| Where does cruise control get its vacuum [message #289073] |
Tue, 20 October 2015 19:49  |
Darryl
Messages: 144
Registered: December 2011
Location: Northern California
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My OEM cruise control hasn't worked since one of our GMC vendors replaced my engine a year and a half ago. I checked all the obvious electrical and vacuum connections and asked whether something might not have been connected properly but finally concluded the transducer needed replacement again(it was replaced a year or so before the engine). I finally got around to swapping the transducer but decided to do a more thorough check of the vacuum lines first so I would have a better understanding of how things worked and what went where. I traced a vacuum line behind the servo under the step and pulled it up and found a tee fitting in the middle of it with nothing connected. Finally looked closer and saw the nipple on the back of the servo and realized the line had probably never been reconnected to the servo. Problem solved? Well, maybe part of it.
Then I started thinking about where the transducer gets its vacuum. There are two nipples on the side of the transducer and only one is connected to a vacuum hose (it goes to the orifice tube, the servo and the brake release switch). The maintenance manual shows a vacuum line from the second nipple to the intake manifold but it's not clear where it connects to the intake manifold. The Christmas tree (TVS valve) has three vacuum lines coming off it. The top one goes to the carburetor, the middle one to the distributor and the bottom one goes to another point on the intake manifold with a tee connection going to a steel line that seems to go down to the transmission.
So, two questions. First, if I run a vacuum line from the transducer to the intake manifold where do I connect it. Should I tee into one of the existing lines? Which one or does it matter? Second, the vacuum lines associated with the transducer are larger (3/8 inch?) than the other vacuum lines (1/4 inch?). Should the new line be the larger diameter?
Darryl Meyers
1978 Eleganza II
El Dorado Hills, CA
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