Finding source of a little drag

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Apr 5, 2025.

  1. pasadena_commut

    pasadena_commut Senior Member

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    (Mentioned in another thread, moving to its own.)

    From a couple of days ago:
    Every once and a while I walk around the car after a long drive and feel the wheels to see if any are hot. They never are. Except today, a little. The driver's side front wheel was slightly warm - roughly the same as my forehead like right now, just sitting typing this post. That would be about 90F. Definitely a different temperature than the other 3 wheels which all felt slightly cold. Ambient air temp was about 65F during that drive. The car was tracking dead straight, no pull at all, and there were no unusual sounds. The sun was hitting the driver's side (which faced south) during the last half of the drive, but the rear as much as the front.

    Today:
    After just driving around, again, driver's side front is a little warmer than all the other wheels. Car doesn't jerk when it comes to a stop. Doesn't pull to one side. MPG is fine.

    So it seems like something is causing a tiny amount of drag on that wheel, either the brakes or the bearing. The warmer corner had the wheel bearing replaced two years ago and at the same time pads and rotors on both front brakes. New tires last week, but hard to see how that could warm up a wheel unless the tire was grossly underinflated - not the case, Inflation is 35/33.

    The brake fluid has not been changed since I have owned the car, around 35k miles. Doing that probably wouldn't hurt, but I doubt it will fix this issue either.

    How does one track down the source of such a small amount of drag?
     
  2. Tombukt2

    Tombukt2 Senior Member

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    I use a temp gun to get some numbers a little hot hot as my forehead yeah that's cool I mean what's the ambient temperature where you're rolling? Tracking down a little drag yeah that's going to be a lot of fun a fish scale and pulling is how they used to check brake drag things like that The bearings are non-lubricated sealed business I guess it's they wear and take on lots of mileage they can add a little play that little bit of play can add some heat certainly But if I'm not mistaken in the southeast United States when I'm flogging down the highway at 73 mi an hour for 40 minutes something like that and pull over at the sheets I used to do the same thing quite a bit but not in the Prius in my Corollas and all four at least the front to hubs would be noticeably very warm so if it's 100 outside the front hub on each side is probably pushing 115 maybe 120 The rears are doing much of nothing they were drum brakes like the Prius
     
  3. pasadena_commut

    pasadena_commut Senior Member

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    I didn't have a thermometer with me when I first noticed this.

    To eliminate sun as a possible contributor the wheel temps were measured after a short night trip. Ambient temp was ~70F with slight variable wind and the driver's front was 84.5 F while the passenger's front was 78.2 F. The back wheels were both close to the passenger's front in temperature. Used an IR thermometer on one of the wheel spokes an inch or so out from the small plastic hub cover on each wheel.

    The causes would be:

    1. wheel bearing
    2. brake dragging slightly (for any of several possible reasons)
    3. something else dragging (like something stuck between the brake dust cover and the rotor)
    4. something nearby heating up the wheel (failed vacuum in heat storage tank? is far away from the exhaust)

    (All wheels have trim rings in place - it isn't due to one having the ring and the other three not.)

    I don't see how to prove it is the first one though, short of swapping the bearing and test driving it. The two front wheels are going to move together because of the differential, so even if the calipers were removed on both sides those wheels should spin down at the same rate, as both are tied to the high friction bearing. What would the test be? Jack the car up, remove the calipers, run the front wheels at 30 mph for a while, measure T? Probably would not give a meaningful result because the load on the bearing is so much lower than in normal usage. ~1000 pounds to ~50 pounds, 20 times less, 6 degrees/20 is about 1/4 of a degree, which is too small to measure accurately.
     
  4. PriusCamper

    PriusCamper Senior Member

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    Too early to tell... Could be nothing... Once it gets bad enough to notice a smell or a noise we can help with a diagnosis.
     
  5. Tombukt2

    Tombukt2 Senior Member

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    Yeah I'd have to wait till temperatures start to really creep up 84° and it's 70 out I would think it would be running it closer to a hundred 70 out at night and whipping down the road 55 miles an hour even the tad's lower just a coefficient of drag and all the business The brakes always are touching they're not dragging per se but they're there they're not supposed to be causing any strife but the little tiny gap that there is and any touching that they can do at speed will generate heat oh well certainly it's not enough to be worried with I mean until you get over 105 or something I wouldn't think and then all of them would be close to that a couple of degrees here and there I can't really worry about I mean the cost to get matching ground front wheel hubs and all that stuff with paperwork and that cost a fortune for a couple of degrees doesn't seem like it would be something to do.
     
  6. pasadena_commut

    pasadena_commut Senior Member

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    It would be nice to fix this at a convenient time and location of my choosing while there is just a 6F degree difference rather than waiting for, let's say a failing caliper, to jump rapidly to 106F degree difference, which will of course occur on some dusty highway in the middle of nowhere.

    Car has 140k miles. How long do the front calipers and the flexible hoses typically last? Don't think either has ever been changed. The hose could have been slightly damaged when the bearing was changed, and it is just now starting to act up.

    The bearing was made by Moog and is now 2 years old with only about 10k miles on it.
     
  7. Tombukt2

    Tombukt2 Senior Member

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    All that sounds way too perfectly reasonable how long do the rubber hoses and all the stuff last If you're not in the rust belt Southern United States California someplace like that where it never rains forever you'll be out of the car I'm coming up on 500k and two of them and everything is original except for brake pads brake actuators one car is actually on the original wheel bearings that came on the Toyota when the car came from the factory The rest of mine all have TRQ type deals on them no problems no noise nothing very boring on the Prius I don't generally get out and touch the hubs much I used to on my Corollas and my celica's. But anything in a hot summer day below say 1:15 here should be good I mean the pavements going to be $125° on a hot day your lower rocker panels will be quite hot All of that stuff but yeah I don't know if there's anything to fix. Don't nothing seem broke and seems working well and you're what did you say $140,000 mi Man you got a long way to go. You've got less miles than my youngest car an '07 with like I don't know now it's 190 on it I think I got it at 170 or 160 loaded every available option except heated seats which I've never seen in the United States personally.
     
