I have an 08 G35xS automatic with 119,000 miles and I’ve been having an issue with, what seems to be, a gear slipping. Basically, if you were to give the car a normal amount of throttle from a dead stop, it seems like there is a “lag period” of a couple seconds and you’ll hear the engine rev up (with with the tach still staying at around 1500) yet the car will barely move. Then after that 2-3 second “lag”, the car will suddenly just for 4000+ RPM for a brief second and then shift into second gear. When it shifts into second, if feels like the whole drivetrain “kicks” forward (pretty violently I might add) for a second. After that initial sequence, the car will shift through all the other gears just fine without any issues. It has the same “kick” after you let off the throttle and reengage a few seconds later (for example, slowing down before a turn and giving it gas after rolling through the turn). Reverse gear has similar issues, albeit with out the “kick”, it just takes a few seconds for the gear to engage once you shift into reverse.
Any suggestions on things to check, replace? I found out that one of my engine mounts was cracked and after replacing that the problem diminished slightly, but did not fix anything. I checked the transmission fluid level and it was good, however it may still be the original fluid so it’s likely overdue for replacement. The check engine light isn’t on, so at this point I have no idea what to do next. Any suggestions or tips would be appreciated. Thanks.

 

Transmission fluid is supposed to be drain/fill replaced every 30k, I'm not surprised you are experiencing a possible transmission failure since the scheduled routine maintenance has been ignored.

Same thing happens to an engine if you never change the oil.

Did you properly check the transmission fluid level? Get it up to temp, stop the vehicle, shift through EACH gear down to 1, then back up to park, make sure it shifts to EACH gear. Place the vehicle in park, and with the ENGINE RUNNING check the transmission fluid level dipstick 5-6 times, making sure to wipe fluid each time until you get a clean accurate reading.

The symptoms you are describing is simply low fluid level, it takes excessive rpm to bring line pressure up but it spikes quickly and is jarring on the drivetrain when the clutches engage.

 

Thank you for the detailed response.
Unfortunately, I have a sealed transmission, so I don’t have a dipstick to check it that way. However, I did get under the car (after I had driven it for a few minutes) and unbolted the fill plug and fluid started seeping out before I could fully remove the bolt, leading me to believe that there is plenty of fluid. However, I will go ahead and replace the fluid as it is long overdue. Is there a specific way to do it? Or do I just do it the same way you would any other automatic car? I’ve just read/heard from other people that these Infiniti transmissions are very picky when it comes to draining/refilling the ATF to the point that they’ll just flat out blow if you do it incorrectly. Something along the lines of keeping it at a specific temp during refilling. Any insight on that?

 

Ok, so wouldn't that be a G37 then or did the 2008 coupe still wear the badge G35?

Yes if you have the 7AT they are non-serviceable by the consumer, the dealership has a special pump to add fluid directly from the overflow plug (screws into place) but they are one of the newer sealed style AT's that most manufacturers have gone to, there are large magnetic pickups to catch metal floating inside the transmission but you still need to watch for leaks and have the fluid level corrected if there is a leak.

The transmission needs to be UNDER 100 degrees F, Consult III shows the current temp so it's not a problem (or you can use an infrared heat gun and just shoot the temperature of the pan), remove the overflow valve and install the pump fitting, drain pan, fill, run engine 3 minutes, turn off engine and repeat the drain process TWO more times. Total exchange is 9qt. (3qt per flush). On the final flush install a new drain plug and overflow plug . After you have exchanged 9 qt's of fluid get the transmission up to temp (GREATER than 100 degrees F) jack up the car again and remove the overflow plug and let fluid drain out from the top, this sets the proper fluid level for the transmission. When it's down to the point it's just oozing out final install of the overflow and you're done.

It's not really HARD to do but it's time consuming. I suspect manufacturers have gone to these "sealed" style transmissions because people were adding the wrong fluid, or getting it serviced at Joe's Burgers & Lube and were getting the wrong fluid and these transmissions are VERY picky about having the proper fluid in them. Make the process hard and folks will have to go back to the dealership for service.

Btw I think any gear oil pump would work if you want to do the fluid change yourself but since you're having issues with it I recommend a trip to Nissan/Infiniti so they can remove the pan and check for varnish and use Consult III to check line pressures and such.