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I recently posted this question about finding the proper U-Joint for my truck (Chevrolet Silverado EC/SB 1500 4x4 Z71 LT3 L33). I'm planning on purchasing U-Joints which have zerks in them, so I can keep them greased on a regular basis. I know that the zerk should be placed on the compression side (on the clockwise from the input shaft as you'd be looking from the front of the vehicle back) to prevent problems with stress risers. My questions are:

  • Does it matter whether the zerk is facing towards the front or the back of the vehicle?
  • If changing multiple U-Joints, should they all be facing the same way, or does it matter?)
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Usually install the zerks so they are accessible first, then lined up where they can be greased at the same time (at the same angle). I think most u-joints have two zerks at 180 degrees so they should be easy to get without rotating the driveshaft.

  • I would have to disagree with your assessment here. Since most drive shafts line up the yokes, you would need to stagger the zerks, or one of the u-joints will be under compression at the zerk when the vehicle is in drive and one will not. A u-joint which is under stretch at the zerk has a huge stress riser and stands likely to fail. Having both zerk areas at compression will alleviate this probability. When I stated "facing the same way", I meant for the face of them to be the same (side with zerk facing forward or backward). I agree with making them accessible, but that may not be possible. – Pᴀᴜʟsᴛᴇʀ2 Jun 21 '16 at 21:34
  • I suppose that would make sense on higher torque or racing applications. Though, in my opinion, a majority of ujoint failures that I have seen have all been because of lack of maintenance or improper/ lack of lubrication. – john D. Jun 21 '16 at 22:15
  • Most stock u-joints don't come with zerks, so you wouldn't see this type of failure normally. – Pᴀᴜʟsᴛᴇʀ2 Jun 21 '16 at 23:02
  • Have you seen ujoints fail because of the stretch or compression of the joint, or maybe fatigue? The only structural failure of ujoints that i have seen, that were not due to either improper installation or lack of lubrication, were due to a shock load in poor traction conditions or from driver error/abuse. I am not saying that you are wrong, I am just curious to know the conditions. It seems that the ujoint may be overloaded or under sized if that is happening. – john D. Jun 22 '16 at 0:08
  • There is a natural stress riser where the zerk is located because of the lack of material holding it together. If the zerk is placed on the compression side, the zerk fills the hole. Under stretch, it doesn't do the same job. Enough stress on the area over time can cause failure. This is a known issue which many don't think about when installing u-joints. – Pᴀᴜʟsᴛᴇʀ2 Jun 22 '16 at 0:12

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