Photo's of 78 cruise control on engine.

[Seventy468]

I have a 78 Chevy 3/4 4x4 truck originally equipped with the 400ci/th400 (which I am sure has been swapped since then) but this truck has the Cheyenne package, and is also equipped with what appears to be a factory cruise control.  This would be the second truck I have had with it, but this one is more complete.  I am working to make this work again, and it appears to be nearly complete.  I found a thread on this site in another area about cruise control but the link was broken.  If anyone has any pictures of the parts on the engine concerning the CC and any other information I may need I would greatly appreciate it.  I apologize if this isn't the correct place for this thread.

Thanks,
Seventy468

[78silver]

My 78 Silverado has a cruise control transducer mounted on the driver side wheelwell.  The speedometer cable is split at the transducer, in from the transmission and out to the speedometer.  I think the carb is controlled by a vacuum actuator mounted on the firewall.  If this sounds similar to what you have let me know and I'll try to get some pictures up.

[Seventy468]

that sounds identical.  it seems as though someone did an engine swap in my truck, before I owned it, and didnt put the carb controlled vacuum diaphram thing back to where it should go.  Also when I was looking at the cc unit on the driver wheel well, i noticed its wiring connector was labeled on the unit itself, and where it says "light" there was no wire.  Was there a factory light that comes on when this unit was activated? thanks for your info!

[78 Chevyrado]

Here' all the pics I got of my 78's cruise setup.  I replaced the transducer after the pics, rockauto had it for about $100 new.  The linkage is made up of stock parts and non stock parts to work right with my edelbrock carb.


Note the wiring goes to the plugs you see on the transducer.  I had it unplugged because it was broken, and if you hit the cruise button it just floored the gas no matter if the truck was driving or parked.  When you're testing be ready to turn off the key if the vaccum release under the dash isnt working properly.  the brake pedal hits a button under the dash that breaks the vaccum to the unit causing it to turn off.



Linkage to my Edelbrock Carb


Just for fun here's the original instructions that came with the cruise control.   The older trucks didn't come with cruise from the factory, they were all dealer installed.
HEre ya go, they hung this on the turn signal stalk when new.

[Seventy468]

haha thanks! thats what I needed!  I take it yours works?

[78 Chevyrado]

Yeah mine works good now, I just had to replace the transducer (the part on the fender well).   everything else was still good.

[HIGHPLAINSDRIFTER]

Yeah mine works good now, I just had to replace the transducer (the part on the fender well).   everything else was still good.

How did you test it?  Mine 78 is the same and it is not working.  I am not sure where to start the troubleshooting.  Thanks

[78 Chevyrado]

The transducer itself may have been good, but that little black boxx on the transducer where the wires connect was bad, and you can't get just that part.  It was bad because it should have stopped the cruise from working when not driving.  mine would floor the engine while in park in the driveway if you hit the button.

[78silver]

I don't have a clue about troubleshooting the transducer, mine did not fail completely.  The first got a little "jerky" in operation with a slight speedometer needle jumping, the second seemed to hold speed but the speedometer needle jumped + or - 15 mph like a cable was broken.  The good news is they seem to last about 100k miles.  I haven't seen the vacuum diaphram in catalogs or online.  You will probably need to find one from a donor or junkyard.  There is a stiff wire linkage about a foot long that connects the diaphram to the carb, which you will need.

[Seventy468]

checked mine yesterday, and  it appears to be working.  (the diaphram is not hooked up and is just laying on the fender) but when I hit the cruise button the vacuum sucks it shut.  I do have a slight feeling that it may pull the accelerator wide open, but wont know until I get it mounted.   speaking of which where exactly does that unit mount to? firewall or engine?