My front and back wheels seem to be out of "sync" sometimes [2020 MX].

[RNHurt]

I'm not sure if this is a problem with MX cars or just AWD Tesla's in general, but my back wheels seem to be out of sync with the front wheels. It's super hard to explain, but during low speed maneuvers (stop signs, parking, stop and go traffic, backing out of the driveway, etc.) the back wheels seem to "settle" when stopping. Some times the effect is so strong that I think that another car might have lightly touched my rear bumper. If fact, one time my wife (who generally doesn't know anything about cars) noticed it and said something like "did we just get hit?"

Again, I'm not sure I'm explaining this correctly. It's not a problem all the time and I can't seem to make it happen on command. I would like to make a service appointment to have it looked at but I don't have a good story to tell about it yet. So, I'm asking here if anyone else has noticed a problem with the front and rear wheels seeming to fight a a bit while stopping. If so, that will let me know that I'm not crazy and I might be able to get Tesla to correct the problem.

A bit of background. I'm a car guy. My dad was a mechanic and I've assembled multiple cars almost from scratch. I drove an A4 Quattro for 20 years so I'm familiar with AWD systems. My previous car was a AWS MY and it didn't have this "problem" at all. This is my first MX (2020) so maybe it's just a thing with the MX models.

 

[mxnym]

I've never experienced what you're describing in my 2017 X. Motors might be different in a 2020, but if they are, I'd expect them to be like the Y motors. This doesn't sound normal at all to me, but I also don't know how you'd ever get the service center to replicate it. Your best bet might be if they could see something in the logs from a timestamp when it occurred, and I have no clue if that is actually a possibility for this particular scenario.

 

[RNHurt]

@mxnym thanks for the validation. That's a good suggestion about the logs, though. I wonder if it would show up in Service Mode? You can drive (slowly) in Service Mode, correct? Maybe I could try to recreate it and see if anything shows up.

I've added it to an open support ticket in the past but they couldn't replicate it so there was no action; I don't really blame them. It's similar to my drivers side window not closing properly sometimes or the fact that my rear trunk doesn't want to close when it's really hot. The difference is that I could capture those things on video and have some "proof" of the problem. It's hard to capture a "butt feeling" on video.

 

[LoudMusic]

On the Model Y I'm pretty sure it operates as rear wheel only at low speeds, but am not a reliable source on that. I have experienced the car being jittery at very low speed. Maybe having trouble determining if it should engage Hold or Regen or just coast.

You might want to try setting the Stopping Mode to the different options and see if the performance is different. Creep, Hold, and Roll should each be very different. You could even do that under different profiles to switch between them quickly.

 

[EbS-P]

When you say stopping are you using the. Break pads or just regen? Has the alignment been checked recently?

Axles, suspension and subframe all in good shape? break caliper bolts tight?

What confuses me is this happens both while turning and senile going straight.

Makes me think it’s in the back. Stock tire sizes? All matching? All worn about the same?

 

[ngng]

Have you drained/refilled and inspected the rear gearbox yet?

 

[EbS-P]

Have you drained/refilled and inspected the rear gearbox yet?

What is the service interval for the gear boxes?

 

[RNHurt]

When you say stopping are you using the. Break pads or just regen? Has the alignment been checked recently?

Axles, suspension and subframe all in good shape? break caliper bolts tight?

What confuses me is this happens both while turning and senile going straight.

Makes me think it’s in the back. Stock tire sizes? All matching? All worn about the same?

I have the car set to HOLD so it's using (mostly) regen. The alignment has not been checked but all the tires look good and are worn the same. Everything about the car is stock (tire size, etc.)

I did change HOLD mode to ROLL mode for a bit to see what happened, and the "problem" seemed to go away. My guess is that there is some slop somewhere and when the regen kicks in the slop gets absorbed. It may be within spec so I'm not super worried about it, but I just wanted to know if anyone else here had the same issue or noticed something similar in their car.

Let's just say that I did want to get Tesla to look at it (before my warranty is expired!), how would you word the service request?

