diff/gear oil

[Boy-z]

Anyone know what oil I would use is it 80/90w or is it different the dealer could not tell me imagine. so anyone who knows I'd appreciate it.
Thanks

[FieroDough]

for the traner, either regular engine oil. 5W30 or gm syncromesh (the best stuff but a bit more expensive)

Cheers!
Eric
 

[Fieroflyer]

Depending on which standard tranny you have some used auto tranny fluid and some used 5w30 engine oil. In my 86 Isuzu I run 5w30 synthetic and have had no problems. I have heard of people using the thicker hypoid oils in the summer with no problems but I prefer the synthetics myself. Biggest problem was the thinner oils not sticking to the spyder gears and running dry at high revs, although I have never actually seen this happen in a Fiero.  

[FieroBUZZ]

I have GM syncromesh fluid in my 86 4 speed.  Nice stuff! I recommend that you use this.  Mine took 3 bottles and a tiny bit more.