Jump/Kick forward after cold start [2021]

[deepimpact]

Hi,

I'm an owner of a 2021 Mustang GT (automatic) and for some days I experienced following behavior, and can't reall tell what the reason could be.

Sometimes when the engine is cold (standing over night) and I am starting the car, driving some meters and break, (after some seconds, still breaking) I studdently feel a big punch, which moves me forward (or at least trying to). It feels like the car is jumping forward. I don't think it's shifting down because, when I'm driving some meters, it should be still in 1th gear. I could only experience it when the engine is cold. I'm pretty sure its not about engine. it feels like transmission/shaft, which creates an impulse somehow.

Did someone experienced a similar issue? After this happens, there no other anomaly while driving. Or restarting the car when motor is hot, or just staying for some hours.

I am going to try to reproduce it, if possible and report.

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[Cobra Jet]

Sounds like low fluid or possibly valve body issue.

This thread has all the 10R80 facts, quirks and knowledge anyone could need. It's a very large thread but you'll find other M6G members have run through similar issues.

https://www.mustang6g.com/forums/th...tions-to-harsh-or-no-shift-conditions.135463/

Make an appointment and when you get there try to demo the issue with a test drive with the Shop Tech or Shop Foreman.

 

[NoVaGT]

Hi,

I'm an owner of a 2021 Mustang GT (automatic) and for some days I experienced following behavior, and can't reall tell what the reason could be.

Sometimes when the engine is cold (standing over night) and I am starting the car, driving some meters and break, (after some seconds, still breaking) I studdently feel a big punch, which moves me forward (or at least trying to). It feels like the car is jumping forward. I don't think it's shifting down because, when I'm driving some meters, it should be still in 1th gear. I could only experience it when the engine is cold. I'm pretty sure its not about engine. it feels like transmission/shaft, which creates an impulse somehow.

Did someone experienced a similar issue? After this happens, there no other anomaly while driving. Or restarting the car when motor is hot, or just staying for some hours.

I am going to try to reproduce it, if possible and report.

It's a 10SPD transmission. You're feeling a down-shift from 2nd to 1st with the car idling high.

Relax and stop obsessing. Just drive the car and let it learn.

 

[Torched10]

Bring it to dealer

 

[deepimpact]

It's me again. They had did a software update on the transmission, and the issue seemd to went away, but maybe it was just a placebo effect... because for weeks I can reproduce it again.


Mostly when engine is cold, and mostly the first meters with the car:

I could record it:

I accelerate (shifts to 2).
And suddently brake (shifts to 1, but with a loud CLUNK and powerful kick forwards).

 

[Vlad Soare]

See post #2 again:

Sounds like low fluid or possibly valve body issue.

All I can tell you is that:
1. It is not normal.
2. It is a mechanical issue. No software update will fix it.

Go back to the dealership and have them fix it properly. The car should still be under warranty. And tell them that if they dare suggest a software update again, you'll burn the place down.
Seriously, the software has nothing to do with it. Suggesting a software update means either that they are clueless, or that they just want to get rid of you as quickly as possible, or both.

 

[deepimpact]

See post #2 again: All I can tell you is that: 1. It is not normal. 2. It is a mechanical issue. No software update will fix it. Go back to the dealership and have them fix it properly. The car should still be under warranty. And tell them that if they dare suggest a software update again, you'll burn the place down. Seriously, the software has nothing to do with it. Suggesting a software update means either that they are clueless, or that they just want to get rid of you as quickly as possible, or both. I'm a software developer too (i think just like you :-)) and I think it could be the software, because the problem is not permanent. It does not always happen. But 70% when cold, and when breaking immediately from 3/2 to 1 gear, like if light turns red, stop sight,... it clunks and kicks me forward. It seems the the software cant cope with a certsin situation i could not define yet. Maybe transmission is too cold? The oil inside to cold? It cant handle immediate speed change and clunks in the next low gear... But yeah next week i have an appointment... Just trying to collect some infos i can give to the dealer...

 

[Vlad Soare]

If there was something wrong with the software, then all automatic Mustangs would have to exhibit the same behaviour. Because it's the same software in all of them. But they don't.
First, I would ask them to check the oil level. A10s coming from the factory with too little oil aren't unheard of. Quite the contrary, it seems to be a frequent occurence.
If the oil is fine, then my money is on the valve body. Many A10s seem to have come from the factory with a defective valve body. Moreover, some people had to replace the valve body twice, because the first replacement was defective as well. The good news is, once you get a good one it won't fail again.

I used to be a software developer, but now I'm more into consultancy and the implementation of business-oriented applications. I still write some code from time to time, though not as much as I used to.

 

[njweatherman]

It's me again. They had did a software update on the transmission, and the issue seemd to went away, but maybe it was just a placebo effect... because for weeks I can reproduce it again.


Mostly when engine is cold, and mostly the first meters with the car:

I could record it:

I accelerate (shifts to 2).
And suddently brake (shifts to 1, but with a loud CLUNK and powerful kick forwards).

Steve,

When the engine is cold and this happens, what drive mode are you in (Normal, Sport+)? On my 2020 with the old trans software and even the new (TSB 21-2357), my transmission when in Sport+ is jumpy and jerky until the car is warmed up. Once the car is warmed up, it works well. To get around this, I take off in Normal mode. Once the car is warmed up, I switch back to Sport+. Try it and see if you notice a difference.

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