Seal, grease ring and rubber

Seals, grease seals and rubber sealing elements keep engine oil, transmission oil, wheel bearing grease and coolant within their circuits while keeping dirt and moisture out. Selection starts with the application: a radial shaft seal for a rotating shaft has different requirements from a static O-ring, flat gasket or rubber dust boot. Wheel hubs and differentials may also use cassette seals with integrated dirt exclusion. Check not only the inside and outside diameters and width, but also the lip orientation, spring design, dust lip and specified installation depth.

Material choice is crucial to service life. NBR (nitrile butadiene rubber) is commonly used with mineral-based lubricants; FKM (fluoroelastomer) is suitable for higher thermal loads and certain more aggressive fluids. EPDM (ethylene propylene diene rubber) is used in cooling circuits, among other applications, but is generally unsuitable for contact with mineral-based engine oil. PTFE (polytetrafluoroethylene) radial seals often require a specific dry installation procedure. For O-rings, also check the cross-section, groove dimensions and Shore A hardness: a matching outside diameter alone does not guarantee correct compression.

This category includes seals, grease seals, O-rings, oil seals, elastomer seals and copper sealing washers. It also covers rubber suspension rings, rubber sealing rings for applications such as diesel tank caps, rubber components for fuel tank mounting and door seals. You will also find sealing washers for drain plugs, valve cover gaskets, coolant flange seals and rubber grommets.

Oil around a crankshaft oil seal on a MAN D26 or Mercedes OM 471 does not automatically mean the sealing lip is defective. Excessive crankcase pressure, shaft play or a worn shaft surface can cause the same leak. On MAN TGL and TGX, Mercedes Actros and Sprinter, and buses such as the MAN Lion’s City and Mercedes Citaro, seals also vary by axle, transmission, year of manufacture and specification. Always identify parts using the chassis number. Visual comparison or selection by model name alone is never sufficient.

Take a step-by-step approach to diagnosis. First clean the area and establish where the fluid is actually escaping; if necessary, use a leak-detection dye suitable for the circuit. Then check breathers for blockages and measure radial shaft play with a dial indicator, in accordance with the vehicle specifications. After removal, inspect the sealing lip for hardening, cracks and uneven wear. Measure the shaft diameter and any grooving with a micrometer, and check the housing for burrs, corrosion or a loose fit. Fitting a new grease seal on a damaged shaft surface will generally not provide a lasting repair.

A leaking hub seal can allow wheel bearing grease onto brake components, so the entire wheel hub should be inspected promptly. Remove the old seal without damaging the housing bore, clean the mating surface and install the replacement using a flat, correctly sized fitting tool. Apply force to the specified area of the seal; do not press on the sealing lip. Follow the application-specific instructions for lubrication, installation orientation and run-in, particularly for PTFE versions. After installation, check the lubricant level and breather, then check the seal again during a test drive. This addresses not only the leak but also its cause.