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About Bearing End-Play

WHEEL BEARING END-PLAY - Let's Take A Look At The Facts

As of late, there's been a firestorm of controversy over the "right" way to adjust wheel bearings. And as we have learned in the last few years, there is no shortage of "opinions" on how to do things when it comes to the trucking business.
And some of these "opinions" are not only flat wrong, but can lead to bearing failure and hub fires. Opinions are all well and good, we just prefer opinions that are based on facts and data.

This has been particularly frustrating because one, it's caused a lot of concern and anxiety for many of our customers and two, we have spent countless hours researching this subject, analyzing temperature data, getting feedback from manufacturers, testing different lubricants and looking for ways that can make for easy and consistent ways to get bearings installed and adjusted to give you the best fuel mileage and longest bearing life.

So our intent here is to help you understand ALL of the variables that need to be considered, to insure that you achieve the fuel mileage gains you're after, without affecting seal life and an understanding how these can be achieved WITHOUT affecting wheel alignment. The first you need to do to determine whether or not the person handing out the advice has a good understanding of the methods they use or recommend. And that is easily determined by asking three simple questions:

1) "What is your personal end-play recommendation?"
2) "What amount of end play are we looking for when we're done?"
3) "In relation to outside temperature, what do you feel is a normal hub temperature range?"



Conventional bearings have a break-in period where the machined surfaces of the races and rollers break down and "flatten out". As this happens, end-play increases. We have found that this is typically about .002" - .003". The MicroBlue process eliminates this problem and there is NO break-in and subsequent increase in end-play. What is important here is we go from "OK" to "too tight" very quickly!


For proper operation and life of all engine and drivetrain components, we rely on lubricants to provide a protective film that is designed to provide a cushion and keep metal parts from making hard contact that results in excessive heat and wear. In order for that to happen, there needs to be sufficient clearance between those surfaces for the lubricant to do it's job. For example, why is there always backlash with gears? To make room for a lubricating oil film. When it comes to wheel bearings, a small amount of end-play is required to keep the rollers from making hard contact with the races, because hard contact creates heat and wear. So think about it, when bearings are put into a pre-load condition, we are forcing metal-to-metal contact and that prevents lubricants from providing a protective film, right? Does that make sense? Of course not.

Then the question becomes, "how much end-play"? Technically very little, .001" would suffice, if there was no flexing of the spindle. So rather than get into "who's right", let's first take a look at what's happening inside those hubs when you're going down the road and how this affects your fuel mileage, bearing life and most importantly, how to avoid getting yourself into a potentially dangerous bearing failure situation.

SPINDLE FLEX: The one variable that's been left out

In 2011, we had an 8-axle customer who installed our bearings, set the end-play between .001" and .002" and saw no gain whatsoever. Unsure as to why, he decided to have a set of Stemco® Pro-Torq nuts installed which increased the end-play to .004". He immediately saw a 1 mpg. gain.

Puzzled (since in theory, it should have made no difference) we set out to figure out why. Then the question came up, "do the spindles that the bearings ride on flex?" To answer that, we set up a steer spindle with bearings in a press with v-blocks and dial indicators. We then applied 5000 lbs. dead center on the spindle and to our astonishment, the tops of the bearings cocked in .004"! Which at that point answered our question as to why, but opened up Pandora's box at the same time.

What we have since found is that as you're going down the road, the bearing rollers are actually moving in and out, top to bottom, like waves of the ocean. And that number appears to be an average of .002" to .003".

Now let's think about what happens when end-play is set at .001". You guessed it, the rollers are constantly hitting the race surfaces which does three things: 1) causes premature wear and bearing surface breakdown, 2) prevents lubricants from providing a protective film between those surfaces and 3) creates heat build-up, which is guaranteed to decrease the life of your bearings.

A word of caution: In the last 12 months, we have had 5 people contact us to let us know, that due to over-tightening of their bearings they suffered damaging hub fires. The poor guy pulling a reefer, lost his trailer and his load, and the car-hauler was just happy that the cars were saved! So be careful of who you listen to. And make sure they have the answers to those three critical questions. Opinions need to be supported by facts, right?

About Spindle Flex


If you take a close look at the wheel hubs on any NASCAR or INDY car, you will find small rectangular stickers on every one of them. If you look more closely, you will see a number of small boxes with numbers next to them. What they do is change color as things heat up and tell the engineers what temperatures the hubs ran at the last session. Because that's the only way they can tell if they got the set-up right, under load, at speed. Because the mission is the same as yours: Allow just enough end-play to let the lubrication do it's job while at the same time keeping the wheels straight and parallel.

Understanding that when there's not enough room for the lubricant, the rollers then touch the races and we all know the maximum amount of friction and wear happens when there's contact. And when there's contact, there's heat, it's that simple. But how do you know when you've got it right? The only way is to try a number of setup's from "too tight" to "too loose", and look at the hub temperatures, and make a graph. When bearings are in a pre-load condition (too tight), there's no room for a oil film and temperatures go up. When we go from a pre-load condition to end-play, temperatures go down.

Hub Temperature Graph


Understanding the need for .003" to .004" end-play, let's look at how to get it done. At first that seems easy. Just measure the in and out movement with a dial indicator. The problem is, when most seals are installed, there's just enough "push back", that you cannot move the hub to measure the end-play. So if you cannot actually measure anything, how do we get the bearings set to any spec? The fact is, you can't. To further complicate things, with a double nut system, when the jam nut is tightened, you now lose .002" to .003" of whatever end-play you may of had. Now think for a moment about all the adjustment methods you've run across and ask yourself two questions: "Is there ANY way to know where they're set"(no) and "Is it at all possible to wind up with two or more hubs set the same way?" (again, no).

Fortunately, the Pro-Torq nut solves these problems in a fast convenient way. The most important (and overlooked) feature is the raised "dots" (which they refer to as "raised face marks) on the face of the nut. 3 or 4 on the steers, 8 on the drives and 4 on tapered trailer spindles. All that's required is to torque the nut to 100 ft./lbs., remove the socket and reference the location of one of them, and simply back-off (loosen) the nut one "dot". That's it. Then just pinch and insert the lock ring in the serrations and you're done. A very fast, easy and consistent .003" to.004" end play.

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