70 Vacuum Tank

[Jeff A.]

The car has no vacuum tank although the build sheets show a part number. One headlight comes up/down sooner than the other, will not having a tank cause this problem? Where does the tank actually mount and with what type of screws bolts etc. Thanks.

[Jack H.]

Re: 70 Vacuum Tank

Vac reservoir installation (where/how does it mount) should be shown in your copy of the AIM. As far as system level effect, the tank is there to 'buffer' vac supply during periods when intake manifold's vac source is low and/or there are system level transient disturbances in vac level (both happen under acceleration and deceleration).

Will the absense of a reservoir make one headlight door open sooner than the other, well it 'could' but the part needs to be in the system to prevent 'dancing' action (headlight and wiper door that 'flutter' or 'dance' under just right conditions. As far as the headlights opening in EXACT unison, with a well maintained car there's little, if any, noticeable difference in synchronization.

Getting one of the Vacuum Troubleshooting guide phamphlets offered by various Corvette parts catalog houses, reading and understanding the dual mode nature of the Shark's vaccum system (a parallel system with one side performing 'servo' functions, actually moving this/that part; and the other side doing control functions, saying when to move this/that) will go a long way toward de-mystifying what's going on and allow you to find/fix problems.

If there are leak(s) in the system, the symptom you describe can also occur even with a vacuum reservoir present. So, the answer's not a clear & dry one.

[Patrick H.]

Re: 70 Vacuum Tank

Jeff,

The tank is mounted just behind the left side wheelwell, "inside" the engine compartment, and just "inside" the left hand gill. You will see the holes in the wheelwell where it should bolt in. I'd be surprised if it's really missing (unless, of course, your car is in parts and it's lost). The number of ingoing vacuum lines don't match the number of outgoing ones, so you'd have problems.

Patrick