{"product_id":"penn-grade1-classic-gl-4-gear-oil-80w-90-1-quart-2-pack-mineral-synchronizer-safe","title":"PENN GRADE1 Classic GL-4 Gear Oil 80W-90, 1 Quart (2-Pack) — Mineral, Synchronizer-Safe","description":"\u003cp\u003e\u003cstrong\u003ePENN GRADE1 Classic Multi-Purpose GL-4 Gear Oil SAE 80W-90 is a mineral-based gear lubricant formulated for manual transmissions and transaxles that use soft metals and synchronizers.\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThis two-quart pack provides a reliable, vintage-friendly lubricant option for classic cars, trucks, and many manual drivetrains. The formula is blended from high-quality mineral base stocks and carefully chosen additives to protect gears, bushings, thrust washers and synchronizer components found in older or classic transmissions. It’s specifically developed to be compatible with yellow metallurgy—brass, bronze and copper—commonly used in synchronizer assemblies, and it intentionally excludes friction modifiers found in some modern formulations so it won’t interfere with synchronizer engagement.\u003c\/p\u003e\n\n\u003ch3\u003eWill this oil work in my classic manual transmission?\u003c\/h3\u003e\n\u003cp\u003eThis GL-4 rated SAE 80W-90 oil suits many classic manual gearboxes and transaxles that specify GL-4 performance and require mineral-based lubricants. It is designed to lubricate gears and wear surfaces without upsetting the friction characteristics of conventional synchronizers.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eCompatible with transmissions using brass, bronze or copper synchronizers.\u003c\/li\u003e\n  \u003cli\u003eDoes not include limited-slip additives or friction modifiers.\u003c\/li\u003e\n  \u003cli\u003eNot suitable where API GL-5 or OEM-specific fluids are mandated.\u003c\/li\u003e\n  \u003cli\u003eSold as a convenient 1-quart bottle, packaged as a 2-pack.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eHow does this oil protect synchronizers and soft-metal components?\u003c\/h3\u003e\n\u003cp\u003eThe formulation balances wear protection and film strength while preserving the natural friction needed for smooth gear shifts. Additives provide anti-wear benefits without introducing chemicals that can make synchronizers slip or delay engagement.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eSpecially blended additives for wear control on sliding surfaces.\u003c\/li\u003e\n  \u003cli\u003ePreserves synchronizer friction because it lacks modern friction modifiers.\u003c\/li\u003e\n  \u003cli\u003eProtects bushings and thrust washers commonly found in older gearboxes.\u003c\/li\u003e\n  \u003cli\u003eMineral base stocks provide stable viscosity at operating temperatures.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhere should I NOT use this GL-4 SAE 80W-90 oil?\u003c\/h3\u003e\n\u003cp\u003eDo not use this product in applications that require API GL-5 extreme-pressure (EP) performance or in gearboxes that explicitly call for specialized OEM fluids. It’s also not intended for limited-slip differentials that depend on specific friction modifiers.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eAvoid if the service spec requires API GL-5 or equivalent EP fluids.\u003c\/li\u003e\n  \u003cli\u003eNot recommended for limited-slip differentials needing friction additives.\u003c\/li\u003e\n  \u003cli\u003eNot for use in modern gearboxes that mandate synthetic or OEM-specific formulations.\u003c\/li\u003e\n  \u003cli\u003eCheck vehicle manufacturer requirements before use.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eHow should I choose and maintain this gear oil in my vehicle?\u003c\/h3\u003e\n\u003cp\u003eSelect this GL-4 SAE 80W-90 when your vehicle manual or parts supplier lists GL-4 compatibility and notes synchronizer-friendly oil. Follow regular drain intervals, watch for metal debris in the fill plug, and replace seals or gaskets when servicing to prevent contamination and maintain gear life.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eRefer to your service manual for the correct spec and capacity.\u003c\/li\u003e\n  \u003cli\u003ePerform routine oil changes and inspect for metal particles.\u003c\/li\u003e\n  \u003cli\u003eReplace seals and gaskets to prevent leaks and contamination.\u003c\/li\u003e\n  \u003cli\u003eKeep oil clean and stored in sealed containers when not in use.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eWho is this for? PENN GRADE1 Classic GL-4 SAE 80W-90 is aimed at owners, restorers and mechanics maintaining vintage or classic manual transmissions and transaxles that use brass\/bronze\/copper synchronizers and require a mineral-based GL-4 lubricant. If you maintain older gearboxes that must avoid modern friction modifiers or do not call for GL-5 or OEM-specific fluids, this two-pack of 1-quart bottles is a practical, shop-friendly option.\u003c\/p\u003e\n\u003csection class=\"product-faq-snippet\"\u003e\u003ch3\u003eFAQ\u003c\/h3\u003e\n\u003cdiv class=\"faq-item\"\u003e\n\u003cp class=\"faq-q\"\u003eQ: Is this oil safe for synchronizers made of brass or bronze?\u003c\/p\u003e\n\u003cp class=\"faq-a\"\u003eA: Yes. This GL-4 formula is compatible with brass and bronze synchronizers and avoids friction modifiers that can impair shifting.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"faq-item\"\u003e\n\u003cp class=\"faq-q\"\u003eQ: Can I use this oil in a limited-slip differential?\u003c\/p\u003e\n\u003cp class=\"faq-a\"\u003eA: No. It lacks the friction modifiers required for many limited-slip devices and is not designed for GL-5 limited-slip service.\u003c\/p\u003e\n\u003c\/div\u003e\u003c\/section\u003e","brand":"PENN GRADE1","offers":[{"title":"Default Title","offer_id":67588160553145,"sku":"B0CHG54RGN","price":83.81,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0822\/3765\/3177\/files\/penn-grade1-front-label-bottle.jpg?v=1790516798","url":"https:\/\/redleafauto.ca\/products\/penn-grade1-classic-gl-4-gear-oil-80w-90-1-quart-2-pack-mineral-synchronizer-safe","provider":"Redleaf Auto","version":"1.0","type":"link"}