Due to the size of FE-series engines and the close confines of the Mustang engine compartment, Ford found it necessary to mount a shield (identified by basic part number 19C842) to protect the heater blower motor (for cars without air conditioning) or the air conditioning expansion valve (for cars with air conditioning) during engine and transmission installation on Mustangs equipped with a 390, 428 CJ, or 428 SCJ engine. This shield is made from stamped steel and is typically painted the same semi-gloss black as the firewall itself. There are no stamped or cast identifying numbers on the shields, but the service part numbers are described in Ford's Master Parts Catalog (MPC) and the engineering numbers can be cross-referenced from the service part numbers. Interestingly, the 1970 Osborn electrical assembly manual (published by Jim Osborn Reproductions and available from most Mustang parts vendors) includes this note:
"AFTER ENGINE DECKING IS COMPLETE AND BEFORE STARTING ENGINE, REMOVE SHIELD & REPLACE EXISTING SCREWS (ITEM-13)"
This suggests that the shield was supposed to be removed by a line worker after the engine and transmission were installed, with the worker reinstalling the screws used to secure the shield. Perhaps Ford accountants wanted the shield re-used to reduce assembly costs. It appears, though, that a great many of these shields were left in place instead of being removed. Observations of original cars indicates that there were multiple shields in different configurations, though not all of the shields were available as service parts. Here are the known engineering and service part numbers according to Ford documentation:
|Application||Engineering Number||Service Part Number|
|1968 428 CJ||C7ZA-19C842-A||C7ZZ-19C842-A|
|1969 and 1970 390 and 428 (except 428 CJ)||C9ZA-19C842-A||C9ZZ-19C842-A|
|1969 and 1970 428 CJ||C9ZA-19C842-B||C9ZZ-19C842-B|
So what are the differences? There were different bases used to mount the shields on 1967 - 1968 firewalls and 1969 - 1970 firewalls, and two different extension arms, or "fingers", used to protect the heater blower motor or air conditioning expansion valve. The fingers could be either cut off, pressed flat, slightly extended with a slight bend at the end, or fully extended with a slight bend at the end. The versions with a fully extended finger have been seen on cars equipped both with and without air conditioning. The versions with a clipped, flat, or slightly extended finger are commonly seen on cars without air conditioning. A clipped finger won't protect the a/c refrigerant lines and expansion valve, and a flat or slightly extended finger will interfere with them.
Top view of firewall shields.
C9ZA-B version at left, C7ZA-A version at right.
The Osborn assembly manuals illustrate a part that looks like the shield show above on the left. Note the differences circled above. The mounting surface and holes (circled in red) are slightly different, and the version on the right includes a fully extended finger (circled in yellow). This finger is absent on the version to the left. The C9ZA-A shield has the long finger of the C7ZA-A shield and the mounting base of the C9ZA-B shield.
Here's a comparison of two different long finger styles. The shield on the left (part numbers unknown) has the 1967 - 1968 mounting base and a flat finger. The shield on the right (a C9ZA-A shield) has the 1969 - 1970 mounting base and a slightly extended finger.
Here are examples of the 1967 - 1968 flat-finger and long-finger shields (images courtesy of Wayne St. Jean (left), Bob Gaines (center), and Paul Byrnes (right)):
Finally, here's an example (image courtesy of Garey Maib) of a slightly extended finger style shield that was bent further for used on a car equipped with air conditioning:
The shield was installed prior to the application of sealer/sound deadener on the firewall. If the shield was removed as described in the assembly instructions, there should be visible witness lines to mark where the shield was.