  8. PriusCamper

    PriusCamper Senior Member

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    It's always interesting the difference between someone who ignores all symptoms even when they're obvious and someone who is noticing symptoms before they can even be confirmed that they are valid. If I were you, I'd find something else more important to think about, especially because your wheel bearings are nearly brand new.

    And I'll admit, we all get tricked into worrying too much if we have good mechanical skills/experience.

    Like yesterday my woodchipper bearing felt a little warmer than usual when I was done using it. It was also the hottest day so far this year (70' F ). But the hassle of replacing chipper bearings is so known to me I keep getting tempted to think about it. But I already promised myself to not get sucked into needless worrying and overthinking until there's way more symptoms to take the situation seriously.
     
  9. Danno5060

    Danno5060 Active Member

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    I would think one of those IR sensing thermometers that measure the temperature where you point the light would be what you'd want to use. If it's the bearing, the parts of the hub that house the wheel bearings will get warmer - you may have to pull the wheel off to get to the surfaces of the hub you want to measure.. If it's drag on the brakes, the temperatures of the discs will be higher - provided you check after you've driven for a while and only coasted to a stop (or used the parking brake).

    For the most part, it doesn't sound early enough to worry about.

    When I still had my Gen 2, I gained a couple MPG back when I pulled the rear brake drums and got rid of the accumulated brake dust that had been circulating around in there.
     
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  10. pasadena_commut

    pasadena_commut Senior Member

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    One reason to address it now is that the warranty on the bearing is 3 years/ 36000 miles. I'm guessing though that if a claim was made they would define failed only as completely blown up, not just starting to drag. Here's the legalese:

    Warranty | MOOG Parts

    Yeah, brake dust does seem to accumulate in the rear drums. We were having a problem getting the parking brake to hold on a slope, and thought the adjust wasn't working right. Opened up the drums, cleaned out a ton of dust, especially around the star gear, put it back together, and then they would adjust properly.
     
  11. PriusCamper

    PriusCamper Senior Member

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    Thanks... You just gave me motivation to getting around to doing original rear brakes at 298K miles. :)
     
  12. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Try a FLIR camera, you can probably rent one if you don't want to buy one outright.

    This will let you literally see the heat sources on and adjacent to the wheel. It'll be pretty easy to see what's hot and heating the wheel up.

    /My money's on that bearing...
     
  13. pasadena_commut

    pasadena_commut Senior Member

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    A FLIR camera would be nice, but the price for purchase or rental is pretty high. Home Depot rents one for $56 for 4 hours. That's not a huge sum, but it is also roughly half the price of a replacement bearing. Probably make more sense to just buy the bearing if the brakes can be ruled out (somehow).
     
  14. PriusCamper

    PriusCamper Senior Member

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    That notion sounds like you're determined to relive your bearing replacement experience of 2 years ago and getting actual proof that you need to do that is something you're not interested in?

    Most people who do home inspections have a thermal camera. Maybe you have a friend or will cross paths with someone who does that and they'd quickly compare temps from both bearings?

    More to the point, you've yet to verify anything out of the ordinary and yet you keep trying... I'm sure you got other stuff that's more concerning in your life than this?
     
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  15. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Oh yeah? Seems unusually cheap. Last time I put a genuine Toyota bearing in my car the part alone was about $300.

    And the time before that when my former mechanic installed a much cheaper bearing? Well... that was exactly why I needed to go back and do it myself with a genuine Toyota bearing...
     
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  16. pasadena_commut

    pasadena_commut Senior Member

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    When the original bearing started to make noise I got in the habit of feeling the wheels once and a while to see if that one was heating up. It never felt warmer than the other wheels, they all always felt the same. (At least, that is my recollection.) That was true even when the bearing became really noisy. After it was replaced I did the wheel feel a few more times, and all the wheels were the same temperature. So I fell out of the habit of doing that check since it never turned up anything. After new tires were put in I did a check after an hour's drive, not really expecting to find anything. But I did, the driver's front was significantly hotter than all the other wheels. All subsequent checks have confirmed that, even one at night, to rule out some sun related heating. So I think something is "definitely out of the ordinary".

    Granted 6F isn't going to boil the grease out of the bearing, whatever is causing the heating. Still, I want to know what this is so that I can make a rational choice about when and how to fix it. If it is the bearing it may make sense to live with it for a while. If the brake is dragging, even a little, I would fix that now.
     
  17. pasadena_commut

    pasadena_commut Senior Member

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    The price was from the after market parts on RockAuto, I know the OEM part is pretty expensive. Who makes those for Toyota? Aisin, Denso?
     
  18. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Last I checked they were using Koyo.

    This post may help you get through the clutter of counterfeit parts

    tl;dr a real Koyo bearing will come in a box with a qr code and a hologram sticker, and the part itself will be stamped with KOYO and a part number.
     
    #18 Leadfoot J. McCoalroller, Apr 7, 2025
    Last edited: Apr 7, 2025
  19. PriusCamper

    PriusCamper Senior Member

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    You didn't mention brand new tires? That could be the source of the problem right there. Once you get past 400-600 miles and new tires are broken in, check for warmth again. It takes tires a while to get past initial wear and start performing with minimal friction.
     
  20. pasadena_commut

    pasadena_commut Senior Member

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    It would be strange if that was the cause since all 4 were new. Still, it is an easily tested hypothesis, swap them and the warmer wheel would move with that tire.