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Flexplate Question

Discussion in 'The Garage' started by Hossbaby50, May 3, 2005.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    Do Th400's and 700R4's use the same flexplate or are they different?

    It is a mid 80's TH400 if that matters.

    Harley
     
  2. Hossbaby50

    Hossbaby50 3/4 ton status

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    Also, will the flexplate from a gas 700R4 work on a diesel Th400 converter?

    Harley
     
  3. Jagged

    Jagged 1 ton status

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    If you can find any decent books at your library, you can get a Mitchell Collision Estimating and Repair Guide. It gives official GM part numbers for everything in question. If they're the same part number, then they're swappable. Excellent resource in any garage :)
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    It all depends on what year 700R4 you're dealing with. 1986 and earlier will work but if you have 1987 or later the bolt circle on the crank is different.
     
  5. Hossbaby50

    Hossbaby50 3/4 ton status

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    My truck is an 85 so I am hoping it will work.

    I need to reword this a little and ask 2 questions.

    *********************************

    Will a Th400 diesel torque converter bolt up to a 700R4 flywheel?

    Will a diesel flexplate bolt up to a 350 SBC (2 peice rear main I think)?

    Thanks
    Harley
     
  6. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the bolt radius on the 700r4 (expect 4cyl and small v6) is 5.35". the th400 can come in a 5.35" or a 5.75" radius.
    the easy way to tell the difference is if the TC uses a bolt and a nut (like most th350s) is the 5.35" radius. if it uses a bolt into a threaded pad on the TC, its the 5.75" radius. becare full because some are metric threads and some are standard threads.

    but i know the flexplates come in a dual pattern, just can't remember the sizes. i know the th350 and 700r4 use the 5.35" pattern.
     
  7. mosesburb

    mosesburb For Rent Premium Member GMOTM Winner

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    It should. All of the 14" flywheels in trucks that I have seen are drilled for both bolt patterns. You will most likely need the larger one.


    No, it will not.
    You should have a two piece rear main unless you have a very late production '85 which I have seen a few of with a one piece, but the vast majority have the two piece unit.

    If you need a dual bolt pattern flywheel, give me a call, as I believe the one you need is very inexpensive.
     
  8. diesel4me

    diesel4me 1 ton status Premium Member

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    ???????

    I've never looked at my 6.2's flexplate,other than the ring gear teeth--but I thoughtI read somewhere the diesels used the heavy duty torque converter with a 6 bolt pattern instead of the usual 3 bolts...and the diesel flywheel/flexplate ONLY bolts to a diesel crank,the bolt pattern is different than the gas GM motors.. :confused:

    I had a 292 six in van with the 6 bolt converter,and I used the tranny on another vehicle ,the 3 bolts out of 6 lined up with the holes in the flexplate,and it seemed to work fine...not sure it the diesel one(bolt pattern) is the same or not.(I know the stall speed is different on a diesel)...most of GM's gas motors flexplates had both the TH350 and TH400 converter bolt patterns holes in them already,makes swapping trannys easy--the exception is a caddy 472/500,which has ONLY the TH400 pattern,since thats all they used in caddys(RWD)--but you can stuff a TH350 converter in a TH400 to get around that obstacle... :crazy:
     
  9. mosesburb

    mosesburb For Rent Premium Member GMOTM Winner

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    I checked on your flywheel and it's 20 bones if you need one.
     

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