It's highlighted in red. Looks like it goes down next to the tranny. This is on a 70 Olds 98. Ichecked my FSM and did not see it listed there...

 

I was trying to figure that out too on my dads 70 88. I think it has something to do with the vacuum modulator line that goes from the tranny to the intake manifold. I could be wrong though. It is really hard to tell where it goes unless you jack up the front end which is what i am going to do tomoro.

 

Actually I just replaced the engine and I see this line in the before picture but I do not see it now. Im not worried about keeping it 100% original, and I am thinking that that line goes to my tranny. If it does go to the tranny, I was wondering if it is ok to connect this line to the carb vacuum port on the front of the carb?

 

It's the tranny vacuum modulator line and it goes to the front port as you said. There should be a three post tower screwed into the intake manifold at the front just forward of the carb...this is temparature control of vacuum for the distributor and tranny...hope this helps

 

The vacuum modulator line to the transmission should only be connected directly to manifold vacuum. It should NOT be connected to any thermal vacuum switch.

 

Thanks Joe! One more thing though. My intake only has 2 vacuum ports (It's from a 76) One of them goes to the brake booster and the other one goes to the vacuum tank for the Heat/AC I still have my carb from the original engine, and the only extra vacuum port is on the left side on the front of the carb. I am not sure if it is ported vacuum or not.

Do you think I can hookup to the carb port, or should I try to T off the one for the Heat/AC system?

 

You can use the carb port so long as it is not ported vacuum. Just connect a vacuum gauge and watch what it does with the engine running. If vacuum at the port is near zero at idle, but goes up as you open the throttle, that's ported. If it has vacuum full time at idle, it's manifold vacuum, which is what you want.

It's also perfectly acceptable to tee into the line to the vacuum storage ball - just be sure you tee in between the manifold and any check valve, not after the check valve. Alternately, just unscrew the vacuum tap from the manifold and replace it with one having more ports.

 

Thanks Joe! Hopefully Ill have er on the road today! Woo hooooo lol

 

The vacuum line goes to the transmisson vaccum modulator,,,,It then routes to the front of the engine where it connects to a T...The other 2 ports on the T connects to the bottow port on the ported vaccum switch,,The other port on the t connects to a air fitting hooked to manifold vaccum

 

My metal trans modulater line is connected to ported vacuum on a 650 edlebrock carb.
there are threee ports on front of carb.
left side (ported vacuum port)
middle (pvc port)
right is (full time vacuum port.)
So you say my trans line should go to the right port which is full time vacuum ,? right now my vacuum advance on the hei is hooked up to the ful time vacuum port ?
car is real sluggish and idles rough.