I read some other posts that don't seem to quite match up with my problem here.
I set the cruise at maybe 60mph. It kicks on and immediately speeds up to about 64 or 65 mph and then turns off. A few seconds later after the car has slowed to 60mph again, the cruise kicks on for another 4-5 mph and then turns off. This process of on and off will just go on indefinitely until I hit the brake to turn it off until set again.

On...then off On...then off On...then off

The transducer is new a year ago but has not been used until now. Could it be a faulty transducer? Although it is essentially new.

We could not find any leaks although there are an awful lot of vacuum hoses under the hood and not very easy to find leaks often. Lights work and no special problems relative to vacuum is noted or has been found??

Hose connection on the transducer perhaps? Purely guessing now. Any help or suggestions would be greatly appreciated. Thank you.

 

Probably just needs the orifice adjusted. Sometimes if the linkage is too tight it can cause a surge.

 

I assume the orifice is the opening that is pointing AT the fender? Pointing to the left from a driver's position.

Looks like maybe a nut on the transducer (orifice) that can be turned. I'm looking at a photo of the transducer right now and I'll be going to adjust it shortly.
It may make sense to try adjusting the linkage first a few times and test driving before adjusting the transducer; does that make sense? Do not want to adjust both at the same time either.

Roger - any more specific info on that, like how to adjust or is that rather evident? Just hit or miss on some test drives to see if it changes anything?
Most people don't know what the transducer is let alone how to fix or adjust so your help is most appreciated. Thanks.

 

Yes you described the orifice tube and its location.
On the linkage just make sure its not binding and when the carb is fully at idle make sure there is a little play in the linkage.
You want to turn the orifice tube in 1/4 turn per mph that it is high. A full turn in should bring it down 4 mph.

 

I think the problem is in your switch, rather than in the transducer head. It sounds like your CC system is stuck in the "Resume" mode when it should be in the "Set" mode. Under the driver's side dash, there is a little connector at the end of the switch wire which goes through the steering column. Find that connector and remove it from the mating cable (which goes to the transducer). Now you can use an ohmeter to check out the switch 'logic' as you try the various conditions. When you press the "Set" button, that should cause one of the contact sets to make a connection; and when you release that button, that circuit should then become 'open'. The circuit conditions for that switch are given in the Chevrolet Chassis Service Manual, I believe.

If the switch circuits check out OK, then the problem must be in the transducer head. Before you replace it, however, remove it, open it up and give it a good cleaning including cleaning out the orifice. Many times that will correct such problems.

 

Since the transducer is a bit of a PITA to get to/work on in place/or deal with all the hoses, we decided to start with the easiest and fastest to rule in or out as the problem.

First we checked all connections, hoses, and electrical items which all seemed fine.
Then we were thinking about the fact that the carburetor is new and quite a different fit than the original plus the transducer is new. This ruled out the simple cleaning of the transducer since it was new. That seems to fix the problem of increasing acceleration rather than up and down fluctuation anyway.

Checking the orifice seemed like a good idea but again it is new so we took the advice of checking the linkage first. We never saw how the linkage was set before the new carb either. Seemed to be a full ½ inch of play in the upper throttle linkage right now.

Roger, you said to tighten linkage to the point of just not binding. We did leaving about one sixteenth of an inch of room at the most. Just not touching with the car turned off. You said during idle but we got lucky it worked fine with adjustment made while the car was not running. (I was in a hurry )

Decided to start there and loosen a turn or so every test drive if it worked.
It worked perfectly and on this first try. It held a constant speed up hills and backed off down hills just right. I'm thrilled and it happened to be any easy fix instead of the more time consuming ones.

Mark this down as solved for sure.

7T1vette - your guide was next if this simple fix did not work. I forgot to mention one other new part that would have maybe swayed your diagnosis too. As I said, the transducer is new, the carb and linkage is new, and the cruise switch on the column (combination turn signal) is also new. I have completely made the inside of this car new over the last year, anything that is anything that is.

Your advice is being given to a friend of mine that also has cruise problems. He has NO new parts though.

Thank you guys very much! Tremendous help and the advice from this thread directly solved the problem!

Greg

 

Very glad you were able to diagnose and resolve the problem.