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70 Olds Cutlass SX cruise control problems


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I am having trouble with my cruise control. It was not a factory option. I had the cruise control installed recently. It was installed using factory instructions. When cruise is engaged while climbing hills the speed decreases (65 mph to 45 mph) and when I am decending downhill the speed increases (65 mph - 80 mph). Does anyone know what could be causing this problem? Thanks.

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First up there are not too many cruise controls that are designed to hold speed going downhill; you are only going to find these on factory fitted top end vehicles.

Most aftermarket units use a vacuum servo which connects to the throttle linkage, so any vac leaks will obviously affect uphill performance, you may also consider any lost travel in worn throttle linkages affecting uphill performance.

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These were never as accurate as the newer set ups. It is normal to pick up speed on steep downhills but it shouldn't lose more than a couple mph on uphills.

The vacuum issue is a good point but also check the cable/chain adjustment that goes from the bellows to the carb linkage. Adjust the chain for minimal slack but not so tight as to hold the carb off the idle stop screw.


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