{"product_id":"classic-multi-purpose-gl-4-gear-oil-sae-80w-90-quart-4-pack","title":"Classic Multi-Purpose GL-4 Gear Oil SAE 80W-90 Quart 4-Pack","description":"\u003cp\u003eOur review of the Classic Multi-Purpose GL-4 Gear Oil SAE 80W-90 looks at who benefits most and why this formulation matters for older manual gearboxes. In short, this product is aimed at owners and mechanics working on classic cars and motorcycles that use yellow metallurgy synchronizers and soft-metal components; the single biggest reason to buy is its intentional GL-4 formulation without friction modifiers, which preserves synchronizer function and improves shifting in older transmissions.\u003c\/p\u003e\u003ch2\u003eKey Features\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eGL-4 formulation:\u003c\/strong\u003e Designed to protect gears and synchronizers that use brass, bronze, and copper without the friction modifiers that can cause harsh shifting.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePremium mineral base stocks:\u003c\/strong\u003e Blended from quality mineral oils to provide consistent lubrication and film strength for typical manual transaxle components.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompatibility with soft metals:\u003c\/strong\u003e Safe for synchronizers, bushings and thrust washers commonly found in classic manual transmissions.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot for limited slip:\u003c\/strong\u003e Intentionally free of friction modifiers to avoid interference with synchronizer performance and not intended for limited slip diffs.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePack size:\u003c\/strong\u003e Supplied as four 1 quart bottles which is convenient for multi-service use or for topping off multiple vehicles.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis gear oil is best for owners and restorers of classic cars and older motorcycles who need a traditional GL-4 lubricant that is compatible with yellow metallurgy synchronizers and soft-metal transmission components. It is especially useful when the goal is smooth gear changes and preservation of original transmission behavior rather than meeting modern extreme-pressure specs.\u003c\/p\u003e\u003cp\u003eThose who should look elsewhere include vehicles or axles that explicitly require API GL-5 or OEM-specified specialist fluids, and drives with limited slip differentials that need friction-modified lubricants. Modern vehicles with manufacturer-mandated fluids also should follow OEM guidance.\u003c\/p\u003e\u003ch2\u003ePros \u0026amp; Cons\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003ePros\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eDelivers smooth gear shifting in syncromesh gearboxes thanks to a GL-4 formula without friction modifiers.\u003c\/li\u003e\n\u003cli\u003eHigh quality mineral base stocks provide dependable lubrication for classic transmissions.\u003c\/li\u003e\n\u003cli\u003eGood value for a 4-pack of quart bottles, convenient for multiple services or multiple vehicles.\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003e\u003cstrong\u003eCons\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\u003cli\u003eNot suitable where API GL-5 extreme pressure properties or limited slip friction modifiers are required.\u003c\/li\u003e\u003c\/ul\u003e\u003ch2\u003eSpecifications\u003c\/h2\u003e\u003ctable\u003e\n\u003ctr\u003e\n\u003ctd\u003eProduct name\u003c\/td\u003e\n\u003ctd\u003eClassic Multi-Purpose GL-4 Gear Oil SAE 80W-90\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBrand\u003c\/td\u003e\n\u003ctd\u003ePENN GRADE1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eViscosity\u003c\/td\u003e\n\u003ctd\u003eSAE 80W-90\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAPI rating\u003c\/td\u003e\n\u003ctd\u003eGL-4\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eContainer size\u003c\/td\u003e\n\u003ctd\u003e1 Quart (4 Pack)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRecommended use\u003c\/td\u003e\n\u003ctd\u003eClassic manual transmissions, synchronizers, bushings, thrust washers\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\u003ch2\u003eOur Verdict\u003c\/h2\u003e\u003cp\u003eThis GL-4 SAE 80W-90 gear oil is a pragmatic choice for anyone maintaining older manual transmissions that use yellow metallurgy synchronizers. It avoids friction modifiers that can harm shifting, uses quality mineral base stocks, and arrives in a convenient 4-pack, making it strong value for restoration shops and classic vehicle owners who need correct, reliable lubrication.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eCan this oil be used in limited slip differentials?\u003c\/strong\u003e\u003cbr\u003eNo. This formulation does not contain friction modifiers and is not intended for limited slip applications.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs this suitable for modern transmissions that specify GL-5?\u003c\/strong\u003e\u003cbr\u003eNo. This product is GL-4 and should not be used where GL-5 or OEM specialized fluids are mandated.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow many quarts are included?\u003c\/strong\u003e\u003cbr\u003eThe package contains four 1 quart bottles for multiple services or vehicles.\u003c\/p\u003e","brand":"PENN GRADE1","offers":[{"title":"Default Title","offer_id":48681189408987,"sku":"B0CHG3X79B","price":36.96,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0724\/1043\/1707\/files\/81WanLt8zyL._SL1500_fac26f80-a7d4-4915-9edd-6ba59f761851.jpg?v=1778692645","url":"https:\/\/gearmusthave.com\/products\/classic-multi-purpose-gl-4-gear-oil-sae-80w-90-quart-4-pack","provider":"GearMustHave","version":"1.0","type":"link"}