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Buick Automatic Transmission Identification

contributed by bob k. mando

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 that's 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:
bellhousing_patterns_2.jpg - 24886 Bytes

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 close up of the blocks. A Chevy 350 and 1970 Buick 350:
bellhousing_patterns_1.jpg - 30918 Bytes

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 ):
bellhousing_patterns_3.jpg - 34508 Bytes

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. Nailhead turbo bellhousing pattern

back of 215 / Land Rover engine 215 bellhousing pattern

Here's a picture of a Dual pattern trans:
BOPC TH350 and Dual Pattern

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
Buick Manual Transmission Bell Housing

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. BOPC manual transmission bell housing

Buick 215 / Rover Bell

  • 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

Dynaflow:
NOTE: Following markings are stamped on aluminum plate low on the transmission, on left side and between the main transmission case and the front pump housing.
IDENTITY
LETTER
USAGE
H '53 40 ser.
J '53 50, 70 ser.
K or M '54 40,60 ser.
P '56 All
R '57 All
S '58 All
T '55 50, 70 ser.
W '59 All

Here's a few code for the Turbo 400s!

 

YEAR APPLICATION CODE
1964 300 V8 LeSabre BU
  401 V8 column shift BJ
  401 V8 console shift BK
  425 V8 column shift BL
  425 V8 one carb console shift BN
  425 V8 two carb column shift BP
  425 V8 two carb console shift BQ
1965 300 V8 LeSabre BU
  401 V8 3.07 axle BJ
  401 V8 Riviera (3.23 axle) BR
  425 V8 4bbl. carb 3.07 axle BN
  425 V8 3.23 axle BT
  425 V8 two carb 3.07 axle BO
  425 V8 two carb Riviera (3.42 axle) BS
1966 340 V8 LeSabre BU
  401 V8 BR
  425 V8 Grand Sport & Riviera BS
  425 V8 all others BT
1967 340 V8 LeSabre 400 BU
  400 V8 GS400 BA
  430 V8 Wildcat, Electra & Riviera BT
  430 V8 Sport Wagon 400 BW
1968 350 V8 LeSabre BU
  400 V8 Sportwagon BW
  400 V8 GS 400 BA
  430 V8 Wildcat, Electra & Riviera BT
1969 350 V8 LeSabre BU
  400 V8 Sportwagon AW
  400 V8 GS 400 BA, BB
  430 Wildcat & Electra BC
  430 Riviera BT
1970 455 GS BA
  455 GS Stage 1 BB
  455 Riviera BT
  455 all others BC
1971 455 GS BS
  455 GS Stage 1 BB, OW
  455 Riviera BT
  455 all others BC
1972 455 GS BS
  455 GS Stage 1 BB
  455 Centurion high performance BU
  455 Riviera GS other models with performance rears BT
  455 all others BK,BC
1973 455 Century & Regal BS
  455 Century & Regal Stage 1 Ram Air BB
  All high performance BT
  All others BC
1974 455 Century & Regal BS
  455 Century & Regal Stage 1 Ram Air BB
  All high performance BT
  All others BC
1975 350 Lesabre (Turbo 375) BK
  400 OC
  455 BC,BT
1976 350 Lesabre (Turbo 375) BK
  455 BC
  455 BT
1977 350 Century wagon BC,BB
  350 OB
  403 OC
1978 350 Electra & Riviera OD
  350 Electra & Riviera OB
  400 BC
  403 OD
1979 350 Electra (Buick engine) BB
  350 Electra (Olds engine) OB
  403 Electra OC,OD
1980 350 Electra (Buick engine) BB
  350 Electra (Olds engine) OB
1981 350 Electra (Buick engine) BB

BOPC bell pattern, begins in 1964 for Buick small blocks.
bopc bellhousing diagram

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

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:
SBC bellhousing diagram

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bob k. mando has worked out an .xls spread sheet that calculates all your powertrain combinations with click in transmission choices!
Click HERE to download it!



 
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