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Signs of Incorrect Tapered Roller Bearing Preload

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  • Signs of Incorrect Tapered Roller Bearing Preload

    I subscribe to a number of various trade publications in order to help me stay abreast of various industry trends and solutions. One of them I read the other day, Todays Trucking, a Canadian publication geared obviously to the transportation industry in Canada, had an interesting tech article related to the problem of improper truck and trailer wheel bearing preload and the related problems associated with that issue.

    More to the point is a comment made by an applications engineer from NTN Bearings regarding the signs of incorrect bearing preload as it applies to tapered roller bearings.
    Just wondering if anyone else has noticed the indicators as described in regards to machines they have examined that were known to have bearing issues and how these signs may apply to machines we typically use in the shop.

    https://www.todaystrucking.com/searc...g-adjustments/

    “Excessive preload will cause excessive friction and the bearing will run hot, compromising lubrication and eventually leading to flaking (material coming off) at the large end of the rollers/races,” he says. “On the other hand, adjusting the bearing too loose causes excessive looseness and vibration in the system. This could lead to a multitude of issues such as, but not limited to, wheel wobble and seal leakage along with ABS and braking problems. Eventually a too-loose setting will cause flaking at the small end of the rollers/races, which can lead to failure and possible wheel loss.”
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

  • #2
    Used to see it a lot in my auto-parts sales days. Never have seen such in a machine tool, but I've only owned a few and don't work on anyone else's.

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    • #3
      I'm going to have to guess that there is probably quite a bit of leeway between what is too tight and what is too loose, depending on application of course.
      When I used to work on cars I cleaned and repacked hundreds of tapered roller bearings on front ends of cars. The rule was snug them up tight, back the nut off about 1/4 turn, never use a torque wrench and never had any come back.

      JL.....

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      • #4
        Willy - can I ask why is this being questioned by you ? it all makes perfect sense and yes iv seen everything described,,,

        one has to keep in mind the rollers of the tapered roller are ground ever so slightly convex, sooooo - tighten too much and you will indeed get flaking in the middle and also create tons of extra heat and get rid of grease in the process,,,

        run too loose and now you exceed the convex angle - now you will get extreme unit pressures on the ends of the rollers again resulting in flaking,,,

        and Joe lee --- how much is "snugging them up tight" that's a pretty vague description ,,,, and you also skipped a critical point, rotating the hub to get the excess grease out of the bearings - it makes a huge diff, so what i do - (on a small axle jap car) hang my hand and forearm on about a foot long fulcrum - then rotate hub while hanging and watch the hand go down every time to take up the slack of all the extra grease getting dispersed, re-adjust hand and forearm to it's at an 90 degree angle and keep spinning till there's no longer any movement --- the wheel bearing is then tight with no slack but not too tight,,, has worked every single time for the past 50 years... no problemo...

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        • #5
          IIRC, per what JoeLee said (same as many others say/do) wheel bearings are kept silly loose compared to most any machine bearing.

          Usually, tighten to where it is not loose at all. Then tighten more until a swift spin and it turns about 1 full turn or a bit more. That always seems to come out right. If you have a better adjustment procedure in the book, use it.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            Originally posted by J Tiers View Post
            IIRC, per what JoeLee said (same as many others say/do) wheel bearings are kept silly loose compared to most any machine bearing.
            Yeah, they have to be really loose in the "classic" non-driven wheels configuration. Long spindle, bearings in O-arrangement and with brakes to heat the outer bearing housing.
            Outer bearing housing could be 150 degrees hotter than the spindle, eating up lots of the free play left in the bearing.
            Nearly all Volksvagon rear wheel bearings from 1960's to 1990's had to be particularly loose..

            Lathe spindle bearing heats up in opposite way and there is not much danger of "thermal runaway".
            (exception to rule is my Kerry lathe spindle where British engineers have figured out to install the bearings in X arrangement. Never seen in any other lathe)

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            • #7
              Bearings need to be preloaded for maximum life and performance but because it's so easy to exceed the correct preload (good example being wheel bearings) many people run them slightly loose just to be on the safe side.

              One example of required bearing preload...I remember the spec for a roller bearing in the final drive of an old JD 420 crawler I have, it was 3 thousandths of an inch and it was to be set by using the correct gasket thickness between one bearing cup holder and the main case. Another example of required preload is to be found in the pinion bearings in differentials. Since it's extremely difficult to set by distance, it's done by torque. Of course it's required to ensure correct mating of the pinion and crown gear but the bearings are preloaded and to a specific spec.
              Location: Saskatoon, Saskatchewan, Canada

