Hello All.

My car is a 2012 G37xS coupe with 7sp-automatic transmission.

So today I got this very distinct thump as I was slowing down (going from 20mph to about 10 mph) in order to make a left turn into a parking lot from the main road. The thump felt like a really rough gear downshift either from 3rd to 2nd gear or from 2nd to 1st gear. The thump happened while the car was still rolling in motion and I did not hear any grinding noise when it happened. The thump that vibrated through the entire car felt like the gear went in really roughly, but managed to get into gear successfully. This was the first time it happened and it only happened once. What could have happened or been wrong that caused the thump? Is this something to be concerned about?

The dealer recently did a transmission flush using Nissan Matic-S transmission fluid on May 17, 2017 (first time at 72,036 miles). The flush used 14qts of Matic-S. Could this have caused an issue? Should I demand the dealer re-do the transmission flush again?

Also, can a faulty crankshaft sensor cause what I described above? If yes, how do I figure out if it is?

 

Have you had all the TSB updates applied?

I get this occasionally but I brake as if I'm driving a manual and keep my right foot next to the acc pedal (heel-and-toe, you know) and sometimes bump it which causes a jarring downshift.

 

When you say you get it occasionally, does it happen when you step on the accelerator or does it happen as it shifts downward? I experienced this without hitting the accelerator at all and had my foot on the brake pedal as I come to a slower speed and then stopping.

I am not sure if all the TSB updates were applied. Is asking the dealer the only way to find out?

Is this a normal thing with the G's 7AT?

 

If it was very hard braking it could have done the braking downshift, this will be a sudden hard downshift that can be alarming the first time you experience it. But a regular speed slow down from 20 to 10 shouldn't be abrupt like you describe.

 

Yeah, it was definitely not hard braking. I was going maybe 40mph and was slowing down to make a left turn when it happened at around 20mph to 10 mph. Any ideas on what could have caused it?

 

Did the dealer perform a pressure flush or the only procedure listed in the FSM, which is the 3x drain & fill? If it was pressure flushed that could cause buildup to be dislodged and possibly cause issues. If this only happened once and hasn't reoccurred it could just be the hesitant nature of this transmission, it does tend to be a bit indecisive at times.
If you aren't sure what exact AT service was performed, I'd contact the dealer for clarity on that.

 

Yes, it was one of those full on flushes. I had asked for the 3x drain and fill as you have suggested in another post and pointed out what was said on the FSM to the dealer, but the dealership went ahead and completed a full-on transmission flush by hooking up my G37xS to a machine. Yeah, I was pissed when I found out they did that despite my specific request not to.

In terms of how many times the issue has happened, it has only been once and that was the first time in the last 5 years. In my attempts to get the hard downshift to happen again, I took my G out earlier today and drove a good 80 miles and so far, it has not occurred at all. I am crossing my fingers hoping that this was just a really hard downshift due to the 7-AT being indecisive.

 

Have the dealer check to be sure the TSBs have been applied. 2012 probably won't have any but ask anyway.

 

I was planning on having mine flushed by the dealer. That is what they do. I just hope it doesn't cause any problems.

 

I'd ask the dealer if the service they provide is detailed in the factory service manual, and if not, ask if they can do the service that is listed in the FSM.

It is possible that they have added a flush process in the FSM but AFAIK that's not the case. Might also consult a Nissan dealer and see what they do.

 

Hey Ezbme. I am planning to take my G into the dealer tomorrow and let them see what is up. If you can wait a bit, I can get back and provide an update on this as soon as I can.

I had known about power flushing causing problems through my research. Some blamed the problem from power flushing on detergents used, wrong fluid levels provided during refill, or debris dislodging and clogging the valve body. I was dead set on taking Brad's advice and specified that to the dealer that I wanted the drain and refill 3x. Unfortunately, they failed the simple task.

To my knowledge, Infiniti does not use detergents when power flushing the transmission and there is not a serviceable filter for the transmission. Maybe, this was just a random issue but I want the dealer to document my complaint just in case things go wrong.

 

Well, the dealer could not replicate the hard downshift. They are keeping the car until Thursday.

I guess this gives me a chance to put some mileage on my 2015 Q50s. At two years old and having only 6,376 miles on it, its time to take it out for a spin.

 

There is an interesting video, I can't remember which car mechanic, but he said that if you have stuff in your fluid, the flush could cause a clog. Last time my cars transmission was serviced was around 120,000, now it has 165,000. I am a bit afraid, I might just get some Nissan Matic and let my shadetree or another place do the drain and fill.

I know that others have mentioned the valvoline as a good product, I know that the Nissan Matic S is around $10 a quart, I might just go with that. I went to this one place and the guy was very professional, don't know if he is still there. He did the fluid change, it didn't change the harsh shift on my old Jag, but it was worth trying.

 

If all your gears shift nice and firm for all gears, then you should be okay. Fresh fluid will restore your line pressure within the transmission, so your downshifts will be more pronounced than when you were on your old broken down trans fluid.

If your transmission slips more between shifts than before the flush, then I would start to worry.

 

My gears are pretty firm. It can be a little rough when I come to a stop in DS and it goes from 3 to 1st. I know the car had a change around 120k, I am tempted to do a drain and fill and see what the condition of the fluid is before I do the full flush.


You can start at 5 mins or 7 mins for best info.