The Carrier Bearing Who What and Why?

Posted by on April 11, 2012 | No Comments

What exactly is the Carrier Bearing? A carrier bearing must be used in automobiles which employ a multi-piece driveshaft. It allows the driveshaft to rotate freely while supporting it and keeping it in alignment. The carrier bearing is commonly bolted to the bottom of your car or truck, either to the frame or transmission tunnel. Ordinarily found on SUVs, trucks, and big sedans the carrier bearing was made to manage two issues relative to the driveshaft.

Driveshaft Critical Speed – The critical speed of the driveshaft is simply a speed measured from the number of revolutions per minute it can sustain safely before it gets unstable due to undesirable harmonics. Aspects that determine this speed include the length of the driveshaft, diameter, and material.

If you want to get technical there are several critical speed calculators available over the internet.

In short though… Longer / Narrower / Steel Driveshafts = Low Critical Speed and Shorter / Wider / Aluminum or Carbon Driveshafts = High Critical Speed

Crtical speed is a very important part of vehicle layout that certainly can not be overlooked. Exceeding a driveshaft’s critical speed can lead to sudden failure of the driveshaft, generally transpiring at high speeds. To defend against this potential problem, manufacturers decided to break the driveshaft up into several parts. Like links in a spinning chain, they need to be reinforced to make sure they remain in alignment. This is why the carrier bearing is critical.

Driveline Angles – In a truck generally the rear differential is lower than the engine and transmission. If you were to draw a line from the tailshaft of the transmission to the pinion of the rear end you would notice that line is not parallel to the ground. This is a good thing as it should have some angle to it for maximum U-Joint life. Generally a good rule of thumb for cars is approximately 3 degrees, but in a lifted truck these angles can exceed 10 degrees. In this situation the U-Joints will experience high wear and the driver will most likely notice a vibration. Multi-piece and telescoping drive shafts are some of the methods used in conjunction with carrier bearings to alleviate these issues.

Under most circumstances the use of a single driveshaft is possible and even advantageous due to lighter weight and lower driveline losses. It’s the cost associated with these large high tech single driveshafts that drive manufacturers to use multiple units in conjunction with carrier bearings.

Other Terms for the Carrier Bearing – Center Support Bearing – Hanger Bearing – Support Bearing – Driveshaft Support Bearing – Center Carrier Bearing

What Generally Fails In The Carrier Bearing That Creates Symptoms? The carrier bearing like most other bearings in a vehicle is made up of a number of rollers. Its a proven design and the relatively large size of the carrier bearing keeps heat low, generally allowing for a working life of over 100K miles. The achilles heel of the carrier bearing is generally not the bearing its self but the rubber isolator that surrounds it. This rubber breaks down over time and allows the bearing, and thus driveshafts to shift and change angle under load. If the bearing does fail you will generally get a squeeking noise that varies with speed. That squeaking noise will grow into a consistent growl as the bearing completely fails.

If you’d like to know the symptoms of carrier bearing failure or carrier bearing replacement please visit carrierbearing dot com.

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