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I have a 79 F250 CS XLT Ranger regular cab long bed. 460/AT. 4BBL CARB. Factory Speed Control. Bought the truck form the original owner with 93k miles. The speed control works as long as you want to go 43 mph! No matter what speed you set, the unit will slow to 43 and then hold that speed. It will cancel with the brake applied or by turning the Speed Control "Off" using the button on the steering wheel. However, the ACCEL & COAST buttons do nothing. I anticipate this has more to do with the overall unit performance.
Thanks Guys, I ran through all of the diagnostics that DL sent (I also have the complete shop manual) and the switch test passed. All of the other components proved to be good as well except the amplifier. It failed the ON Circuit test. It shows 12 volts when your depress the "ON" Switch, but doesn't hold the volts when the "ON" button is released. The Ground and the Fuse are good. The diagnostics indicate that the Amplifier should be replaced.
@Bill, could you tell me if the AMPLIFIER is available as NOS from anyone?
My cruise control on my 1979 Ford F350 isn't working. I've tried everything. Any ideas? After days of tinkering, it finally worked. Then I tried to re-mount the amplifier on the firewall, and it broke again. I took it apart and started from scratch, but still nothing. Does anyone have any ideas or information on what measurements I can take? I'd love to hear them.
It has every step and component to test and the results to expect. Even though it is for a 78, it should be exactly the same for a 79 truck. Both of those years were wired the same, but earlier years have differences.
A problem you might run into is discovering you have a faulty part that is no longer available new. In that case look in junk yards and ebay for NOS parts. Keep in mind ford lincoln and mercury cars from the 70s through the 80s used a lot of the same components for speed control.
Correct, I have done all those tests and everything seems to be correct, so I don't know where to go. All the values from the buttons and servo are correct and you even hear the module beep when you press the buttons, but it just doesn't start working. Does anyone have any ideas?
Mine on my '77 is an aftermarket I bought and put on in 1986, I had put one on a Chevelle before that. Local Sears surplus store offered them then for $25, I had bought a couple. Dana made it, but was sold by Sears/Allstate # 318.20302. I've seen a few OEMs years ago, looked like Ford used the same or very similar one with slight changes to incorporate them on an assembly line. A few short years ago I bought a new never opened on off Ebay just to have for spare parts if ever needed. Might be they way?
Well I am thinking if it sets and loses speed, your servo vacuum might be leaking down. Did you use a vacuum pump to test it? I have to remove my gauges again to fix a light so maybe I will test mine soon as it is also no longer functioning.
The servo is a NOS model. I've had three different ones, and this one worked before I hung the amplifier on the firewall, so it seems odd that it's suddenly broken. I did take it off yesterday and vacuum-sealed it, but it was sealed.
Somewhere, I'm not sure where ..... even on a factory install, there is a brake pedal mounted or controlled deactivation switch that both electrically deactivates the CC .... AND ....dumps vacuum.
Might be an adjustment is letting it dump or deactivate as if the pedal was depressed. Mine is a switch with spring loaded arm mounted to the brake pedal arm, and a ball chain runs to the anchor on the firewall. I have it adjust so I just depress or tap the pedal, it deactivates and dumps vacuum.
My truck is an automatic, but on my Chevelle was a 4 speed, the ball chain ran through a pulley like anchor and then to a real anchor point on the clutch pedal arm, so depressing either clutch or brake pedal deactivated the CC.
