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    AOD Swap Flexplate and TC drain plug

    About to pick up a 28oz 164 tooth flex plate for the 351W /AOD swap. I notice the AOD torque converter has a drain plug the original C4 did not have, does this interfere when bolting up to an older small block 28/164 flex plate? I have seen that there are aftermarket versions that have a cutout for this, but I'm guessing the originals didn't. 

     

    12/12/2025 11:42 AM  #2

    rpm
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    From: Bakersfield, Ca
    Registered: 9/17/2013
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    Re: AOD Swap Flexplate and TC drain plug

    Is the aod flex plate you are picking up or or aftermarket? Be aware that not all flex plates are symmetrical, and have different offsets.

    Bob. 69 Mach 1, 393W, SMOD Toploader, Armstrong  steering, factory AC.
     

    12/12/2025 12:55 PM  #3

    Jieve
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    Re: AOD Swap Flexplate and TC drain plug

    It's not aftermarket, the weight is stamped D91P-AA (so '79). I have no idea what vehicle this is from, I don't think the owner knows either, and I'm still waiting to verify that this is indeed 28oz (although I thought 50oz was introduced in '81). Unfortunately every C4-AOD swap site I've read makes mention of the 164T and 28oz, but I haven't seen a single post anywhere that mentions offsets, torque converter drain plug, etc

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    12/13/2025 10:27 PM  #4

    Greg B
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    Re: AOD Swap Flexplate and TC drain plug

    I have a few 164 28oz.  flex plates laying around.   What exactly would you like a picture of?  I can check them tomorrow and make sure they have holes that align with a drain plug.  So if it does, the picture can give you reference where the hole should be.

    If multiple things can go wrong, the one that will go wrong will be the one that causes the most damage.
     

    12/14/2025 1:11 PM  #5

    Greg B
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    Re: AOD Swap Flexplate and TC drain plug

    I looked pretty quick cause it's like 10 degrees down there, I quickly dug out 4 164 tooth flex plate s.  All four have four holes for the drain plug making it impossible to install it wrong.







    I do notice a couple are oblong, and a couple are round.

    If multiple things can go wrong, the one that will go wrong will be the one that causes the most damage.
     

    12/14/2025 3:57 PM  #6

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: AOD Swap Flexplate and TC drain plug

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    12/16/2025 2:58 AM  #7

    Jieve
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    Re: AOD Swap Flexplate and TC drain plug

    Thank you guys for the responses, and thanks Greg B for braving the ice box for the sake of this discussion. So the bigger holes are specifically for drain plug access, got it. 

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    12/28/2025 1:51 AM  #8

    Jieve
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    Re: AOD Swap Flexplate and TC drain plug

    Re-visiting this as I've ended up with 3 flexplates now, none of which are workable for the 351W / AOD swap. I see that California Pony Cars has a 164T 28oz Flexplate they claim has a 7/8" offset as opposed to what they say is the typical 1" offset commonly found. This flexplate is double the price of some new ones I've found elsewhere, anyone know what the significance is of this offset?  Does it have something to do with the 2-piece main seals on early 351W engines? (I seem to recall reading something about this)

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    12/28/2025 1:10 PM  #9

    MS
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    From: Canyon Lake, Texas
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    Re: AOD Swap Flexplate and TC drain plug

    Type of rear main seal has zero to do with the flexplate.
    The ones in the pic I posted are extras, if you should need one.  One is 157, one is 164T.  Both are 28 oz. imbalance.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    12/29/2025 3:08 AM  #10

    Jieve
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    Re: AOD Swap Flexplate and TC drain plug

    Thanks for the offer MS. Can you PM me what you'd want for it?

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    1/14/2026 10:38 PM  #11

    Jieve
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    Re: AOD Swap Flexplate and TC drain plug

    MS, received the flexplate, thanks!

    I'm revisiting this thread as I've noticed that using the original spacer plate/ring from the 351W that attaches to the bellhousing side of the flex plate causes the crank screw heads to stick out far enough to contact the AOD torque converter, and bows the flexplate very slightly when the nuts are torqued down. Is there a different spacer ring that should be used, or should this spacer ring be removed altogether with an aftermarket flexplate? 

    Last edited by Jieve (1/14/2026 10:38 PM)

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    1/15/2026 6:21 AM  #12

    MS
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    From: Canyon Lake, Texas
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    Re: AOD Swap Flexplate and TC drain plug

    Jieve wrote:

    MS, received the flexplate, thanks!

    I'm revisiting this thread as I've noticed that using the original spacer plate/ring from the 351W that attaches to the bellhousing side of the flex plate causes the crank screw heads to stick out far enough to contact the AOD torque converter, and bows the flexplate very slightly when the nuts are torqued down. Is there a different spacer ring that should be used, or should this spacer ring be removed altogether with an aftermarket flexplate? 

     
    It is called a flexplate because it bends as the bolts to the torque converter are torqued down. The spacer plate you speak of…. Is that the washer looking thing that has six bolt holes in it?   It goes on after the flexplate is fitted to the crankshaft, and provides extra bearing area for the bolt heads against the flexplate.  The bolts typically have a thinner head than a normal grade 8 bolt. It can be omitted but you should be able to use it.  Be sure your block spacer plate is perfectly flat.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    1/15/2026 12:05 PM  #13

    Jieve
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    Re: AOD Swap Flexplate and TC drain plug

    Yes, the thing I'm calling a spacer plate is the plate with the 6 holes. I have the crank-to-flex-plate bolts from the original C4 and the current 351W plates, they have the same head size. I get that the flex plate is supposed to be able to flex, what I'm not sure about is if those bolt heads are supposed to be contacting the converter the way they are. This is the stock AOD converter, I'll likely use a reman one once installed but want to make sure everything will bolt up correctly. 

    Last edited by Jieve (1/15/2026 12:05 PM)

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