Sorry this is 100% complete BS, that's not how transmissions work. The reason for changing the fluid is you ALREADY have particles (clutch friction plate material) being washed through your transmission (Jatco only uses a large particulate screen not even a real filter), you drain and fill the fluid to remove particulates.

There's a lot of old wives tales surrounding auto tranny's, this is one of them. Let me dig up an old post I wrote about this exact subject, it does a pretty good job of explaining why people think this.

 

Have you changed atf on high mileage? Im about to do mine again at 172k and im worried about leaking seals. Worse case scenario is transmission rebuild.

 

Here's a link to that post, scroll down to post 10

​https://g35driver.com/forums/g35-sedan-v35-2003-06/461849-mechanic-used-off-brand-transmission-fluid-do-i-need-concerned.html

Also, changing your fluid is not going to make you input or output shaft seal start leaking.

 

 

Like cleric stated it's an old wives tale. A lot of people have a herd mentality and follow blindly what the crowd does and says because it's easier to do that than think on your own. Plus it gives them an excuse to not do something the way it should be done.

 

fantastic read. My issue now is, I bought this car used In 2016 and it's been my daily driver ever since and I was one of those in the herd who followed the ' DO NOT FLUSH' mindset. Given my current situation with my 2003 5AT (slipping and staying in one gear after a few mins, not reversing when the vehicle is cold, and jerking through gear changes after gear 2) should I still flush it or do the rebuild?

 

Certainly won't hurt. Post up your results!

 

I was speaking with a mechanic about a potential used tranny I was interested in purchasing (a 2003 tranny with 60k miles) for $700, and he said even if I replace my bad tranny with the good used one, it may potentially have problems early on, possibly within the first month of replacing it. He was recommending just rebuilding it and he would charge me $1600, as opposed to this other transmission place that was charging me $4k....Note that I have only been communicating with this mechanic via online through his company's website, so he has not seen the car to inspect it as yet, just going off my description of the problems (ie slipping, not going in reverse etc). What do you guys recommend, just go with the rebuild or still switch it out?

 

He's right, but he's also trying to scare you giving him your business. You never really know 100% with used parts, and if the used trans you put in turns out to have a problem it will likely "manifest itself early on, possibly within the first month of replacing it".

If you want to pay more for the rebuilt transmission with the guarantee it won't break, that's your call and a completely valid path forward IMO.

Personally I'd swap it myself and justify installing a transgo kit with the savings.

 

I have a 2003 infiniti g35 coupe transmission not knowing that my car is a 3plug transmission i bought a 2004 transmission and it said online n warehouse transmission it will fit my 2003 infiniti so i purchase the 2004 transmission only problem was that the 2004 is a single plug' i had to install it i swich my original 3plug to a single plug ' now doing this my car is not finish it drives but its not shifitng properly i called infiniti dealership n they told me since i install a 2004 transmission is more newer id have to get it reporgam they charge $180 since i switch to a single plug and that will fix the shifting probelm its a 50 percent shot.It be best to look for a 3plug so you dont have any issues like me hope this helps any infiniti g35 coupe with a transmission swamp.

 

Just take the valve body and harness from your 2003 transmission and put it in the 2004 transmission. Your 2003 TCM is located in the cabin next to the ECM, that other harness with the single plug has the TCM inside the transmission behind the valve body. Then you keep your existing TCM which was a known working item.

You can't just take the internal TCM transmission and make it work with the old style ECM which uses the external TCM.

The transmission housing is exactly the same, where the wires go through the tranny housing is just a grommet, pop it out from the inside, you'll see the retainer.