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Drive unit failure/problem posts decreasing - reliability going up?

ecarfan

Well-Known Member
Sep 21, 2013
19,202
13,854
West Vancouver, British Columbia
The only thing that worries me is that someone on the forum said that the milling noise was a symptom of a drive unit failure later down the road. The milling noise on my car has gotten much worse the last week or so and I'm worried that I'll have a DU failure before my scheduled service visit more than a month from now.
I certainly understand your concern. But actual failures, as in the car won't move, are rare. The milling sound tends to get louder with time. That does not mean that the DU is going to fail in a day, or a week, or in months.
Anyone who states that the milling sound will inevitably result in DU "failure" (car won't move) is speculating.
 

qwk

P130DL
Dec 19, 2008
3,024
766
I certainly understand your concern. But actual failures, as in the car won't move, are rare. The milling sound tends to get louder with time. That does not mean that the DU is going to fail in a day, or a week, or in months.
Anyone who states that the milling sound will inevitably result in DU "failure" (car won't move) is speculating.
You are right, the bearing wear(cause of the drone and milling sound), won't cause a failure right away, but the bearings will eventually seize or come apart. The reason that we haven't seen many failures, is because Tesla replaces the DU once it hits a certain noise threshold(either car or owner).
 

DDotJ

Member
Feb 28, 2013
747
1,151
California
I certainly understand your concern. But actual failures, as in the car won't move, are rare. The milling sound tends to get louder with time. That does not mean that the DU is going to fail in a day, or a week, or in months.
Anyone who states that the milling sound will inevitably result in DU "failure" (car won't move) is speculating.

Thanks, that's a relief. I just hope they can get me a DU replacement with a revision that fixes this issue once and for all.
 

nienco2

Member
Sep 30, 2015
178
68
SC
Anyone who states that the milling sound will inevitably result in DU "failure" (car won't move) is speculating.

Define Failure

How to define "failure". How about anyone who doesn't think the milling sound is a failure offer to swap their DU with someone who has a noisy DU?
 

Todd Burch

Voltage makes me tingle.
Nov 3, 2009
7,913
29,540
Smithfield, VA
How about anyone who doesn't think the milling sound is a failure offer to swap their DU with someone who has a noisy DU?

Just because someone believes a noisy drivetrain doesn't qualify as a failure doesn't mean that they think it's acceptable.

By that metric virtually every gas car on the planet has a failed drivetrain.
 

CHG-ON

Still in love after all these miles
Jun 24, 2014
3,079
636
Santa Cruz Mountains, USA
I'm still trying to figure out what the "milling" noise sounds like. Is it a hum, a buzz, a whine? I watched a video of it. But there was too much ambient noise for me to make anything out. I hear a faint hum that I did not notice before, when the stereo is not on at about 65-70. But I have no idea if it has always had that and I have just begun to notice it as I have become accustomed to the silence of the car on smooth pavement. If I do have it, I would like to be able to definitively state that to the techs so that they can't simply brush it aside. I have just about 19K and I started noticing it at about 16K. Since I usually have talk radio or music playing, I rarely hear it.

Thanks.
 

DDotJ

Member
Feb 28, 2013
747
1,151
California
I'm still trying to figure out what the "milling" noise sounds like. Is it a hum, a buzz, a whine? I watched a video of it. But there was too much ambient noise for me to make anything out. I hear a faint hum that I did not notice before, when the stereo is not on at about 65-70. But I have no idea if it has always had that and I have just begun to notice it as I have become accustomed to the silence of the car on smooth pavement. If I do have it, I would like to be able to definitively state that to the techs so that they can't simply brush it aside. I have just about 19K and I started noticing it at about 16K. Since I usually have talk radio or music playing, I rarely hear it.

Thanks.

I tried to get it on video, but it's hard to get the sound in the video. Mine started as a faint hum at a specific power band so I thought it was normal. After a few months it just kept getting louder and louder at almost all speeds below 50. Now you can't ignore it, it's like a whine/hum + ying-ying-ying-ying noise. It's not too loud, so you can't hear it with a full car of talking people or music playing. You hear it while you're alone in silence going through a parking lot.

