1968 Cadillac Vacuum Manifold V2

This is the second version of my take on classic Cadillac's vacuum manifold. The first version, while more dimensional accurate and closer to the original, is a lot harder to print and more fragile (see here).

What is it?

The vacuum manifold takes engine vacuum and distributes it to various multiple devices (automatic climate control, vacuum door locks, vacuum storage tank and others). Over time, these tend to become very brittle and it doesn't take much to break off one of these ports. If it breaks, you'll have a hard time finding a replacement, because these parts have become quite rare. You might get away replacing the whole thing with a few T-pipes, but this leaves behind some of the functionality. 

Only three of the ports are “full vacuum”, the other two contain a restriction of 0.5 mm (0.020") to reduce the air flow. The vacuum diagram (see attached pictures) only mentions one restriction. However, when I disassembled my broken vacuum manifold, I discovered two intentional restrictions - one on the check valve (right outlet when viewed with mounting tab pointing south), supplying vacuum to the control head vacuum valve and another one in the single outlet with smaller diameter, connecting to the neutral switch vacuum valve.

Additionally, one of the restricted ports contains a check valve to allow air flow only in one direction. This check valve is of course not printable, but I found a good replacement - just check this Google search.

Improvements over version 1

• increased wall thickness, adds lots of stability
• added option for 4 or 5 port version (needs confirmation until I publish it)
• moved 0.5 mm (0.020") restrictions outwards so they can be drilled to final size easier using a proper drill bit
• moved ports away from bottom to increase distance to firewall for easier tube installation
• added internal support structures for easier printing
• made bottom side completely flat to reduce amount of necessary support
• moved project to OpenSCAD for better accessibility

A few tips for making the part

• use ABS (or something with even better temperature stability), PLA won't do!
• layer height: 0.1 mm (0.3 mm initial layer)
• minimum wall line count: 3
• wall ordering: inside to outside
• top/bottom thickness: 1.2 mm
• infill: 40%
• support is needed only for the ports: normal support (not tree support), only touching buildplate (otherwise your slicer might try to generate support inside of the ports), dense support interface
• the usual ABS parameters (brim, heated chamber/bed, 50% cooling fan, …)
• sand the ports with fine sand paper (see below)
• use a 0.5 mm (0.020") drill bit to drill the restrictions in the two smaller ports to their exact size (although it should also work if you use it “as is”).

I checked the printed part with hose loops, vaccum pump and a vacuum meter. First, I was disappointed because the vacuum dropped quite quickly. After sanding the ports with fine sandpaper to remove any small steps and residues, it was much better. It got nearly perfect when I added some vaseline (other grease might do, too) to the ports before connecting the hoses - now it holds vacuum really well.

If you have anything to add, please comment, I would be happy to improve the model!

Open questions

• Which model years and models was this part used? I'm not sure with the range 1967-1970.
• Which ports does the 4 port version have? I've seen pictures, but I'm unsure if just one port is left out or if they re-ordered the ports (regarding the air flow restriction).