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Thread: Identify your transmission bell

  1. #1

    Identify your transmission bell

    Both the Chevy and BOPC ( Buick, Olds, Pontiac, Caddy ) transmissions were 6 bolt housings for most of their production life. The original Chevy housing was 7 bolt and thats why their trans housings have a peak. In fact, most Chevy blocks were manufactured with the top center bolt hole drilled and tapped long after Chevy had changed to a 6 bolt housing.

    So how do you tell the difference between the common as dirt Chevy pattern and the far more desirable ( to us ) BOPC housing?
    1. Well, the first and most commonly stated visual reference is the Chevy peak versus the BOPC saddle at the top of the bell housing.

    Here's a picture of the Chevy ( L ) and BOPC ( R ) pattern bells:

    Notice the engines in the background? We'll be taking a closer look at them in a second.

    2. Also, only the two bolts below the alignment dowels share the same position between the two patterns. This is why a dual-pattern housing has 10 bolts, all the holes above the dowels must be duplicated. A Chevy bell has two bolts on each side aligned vertically with the respective alignment dowel. A BOPC bell only has the bottom bolts aligned vertically with the dowel and the higher bolts are moved inboard.

    Here is the closeup of the blocks. A Chevy 350 and 1970 Buick 350:


    Then we have the differences between the most common GM automatics, the TH-400 BOPC short-tail ( L ), BOPC long-tail ( C ) and Chevy TH-350 ( R ):


    Here's a Super Turbine 400 ( early name for what is basically a Turbo-Hydromatic 400 ) for a 1965 401 Nailhead. Notice that even though it's still a 6 bolt pattern ( the second hole up from the bottom on both sides is for a guide pin, not a bolt ) it's wildly different from the later 'standardized' patterns. I have no idea if this pattern is found on anything besides Nailheads.





    back of 215 / Land Rover engine
    Roverbell-backofengine_zps7a351c10.jpg
    Last edited by bob k. mando; 01-24-2015 at 02:05 PM.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

  2. #2
    Here's a picture of a BOPC TH350 connected to an Olds engine and a Dual pattern trans:


    Interestingly, I've seen a factory dual pattern Manual housing within the last month.

    Manual transmission bells:
    Buick bell (cutout for starter on passenger side only) with a GM manual trans pattern on the back


    BOPC bell (has cutouts for a starter on both sides of the bell) with both a GM and Ford manual trans pattern on the back. The GM pattern has the 4 bolts in it.



    Buick 215 / Rover Bell
    RoverLT77bellhousing_zps6770580e-1.jpg
    Last edited by bob k. mando; 01-24-2015 at 02:03 PM.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

  3. #3
    Join Date
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    Thanks for posting this important information with photos
    this will help many owners with their projects.
    Guyopel
    The early bird gets the worm but the second mouse always gets the cheese.

  4. #4


    1 - Aluminum Powerglide 14 bolts
    2 - TH200 Metric 11 bolts
    3 - TH350 13 bolts
    4 - TH400 13 bolts
    5 - TH200-4R 16 bolts
    6 - TH700-R4, 4L60, 4L60E 16 bolts
    7 - 4L80E 17 bolts




    BOPC bell pattern, begins in 1964 for Buick small blocks



    pre-1965 Pontiac transmission bellhousing bolt pattern and dimensions, THIS IS NOT A BOPC PATTERN:


    Chevrolet transmission bellhousing bolt pattern and dimensions, note that while Chevy retained the center peak, they have not actually used the top hole since the 1960s. This means that most Chevy transmissions that you find will only have 6 holes in the transmission bell. You must compare the holes above the dowels to truly determine whether you're dealing with a Chevy, BOPC or early Pontiac bell:
    Attached Images Attached Images
    Last edited by bob k. mando; 01-01-2015 at 08:25 PM.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

  5. #5
    heh, we took an extra TH-400 over to the guy with that dual pattern manual bell (he needed one for his 500 Caddy powered 1 ton pickup) and he just handed us the bell + saginaw trans. bonus!
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

  6. #6

    Exclamation 400 nailhead trans bellhousing picture

    This is off a 1965 401 nailhead .It is a turbo 400. out of a 65 rivthe second holes from the bottom on each side are guide pin holes.I have more pic ,but no more room .If you would like to have pics ofthe back of the bell or engine block.Just contact me thru this site

    Rocky
    Last edited by SFC ROCK; 01-02-2007 at 06:56 PM.

  7. #7
    can you post a pic from the rear of the trans also? i've already copied this one if you need to delete for space reasons.

    edit: full size pic added to OP.
    Last edited by bob k. mando; 01-01-2007 at 11:36 AM.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

  8. #8

    Identify your transmission bell

    Here's a picture of the back of the bell housing. Will put a full lenght picture on as soon as I take it.This trans look like any other GM 400 except for the bell housing
    Attached Images Attached Images

  9. #9

    Message to Bob

    Hey Bob did you get the picture of the back of the nail head bell housing?
    Last edited by SFC ROCK; 01-11-2007 at 07:15 PM.

  10. #10
    yep, got it.

    thanks!
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

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