Trans oil +/- fuel milage

[thesoundofspeed]

Hi guy's, just wondering if theres anyone out there who's used alternate types of Tranny oil in these cars?
I understand the manuel says 70-80/90w gear oil for the 5 spd, but has anyone run thinner to help up fuel milage???
I had a '65 Mustang, my dad and I dropped in an '84 HO 5.0L with a late model 5 spd. Not being familliar with those 5 spd's at that time, we put in regular gear oil. The tranny made noise like you would'nt believe. Then we found out that it required ATF!!! After changing it, all was well. Would I be up poo-creek trying ATF? My '85 Sprint wants to pull forward when I let out the clutch in neutral! I think it's more than an oil issue, btw, it has 489,300km's/305,812miles. but....I'm open to your input, Thanks.

[daver51]

I had a similar problem with my 93' when first purchased. It had 80-90 WT gear oil. My synchros weren't doing so well though, as Geo's require GM's Syncro-mesh oil, and is very expensive when you can find it at a dealer. Just look for Pennzoil Synchromesh, 100% GM compatible gear lube. Yes it is red, but I can not say it's an ATF product. AutoZone sells it and once I put it in, the synchros are now working per the book specs. Downshift to first gear at 25MPH or slower, where it wasn't working until 10MPH or less with the 80-90WT stuff. Hope this helps…

[thesoundofspeed]

Sweet, thanks! I'll give it a try.