Hi Olds fans - I hope you are finding yourself well. I am looking for some technical advice regarding vacuum lines - what vacuum hose routings should the engine have?? Under the hood of my '68 Delmont is a 455 with a Rochester 4BBL QuadJet. The Delmont is currently in storage (for only a few more weeks!!) and I am going only by memory and the attached picture. As you can see, the engine has a (circled) Thermal-Vacuum Switch (TVS) that currently has no attached vac lines. So starting from the TVS, what are the typical vacuum line routes? Does anyone have a diagram or advice? I think a vac line should run from the upper port of the TVS to the distributor vac advance, the middle port of the TVS to the carb, and the lower TVS port to the intake manifold. But I could be wrong... Please excuse my novice understanding and descriptions. So again, trusting the knowledge of the classicoldsmobile community, I am looking for the vac line routing diagram/description for my 1968 455. ANY advice will be appreciated!

THANKS

 

Jerry, if the engine is running fine without it hooked up, it's really not needed. All it does is switch distributor vacuum advance from ported to manifold vacuum if the coolant temp gets above 220 degrees. That will advance timing and help cool the engine. It was part of the 1968 emissions controls, and with the new lean carb settings the engines tended to run hotter than before.

If you want it hooked up though, look at the switch. The ports should be labeled M (or MT) for manifold vacuum, D for distributor, and C for carb ported vacuum. If not, as you've guessed the bottom port connects to manifold vacuum, the middle port connects to the carb ported vacuum (where your vacuum advance is currently connected) and the top port goes to the distributor vacuum advance diaphragm.

You'll need a tee fitting to splice into the manifold vacuum line to the trans modulator. There was originally a rubber tee with plastic nipples to splice it to the other vacuum lines, but they're unobtainium.