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Q & A

U-Joint Lubrication

“We are having problems with U-joint failures on our line haul trucks. I believe that these failures are lubrication related. Can you recommend a lubrication interval and procedure?”

Inadequate lubrication is one of the most common causes of premature U-joint failures. You'll typically want to follow OEM recommendations for lubrication intervals, but a for a typical line haul truck, regreasing the U-joints every 20 to 35 thousand miles is a good rule of thumb. Here are some general guidelines for lubricating U-joints:

1. Grease the U-joint through the grease fitting on the U-joint using the recommended grease. Apply the grease until the new grease purges from all of the journal cross bearing seals.

2. Make sure that new grease is flowing from all four bearing seals. If it is not, loosen the bearing cap bolts and continue greasing until grease purges at all four seals.

3. If grease still doesn't purge from all four caps, replace the U-joint.

4. When a different grease is being used, ensure compatibility with the old grease and purge out the old grease with the new grease.

Today's Tip

• Here's a checklist for troubleshooting foaming and aeration
  in lubricating oils:

  • Ensure there are no leaks introducing air into the oil on the suction side of the circulating pump.

  • Improper oil viscosity (especially higher viscosity) can increase the risk of foaming.

  • Outside contaminants such as grease, dust or moisture can delay air release from oil.

  • Provide maximum separation of the suction and return lines to give air a chance to separate from the oil. Tank baffles provide further help.

  • Be sure that the oil return line is below the oil surface in the reservoir. If it is above the oil level, oil could splash into the tank putting air into the system.

  • Ensure that there is adequate residence time of the oil in the reservoir to allow the air to release.

  • Consider employing a diffuser on the return line to allow oil to "ooze" into the tank, reducing agitation.
    

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Book Bits

The later the bearing can be lubricated (packed with grease) the better it is protected from contamination during mounting and installation. There are several reasons for this. Some of them are concerned with the bearing type; for example, bearings with tapered bores, the reduction in the radial clearance when the bearing's pre-load is being set cannot be measured accurately if the bearing is lubricated. Others relate to the method of mounting, the bearing may possibly have to be heated, therefore any pre-greasing would be pointless.

The most important reason, however, is the cleanliness requirement. The later the grease is applied, the better the chance of preventing contamination, which leads to premature bearing failure.

For more information about the "Rotating Equipment Handbook" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=22

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