Ok so for a while now I've been experiencing a weird thumping sound on acceleration when the car is cold..but recently I've noticed what feels like a transmission slip from 3rd to 4th under medium acceleration. The strange is that it only does it every once in a while and only it in auto but never when shifted manually.​ ​​​The car is currently at 110k and ATF was changed 2x at 75k and 1x at 90k. Any ideas or suggestions?

 

Rule number one: Don't change out the transmission fluids when you don't need it. It does more harm than good, especially if the gears and parts are worn out. I don't see why it had to be changed at 90k when it's a sealed automatic. How long have you been feeling this?

 

I don't buy into the sealed transmission stuff. I lookedi backaback and actually it was 75k 2x drain and fill and then did a 1x drain and fill at 90k and no issues at all..It has 110k on it now and just started the issues I listed...granted it's only "slipped" like 4 or 5 times total but I'm not sure what it is since I cannot get it to do it no matter how hard I drive it once it's warmed up or while shifting manual.

 

Have you refreshed the transfer case fluid? After that, check the motor, transmission and all the driveline bushings. Thumping is usually an indication of driveline lash. Usually diff, trans or motor mounts going bad, and diff bushing are known to go at 70k-ish.

Would like to hear your thoughts and reasoning on this, and when you "need it"
Lot's of talk about 3x d&f at 60-70k as PM. Definitely at 100k, since thats what mfg. calls "Lifetime". But from your logic, a fluid swap when you "need it" would more often than not be on a higher mileage/worn out trans, which is more harmful? Paradoxical

 

I did a rear diff swap at 70k and swapped the rear diff bushings with whiteline. I haven't checked the transmission mount mainly because it only does the "thumping" when it's cold and goes away once it's driven for a few miles.

 

You’re not acquanted with the mechanics of an automobile are you? These newer cars are engineered in a way that you shouldn’t even change out the transmission fluids. The only people that change it are only looking for trouble and end up having slipping transmissions. Fluids have all the necessary material in them for all the parts to stick and work that last for a long time. If you drain, you’re losing all that material and the adherence since you’re putting in new fluids that are “clean.” It’s not an old school manual and it makes me cringe seeing folks changing out the automatic transmission fluids in these cars because it’s “maintenance” or because the dealer told them. And for some reason it is always the American market too that falls for it. Had other automatic cars that I never changed the automatic fluids in them and hit high mileage and never had a problem. For some reason the ones that always experience slip are almost always the same ones who messed with the automatic’s fluid.

Op: It sounds like something internally. If you’re slipping gears and no hear a thumping noise, I can only pray that you don’t end up stranded. Sounds like you either have low fluid levels, bad fluid (which I mentioned up above), or air in bubbles in the lines. The symptoms you mentioned are all signs of a failing transmission unless the mounts have gone out. If that is the case, I would still not cheap out and go ahead and repair the transmission.

 

The fluid is new and the level is correct it's been checked by me and by the shop...as far as the lifetime fluid goes according to infiniti lifetime is until the transmission fails which could be 60k or 200k. There are tons of folks with the 7at that change the fluid at 60-70k with no issue and if I remember correctly that was the recommendation for the 7at g37 a few years back. The "slipping" if that's what it appears
​​​​​to be very sporadic has happened maybe 4-5 times the last 3k miles..it absolutely could be the transmission failing but seems like it may be something else since it has never done it when manually shifted no matter how hard I drive it..I guess I'm trying to figure out why that's happening and what else it could be.

 

Did you change the transmission filter if you changed out the fluids?

 

No but I did drop the pan and clean it really well.

 

Ok so I drove around 300 miles the last couple of days in D, DS Auto and manual. I was only able to get it to "slip" or more like a ​​​​​​flare ​​​​​when up shifting from 4th to 5th. It always happens while driving in auto D or DS but never not even once when I shift manually no matter how easy or hard I accelerate..Any ideas what this could be?