9785581
General Motors Bellhousing Part Number 9785581
The B.O.P. "581" is an all aluminum bellhousing.
These clutch and flywheel assembly covers were
manufactured for multiple applications, as evidenced
by two starter housings and dual transmission mounting
bolt patterns.In 1965 General Motors used Dearborn
built (Ford) 3 speeds as a heavy duty option to the
Muncie 3 and 4 speed trans on some models. Instead
of casting different bells they made these more universal.
Front view
Here you can see the two trans mounting bolt
patterns. Four holes tapped 7/16"-14 for Ford 3
speed manual transmissions and four tapped
1/2"-12 for the optional GM production trannys.
Although the housing looks skewed the General
Motors transmission bolt pattern is parallel with
the upper engine mount holes and the gravel
guard flange.
Part #
The part number is cast into drivers side starter "ear".
All original "581" clutch housings I have seen have
the 7 Raised like a speedometer rolling over.
Top view
This picture shows the "V" in the engine mating
flange and is indicative of a Buick, Oldsmobile and
Pontiac clutch cover. There are two 1/4" x 1" slots
above the transmission mounting surface and another
smaller one on the engine mounting flange.
Fork side
The fork hole is 2 1/4" x 3" and accepts the "355"
clutch fork boot. There are two 3/8"-16 taped holes
for the B body z-bar bracket.
Bottom
These bells utilize a one piece sheet metal inspection
cover that wraps around from engine side to bottom,
and is attached by three 1/4"-20 bolts.
Passenger Side View
Passenger side is unencumbered except for the Buick
starter bump.
Engine Side View
Here you can see the two starter "ears" and the engine
mounting flange, with six clearance holes for bolts
and two dowel holes. The starter "ear" on the right is
for Oldsmobile and Pontiacs
while the "ear on the left accepts Buick starters.
Inside View
This view reveals the fork mounting stud location and
beefy reinforcements around all mounting holes.
The BOP bell housings are much stouter and heavier
than Chevrolet bells.
ApplicationsThe B.O.P. "581" is an all aluminum bellhousing.
These clutch and flywheel assembly covers were
manufactured for multiple applications, as evidenced
by two starter housings and dual transmission mounting
bolt patterns.In 1965 General Motors used Dearborn
built (Ford) 3 speeds as a heavy duty option to the
Muncie 3 and 4 speed trans on some models. Instead
of casting different bells they made these more universal.
Front view
Here you can see the two trans mounting bolt
patterns. Four holes tapped 7/16"-14 for Ford 3
speed manual transmissions and four tapped
1/2"-12 for the optional GM production trannys.
Although the housing looks skewed the General
Motors transmission bolt pattern is parallel with
the upper engine mount holes and the gravel
guard flange.
Part #
The part number is cast into drivers side starter "ear".
All original "581" clutch housings I have seen have
the 7 Raised like a speedometer rolling over.
Top view
This picture shows the "V" in the engine mating
flange and is indicative of a Buick, Oldsmobile and
Pontiac clutch cover. There are two 1/4" x 1" slots
above the transmission mounting surface and another
smaller one on the engine mounting flange.
Fork side
The fork hole is 2 1/4" x 3" and accepts the "355"
clutch fork boot. There are two 3/8"-16 taped holes
for the B body z-bar bracket.
Bottom
These bells utilize a one piece sheet metal inspection
cover that wraps around from engine side to bottom,
and is attached by three 1/4"-20 bolts.
Passenger Side View
Passenger side is unencumbered except for the Buick
starter bump.
Engine Side View
Here you can see the two starter "ears" and the engine
mounting flange, with six clearance holes for bolts
and two dowel holes. The starter "ear" on the right is
for Oldsmobile and Pontiacs
while the "ear on the left accepts Buick starters.
Inside View
This view reveals the fork mounting stud location and
beefy reinforcements around all mounting holes.
The BOP bell housings are much stouter and heavier
than Chevrolet bells.
9785581
0.683 HOUSING, Flywheel housing
65-75 All v/8 M.T. exc. 307 (Pontiac)
68-69 350-400 Eng. C.T. (Buick)
70-73 All V-8 (C.T.) (Buick)
76-77 A,X(231) (Buick)
77-78 X(M15) (Buick)
64 F85 V8 S.T. (Olds)
65-75 V8 S.T. (Olds)
66-74 Irrig. Eng. (Olds)
75 260 Eng. S.T. (Olds)
76-77 All(260) (Olds)
77 A (V8 & 6cyl) (Olds)
77-78 X W/M.T.(M15)(V8 & 6cyl) (Olds)
Disclaimer:
Factory correct applications are your responsibility. GM made part and part # changes with no rhyme but a reason (no production interruptions at any cost).
Application charts are for replacement parts that were available at the time of parts book printing, and when possible model specific assembly manuals.
My observations come from the parts I have in my collection or other reliable sources your parts may differ.
If Factory correctness is your goal, do more research, join car clubs,
forums and buy an assembly manual if one is available for your Project Car (you wont be sorry).
This is a fun and interesting part of the hobby!