Apr 11 2012
The Carrier Bearing Who What and Why?
What Is The Carrier Bearing? A carrier bearing is used in vehicles which utilize a multi-piece driveshaft. It allows the driveshaft to spin freely while supporting it and keeping it in alignment. The carrier bearing is generally bolted to the bottom of the car or truck, either to the frame or transmission tunnel.Generally found on SUVs, trucks, and large sedans the carrier bearing was designed to address two issues in relation to the driveshaft.
Driveshaft Critical Speed – The critical speed of the driveshaft is basically a speed measured in the number of revolutions per minute it can sustain safely before it becomes unstable due to undesirable harmonics. Factors 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 usually the rear differential is lower than the engine and transmission. If you were to draw a line through the tailshaft of the transmission to the pinion of the rear end you’d notice that line is not parallel to the ground. This is a good thing mainly because it needs to have some angle to it for max U-Joint life. Generally an excellent guideline for cars is around 3 degrees, nevertheless in a raised truck these angles can go beyond 10 degrees. In cases like this the U-Joints will experience significant wear and the driver might notice a vibration. Multi-piece and telescoping drive shafts are one of the methods used in conjunction with carrier bearings to ease these problems.
Under nearly all instances the use of a single driveshaft is feasible and in some cases advantageous due to lighter weight and lower driveline losses. It’s the cost connected to these large advanced single driveshafts that drive manufacturers to utilize 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 many other bearings in a vehicle is comprised of several rollers. Its an effective design and the fairly substantial size of the carrier bearing keeps temperature low, commonly enabling an operating lifetime of over 100K miles. The achilles heel of the carrier bearing is frequently not the bearing its self, but the rubber isolator that envelopes it. This rubber breaks down with time and allows the bearing, and therefore driveshafts to shift and change angle under load. If the bearing does fail you will normally get a squeeking sound that varies with speed. That squeaking noise will turn into a steady growl as the bearing totally fails.
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