Sorry, but my manual says 75w90 oil. You can play with the viscosity rating a little bit depending the application for which it is being used. Generally Auto trans fluid was used to reduce the cold hard shift problem, it offers poor friction properties and does not cushion the gear impacts adequitely. The ATF fluid has high pressure additives, but it also contain anti-foaming agents. The viscosity is really to thin to use in any real performane application.

 

Bringin it back with new info...

According to an SAE paper i checked out in my school's library, there isn't very much difference between GL-4 and GL-5, except that GL-4 has about 50% less additives to prevent wear, corrosion of yellow metals, etc. So i would think that GL-5 would be fine. I'm going to check a GM dealer this weekend to see what spec the GM synchromesh is, but seeing as the local auto-parts stores only carry GL-5... wink

*EDIT*
Here's the SAE publication i got my information from for all those anal/bored people like me who like these sort of documents.
"Fuels and Lubrications Primer for Automotive Engineers - Second Edition"
Article is "Fundamentals of Automotive Gear Lubrication", by LF Schiemann and JJ Schwind, and starts on pg. 105.

Oh yeah, DO NOT USE AUTOMATIC TRANSMISSION FLUID IN A MANUAL TRANSMISSION. ATF is not designed for the stresses, temperatures, and viscostity needs of a manual transmission. This is covered in the article posted above as well.

 

What ever they have been using ATF in manual trans since 1985 maybe sooner! Who ever wrote that article is bias on ATF! If you can use ATF in a 300HP mustang 5spd and not tear it up then they must be doing something right!!!

And it can be done because I did it!!

Use what the manufacture recomends!! If it says use ATF then use it! If it says Gear lube then use it!!
END OF STORY!!!!

 

I have been running the slick 50 gear lube in mine and it is sae 80-90w GL-5 and it has worked fine for me. Isnt the GL-5 just a classification that corresponds with the weight of the oil? If the weight of the oil is within the recommened range then it shouldnt matter if its a Gl-5 or GL-4.

 

This is the recommended oil:

Hypoid gear oil, SAE 75W/85W, API-GL4

for a 97 tib straight from the hma service

 

I am not trying to argue all I am saying is run what is recommended!!!

 

What I have heard is that if you use synthetic products, such as synthetic motor oil or synthetic gear oil, as being discussed here, you can NEVER go back to "regular" stiff. This is what I have heard. So those who are thinking of going the synthetic route, be warned.

Please correct me if I am wrong. This is what I have heard. I have been using the normal stuff ever since I started doing my own maintance. Never used synthetic products before and never will. Heck, as far as transmission fluids/oil go, I haven't changed the transmission fluid in 130,000 miles on my Jeep Cherokee. I check it routinely and the fluid is still pink as day one and shifts like silk (Well, as far as American cars go lol)