My Muncie 4-speed probably has the original fluid in it and I would like to change it with the correct fluid that it would have had in the 80's...

(NOTE: Yes I have used synchromesh in the past on 2 of my Fiero's, yes I know that is what many recommend, however I also know that many Fiero owners over the last 20 years that developed leaks immediately after switching, so I'm not interested in using synchromesh or synthetic in my 36-year-old car)

Was hoping somebody knowledgeable could answer these questions...

Question #1: Was the original fluid on the assembly line equivalent to 5w30 or 10w30 or similar other?

Question #2: My understanding is the original fluid didn't have detergents, so a pure racing dino motor oil would be the closest equivalent correct?

Thanks

The factory recommended lube for the 84 4 speed is 5w 30 motor oil. They also had a plastic tag on the fill port stating this.

Thanks for reply, mine is an 86, different final drive ratio, but pretty much the same none the less. Figures it would be 5w30, cause 10w30 would have been too easy, haha. I could do 10w30 being summer only car, but colder temps in spring/fall could make things more stiff in the early going.

https://www.summitracing.com/parts/jgr-01906

[This message has been edited by Skybax (edited 05-08-2021).]

See my Cave, Manual Trans Fluid

Note that Any New Trans can wash out crap keeping oil in.
Also many claim Oil causes leaks often did other things that make leaks.
Like install axle seals w/ dry outside metal then small scratches leak. Is why you use thin coat of Super 300 etc paint where seal in driven into case hole.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

quote Originally posted by theogre: See my Cave,

Been there many times over the past 20 years, great resource, many thanks.

quote Originally posted by theogre: Also many claim Oil causes leaks often did other things that make leaks.

I was referring specifically to the ones that developed leaks immediately after switching to synchormesh on a nice leak-free original unmolested Fiero.

quote Originally posted by theogre: Note that Any New Trans (fluid) can wash out crap keeping oil in.

Agree, changing the fluid always has that risk with any old car with old fluid and old seals, that's why I'm trying to minimize risk with detergent-free 5w30 dino.

[This message has been edited by Skybax (edited 05-10-2021).]