{"product_id":"usa-standard-ring-pinion-gear-set-for-gm-12-bolt-car-in-a-3-90-ratio","title":"Yukon ZG GM12P-390 GM 12-Bolt Car 8.875in Ring Pinion 3.90 for 1964-1972","description":"\u003ch4\u003eVehicle Fitment\u003c\/h4\u003e\u003cul\u003e \u003cli\u003e1964-1972 Chevrolet Bel Air, Biscayne, Impala\u003c\/li\u003e \u003cli\u003e1964-1972 Chevrolet Chevelle\/Malibu\u003c\/li\u003e \u003cli\u003e1964-1968 Chevrolet Chevy II\/Nova\u003c\/li\u003e \u003cli\u003e1965-1972 Chevrolet El Camino\u003c\/li\u003e \u003cli\u003e1966-1970 Chevrolet Caprice\u003c\/li\u003e \u003cli\u003e1967-1972 Chevrolet Camaro\u003c\/li\u003e \u003cli\u003e1968-1972 Chevrolet Nomad\u003c\/li\u003e \u003cli\u003e1970-1972 Chevrolet Monte Carlo\u003c\/li\u003e \u003cli\u003e1964-1972 Buick Wildcat\u003c\/li\u003e \u003cli\u003e1969-1972 Pontiac Firebird\/Trans Am\u003c\/li\u003e \u003cli\u003e1970-1972 Pontiac GTO\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch4\u003eFitment Notes\u003c\/h4\u003e\u003cul\u003e \u003cli\u003eThis is the GM 12-bolt passenger car differential (8.875\" ring gear, oval-shaped cover) - a physically different, non-interchangeable axle from the \"GM 12-bolt truck\" differential used in G\/K\/C-series trucks and vans of the same era\u003c\/li\u003e \u003cli\u003eStandard rotation only\u003c\/li\u003e \u003cli\u003eThis is a ring \u0026amp; pinion gear set only - it does not include bearings, races, shims, or seals; pair it with a separate install or master overhaul kit for a complete gear swap\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch4\u003eFeatures\u003c\/h4\u003e\u003cul\u003e \u003cli\u003eHigh-performance ring \u0026amp; pinion gear set for the GM 12-bolt passenger car differential\u003c\/li\u003e \u003cli\u003e3.90 gear ratio\u003c\/li\u003e \u003cli\u003e30-spline pinion\u003c\/li\u003e \u003cli\u003e12 ring gear bolts\u003c\/li\u003e \u003cli\u003e8.875\" ring gear diameter\u003c\/li\u003e \u003cli\u003eManufactured by USA Standard Gear to exceed OEM specification\u003c\/li\u003e \u003cli\u003eDesigned for quiet, precise operation and straightforward setup\u003c\/li\u003e \u003cli\u003eBacked by a 1-year warranty against manufacturer defects\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch4\u003eSpecifications\u003c\/h4\u003e\u003cul\u003e \u003cli\u003eDifferential: GM 12-bolt passenger car\u003c\/li\u003e \u003cli\u003eRatio: 3.90\u003c\/li\u003e \u003cli\u003ePinion spline count: 30\u003c\/li\u003e \u003cli\u003eRing gear bolts: 12\u003c\/li\u003e \u003cli\u003eRing gear diameter: 8.875\"\u003c\/li\u003e \u003cli\u003eWarranty: 1 year against manufacturer defects\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch4\u003eIncluded Components\u003c\/h4\u003e\u003cul\u003e \u003cli\u003e1x Ring gear\u003c\/li\u003e \u003cli\u003e1x Pinion gear\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch4\u003eProduct Description\u003c\/h4\u003e\u003cp\u003eThe Yukon ZG GM12P-390 is a high-performance ring \u0026amp; pinion gear set for the GM 12-bolt passenger car differential - widely regarded as the strongest live-axle rear end GM offered during its short 1964-1972 production run, and a favorite among Chevelle, Camaro, GTO, and full-size muscle car builders. At a 3.90 ratio, this set is a common choice for aggressive street or strip use where quick acceleration matters more than highway cruising RPM.\u003c\/p\u003e\u003cp\u003eBuilt with a 30-spline pinion, 12 ring gear bolts, and an 8.875\" ring gear diameter to match factory specifications, this set is engineered for quiet operation and straightforward setup. Because GM also built a separate, physically different \"12-bolt truck\" differential during the same years, confirming you have the passenger car version - identifiable by its oval-shaped differential cover - is an important step before ordering.\u003c\/p\u003e\u003cp\u003eThis is a gear set only, not a full install kit - it doesn't include the carrier bearings, pinion bearings, shims, or seals needed to complete a gear swap. Pair it with an appropriate master overhaul or bearing install kit for your specific application. Installation requires differential disassembly and proper backlash and pinion depth setup, so it's best handled by an experienced DIY installer or a differential shop.\u003c\/p\u003e\u003cmeta name=\"description\" content=\"Upgrade your 1964-1972 GM with Yukon ZG GM12P-390 ring \u0026amp; pinion. Achieve quick acceleration with a 3.90 ratio for performance driving!\"\u003e\u003cmeta name=\"keywords\" content=\"Yukon 12-bolt gear set, GM ring and pinion 3.90, Chevrolet differential parts, high-performance gear set, 1964-1972 Chevy performance, muscle car gears, differential upgrade kit, Chevy Camaro 3.90 ratio, automotive differential components\"\u003e","brand":"Yukon Gear \u0026 Axle","offers":[{"title":"Default Title","offer_id":53864410972479,"sku":"YUKZG GM12P-390","price":282.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0832\/7308\/9343\/files\/3d7f5d058c8c30c3778709c8c44b77f6.jpg?v=1782577428","url":"https:\/\/wcaperformance.com\/products\/usa-standard-ring-pinion-gear-set-for-gm-12-bolt-car-in-a-3-90-ratio","provider":"WCA Performance","version":"1.0","type":"link"}