Revised May 2024 The EASA Technical Manual is the association's definitive and most complete publication. It's available FREE to members in an online format. Members can also download PDFs of the entire manual or individual sections.

Bearinghousing tolerance

Driving on a bad or failing wheel bearing is dangerous. If ignored, it can quickly turn into a safety issue and an expensive repair.

However, on some vehicles, it can be less than $100 per wheel. And you can save hundreds in labor if you DIY. If you don’t have the tools, most auto parts stores will lend you the specialty tools and equipment needed.

Much has been said and much work performed to produce the “perfect” bearing fit. For any single bearing, there is an inner fit to the shaft and an outer fit to the housing. It is required that one of the two fits be able to slide in order to assemble the machine. If the bearing-to-shaft fit (journal) is tight, then the bearing-to-housing (bore) must be loose. Of course tight and loose are relative terms and the quest for the perfect fit must define these terms.

Wheel bearings allow cars and trucks to run smoother and more efficiently by reducing friction and supporting vehicle weight.

Under normal driving conditions, wheel bearings should last 85,000 to 100,000 miles. They can fail for several reasons, including:

The cage and rollers are held together inside a hardened metal ring called a “race.” The seal keeps grease in and damaging water and debris out. Wheel bearings are installed inside, and secured to, the suspension, either by press-fit, bolts or a snap-ring. Once mounted, the wheel bearing rides on the axle shaft, allowing the tire/wheel to spin effortlessly.

In my 50 years in the auto repair industry, I can’t recall one good story about wheel bearings. Most involve some sort of brake system failure, tires exploding, or fire from a seized red-hot bearing igniting axle grease. Bad wheel bearings should not be ignored.

NOTE: Whether you DIY or your mechanic replaces the bearing, always install a new axle hub nut. Most hub nuts are prevailing torque fasteners. They’re used on critical components, like securing axle shafts to hub bearings, where a loose nut could lead to disastrous consequences.

H8 tolerance

My opinion? If your vehicle has more than 50,000 miles or has been driven in harsh conditions, then it’s logical to replacing wheel bearings on both axles. However, if your vehicle has low mileage and the other bearing is in good condition, replacing only the damaged bearing should not be a problem.

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Never reuse any wheel bearing (sealed or tapered) that’s loose, worn, noisy or shows any signs of wear. Trying to fix a loose or damaged wheel bearing can result in an accident and severe injury. Even if a pro suggests repairing a bearing, don’t let them.

The average cost to replace a sealed wheel hub bearing is around $350 per wheel. However, depending on the make and model, the shop labor rate ($47 to $215 per hour, according to AAA) and any additional damage could push the cost beyond $1,000 per wheel.

The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors Tests prove Premium Efficiency/IE3 Motors can be rewound without degrading efficiency.

A tight fit, also known as an inter­ference fit, is usually recommended for a motor bearing journal. The range for radial ball bearing journal fits is from j5 to m5, and the housing fit is H6 (see Table 1). These are the “standard” fits and may be different depending on the machine design­ers understanding of the application. Table 1 is derived from Table 2-13 of ANSI/EASA AR100 Recommended Prac­tice for the Repair of Rotating Electrical Apparatus. It shows the relationship of bearing size to fit tol­erances. Generally, as the bearing gets larger, the tolerance widens. The key to this chart is that the journal fit is always interference and the bore fit is always line-to-line to loose. See AR100 for additional radial ball and roller bearing sizes.

Interference fit

Recommended Practice for the Repair of Rotating Electrical Apparatus This is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.

This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors.

Fit tolerance

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Older rear-wheel-drive cars or trailers use a set of two tapered roller bearings that face each other. These should be routinely serviced every 20,000 miles, or once a year.

I’ve replaced hundreds, if not thousands, of wheel bearings. One thing I’ve learned: A bad wheel bearing always gives an indication it’s failing. These include:

On modern front- and four-wheel-drive cars, wheel bearings are a set of permanently sealed, precisely machined steel ball or straight roller bearings. The balls or rollers are encased in a “cage” that supports the bearings, allowing them to rotate freely.