Had a quick hard stop earlier today, nothing too crazy, just someone not knowing where they were going. When I let off the brake I noticed I wasn’t rolling at all. Gave it some light throttle and it freerevved a little bit, then slammed itself back into first.

Im curious if this is a safety feature where drive is disengaged to allow for a quicker stop. I know the car automatically downshifts at higher speeds to allow for engine braking, but I wasn’t aware of something I’m experiencing. Has happened a couple times before, exact same scenario. Outside temp isn’t a factor, as it’s happened once in summer and once or twice on winter.

had the tranny drained and filled about a year ago, never had any issues. Wouldn’t consider this an issue just yet, until I’m proven wrong.

TIA!

 

I am not aware of any "safety" protocol to where a automatic transmission would shift itself to N (neutral) during a panic stop then "pop" itself back into gear. Also, the FSM does not make any reference to such feature.

Such a feature would be pointless in a auto trans as there is only a fluid connection between the engine and trans (as opposed to a mechanical connection on manual gearboxes). Even if the axles/driveshaft locked up during hard braking the engine is still free to spin independently. However, in this day and age of what I call "Nanny Technology" it would not surprise me. Perhaps others may know more....

Sounds to me that the trans might have been in a higher gear when you tried to move again and it took a moment for the trans to fully shift down to 1st. I think it is just the sluggish nature of the 7AT... Having the 5AT- and having been in a few severe panic stops (damn tourists)- I haven't experienced any of the symptoms you mentioned.

If your car drives fine, shifts fine, and has no other symptoms, enjoy your car.

 

Yeah I didn’t think so either. I’m going to see if I can get a video of it because the trans is definitely not engaged when I lift my foot from the brake, and is super not engaged when I give it a bit of throttle. The lurch is pretty noticeable and it also makes a funky clunking noise. (Sounds like rear end noise but hard to pinpoint)

 

With symptoms like you're describing, I wouldn't be surprised if you had some broken parts in that transmission. See if you can get the car scanned with a proper scanner that can pull transmission codes and see if you're throwing any. An auto that's popping out of gear though usually is a tell-tale sign of a trans that's going to need a rebuild.

 

https://imgur.com/a/Li98iuR

Its not an amazing video and it’s hard to tell, but at the moment I say it’s popped out, the revs bounce slightly from ~650 to ~800. My car usually does that rev when I put it in park or neutral. It didn’t make any noises but you can see with how much I moved how the lurch was. This wasn’t as severe as I’ve had it before, but it was there.

 

I don't know what to say about that issue. That behavior is definitely not normal for a auto tranny. Maybe others will have better ideas.....

 

Sounds like a torque converter issue, most likely a programming defect. You might have Infiniti hook up their Consult and check the firmware status of the TCU.

My car has the original programming and doesn't display this behavior, not even during HPDEs, but I use manual mode and paddles almost exclusively.

 

I usually drive like you, manual mode. I'm going to have to do some more testing (soon, snow came in...) with different scenarios and speeds. Just wondering how this could relate to the torque converter? It's just a fluid coupling with a lockup clutch, right? I wouldn't think I'd have no drive unless the transmission itself is coming out of gear.

I never took my car to get it reprogrammed, and I do sometimes get a flare in the 3-4 shift. From what I understand I would need an update to remedy that. Sadly I'm not able to get anything done with school and work, so I'll see what can be found out.

 

I doubt it is the torque converter. If the lockup clutch was not releasing the engine would likely stall out when the wheels lock up (during ABS modulation).

 

I'm not claiming lock-up as the culprit, I'm suggesting the torque convertor is stalling at a much higher rpm than normal. 7AT torque convertors have been known to fail though that's uncommon.

 

I just did a stall speed test. Pushed all too the floor, got the front brakes to chirp lol. Stalled at 2100rpm, not a hair over. May have wussed out on the throttle as I was facing my best friends house... I did a quick google search and didn’t come up with an answer as to what the spec is for this car. It feels solid.

something to point out is sometimes I get a VERY loud mechanical click when I brakestand it. It’s one single noise, and I swear it sounds like it’s coming from the ABS pump. I can’t be certain tho, as I don’t do many of these. Save my drivetrain...

 

The ECU supposedly can detect when throttle and brakes are applied at the same time and will take measures to avoid damage. Maybe that's what you're hearing.

 

Interesting. I didn’t hear it last night, but I didn’t launch after the test. I recall when I first bought the car sitting revs in neutral would make the noise as well. Not to stray from the topic at hand but maybe it’s related? Something within the trans that I just don’t know about? Could possibly do a trans fluid change in the driveway and drop the pan, see what I’m looking at inside. But that’s a summer job...

 

https://imgur.com/a/BHO58jV

Another test, this time in manual mode. I stayed steady for a little bit longer. I wish I had a better way to depict the trans letting go, but watch the revs. You’ll notice once I come to a stop the revs do the same jump from ~650 to ~800, but this time went to 900. Because I didn’t apply throttle you can see the revs get dragged back down as it goes back into gear. I’m really confused at this point. Still need to get a stretch where I can do this at higher speeds.

 

I have had this issue a few times, and I had it today also. When I brake the car seems like it gets out of gear and when you press the gas it takes a bit and then throws you backwards. My theory is that, since our transmission isn't the quickest, that when we slam the brake quickly the car throws it self into neutral because it is not able to downshift that quickly, and then takes a bit to know which gear to go into which causes the jerking when you apply the gas.