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Early drive unit milling noise FIX

Discussion in 'Model S' started by Schenkzoola, Mar 8, 2019.

  1. Schenkzoola

    Schenkzoola Member

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    Hi everybody, I recently purchased a Rav4 EV with 126,000 miles. This car had terrible drive unit bearing noise, so I took it upon myself to try to fix it.

    The Rav4 uses almost exactly the same drive unit as the model S with the large motor, so it has almost exactly the same issues. This was cross posted in the myRav4EV forums, but I thought you might be interested too.

    ALL of the noise was caused by bearing failure, however taking it apart exposed a seal failure as well.
    Three bearings were in bad shape. The motor bearings had axial play, and the gearbox pinion bearing had fretting on the outer race, indicative of shaft voltage.

    Here is a google doc describing it: Rav4 EV drive unit “Milling” noise repair

    Please excuse the crudity of the document, I didn't have time to build it to scale, or to paint it.

    Lots more pictures here:
    https://photos.app.goo.gl/fUffopAvPV64R6kBA

    This is my first experience working on an EV, and let me tell you, they are so much easier to work on than gas cars.

    Since there are no drive unit service manuals or internal parts available from Toyota, or presumably Tesla, I would encourage others to share as much as you can about replacement pieces and procedures.
     
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  2. skitown

    skitown Member

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    Very cool, thanks for sharing this project!
     
  3. bart_dood

    bart_dood Member

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    #3 bart_dood, Mar 8, 2019
    Last edited: Mar 8, 2019
    Wow neat, love this.

    Usually bearings in this kind of application have shims of some kind to correctly place them or pre-load them. Did you find any?

    Also when FYI when I changed the oil in my 2014 S I discovered Tesla factor fill was right up to the fill plug, much more than the manual which states 1.5 quarts or so. It equals about 1.8-1.9 quarts.
    My theory is Tesla discovered putting more oil in makes the drive train more reliable.


    Also reading your write up, it's really disappointing Tesla put a goofy liquid cooling rotating tube in there that relies on a rotating seal. Failure dumps coolant into the motor. I'm sure the model 3 doesn't have such a device, I guess that's the price you pay for being an early adopter
     
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  4. Schenkzoola

    Schenkzoola Member

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    I had a hard time getting 1.5 quarts in, but the vehicle wasn’t level when I filled it.

    I think the tube thing is pretty clever in that they only needed one seal instead of two. Gas cars have rotating water seals, so I’m not too critical of a single seal.

    The motor bearings were preloaded with disc springs, but the transmission was not. The helical gear cut does axially load the transmission bearings, and the race was damaged on the load side.

    I’m convinced the damage was from the motor shaft inducing current flow through that bearing, not from lack of preload. The ceramic bearings in that motor would leave only the grounding brush and the transmission for a current path. If the grounding brush was not effective, it just leaves the bearing.
     
  5. esrandl

    esrandl Member

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    fantastic write up. thank you for doing this!
     
  6. cab

    cab Member

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    Very nice job! This is the first DIY I’ve seen on a drive unit repair!
     
  7. bart_dood

    bart_dood Member

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    They could have cooled the motor internally with oil then had an oil to coolant thermal transfer with static seals (no sliding or rotation to cause wear). I might be wrong but I think this is what the model 3 rear motor has. The downside is you need some kind of oil pump to force oil through the motor and the heat exchanger; a pump does give you the advantage of being able to put a filter in to catch wear material. The 3 rear motor has such a filter and pump.

    You are right gas cars have rotating water seals, but gasser water pumps usually only go 100k miles before they fail and the pump is on the outside, not internal to the motor requiring a motor drop.

    The 3 rear motor is a superior design to the S its just the way of evolving designs when you move as fast as tesla does to the market.
     
  8. Sublimobile

    Sublimobile Member

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    Just because it's later, doesn't necessarily mean it's better. Many times companies over engineer early models and then cut costs as they evolve. It's most likely some things are better and some are a little worse.
     
  9. freeewilly

    freeewilly Member

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    Brea, CA
    Thanks for the pictures.
    The hardest project I did was to replace a couple gears in KitchenAid mixer. This a on a different level...
     
  10. bart_dood

    bart_dood Member

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    I'm not sure that's true here. This motor has the highest mileage of an single S motor I've seen. The other high mileage S cars that I've seen have had multiple motor swaps.

    Tesla has tested the M3 motor to 1 million miles and shown pics of the tested motor internally.
     
  11. Schenkzoola

    Schenkzoola Member

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    I’m not the original owner of this vehicle, but I do have the service history. This drive unit was replaced at ~60,000 miles. So this drive unit had roughly 65,000 miles on it before I tore it down. The gears themselves looked to be in great condition. Even though it was replaced, it was still a rev F unit. I hear things got much better in terms of longevity at rev Q.

    I hope my M3 lasts to 1M miles!
     

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