What is this for (vacuum-->transmission line?)

[botboy]

Just curious what this is. I have either a TH350 or TH400 transmission, auto, in my '72 Chevy truck. There's a length of tubing running from a vacuum port in a boss in the intake to the transmission, just curious what this is for and if I'll hurt anything by putting around the yard without it hooked up? I had a vacuum leak there apparently (at least plugging the hole fixed the rough idle problem I had) and I want to drive the truck into the garage since its damn cold out there, but don't want to hurt anything (at least till I can put a manual in its place )

[70short/step]

if you dont drive it far it shouldnt hurt anything. The vaccum line goes to the modulator that you need for it to shift properly. good luck! 70short/step

[dmurphy68]

that vaccume actually shifts you tranny. when it gets to a certian pressure than it shifts. I can not rember what it is called. but it will not hurt anything if it is a short distance
Darren

[Longhorn Man]

putting around the yard is OK, but you won't shift into second untill about 5500 RPM or so.
If you need to drive it down the road like this, you can shift in manually and it'll shift fine. (Start off in low1 and manually go to low2, and then drive)
To figure out which tranny you have at a glance, look for a kick down cable going from the passenger side of the tranny up to the carb. If you have a cable there, it is a TH350, if no cable, then it is a TH400.

[Low67C10]

It goes to the vacuum modulator on the transmission. its just there to help the transmission to decide how early/late or harsh/soft to shift. As long as your just gonna stay in 1st gear its OK to run w/ it unhooked.