ATF in a 203/205

[grendel]

Ok, so I used to run 90/150 weight synthetic in my doubler cases behind my SM465.

Now running a TH475. The cases are sealed off from each other, to the best of my ability, but I have to believe that some will pass through.

Can I run a decent synth ATF in all three?

 

[Stephen]

You can but I don't recommend it, ATF has been spec'd from the factory for the 205 and the 203 uses similar bearings and construction but ATF is not as good a lube for bearings and gears as 80-90. You will see reduced life if you run ATF. If you do spring a leak, it's not the end of the world, but you should start with gear oil in the gear drive cases.
The seal at the front of the NP203 is pretty effective, as long as it's in decent condition. It's also a very common part that you can find at a parts store if you need to replace it.

 

[ramjet gmc]

sorry doing some grave digging looking for a ?????

my setup is a 700r4 203 ORD 205
from the 700r4 to the 203 looks like it will just pour atf in to the 203 threw the bearing is this the case ?? could i be missing a seal ??

 

[sled_dog]

I have the same question but mines an SM465 to NP241, its just vice versa. I think the input on the 241 is pretty well sealed but I know the 465 dumps gear oil back into the adaptor on grades(it did when I pulled the sucker out).

 

[Seventy4Blazer]

the 465 is not sealed on the output end at all. the 241 is sealed very well.

the 203 for any version i have seen is sealed well on the input side. on the output side however (once the 203 back half is removed) it is not sealed at all with the exception of the double adaptor and gasket, BUT it will leak fluid into the 205. the 205 IIRC is nto sealed in the large short 31 and 32 spline input bearing design.
i BELIVE this is why some later 205's were speced with ATF vice 80/90 weight. i could be wrong, and if i am chime in and correct me please.

sitting here thinking about it now, i BELIVE(without looking at it) that my 205 is sealed up front. i ahve a long input 32 spline version. BUT i cant go look at it for the next 10 months or so.
once again, please correct me if i am wrong, as this is all from memory ov about 8 months ago.

PS, those of you who dont know me, i have a memory of a 2 year old on caffieen fiending for crack.
Grant

 

[Stephen]

Run gear oil in the 203 and 205, ATF in trans.
the 203 should have a good input seal in the front
The Doubler adapter has the seal in it to keep the 203 and 205 oil separate.
The factory probably spec'd ATF in the later years to make CAFE fuel economy standards.
Most adapters in the GM's run wet, in fact, I think they all do.

 

[bigredk5blazer]

What about the 208? I'm still running a stock T-case for now, and was suprised to find ATF in it when I drained it.

FYI, a lot of stuff that used to run gear oil is going to ATF. Most manual car transmissions since the late 80s have switched, especially the high performancer stuff (TKO, T56, ect.). It has to do with the new synchro designs they use, as well as the tighter tolerances (typically only a few thousandths for endplay). The bearings do seem to take a bit of a beating though. You don't want to run gear oil in one of these transmissions though, as it will kill the bearings and fry the synchros. The bearings are set up with feed orifaces that are so tiny the gear oil can't effectiveyl move through them to lube the bearings fast enough, and they burn up. Many a T5 has tied a horrible death from just such a swap.

 

[Stephen]

The 208 is ATF only. About the only thing you can do is go with a synthetic oil or a specialty oil that would be better for the bearings but you're right, a lot of gearboxes are designed for free flowing oil and 80-90 isn't like that till it gets pretty hot. On a cold day, 80-90 barely moves around at all much less than pumping through small holes.