 

[silentsnow31802]

Do you use the 1 pedal driving feature? Sometimes on my S there is a second between the car stopping and the hold coming on and the car will jerk a little. Will almost feel like someone very lightly bumped me. I assume this is what you are feeling. Does not happen all the time.

 

[RNHurt]

Do you use the 1 pedal driving feature? Sometimes on my S there is a second between the car stopping and the hold coming on and the car will jerk a little. Will almost feel like someone very lightly bumped me. I assume this is what you are feeling. Does not happen all the time.

Yes, I use 1 pedal driving (HOLD) almost exclusively. And yes, your description sounds like what I'm experiencing. Mine doesn't happen all the time either but it does happen frequently. Maybe I'm just being too sensitive.

 

[EbS-P]

Does hold mode use parking break on new models like it does on my 2016?

 

[DCGOO]

Does hold mode use parking break on new models like it does on my 2016?

You are referring to Hill Hold, which requires you to step on the brake to invoke it. That feature is different from the drive mode Hold, which is integrated as part of the One Pedal Driving feature on newer cars. It goes into Hold automatically, without ever touching the brake.

 

[RNHurt]

** UPDATE **

I had some work done on my passenger side window yesterday (just needed to be re-calibrated) and asked the Tesla service guy about this problem. He said that it is a known issue with legacy MX with Raven (permanent magnet) front motors. Tesla is updating the acceleration power curves and changing the way the motors cooperate at slow speeds. They are also updating the braking profiles at slow speed, which can cause this type of behavior.

While I'm not happy that the problem is happening at all, at least it doesn't seem to be anything specific to my MX. That's quite a relief! Plus I found out that I have a Raven motor in the front. I'm not sure what that means but it sounds special.

 

[snorp]

I had same thing happen on my 2020 MX. I was able to reproduce at slow speeds by accelerating hard from a stop up to about 10mph and then letting off the pedal until I came to a stop. Did this 5 times in a row and the banging from the rear end become severe.

After much arguing at the service center with multiple people, they finally replaced the rear drive unit under warranty and the problem is 95% gone.

They wouldn’t tell me what was wrong with the original drive unit and the paperwork didn’t offer an explanation.

 

[Smh2210]

I have the car set to HOLD so it's using (mostly) regen. The alignment has not been checked but all the tires look good and are worn the same. Everything about the car is stock (tire size, etc.)

I did change HOLD mode to ROLL mode for a bit to see what happened, and the "problem" seemed to go away. My guess is that there is some slop somewhere and when the regen kicks in the slop gets absorbed. It may be within spec so I'm not super worried about it, but I just wanted to know if anyone else here had the same issue or noticed something similar in their car.

Let's just say that I did want to get Tesla to look at it (before my warranty is expired!), how would you word the service request?

My 2020X had that sort of event you described and I figured it to be the 'hold' as well. I also noticed that accelerating out of 'Hold' I could feel the slop you mention in the rear. I just traded for a 2023 X and will see if it does this too. My 2020 X had about 50,000 miles.

 

[RNHurt]

I had same thing happen on my 2020 MX. I was able to reproduce at slow speeds by accelerating hard from a stop up to about 10mph and then letting off the pedal until I came to a stop. Did this 5 times in a row and the banging from the rear end become severe.

After much arguing at the service center with multiple people, they finally replaced the rear drive unit under warranty and the problem is 95% gone.

They wouldn’t tell me what was wrong with the original drive unit and the paperwork didn’t offer an explanation.

Interesting! I'll have to try reproducing the problem in my MX to see if it's the same thing or not.

 

[Smh2210]

Interesting! I'll have to try reproducing the problem in my MX to see if it's the same thing or not.

I do not feel the same 'slack' in my 2023 X, as I did in my 2020 X.

 

[RNHurt]

I do not feel the same 'slack' in my 2023 X, as I did in my 2020 X.

Yes, "slack" is a good way to describe the issue! I'm glad that your new MX doesn't have the problem.

Yesterday I tried reproducing the problem using the method that @snorp outlined, but it didn't work. The only thing that happened is that I got a bit queasy from all the stopping and starting.