And I don't think a noisy DU counts as a failure. It could be a symptom of abnormality or a possible failure and should be fixed. But a failure would be when the motor is no longer operational and leaves me stranded.
 

fact200

Member
Sep 25, 2014
107
64
San Francisco
I'm still trying to figure out what the "milling" noise sounds like. Is it a hum, a buzz, a whine? I watched a video of it. But there was too much ambient noise for me to make anything out. I hear a faint hum that I did not notice before, when the stereo is not on at about 65-70. But I have no idea if it has always had that and I have just begun to notice it as I have become accustomed to the silence of the car on smooth pavement. If I do have it, I would like to be able to definitively state that to the techs so that they can't simply brush it aside. I have just about 19K and I started noticing it at about 16K. Since I usually have talk radio or music playing, I rarely hear it.

Thanks.

It's very noticeable if you oscillate between forward power and regen at around 10-20mph (tire noise will drown it out at high speeds). IMO it's an electrical noise rather than mechanical as it almost has a digital nature when you're around the threshold (of power/regen) as it cuts in and out very abruptly.
 

bmanke

Member
Mar 1, 2015
74
28
Chesapeake, VA
It's very noticeable if you oscillate between forward power and regen at around 10-20mph (tire noise will drown it out at high speeds). IMO it's an electrical noise rather than mechanical as it almost has a digital nature when you're around the threshold (of power/regen) as it cuts in and out very abruptly.

This is how ours started and I also thought it was electrical. Over the course of another 10,000 miles it started growling at low speed and the "buzz" became noticeably louder. So much so people at work in the parking lot began to notice. Just had our drive unit replaced - wow - soooo much quieter now! And we have an 80,000 VIN.....
 

Zetopan

Member
Oct 10, 2015
100
83
Hillsboro, Oregon
IMO it's an electrical noise rather than mechanical as it almost has a digital nature when you're around the threshold (of power/regen) as it cuts in and out very abruptly.
I have an alternative mechanical explanation which I consider more likely. In the interest of quietness the pinion and spur gears are helical. This provides for a quieter torque transmission mesh. One downside is that is it slightly less efficient, but the larger downside is that end thrust is generated on both gear shafts. The torque in the forward and reverse directions causes end thrust in opposite directions. Hence when traveling forward the end thrust is in one direction and when in regen or reverse the end thrust is in the opposite direction. I have listened to the "milling" noise recordings and to me it sounded like the thrust bearing was starting get rough and to come apart. The thrust bearing balls or rollers will eventually spall if sufficiently overloaded and the non-round results will only get worse with further use. Note that reverse and regen apply an end thrust in the opposite direction, unloading the failing thrust bearing and loading the opposite thrust bearing. Hard acceleration would also accelerate the failure mode and increase the sound level. My estimate is that this is what is actually happening.
 

kennybobby

Member
Sep 14, 2014
478
36
Heart o' Dixie
I have an alternative mechanical explanation which I consider more likely. ... Note that reverse and regen apply an end thrust in the opposite direction, unloading the failing thrust bearing and loading the opposite thrust bearing. Hard acceleration would also accelerate the failure mode and increase the sound level. My estimate is that this is what is actually happening.

+1, i'm with you on this one. we've even talked about it before in several other threads. And they are not using thrust bearings, but plain old everyday-bloomers radial ball bearings. There are pictures of them in one of the other threads, maybe i search for it later and update before the edit expires...
 

Zetopan

Member
Oct 10, 2015
100
83
Hillsboro, Oregon
And they are not using thrust bearings, but plain old everyday-bloomers radial ball bearings.
There are classes of radial ball bearings that are designed to resist axial loads. These are often used in pairs on milling machines, among other things. Their generic name is "angular contact" ball bearings. The angular contact ball bearing is a combination of a conventional ball bearing and a thrust bearing. My explanation is still applicable since changing from forward to reverse alters which angular contact face that is being loaded. I suspect that Tesla didn't quite complete the design by using FEA (Finite Element Analysis) to analyze the end thrust caused by the helical gear pair. The drive motors generate quite large torques relative to their IC counterparts.

An alternative possibility is that the gear teeth face are actually breaking down, since reversing direction also reverses the tooth face being loaded, but I still suspect that the problem is actually due to the bearings breaking down.

