My cruise control surges when engaged and gets really bad the longer it's engaged. Unusable. The unit was replaced 20 years ago but probably doesn't have 200 miles of use. The vac control attached to the carb does not leak. Does this sound like a diff. vac. leak or possably the module sticking from old age?
1979 L-48 30,000 mi.
1979 L-48 30,000 mi.
Mine used to do the same thing. I removed the transducer, took it apart and cleaned it, then reinstalled. It works fine now, but I didnt really find anything wrong inside. I think the hoses on the transducer werent sealed well and they got a better seal when I reinstalled them. So definetly check all the hoses that are associated with the cruise control and make sure they are not leaking.
When this 100 deg. heat goes away and the show season is over that will be a good project. I will check the hoses asap.
Make sure the cable is adjusted with no slack in it. I adjusted mine and it stopped the surging.
The only cruise control linkage adjustment on my 78 - yours should be the same - is where it attaches to the throttle bellcrank on the drivers' side of the carb. That attachment is a metal clevis on the threaded end of the rod from the cruise control actuator. My shop manual says there should be 0.02"-0.04" clearance between the pin on the throttle bellcrank and the front of the clevis loop when the motor is off. Adjustment is by removing the clevis from the pin on the throttle bellcrank and rotating the clevis in or out on the threaded rod.
FWIW, mine was surging badly a couple years ago, but the surging was associated with similar variation in the speedometer reading. Cause was interference between the rotating disk and the sensor in the transducer. I could hear and feel dragging when I rotated the transducer using the tang of a small file inserted where the speedometer cable from the transmission is connected. Fix was carefully tapping on the shaft through the rotating disk to move the disk enough so I could no longer feel or hear the dragging. I also cleaned the transducer and very sparingly lubed (light oil) all wear points inside the transducer. Works pretty well and the speedometer is rock steady now, but the cruise control is still very fussy about how steady I hold my speed while it engages.
FWIW, mine was surging badly a couple years ago, but the surging was associated with similar variation in the speedometer reading. Cause was interference between the rotating disk and the sensor in the transducer. I could hear and feel dragging when I rotated the transducer using the tang of a small file inserted where the speedometer cable from the transmission is connected. Fix was carefully tapping on the shaft through the rotating disk to move the disk enough so I could no longer feel or hear the dragging. I also cleaned the transducer and very sparingly lubed (light oil) all wear points inside the transducer. Works pretty well and the speedometer is rock steady now, but the cruise control is still very fussy about how steady I hold my speed while it engages.
I suspect the rotating disk interference is the problem. My speedo is rock solid when not surging and is a perfect match to the speed on my GPS.
