Wonky Cruise Control

[Carl Stouffer]

Also in my previous thread, I mentioned that my cruise control was giving me problems part of the time on my last two cross country trips. It would hold the speed fairly well, but would surge while doing it. This seemed to coincide with the speedometer jumping around a little (cause or effect?).

After our big Spring trip, I disconnected the cables from the transducer and sprayed some penetrating oil on the outside of the moving parts, disassembled the speedometer correction box, down on the transmission, and lubricated it, and cleaned and lubricated the lower speedometer cable.

The only thing I DIDN'T do was to clean and lubricate the upper cable (the one from the transducer to the speedometer). I suppose that could be the problem. Before I send the transducer out to be rebuilt (again) I just wanted to check with the collective and see if anyone has any more experience with this than I do, or a theory as to why it is acting this way.

Thanks

 

[Keith V]

lube your speedo cable

 

[tmsnyder]

Also in my previous thread, I mentioned that my cruise control was giving me problems part of the time on my last two cross country trips. It would hold the speed fairly well, but would surge while doing it. This seemed to coincide with the speedometer jumping around a little (cause or effect?).

After our big Spring trip, I disconnected the cables from the transducer and sprayed some penetrating oil on the outside of the moving parts, disassembled the speedometer correction box, down on the transmission, and lubricated it, and cleaned and lubricated the lower speedometer cable.

The only thing I DIDN'T do was to clean and lubricate the upper cable (the one from the transducer to the speedometer). I suppose that could be the problem. Before I send the transducer out to be rebuilt (again) I just wanted to check with the collective and see if anyone has any more experience with this than I do, or a theory as to why it is acting this way.

Thanks

When you say "surge", do you mean it overshoots the setpoint?

Do you have two healthy return springs on the carburetor, pulling the throttle closed? I wonder if the diaphragm is pulling open the throttle to get the coach up to the setpoint, then overshooting if you're throttle-closing springs are weak or missing.

The vacuum diaphragm will pull the throttle open, but it won't push the throttle closed.

 

[Carl Stouffer]

lube your speedo cable

I will definitely do that and see if it makes a difference on my next relatively short trip.

 

[Carl Stouffer]

When you say "surge", do you mean it overshoots the setpoint?

Do you have two healthy return springs on the carburetor, pulling the throttle closed? I wonder if the diaphragm is pulling open the throttle to get the coach up to the setpoint, then overshooting if you're throttle-closing springs are weak or missing.

The vacuum diaphragm will pull the throttle open, but it won't push the throttle closed.

It does not overshoot the set-point, although it sometimes creeps up a few MPH as I am driving over a distance of several miles.

Yes, I do have two springs on the throttle return. This is a relatively new behavior.

 

[tmsnyder]

It does not overshoot the set-point, although it sometimes creeps up a few MPH as I am driving over a distance of several miles.

Yes, I do have two springs on the throttle return. This is a relatively new behavior.

It would be interesting to T into the line going to the bellows / diaphragm with a vacuum gage to see if the surging is coming from the cruise control transducer. You might see the vacuum needle pulsing up/down matching the surging.

Maybe track down the source of the surge through the system.