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Swap-a-bility of flexplates

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by PetaKane, Feb 15, 2003.

  1. PetaKane

    PetaKane 1/2 ton status

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    Did Chevy change the flexplates very often? I've got a block from a 97 and I'm using a flexplate from my 87. Both motors being 350's, were there any differences? The tranny I'm using is a T400 I'm not sure that makes any difference though. Anyway I'm gettin ready to pull the tranny for a rebuild and I may as well change the flexplate as well. Just wondering if I need one for a 97 or if the regular ones from Summit will work. Thanks
     
  2. the professor

    the professor 1/2 ton status

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    There were some large diameter flex plates..or small diameter ones...Mostly early and BB's have the large dia one
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    Either will work, but you need to match the starter to the number of teeth on the flywheel
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    Most late models use the smaller flexplate, so your 87-90 should be ok..
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    There are also 2 diameter torque converter mounting holes...for an 11" and 12" (most lock-ups are 12")-not counting specialty...
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    Some, but not all, flex plates are drilled for both diameters....they will have 6 TC holes instead of 3...
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    SB400 & BB454 carry an "imbalance weight" on the flywheel/flexpalte,... external engine balance...and CANNOT be used on anything else..and MUST be used on those engines..
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    TH350 & TH400 torque converters will interchange.....not TH350c lock-up or the TH400 variable pitch...700's are completely different
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    USUALY a SB will use the 11" converter a BB the 12"
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    Has to do with torque capacity and stall speed..bigger more ccapacity, lower stall
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    Use a small diameter TC, in something heavy, with a BB..you get 22-2300 stall, and alot of slippage (I tried one in my K20/454)..use a 12" now...crisper response...

    11" is uaual on a SB..but some people like the lo-stall (around 15-1800rpm) of a 12" converter on a SB /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     
  3. PetaKane

    PetaKane 1/2 ton status

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    Thanks Professor.. How can you tell if your T400 is variable pitch or not? I don't know what year mine is the only thing I know about it is that it came out of an M1008 and it's mated to a 208 transfer case. I'm gonna try to tackle my torque converter squeal with a new flexplate and converter and I needed to make sure that I ordered parts that would work together. Looking at TCI flexplates in the Summit catalog, I see that they offer a 168 tooth plate for 'all chevy V8' and it's internally balanced. Then they've got one for 86-94, externally balanced. It's a 168 tooth also, and they both have the dual bolt patterns. Does anybody know why the 86-94's are externally balanced? Thanks again.
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    The crankshaft bolt circle on the 85 and earlier is different than the 86 and later, 85 and earlier being 3.58" and the 86 and later being 3.00" bolt circle. All SBC's 86 and later use an external balanced flexplate.
     
  5. ZonkRat

    ZonkRat 1/2 ton status

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    Just want to add,the flywheels bolt circle changed when GM went to one piece rear seal about 85 or86. /forums/images/graemlins/thumb.gif
     

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