67-69 L88 distributor vacuum control, 1115373

[Richard K.]

Since the 67-69 L88 distributor vacuum advance unit doesn't have a connection for a vacuum hose, does it serve a vacuum function? Was this a "dummy" unit that was installed at the factory for convenience and appearance?

[Paul D.]

Re: 67-69 L88 distributor vacuum control, 1115373

I think it is in place to hold the breaker plate stationary. Having never held one in my hand, I can't say if it contained a spring and diaphragm. If it does, it would act just like a non functioning unit or one without vacuum hooked up. I guess this was easier than a bracket or special part to accomplish the same thing. If there was a specific reason, I would love to hear it. Chip.

[Duke W.]

Re: 67-69 L88 distributor vacuum control, 1115373

The single point breaker plate and TI stationary pole piece are free to rotate. The VAC is what establishes rotational orientation of the breaker plate/stationary pole piece, and its static position (zero vacuum) establishes initial timing.

Since the L-88 is a racing engine, not intended for road use, there was no need for a vacuum advance, but a method was needed to "lock" the rotational orientation of the stationary pole piece. The decision was to use a conventional VAC. Offhand I don't recall the part number, but it didn't make any difference because the nipple was cut off at Tonawanda to preclude anyone from trying to connect the VAC to a vacuum source.

My Cosworth Vega's HEI has no VAC - an emission control decision, but a VAC or something else is required to lock the stationary pole piece in place, so a molded plastic piece was designed to do the job. I don't know if it was used in any other HEI applications.

Duke

[Joe L.]

Re: 67-69 L88 distributor vacuum control, 1115373

The single point breaker plate and TI stationary pole piece are free to rotate. The VAC is what establishes rotational orientation of the breaker plate/stationary pole piece, and its static position (zero vacuum) establishes initial timing.

Since the L-88 is a racing engine, not intended for road use, there was no need for a vacuum advance, but a method was needed to "lock" the rotational orientation of the stationary pole piece. The decision was to use a conventional VAC. Offhand I don't recall the part number, but it didn't make any difference because the nipple was cut off at Tonawanda to preclude anyone from trying to connect the VAC to a vacuum source.

My Cosworth Vega's HEI has no VAC - an emission control decision, but a VAC or something else is required to lock the stationary pole piece in place, so a molded plastic piece was designed to do the job. I don't know if it was used in any other HEI applications.

Duke

Duke------

The distributor vacuum control GM #1115373 was manufactured without a vacuum nipple. I don't think that any were removed at Tonawanda. I have seen these with 2 different configurations, though. One style has an outward tit in the center. The other has a hole that is somehow sealed with a tiny internal plug that is sealed by a flare. Curiously, all of these 1115373 vacuum controls have "12" embossed on the bracket in the area that would normally have embossed the maximum degrees advance the control could produce.