* Online Repair Manuals: Sites like Haynes, Chilton, and others offer online access to repair manuals for classic cars. These often include detailed vacuum diagrams. Search specifically for "1978 Pontiac Trans Am 400 repair manual" on their websites. Be sure it's the correct year and engine size.
* eBay or Online Classic Car Parts Sites: You might find a reproduction shop manual or parts catalog on eBay or similar sites. These often contain the diagrams. Look for terms like "1978 Pontiac Trans Am shop manual," "Pontiac 400 vacuum diagram," or "1978 Trans Am parts catalog."
* Classic Car Forums: Join online forums dedicated to Pontiac Trans Ams or classic Pontiacs. Experienced owners are a great resource and may have scanned copies of diagrams or be able to point you to reliable sources. Search for forums using terms like "Pontiac Trans Am forum" or "1978 Trans Am forum."
* Local Mechanic Specializing in Classic Cars: A mechanic specializing in older vehicles might have access to the diagrams through their resources or repair manuals.
Important Considerations:
* Engine Variations: Even within the 400 cubic inch engine family, there could be variations (e.g., different carburetion setups, emissions systems) affecting the vacuum routing. Be certain to note any specific details on your engine, such as the carburetor type and emission control system if you find a diagram.
* Diagram Accuracy: Always double-check any diagram you find against the actual components in your car. There could be modifications or inconsistencies.
Starting with online repair manuals is likely your best bet. Remember to carefully verify the information with the specific details of your Trans Am's engine and components.
