[Norwood]

I have five 71-72 THICK shakers in my possession right now, one 70-72 "NOS/Service Replacement" and one 73
All the 71-72 Born on car shakers have on the inside of the Fiberglass
BARNUM BROS FIBRE CO INC P
481689
They have a door hinge frame glued in the rear opening
The steel riveted on part has a distinct step all the way around the outside border as well as the hold down wings stamped as one piece. This is the part that is hardest to find and all attempts need to be made to save these as they are distinct to REAL born on 70-72 shakers.
Part# on born on unit

bottom of ear on born on

step on born on

The 1970-72 NOS/ Service Replacement and the 73 have on the inside you can also readily see that the numbers were changed from 481689 to 491982 in a crude manner.
BARNUM BROS FIBRE CO INC P
491982
This tells me that after the 1st design 70-72 steel riveted parts were used up they converted the 73-76 steel by spot welding the mounting ears on in order to hold the unit onto the 70-72 air breather base that's why there are NOS units out there that won't fit the base tabs and also spot welding on the same solenoid bracket that was used on the 70-72. They also used the 73-76 fiberglass by glueing in a 70-72 door frame instead of the frame for the block off.
spot welded on ear



chopped away so they could spot weld the ear on
73-76 lip

changed part number

Of course I can't tell you when Pontiac ran out of the REAL parts and started modifying later parts to work as replacements but that is what they did. So when you say NOS it may not mean DESIRABLE as it very well may be and is most likely different than a born on unit.
So as shakers go Steve's has the CORRECT born on steel and believe me this is the hardest part to find in good shape. I am seeing more and more of these in very bad and rusty shape and most need major repair. So much so that I have repoped the rear sheet metal as its easier to replace it than try to fix it. Steve's is actually in my eyes more desirable than a NOS/Service Replacement unit. JMHO
this is what I see on most. I fabbed a new part for this one to save it