PENN GRADE1 Classic GL-4 Gear Oil SAE 80W-90 — 4×1 qt, Mineral Formula for Soft-Metal Synchronizers

PENN GRADE1 Classic Multi-Purpose GL-4 Gear Oil SAE 80W-90 is a mineral-based lubricant formulated for classic manual transmissions and transaxles that use yellow metallurgy.

This four-quart pack of GL-4 80W-90 gear oil is blended from premium mineral base stocks and tailored additives to protect synchronizers, bushings, thrust washers and other components commonly found in older manual gearboxes. It avoids modern friction modifiers so it doesn't disrupt synchronizer engagement, and it's not an API GL-5 extreme-pressure product—so it's ideal only where GL-4 performance is specified or where soft-metal compatibility matters.

Will this oil protect synchronizers and brass/bronze components?

Yes. The formulation is deliberately compatible with yellow metallurgy—brass, bronze and copper—used in synchronizers and related parts. It reduces wear and helps maintain smooth shifts without the negative effects some friction additives produce.

• Formulated for soft-metal compatibility in synchronizers and bushings
• Free of friction modifiers that can impair synchronizer action
• Mineral base stocks chosen for stable film strength at operating temperatures

Is this gear oil suitable for limited-slip or GL-5 rated applications?

No. This GL-4 product is not intended for limited-slip differentials or applications requiring API GL-5 extreme-pressure protection. Using it where GL-5 or specific OEM fluids are required could under-protect gears under very high-pressure conditions.

• Not formulated with EP additives typically found in GL-5 oils
• Avoid in limited-slip units that require special friction characteristics
• Check vehicle manual; use only when GL-4 is specified

How much product do I get and how is it packaged?

Each purchase contains four 1-quart bottles—convenient for a full service or multiple fill-ups. Quart bottles are easy to store in a garage or bring to a shop, and the multi-pack helps ensure you have the correct fluid on hand for classic vehicles.

• Quantity: 4 × 1 quart bottles per pack
• Packaging suited for storage and garage use
• Bring to service appointments or keep as a spare supply

What vehicles and situations is this brand best used for?

PENN GRADE1 80W-90 GL-4 is targeted at older cars, trucks and motorcycles with manual transmissions or transaxles that specify GL-4 and use soft-metal components. It’s also useful for restorations and maintenance of vintage gearboxes where preserving original materials and shift feel is important.

• Classic and vintage manual transmissions that call for GL-4
• Restoration projects where original metallurgy must be preserved
• Owners seeking a mineral-based option without friction modifiers

Who this is for: Mechanics, restorers and owners of classic vehicles who need a reliable GL-4 80W-90 gear oil that respects yellow metallurgy and synchronizer performance. If your vehicle manufacturer specifies GL-4 (not GL-5) or you maintain older transmissions with brass/bronze parts, this PENN GRADE1 four-quart pack gives a practical, correctly formulated choice for routine service and preservation.