1968 vacuum issue

[Hank H.]

Guys, you have been very helpful to me tonight on some other issues. I have one more question re: 1969 BB

On a cold engine I have very little vacuum, even after kicking the fast idle down. Headlight doors are very slow (one faster than other) and wiper door is inop. After driving several minutes, all systems work properly until the next shutdown. Ideas? thanks

[Gene M.]

Re: 1968 vacuum issue

Use a vacuum gauge to check engine at start up. I would suspect the problem in in the hoses or check valve. Some where there has to be a small leak, maybe in the stowage air tank. If lights are going up (even if slow and not together) then intake manifold has vacuum.

[Jack H.]

Re: 1968 vacuum issue

Plus, don't presume there's only ONE leak in the system! The BW to troubleshoot is by getting a vacuum system troubleshooting pamphlet (several different versions are available from various catalog houses) to understand the flow of the system in general.

Then, you start at the intake manifold and work your way along the various sections checking vac pressure relative to what you started with looking for drop(s) of more than 1-2 psi.

Common culprits are:

(1) The system filter is plugged (they were to be changed periodically) resulting in SLOW air movement.

(2) The check valve downstream from the in-line filter isn't closing properly allowing vac to leak backwards.

(3) Rubber hoses are cracked around connecting nipples.

(4) Vacuum actuators (headlights & wiper door) are leaking.

(5) Vacuum relays are leaking.

(6) Vac reservoir is leaking.

(7) Cockpit vac lines (headlight switch, wiper servo, and override switches) are disconnected, mis-routed...