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Nasty noise on hard acceleration

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O

Obsession

Member
May 2, 2015
13
0
Lake Mills Wisconsin
#1
I bought at a new P85D on June 25, 2015. I absolutely love this car. The car has been perfect accept for a very nasty noise on acceleration. The noise is intermittent but getting worse. It is definitely getting much louder. It sounds mechanical and coming from the front of the car. It is most noticeable after parking the car for a few minutes or more. The noise is present only under hard acceleration. After a few events the noise diminishes and nearly goes away. It is apparent at all acceleration speeds but more noticeable from low speed under hard acceleration. And more noticeable under load especially going up a hill. Tesla replaced both front axles twice but the noise is always the same. The work had no impact on the noise at all.

No noise at steady speeds. No noise under deceleration/regen. Noise seems to be coming from the front of the car. The noise is independent of outside air temperature. It's bad in summer or winter. The noise is not affected by the level of battery charge. The frequency of the sound is some what related to the acceleration. In other words it groans faster with the increasing speed. I uploaded the noise from my phone recording at:

http://www.obsessiontelescopes.com/tesla/video-1.mov

If anyone knows what is causing this noise, myself and the Tesla mechanics at the Highland Park Chicago store would love to know!
 
#7
My 85D has that noise on hard acceleration sometimes. It's not quite as prominent as yours, but it's the exact same sound -- a distinct repetitive knocking from the front drive system. Mine's done that since day 1.

It seems to me that the amplitude of the noise (i.e. the audible volume) is proportional to the torque being produced. The knocks get louder at first (about 0-30 MPH), then get quieter and disappear (30-60 MPH). My (completely speculative) theory is that the noise is coming from the planetary and driven bevel gears in the differential as the torque oscillates between the left and right front wheels. The imbalance is set up by having the steering slightly off straight ahead during the acceleration run, which causes uneven counter-torque from the tires.

The Tesla differentials are the standard open differential type, which due to their design almost always distributes even torque to both sides. The heavier counter-torque from the tire on one side causes slack to be taken up by the bevel gears, and the opposite side wheel to spin slightly more, pulling that wheel and the associated suspension components a smidgen further forward. This changes the steering angle, reverses the counter-torque from the tires, and thus immediately reverses the forces on the bevel gears, taking up the slack in the other direction. This process oscillates as long as the torque is high enough to affect the steering geometry.

The rear drive system doesn't make this noise because the wheels don't steer and are always pointed the same direction, so there is no unbalanced counter-torque. Thus the oscillation never starts.

Again, all of this is my wild ass guess, could have something to it, or could be completely out of left field, I have no idea. :)

I'll try to record mine and post it here for comparison.
 
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#8
Then why does the noise diminish significantly after a few miles? If I park the car for a few minutes then do hard acceleration the noise is back. First hard acceleration is the loudest like in my video. Second time much less. Third time nearly absent. Park for ten minutes and repeat.
 
#9
Obsession said:
Then why does the noise diminish significantly after a few miles? If I park the car for a few minutes then do hard acceleration the noise is back. First hard acceleration is the loudest like in my video. Second time much less. Third time nearly absent. Park for ten minutes and repeat.
Click to expand...

Possibly temperature dependence? As components heat up the tolerances get closer and there's less things to knock together?

Cool them off and they knock again.
 
#10
Drive shafts. Had the EXACT same issue with my 2015 85D only 3-4 months after delivery. Same scenario, only happened after the car had sat for a while and couldn't be repeated on demand unless it was off for several hours. Not cold as in temperature outside but the car not running for several hours. I took several videos with my phone and emailed them to my SA and both drive shafts were replaced 3 days later.
 
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#11
boonedocks said:
Drive shafts. Had the EXACT same issue with my 2015 85D only 3-4 months after delivery. Same scenario, only happened after the car had sat for a while and couldn't be repeated on demand unless it was off for several hours. Not cold as in temperature outside but the car not running for several hours. I took several videos with my phone and emailed them to my SA and both drive shafts were replaced 3 days later.
Click to expand...

You mean axle shafts...

Some people have indicated that the newest replacement shafts are quite a bit beefier than the original. It could be that the CV joints aren't holding up over time.
 
#12
I have a P85D produced early 2015 and I got the exact same noise though not that load. It only happens when the car has not been driven for a while but is not always possible to reproduce when the temperature is above ~10 °C. The service center was not able to reproduce the noise but I hear it almost every time on hard acceleration.
 
#19
Some people say the driveshafts get permanently damaged if you accellerate hard with suspension in high/very high, thus resulting in the noise.

This could explain it and why some people have had issues returning after replacing driveshafts.

I cannot understand why Tesla doesn't limit the power when suspension is high/very high..
 
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