The difference between a SB and BB 727

[d72hemi]

I am about to go junk yard hunting for a BB 727. How do you tell the difference between a SB and BB 727 if you can't read the numbers? is there any visual clue between them?

Ian

[BigBlockSam]

 

[Ghoste]

The smallblock one is 15.32 inches side to side on the bellhousing and the big block one is 15.93 across the width.(that's from center to center of the outside bolt holes)  Also the starter centerline is slightly under the centerline of the trans on the small block and even with the trans center on the big.  The bolthole pattern is also slightly different between the two and the overall shape of the bellhousing with the smallblock one being somewhat flatter across the bottom.

[Ghoste]

Diagrams, small.

[Ghoste]

And big.

[tecmopar]

First thing that catches my eye is no bolt hole at top center on a BB bell area.

[375instroke]

The starter nose boss is also in line with the input shaft on a BB, and lower on a SB.

[d72hemi]

Thanks to all of you! Time to find a BB 727 for my first trany rebuild attempt!

Ian

[gtx6970]

small blocks trans have two 3/8" threaded bosses on the lower bellhousing for the re-inforcements struts to atttach.
big block trans have 4 smaller ( 1/4x20 )  threaded bosses to attach the shield to

[GreenMachine]

   The easiest way for me to tell the difference is the upper 2 boltholes on the SB are further apart. That means that the square hole is further away from the upper right bolthole. There is a distance of about 2 fingers (side by side) from those 2 holes on a SB, and a tad more than 1 finger on BB.

[BROCK]

Thanks to all of you! Time to find a BB 727 for my first trany rebuild attempt!

Ian

The 727 is a simple straitforward design & a pleasure to rebuild!  I used a B&M kit.  It
is invaluable for its directions as is the factory service manual.  I did have to find other
service parts beyond what the B&M kit provided though.

Enjoy!

[John_Kunkel]

The bottom bolt holes are the easiest way to tell a BB from a SB.