The majority of coil spring manufactured by Chevrolet Livonia and it's outside suppliers were produced from 5160 steel and had a propensity to sag over time or "competition" use. To minimize the amount of sag Livonia and OSP performed a "bulldozing" operation immediately after shot peening and tapped the side of the coils lightly to relieve stress. Later the SAE spring committee in conjunction with steel suppliers developed an improved sag resist material called 5160 modified. This material had several of the properties of 9260 without the cost implications and a wider heat treat range. Cadillac division was the only car group within GM that released 9260 as a production material.
The production finish of all GM coil springs, up until the early eighties, were natural steel. The addition of a rust inhibitor change the appearance to a "dark metallic finish". If you can imagine the finish as a shot peened surface it would appear to be "silver" in appearance and would begin to oxidize within several hours, depending on the humidity. The rust inhibitor specified by CEC was "tectyl" dry to the touch oil. Springs were palletized and the entire pallet was dipped into a bath of Tectyl, permitted to dry then shipped to the assembly plant. During the fifties and sixties there wasn't the attention to detail that exists today. These plants were "profit center" and manufactured components utilizing the best competitive method of manufacturing available at that time.
The SAE spring committee published an Technical Paper on March 1, 1985 titled "Evaluation of Torsional Fatigue in Automotive Suspension Coil Springs Steels" written by Warren Krohn and Ken Campbell of Rockwell International's Suspension division which addressed the sag issue. There were two additional SAE publications written on the subject that are very informative. Reference SAE publication numbers: 850059, 850060 & 850061 and are available by contacting the SAE @ www.sae.org.
For you leaf spring buffs Ken was Chief engineer of OSP's spring division, prior to being acquired by North American Rockwell later known as Rockwell international and was responsible for the engineering of the transverse Corvette spring. OSP in conjunction with Chevrolet engineering and Eaton Corporation developed the mid-year spring that was ultimately released for production.
The production finish of all GM coil springs, up until the early eighties, were natural steel. The addition of a rust inhibitor change the appearance to a "dark metallic finish". If you can imagine the finish as a shot peened surface it would appear to be "silver" in appearance and would begin to oxidize within several hours, depending on the humidity. The rust inhibitor specified by CEC was "tectyl" dry to the touch oil. Springs were palletized and the entire pallet was dipped into a bath of Tectyl, permitted to dry then shipped to the assembly plant. During the fifties and sixties there wasn't the attention to detail that exists today. These plants were "profit center" and manufactured components utilizing the best competitive method of manufacturing available at that time.
The SAE spring committee published an Technical Paper on March 1, 1985 titled "Evaluation of Torsional Fatigue in Automotive Suspension Coil Springs Steels" written by Warren Krohn and Ken Campbell of Rockwell International's Suspension division which addressed the sag issue. There were two additional SAE publications written on the subject that are very informative. Reference SAE publication numbers: 850059, 850060 & 850061 and are available by contacting the SAE @ www.sae.org.
For you leaf spring buffs Ken was Chief engineer of OSP's spring division, prior to being acquired by North American Rockwell later known as Rockwell international and was responsible for the engineering of the transverse Corvette spring. OSP in conjunction with Chevrolet engineering and Eaton Corporation developed the mid-year spring that was ultimately released for production.
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