Bakfjädrar, Variable rate (Progressiva) spiralfjädrar (Par). Passar många modeller, Buick 1940 – 1960
Motståndet ökar ju mer de komprimeras. Det ger en mjuk och bekväm gång vid små ojämnheter, men blir betydligt styvare vid hård inbromsning, tung last eller aggressiv kurvtagning.
| År | Modell | Standard/Heavy Duty | Applikation |
| 1954-55 | Century | Standard |
|
| 1956 | Century | Standard |
|
| 1957-58 | Century | Heavy Duty |
|
| 1940-42 | Century Series 60 | Standard, Modell #s 66, 66C, 66S | |
| 1959-60 | Electra, Invicta, Lesabre | Standard |
|
| 1958 | Limited | Standard, Riviera |
|
| 1950-53 | Roadmaster | Standard |
|
| 1954-58 | Roadmaster | Standard | |
| 1940 | Roadmaster Series 70 | Standard Modell # 76S | |
| 1941 | Roadmaster Series 70 | Standard Modell #s 76C, 76S | |
| 1954 | Skylark | Standard | |
| 1950-53 | Special | Standard | |
| 1954-56 | Special | Standard |
|
| 1957-58 | Special | Heavy Duty |
|
| 1940 | Special 40 | Standard (Passar ej Business & Sport Coupe Modell #s 46 & 46S) | |
| 1946-48 | Special Series 40 | Standard med 16″ hjul | |
| 1949 | Special Series 40 | Standard | |
| 1941 | Special Series 40-A, 40-B | Standard Modell #s 41, 41SE, 47 | |
| 1942 | Special Series 40-A, 40-B | Heavy Duty Modell #s 44, 44C, 46, 48 | |
| 1950-58 | Super | Standard |
|
| 1940-41 | Super Series 50 | Standard Modell #s 51, 56C, 56S |













