Why did Mopar use the auto fluid in the GenII cars in the transmission?

[Qualitywires.com]

I had a 1994 that I switched out the trans fluid to the heavier wieght oil. So my question is, if this is a fix for the NGR noise, then why didn't they use thicker oil in the Gen II cars? The NGR noise in my 1998 can get a bit loud at times.

 

[Tom F&L GoR]

Fuel Economy. Gear oil and transmission fluid don't warm up nearly as quickly as engine oil does, it takes potentially an hour to get them to operating temperature under the conditions of the CAFE fuel economy test. The fuel economy and emissions test are only about 40 minutes and have a 10 minute off-time included.

 

[Tom and Vipers]

When you say switched out to thicker oil did you mean:

It had ATF in it and you went to SAE 90 Gear Oil?

 

[Qualitywires.com]

I used the syntorque oil...it's also mopars..oil too. It's the 75/90 wieght oild. seem to work great. haven't don it with my 1998 GTS yet. Don't use Mobil 1 heavy wieght oil in the trans!! The oil isn't compatiable with the brass syncro's. I don't know if the Viper has brass syncro's but I asked Mobil one and they said it wasn't.

 

[Tom and Vipers]

I've seen the brass synchros in the T56 and must report that they are not what you find in Muscle car transmissions...

While the overall dimension are the same, the actual friction surface is not the machined concentric knife edges normally encountered.

I did not inspect every ring so my observations technically only apply to the few rings that I did inspect.

What I did see was a conical surface with some kind of probably non-metallic lining - maybe something like you would find in a transmission clutch plate perhaps.

My immediate thought was that they had modified the rings to work with ATF.

So my question is: How does the transmission shift with 90 wt gear lube?

Also, I have seen the actual gear teeth in the T45 literally worn (eroded) away so that the tips were actually sharp!

I have never seen this in muscle car transmissions.

Of course, the teeth in the T56 are unlike any I have ever seen. First the helical angle is virtually 45 degrees and the teeth are almost half as tall and twice as many for a comparable pitch diameter in a muscle car transmission. They resemble sun gear teeth in an automatic. Again, the ATF relationship...

You might say a T56 is an Anti-Rock Crusher Muncie (M22?)