Mercury Quicksilver Driveshaft Oil Seal 26-804156 | Outboard & MerCruiser Gearcase

Driveshaft Oil Seal for Mercury & Mariner Outboard Gearcases

The Mercury Quicksilver 26-804156 is an OEM radial shaft oil seal that fits around the driveshaft in select Mercury and Mariner outboard gearcases and MerCruiser powertrain assemblies. It retains gear lubricant inside the housing while blocking water and contamination from entering — a critical function for protecting the lower unit from premature wear and corrosion.

This is a location-specific seal. Matching the outside diameter alone is not enough to confirm fitment — shaft diameter, lip direction, housing bore, and installation depth must all match the Mercury parts diagram for your specific engine serial number. Replace this seal any time the gearcase is opened for service, or when gear lube leaks or water intrusion are present.

Part Information

• Part Number: 26-804156
• Short Reference: 804156
• Brand: Mercury / Quicksilver
• Official Product Type: Radial Shaft Oil Seal – Driveshaft
• Barcode / UPC: 745061204156
• System: Lower unit / gearcase driveshaft
• Approximate Weight: 20 g (0.02 kg)

Compatible Applications

• Mercury and Mariner outboard engines approximately 35–200 HP – 2-stroke carbureted, Laser, EFI, XR4, and Magnum II engine families
• Select MerCruiser powertrain assemblies where 26-804156 appears in the parts diagram
• Verify fitment by engine or drive serial number and gearcase diagram before ordering — shaft diameter, housing bore, lip direction, and installation depth must match

System & Diagram Position

This seal is part of the lower unit / gearcase driveshaft assembly. In the Mercury parts diagram it appears in the gearcase section at the driveshaft entry point — the bore where the driveshaft passes from the midsection into the gearcase housing. It is the primary seal preventing gear lube from escaping upward around the rotating driveshaft and preventing water from entering the gearcase from above.

Dimensions

Exact published dimensions are not available in catalog data for this part number. Confirm shaft diameter, housing bore, and installation depth against the Mercury parts diagram for your specific engine serial number before ordering.

When to Replace

• Gear lube is leaking from the gearcase housing
• Water is found in the gear lube during a drain-and-fill service
• The seal lip is worn, hardened, or cracked
• The garter spring is damaged or displaced
• Any time the gearcase is opened or the driveshaft is removed for service

Service Interval

Inspect gear lube condition at least annually or every 100 hours. Water contamination (milky or discoloured lube) or external leakage at the gearcase indicates the seal should be replaced. Replace as a matter of course any time the gearcase is fully disassembled.

Installation Notes

• Inspect the driveshaft sealing surface before installing the new seal — grooves, corrosion, or pitting will damage the new seal lip and cause repeat leaks
• If the shaft surface is damaged, a driveshaft sleeve kit such as the Mercury Mariner Driveshaft Sleeve Ring Kit 42461A1 can restore the sealing surface without replacing the entire shaft
• Install the seal squarely using the correct seal driver — do not hammer directly on the seal face
• Lubricate the seal lip lightly with gear lube before installation
• Pressure-test the gearcase after reassembly where applicable

Related Parts

• Mercury Mariner Lower Unit Gear Housing Seal Kit 26-43035A4
• Mercury Mariner Driveshaft Lower Unit Oil Seal 26-43036
• Mercury Mariner Upper Driveshaft Oil Seal 26-43035
• Mercury Quicksilver Lower Unit Seal Kit 26-33144A2
• Mercury Mariner Driveshaft Sleeve Ring Kit 42461A1
• Quicksilver High Performance SAE-90 Gear Lube & Pump Kit 8M0222069
• Mercury MerCruiser Quicksilver SAE 90 High Performance Gear Lube 8M0222066
• MerCruiser Gearcase Drain Screw Seal 8M0187157 (Blue)
• Mercury Gearcase Drain Plug Gasket – Part 354 (5-Pack)

Technical FAQ

Q: Can I reuse this seal after removing the driveshaft?
A: No. Radial shaft seals deform on installation and should always be replaced when disturbed. Reusing an old seal is a common cause of repeat gearcase leaks.

Q: Is matching the outside diameter enough to confirm fitment?
A: No. Shaft diameter, lip direction, housing bore, and installation depth must all match the Mercury parts diagram for your specific engine serial number. Two seals with the same OD can have different shaft diameters or lip geometries.

Q: What causes this seal to fail prematurely?
A: A grooved or corroded driveshaft sealing surface is the most common cause. The new seal lip contacts the same worn groove and fails quickly. Always inspect the shaft surface before installing a new seal — if it is damaged, a sleeve kit can restore it.

Q: How do I know if this seal is leaking vs. another gearcase seal?
A: The driveshaft seal is at the top of the gearcase where the shaft enters from the midsection. Gear lube leaking from the upper gearcase area or water found in the lube during a drain-and-fill service are the primary indicators. A pressure test will confirm the leak location.

Parts Desk Insights

Best use case: This seal is the right part for any gearcase service on a compatible Mercury or Mariner outboard where the driveshaft is being removed — whether you are chasing a gear lube leak, dealing with water-contaminated lube, or doing a full lower unit rebuild. At this price, it should always be replaced rather than reused whenever the gearcase is open.

Common issues: The most frequent issue is installing a new seal over a grooved or corroded driveshaft sealing surface. The new seal will fail quickly and the gearcase will leak again — always inspect the shaft before installing. A second common issue is ordering by outside diameter alone without confirming the shaft diameter and lip direction against the parts diagram for the specific engine serial number. Two seals that look identical can have different internal geometries and will not seal correctly if mismatched.