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              • #8
                Originally posted by A.K. Boomer View Post
                Willy - can I ask why is this being questioned by you ? it all makes perfect sense and yes iv seen everything described,,,

                one has to keep in mind the rollers of the tapered roller are ground ever so slightly convex, sooooo - tighten too much and you will indeed get flaking in the middle and also create tons of extra heat and get rid of grease in the process,,,

                run too loose and now you exceed the convex angle - now you will get extreme unit pressures on the ends of the rollers again resulting in flaking,,,

                and Joe lee --- how much is "snugging them up tight" that's a pretty vague description ,,,, and you also skipped a critical point, rotating the hub to get the excess grease out of the bearings - it makes a huge diff, so what i do - (on a small axle jap car) hang my hand and forearm on about a foot long fulcrum - then rotate hub while hanging and watch the hand go down every time to take up the slack of all the extra grease getting dispersed, re-adjust hand and forearm to it's at an 90 degree angle and keep spinning till there's no longer any movement --- the wheel bearing is then tight with no slack but not too tight,,, has worked every single time for the past 50 years... no problemo...
                Yes, rotating the hub while tightening was also part of it, I just forgot to mention it. "how much is "snugging them up tight" that's a pretty vague description" good question, all done by feel. What might have felt tight to me may have felt loose to someone with bigger arms and a big beer belly, Ha, ha. I wasn't that technical back in those days, not many mechanics were. I don't even remember a torque being specified in any of my old motor manuals. The only thing I ever remember using a torque wrench for was head bolts.
                So it just goes to show you how forgiving tapered roller bearings are.
                The newer style ball bearings in the front wheel drive cars of today, not so forgiving. My father had a buick where the front wheel bearing got noisy. My brother in law changed it out in the driveway. There was a warning on the box not to over tighten and it specified a torque. Brother in law being a cob artist drove the nut on with an air impact wrench with 180 psi behind it. That bearing lasted about ten miles before it started to hum.

                JL.................

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                • #9
                  Before disc front brakes, the rule for cars was a slight bit of play for the bearing. With front disc brakes that changed to no play and the procedure to make sure they are snugged down and spun and then released and re tightened to just no play became the norm. Trailers and other roller bearing applications still require some play as far as I know. I don't know how the machine tools are suppose to run, but I do run my little Atlas at almost no play and have no issues with it. Mike

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                  • #10
                    Originally posted by JoeLee View Post
                    So it just goes to show you how forgiving tapered roller bearings are.


                    JL.................
                    For the most part they are pretty forgiving,,, proof in the pudding is some auto manufacturers method of adjustment is downright awful,,, iv seen about everything under the sun, while some are infinitely adjustable (like the double locking nut's with the special washer in the middle that has a tang that fits into the spindle groove or the old VW nut with a slice cut on one side and an allen head to cinch it tight) other's lack the proper increments to get close enough to actually feel like you got in the sweet spot,,,

                    the hex castle nut is actually not a bad way to go and can be dialed in close enough IF the spindle has two holes for the cotter pin ---- I have seen them with only one,,, this sucks for dialing things in but is kinda proof that they can handle a fair amount of deviation and still work "ok"

                    if an auto manufacturer is too cheap to drill two holes in the spindle then they should forgo the castle nut all together and just use one of those special nut cages that slip over the hex and have all kinds of possibilities where the cotter pin can go esp. when changing the cages position on the hex changes the relationship of said cotter cut out's...
                    Last edited by A.K. Boomer; 04-18-2019, 10:01 AM.

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                    • #11
                      On trailers I always just go hand tight with the nut.

                      The trucks get maybe 10 ft/lbs.
                      Andy

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                      • #12
                        Years ago, I had a Jet 1024 lathe that loved to chatter. The spindle ran on the typical tapered roller bearings and I questioned the preload. I called into Timken support and talked with a engineer about it. He told me the best way to judge preload was by temperature after it ran a while. It should get reasonably warm approaching hot but if too hot to keep your hand on the preload was excessive. There are quantitative temperatures available of course but the average home shop couldn't get a accurate measurement anyways. I have later seen were temperature was the benchmark for spindle break in with angular contact ball brearings also. (the angular ball bearings don't really break in as such, its a matter of the grease being distributed that lowers the temp when new)

                        Basically, if the bearings/housing is cold after a half hour or so running, the preload is too low. If you can't comfortably leave your hand on it, the preload is too high. Yea, its not a precision method but a good seat of the pants check.

                        Monitoring the temp is pretty much out of the question for some things, like wheel bearings but easy on a lathe spindle.

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                        • #13
                          Originally posted by JoeLee View Post
                          So it just goes to show you how forgiving tapered roller bearings are.
                          The newer style ball bearings in the front wheel drive cars of today, not so forgiving. My father had a buick where the front wheel bearing got noisy. My brother in law changed it out in the driveway. There was a warning on the box not to over tighten and it specified a torque. Brother in law being a cob artist drove the nut on with an air impact wrench with 180 psi behind it. That bearing lasted about ten miles before it started to hum.

                          JL.................
                          I'd say that its typically opposite.
                          Modern bearings (at least about every euro/jap and related fwd US cars) typically don't rely on the correct torque, just needs to be "tight as hell" as they rely on internal dimensions to maintain correct bearing clearance/preload and tightening torque has very little effect on that and there is nothing to "adjust"

                          They all also seem to be angular contact ball bearings with the exception of some British oddities (Lotus Elise, Rover Metro and MG-F that use tapered roller bearing unit with single-piece outer race)

                          Elise bearing:

                          Two "matched" tapered roller bearings built into single unit, nothing to adjust, it just works (mostly)
                          Last edited by MattiJ; 04-18-2019, 10:13 AM.

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                          • #14
                            Im in agreement Matt - I read that and figured he must have done something else wrong,,, they will disintegrate if ran loose but it's pretty damn hard to overtighten them...

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                            • #15
                              Never saw tapered bearing problems until these sealed front vehicle hubs started coming around. Now I see rough running ones probably from too much pre load and sometimes a loose one from maybe too little. Obviously a "newer and better front hub system" that isn't as good as the old adjustable and relubeable system.

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