Cruise control adjustment

[bnoon]

I repaired some of my wiring harness over the weekend and functionally the cruise control is working. But say I set it at 70 MPH, it will slowly lose speed down to about 60, then run up to about 75, before again going down to about 60, repeat. How are these older units adjusted for speed control? This is the single button vacuum operated system with two speedometer cables. Vacuum lines and diaphragms seem to hold vacuum fine.

I guessed it would probably need adjustment since I pulled this transducer unit from a 1976 Malibu in the scrap yard since mine was stripped out due to an under lubricated upper speedometer cable. I also pulled the 28% increase speedometer cable adapter unit from this car as well. Cost was less than 20 bucks! I love pull your own auto parts!

[bnoon]

Just noticed something while posting that picture. Is it possible that the cable is too loose? I see that the adjuster looks to be adjusted all the way out. Hummmm.

[77 Sport]

From the 1977 Light Duty Truck Service Manual:

[bnoon]

Thanks for posting that. I already went out and checked the slack in the line and it is a bit too loose for my liking. I'll have to move the chain up probably two balls since the sheath adjustment is all the way out right now.

I also found that there is an adjustment for the vacuum bleed (brass fitting with the jamb nut and a vacuum hose going to it) that's supposed to slow down or speed up the reaction of the transducer. This is called hysteresis adjustment. I knew it was a weird word, just couldn't remember what it was. This is where most of the "above and below set speed" adjustment will take place. Guessing that the replacement transducer hysteresis will need a lot of adjustment since it came from a small block and is now on a 454. Can't adjust this until the cable is adjusted though.