I dont get it.

Cheers from Copenhagen,

Christian

 

Where are you reading this? The 928 manual (all years) calls for 75w-90 gear lube.

There are manual transmission that use ATF, certain BMW's come to mind.

 

Nope, just checked the manual again. 78 manual use ATF Dexron only!!?

 

No no no, ATF is used in the power steering and in the automatics.

Manual traNS gets gear oil, LSD versions need an special oil. Best is Mobil 1 75w90 LS.

 

Pic from manual

 

That's obviously the Australian manual and has a miss print or ATF-Dextron Only means gear oil down under.

 

That's interesting.

"Dexron" has changed significantly over the years. Dexron II was the equivalent of a straight 80w gear oil back when the manual was probably printed.

If you pour in the current generation Dexron IV I can only imagine what that would do to the transmission, it's significantly thinner.

Yes I know the current bottles claim they are backwards compatible. I recently went through this with the local automatic transmission shop to change the fluid in my 2003 Denali. The specifications of that transmission is Dexron III, I was warned that putting in the thinner Dexron IV would not be good for it, especially if I do any towing.

Dexron II underwent a few changes / versions in the 70's. At some point Porsche must have realized it wasn't going to be the best fluid for their gears and changed the specifications to gear lube.

If it makes you feel any better, here is the WSM which IMO supersedes the owners manual.



-

 

^^^^ yep ^^^^


But IF you do try it, please let us all know how that works out for you

Edit: interesting find on the older Dex

 

More than a few folks have discovered that early Dex makes cold shifting easier in gearboxes that originally spec'd 80W- and 90-weight hypoid oil. But... the thinner ATF, while it makes cold shifting easier, is a longer-term death sentence for the ring-and-pinion set. It's also tough in clutch-type limited-slip units.

There are some better 75W-90 hypoid oils that work wonders in early boxes. Redline, Bel-Ray (an old race-car sponsor), and M-1 are good synthetics. Swepco is pretty good with worn early Porsche-style syncro's I read someplace.

 

Great find, Hack. Thanks to sll of you guys.

By mistake I bought Swepco 210 for my 912E. It works really well. Will get that for the 928 as well.

Cheers,

Christian

 

Be careful of Swepco. Best to stick with Porsche specs.

 

"Dexron", without a suffix (as is the OP's manual), was the original GM transmission oil which used Sperm Whale Oil, a terrific high-pressure lube but had certain environmental issues.

This was reformulated and became Dexron-II (introduced in 1972 in the US, possibly later in Europe). Not so good. Dex-III was introduced in 1993.

Search Dexron and "sperm whale oil" for more info.