Was driving and noticed that the engine would rev up but the car would have less acceleration. Later I realized that the transmission was slipping and there was no more acceleration on the freeway (imagine a manual transmission car having its clutch completely fail). I pulled over on the shoulder and turned off the car. 10 minutes later the car can go into drive again and accelerate.

I did a transmission fluid drain (4 quarts) because the fluid looked black. I tried driving the car but now what happens is that it drives normally for 30 seconds, starts to slips then completely fails. 10 minutes later it can drive again.

The car only has 72k miles so I'm hoping the transmission hasn't already failed, but it sure feels like it has.

Does anyone know what could be the problem?

 

Was it foamy?

 

I just checked the transmission dipstick and noticed a few bubbles on it and also the fluid is overfilled somehow even though I replaced the exact same amount in.

 

I don't have any experience with AT equipped 350Zs so take this with a grain of salt...

Double check the transmission fluid level, make sure it's within factory spec on level ground. Most automatics are incredibly sensitive to fluid flushes, drain and fills, etc... especially if fluid services were skipped. I would only use OEM fluid. The mileage stated is well below average so I would hope that Trans doesn't need a rebuild. If the fluid levels all check out and you used the right stuff, then my only other "fix it yourself" thing I would recommend is a friction modifier additive like Lucas Oil. Not a huge fan of using these things, but if the transmission is truly hosed, why not give it a shot?
Good Luck!
-Icer

 

The Lucas Oil "should" help with foaming/bubbles. When you checked the fluid level, were you on level ground? Did you allow the vehicle to sit for 10-15 minutes?
-Icer

 

Something else I just thought of. When you did the drain and fill, did you also replace the fluid filter? A clogged filter can cause the very symptoms you are experiencing.
-Icer

 

Might check, IIRC the transmission cooler is inside the radiator. This developed a problem for the Nissan Frontier, typically surfacing at around 80k miles. Nissan corrected this in 2009, many owners installed an external cooler as a preventive measure.

If you find "bubbles" on the dipstick and they are antifreeze, your transmission is most probably toast.

 

I went through the gear shift and then checked the dipstick in park with the car running according to the service manual.

It looks like it was overfilled by a quart. The problem still happens after removing a quart. I think the bubbles were from being overfilled as I don't see them anymore. But I'm really confused as how the car ran fine if it was overfilled with a quart before.

I tried holding in the brake pedal while in drive and after about 5 minutes I could hear the transmission repeatedly come in and out of drive.

I don't think coolant got in there as the coolant tank has been at the same level for all the years I have owned the car.

This might be it. The reason I didn't change out the filter is because I read somewhere that its just a screen and doesn't need to be changed. Considering the old fluid was almost completely black its probably needs to be changed.

 

It is just a metal screen. Doubt that's the problem to be honest. But I don't have any real other suggestion, sounds like its overheating quickly though.

 

The car also had a whining noise (similar to when power steering has low fluid) that would get louder with more rpm. The noise would get quieter as the car was driven. Since the noise would happen when in park I'm assuming it wasn't related to the transmission but I'm not entirely sure.

 

You can blow the tranny from being overfilled, which is why I asked if it was foamy.
Doesn't sound like something that is going to be fixed with a flush

 

If the transmission already slipped badly, enough to burn the fluid, it's likely toast. No fluid changes are going to bring back clutch pack material.

 

Looks like it was the filter. It drives great now. Thanks guys.

 

Sounds like someone was slipping on that maintenance...

Glad its back to fully operational

 

Happy to hear it was a simple/cheap fix. Did you happen to take any pictures of the filter (or screen mesh)? I'm just curious since I've never bothered to look into the auto-trans on the Z.
-Icer

 

Lucky, very very lucky