Vacuum system requirements for Bullnose trucks.
The vacuum systems on these trucks ran from extremely complex on the later ones to quite simple on some of the earlier ones, especially those w/o A/C or other accessories. But, the vacuum hoses and various components of the "vacuum systems" are, by now, getting quite old and are hard to maintain. So, many times people ask what the minimum is for vacuum lines and components. I would stay that would be:
- Brake Booster: If your truck has power brakes the power usually comes from a brake booster right behind the master cylinder. That hose doesn't usually go bad, but it can happen.
- Vacuum Advance: If you don't have a computer-controlled ignition you'll have a vacuum advance canister on the distributor. It needs vacuum, and I like to run it with ported vacuum from the carb.
- HVAC: Most of the heating and A/C systems use vacuum to control the doors inside the dash as well as the fresh-air vent. A vacuum line usually comes off the little plastic manifold on the firewall and goes to a tee/check valve near the passenger's-side hood hinge or blower motor. One leg after the tee goes to a reservoir that is there to provide vacuum to the system if you floor the accelerator, which kills the engine's vacuum. And the other leg goes into the cab to the HVAC controls and associated vacuum doors - as shown in the EVTM here.
- Transmission: The C6 auto has a vacuum modulator and it gets its vacuum from either the plastic manifold on the firewall or a vacuum tree on the rear of the intake manifold. In the pictures below the plastic manifold on the firewall feeds the transmission, and gets its vacuum from the "vacuum tree" screwed into the intake manifold.
- Speed Control: The factory speed control used vacuum, and that hose usually comes from the vacuum tree on the manifold.
- PCV Valve: You'll have a large hose supplying vacuum to the PCV valve, and the vacuum source is usually a port below the carb.