Here are some typical photos. https://www.google.com/search?q=ang...X&ved=0ahUKEwjspbWoh9HKAhUW9mMKHd2ADwQQsAQIKg
 

Zybane

Member
Oct 22, 2015
357
97
Washington D.C.
Isn't it typical that a bearing will either fail relatively quickly (say within the first year of operation) or it will last a long time? With the quality/tolerances involved, if there are any tolerances that are off or contamination in the bearing, it would lead to early demise. But if those two conditions are good, it could last a very long time.
 

tom66

Member
Dec 17, 2013
625
28
United Kingdom
Isn't it typical that a bearing will either fail relatively quickly (say within the first year of operation) or it will last a long time? With the quality/tolerances involved, if there are any tolerances that are off or contamination in the bearing, it would lead to early demise. But if those two conditions are good, it could last a very long time.

That's the case for many devices. Bathtub curve - Wikipedia, the free encyclopedia
 

Alysashley79

Active Member
Oct 4, 2013
1,198
512
Seattle(ish) WA
Has anyone with a DU failure noticed a slight halting going from reverse to drive almost like the engine if you will is cutting out. I've brought it up to the techs at the SC and they just shrug their shoulders at me like they aren't sure what I'm taking about but several people that have driven my car have noticed it. It's only notible at very low speeds like 2mph. Has anyone else noticed this?
For reference I have a p85
 

tom66

Member
Dec 17, 2013
625
28
United Kingdom
Has anyone with a DU failure noticed a slight halting going from reverse to drive almost like the engine if you will is cutting out. I've brought it up to the techs at the SC and they just shrug their shoulders at me like they aren't sure what I'm taking about but several people that have driven my car have noticed it. It's only notible at very low speeds like 2mph. Has anyone else noticed this?
For reference I have a p85

I think this is torque sleep. The motor drive gets turned off in the region of low torque. Might cause a sensation of loss of power at low speeds.
 

demundus

Active Member
Jul 5, 2015
1,312
843
Oceanside, CA
Has anyone with a DU failure noticed a slight halting going from reverse to drive almost like the engine if you will is cutting out. I've brought it up to the techs at the SC and they just shrug their shoulders at me like they aren't sure what I'm taking about but several people that have driven my car have noticed it. It's only notible at very low speeds like 2mph. Has anyone else noticed this?
For reference I have a p85


Alysahley, check out my thread here. I had a similar problem i think? Noted the times it happened and got a DU replacement from it, unprompted. SC lead eng determined i needed a swap

Shudder/Hesitation from park to drive
 

TaoJones

Beyond Driven
Nov 10, 2014
3,064
2,857
The Americas
Drive unit replaced at 1 year and 3 weeks (36,500 miles) during an extended annual service visit.

Started whining 3 months ago (noise #14).

Was I stranded because of it? No. Did I have it checked out twice? Yes.
 

Zetopan

Member
Oct 10, 2015
100
83
Hillsboro, Oregon
Isn't it typical that a bearing will either fail relatively quickly (say within the first year of operation) or it will last a long time? With the quality/tolerances involved, if there are any tolerances that are off or contamination in the bearing, it would lead to early demise.
Your statement about contamination is correct. However, the eventual failure due to overstressing a bearing depends on the usage history. For all ball bearings the balls distort with loading; the actual distortion being a function of the bearing design. A simple first approximation would be to assume that the ball will become an oblate sphere with loading. As the ball rotates the oblate spherical shape does not rotate and as a result the ball heats up due to the continually changing forces distorting its initially spherical shape. If the temperature build up is less than the rate at which the heat increase can dissipate through the surrounding structure (the ball race) the temperature will stabilize. It the heat created cannot be dissipated fast enough the temperature continually increases and it can reach high enough values that the materials start to weaken. Since higher loading and higher RPM both contribute to the temperature rise the time integral of both of those heat sources determine the useful life of the ball bearing. Pre-stressed angular contact bearings are used in lots of machinery. If the amount of pre-stress is too high or the loading is too high or the RPM is too high, etc. the lifetime will be significantly impacted.

So what I am ultimately saying is that the ball bearing lifetime depends on your driving habits as well as the amount of preload, lubrication, any contamination, etc. Rapid acceleration and high speeds both cause higher temperatures in the bearings. If the bearing design is marginal these effects will significantly impact the bearing lifetime.
 

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