I have a 1984 Corvette that I've rebuilt and I'm working on the cruise control. When you first start driving the cruise control works fine, but after about 15 minutes of driving at highway speeds, it quits working. The 700R4 transmission was rebuilt and the speedometer always works fine. The turn signal lever is new and all the voltages work. I just installed a rebuilt cruise control servo assembly. Almost all of the vacuum lines are new and after it quit working today, I removed the brake sensor vacuum line at the servo and capped it. It still did not work while the car was warm.

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I would look at is to make sure your cable is properly attached to your throttle body.
I would also check the wires on the end of your stalk to make sure they are not loose or cracked,

Wires at the end of the stalk, not sure what you are talking about. But, I think I've check every wire that has anything to do with the cruise control system.

maybe you have a different vac leak thats allowing the vac to go to low to operate the cc.i doubt it would take much.

Considering this happens when the engine is hot I would be looking over the electricals. Something is getting hot and cutting out. Place some ice on the cruise module after it cuts out to cool it down. See if that helps. Another possibility is the crank sensor. If that'* acting up a little bit when hot it will loose the RPM readings and that could effect the cruise control.

Dan, I thought about the speed sensor, but the rpm and displayed speed are not affected and I think they use the same sensor. Also, the cruise control module is embedded in the dash LCD and not easy to get too. Some freeze spray may work if I can figure out which board is for the cruise control.

I'm going to put a vacuum gage on the cruise control inlet to see what the actual vacuum is.

thanks all.

Keep us up to date on what you find.